Power Electronics Lab - 2011

Department of Electronics & Communication

JSSATE , BANGLORE 1

JSS ACADEMY OF TECHNICAL EDUCATION

(AFFILIATED TO VTU)

Uttarahalli-Kengeri Main Road, Mylasandra Bangalore – 560060

DEPARTMENT OF ELECTRONICS & COMMUNICATION ENGINEERING

POWER ELECTRONICS LAB MANUAL (06ECL78) (VII SEM)

B. G. Shivaleelavathi, Assistant Professor, E&C Dept.,

JSSATE, Bangalore.


JSSATE , BANGLORE 2

INDEX

SERIAL NO.

CONTENTS PAGE NO.

1 Power Electronics lab syllabus

3

2 Static characteristics of MOSFET and IGBT

4 to 9

3 Static characteristics of SCR, TRAIC and DIAC

10 to 17

4 Controlled HWR and FWR using RC triggering circuit

18 to 25

5 SCR turn off using i) LC circuit ii) Auxiliary Commutation

26 to 33

6 UJT firing circuit for HWR and FWR circuits

34 to 43

7 Generation of firing signals for thyristors / TRIACs using digital circuits/microprocessor.

44 to 47

8 AC voltage controller using TRIAC-DIAC combination

48 to 50

9 Single phase Fully Controlled Bridge Converter with R and R-L loads

51 to 73

10 Voltage (Impulse) commutated chopper both constant frequency and variable frequency operations

74 to 83

11 Speed control of a separately exited DC motor.

84 to 89

12 Speed control of universal motor.

90 to 91

13 Speed control of stepper motor.

92 to 96

14 Parallel / Series inverter

97 to 105

15 Model questions

16 Viva questions

17 Bibliography


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Acknowledgements: I take this opportunity to thank my husband, parents, son, HOD of E&C Dept, E&C Department staff members and my colleagues

POWER ELECTRONICS LAB Subject Code : 06ECL78 IA Marks : 25 No. of Practical Hrs/Week: 03 Exam Hours : 03 Total no. of Practical Hrs. : 42 Exam Marks : 50 1. Static characteristics of MOSFET and IGBT. 2. Static characteristics of SCR, TRIAC and DIAC. 3. Controlled HWR and FWR using RC triggering circuit 4. SCR turn off using i) LC circuit ii) Auxiliary Commutation 5. UJT firing circuit for HWR and FWR circuits. 6. Generation of firing signals for thyristors/ TRIACs using digital circuits/microprocessor. 7. AC voltage controller using TRIAC-DIAC combination. 8. Single phase Fully Controlled Bridge Converter with R and R-L loads 9. Voltage (Impulse) commutated chopper both constant frequency and variable frequency operations. 10. Speed control of a separately exited DC motor. 11. Speed control of universal motor. 12. Speed control of stepper motor. 13. Parallel / Series inverter.


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1) STATIC CHARACTERISTICS OF MOSFET AND IGBT (i) STATIC CHARACTERISTICS OF MOSFET . AIM: To plot input and transfer characteristics of an MOSFET and to find ON state resistance and trans conductance. APPARATUS: 1. 0 – 50V DC Voltmeter 2. 0 – 100V AC Voltmeter 3. 0 – 100mA AC Ammeter 4. Regulated power supply 5. n-channel MOSFET(IRF-840) 6. Resistance (500Ω/5W). DEVICE SPECIFICATIONS: IRF 840. 1. VDss-Drain to Source Breakdown voltage : 400 Volts. 2. Rds (on)-On state Resistance : 0.55 ohms. 3. ID-continuous drain current-25° C : 10 Amps. 4. ID-continuous drain current-100° C : 6.3 Amps. 5. RJC-Max thermal resistance : 1° C/Watt. 6. PD Max-power dissipation@ 25° C : 125 watts. CIRCUIT DIAGRAM:

0 -5 0 0 m A

V

V0 -1 5 V

0 - 5 0 V

R

G S

V D S

DI1

2R

2

V1

PROCEDURE: i)Trans Conductance Characteristics: Make the connections as shown in the circuit diagram including meters. Initially keep V1 and V2 minimum. Set V1=VDS1=say 10V. Slowly vary V2 (VGS) and note down ID and VGS readings for every 1 Volt and enter in the tabular column. The minimum gate voltage VGS that is required for conduction to start the MOSFET is called Threshold Voltage VGS(Th). The Drain current depends on magnitude of the Gate Voltage VGS which may vary from 2 to 5 Volts. Repeat the same for different VDS and draw the graph of VGS V/s ID.


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ii)Tabular Column: VDS1 (Volts) VDS2 (Volts) VGS (Volts) ID (mA) VGS (Volts) ID (mA)

iii)Drain Characteristics: Initially set V2 to VGS1=3.5 Volts. Slowly vary V1 and note down ID and VDS. For a particular value of VGS1 there is a pinch off voltage (Vp) between drain and source. If VDS is lower than Vp, the device works in the constant resistance region and ID is directly proportional to VDS. If VDS is more than Vp, constant Id flows from the device and this operating region is called constant current region. Repeat the above for different values of VGS and note down VDS Vs ID. Draw the graph of VDS Vs ID for different values of VGS.

iv) Tabular Column: VGS1 (Volts) VGS2 (Volts) VDS (Volts) ID (mA) VDS (Volts) ID (mA)


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WAVEFORMS :

Ohmic

ID

mA

0

GS4VActive

GS3VGS2VGS1V

GS4V > GS3V > >VGS2 VGS1

DSVvolts Output Characteristics

DI

DSV Transfer CharacteristicsVGS (th)

RESULT: ΔVDS 1. RD = -------------- = ------------------------------ Ω. ΔID ΔID 2. Gm = -------------- = ------------------------------ mho. ΔVDS CONCLUSION: We conclude that MOSFET is a voltage controlled device. VDS remains constant after it crosses the Vpeak value.


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(ii)) STATIC CHARACTERISTICS OF IGBT. AIM: To plot the characteristics of IGBT. APPARATUS: 1. 0 – 50V DC Voltmeter 2. 0 – 100V AC Voltmeter 3. 0 – 100mA AC Ammeter 4. Regulated power supply 5. Resistance (500Ω/5W). 6. IGBT (IRGBC-20S) DEVICE SPECIFICATIONS: IRGBC 20S 1. Vce-Collector to emitter Voltage : 600 Volts. 2. Max Vce(on)-Collector to emitter Voltage : 3.0 Volts. 3. Ic-continuous collector current @ 25° C : 19 Amps. 4. ID-continuous collector current @ 100° C : 10 Amps. 5. Pd max-Maximum power dissipation : 60 Watts. CIRCUIT DIAGRAM:

0-500mA

V

V0-15V

0 - 50V

GE

VCE

CI

R

2

2

1R

V1

PROCEDURE: i)Transfer Characteristics: Make the connections as shown in the circuit diagram with meters. Initially keep V1 and V2 minimum. Set V1=VCE1=say 10V. Slowly vary V2 (VGE) and note down IC and VGE readings for every 1.0 Volt and enter in the tabular column. The minimum gate voltage VGE which is required for conduction to start the IGBT is called Threshold Voltage VGE(Th). If VGE is greater than VGE(Th) only very small leakage current flows from Collector to Emitter. If VGE is greater than VGE(Th), the Collector current depends on magnitude of the Gate Voltage. VGE varies from 4 to 8 Volts. Repeat the same for Vc and draw the graph of VGE V/S IC.


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ii)Tabular Column: VCE1 (Volts) VCE2 (Volts) VGE (Volts) IC (mA) VGE (Volts) IC (mA)

iii) Collector Characteristics: Initially set V2 to VGE1=5 Volts. Slowly vary V1 and note down IC and VGE. For a particular value of VGE1 there is a pinch off voltage (Vp) between Collector and Emitter. If VGE is lower than Vp, the device works in the constant resistance region and IC is directly proportional to VGE. If VGE is more than Vp constant IC flows from the device and this operating region is called constant current region. Repeat the above for different values of VGE and note down VCE V/S IC. Draw the graph of VCE V/S IC for different values of VGE. iv) Tabular Column: VGE1 (Volts) VGE2 (Volts) VCE (Volts) IC (mA) VCE (Volts) IC (mA)


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WAVEFORMS: COLLECTOR CHARACTERISTICS

I C

(m A )

G E3V

G E2V

G E1V

C EV (vo lts)

VC E CI

R esistanceO U TPU T = V

I C

C E =

TRANSFER CHARACTERISTICS

G EVCI

C EV

T r a n s f e rR e s i s ta n c e = G EV

CI

G EV ( v o l ts )

=( m A )CI

RESULT: ΔVCE 1. RON = -------------- = ------------------------------ Ω. ΔIC 2. VGSTh = ------------------------------ Volts CONCLUSION: We conclude that IGBT is a voltage controlled device. VCE remains constant after it crosses the Vpeak value. 2) STATIC CHARACTERISTIC OF SCR, TRIAC & DIAC

(i) STATIC CHARACTERISTIC OF SCR

AIM: To plot the characteristics of an SCR and to find the forward resistance, holding current and latching current.


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APPARATUS: 1) 0 – 50V DC Voltmeter 2) 0 – 500mA DC Ammeter 3) 0 – 25mA DC Ammeter

4)Resistor (1kΩ/5w) 5)Regulated power supply 6)SCR (TYN616) 7)Rheostat DEVICE SPECIFICATIONS: TYN 616 1. Vrrm : 600V. 2. It(rms) : 16 A. 3. It(av) : 10 A. 4. It(sm) : 160 A. 5. It : 128 A/µs. 6. di/dt : 100 A/µs. 7. Igt : 25 mA. 8. Vgt : 1.5 V. 9. IH : 40 mA. 10. IL : 70 mA. 11. tq : 70µs. 12. dv/dt : 500 V/µs. CIRCUIT DIAGRAM:

I G

V

R0-25mA

AI

VAK 0-50V1

0-500mA

2

1R

2

V

PROCEDURE: i). V-I Characteristics: Make the connections as given in the circuit diagram. Now switch ON the mains supply to the unit and initially keep V1 & V2 at minimum. Set load potentiometer R1 in the minimum position. Adjust Ig-Ig1 say 10 mA by varying V2 or gate current potentiometer R2. Slowly vary V1 and note down VAK and IA readings for every 5 volts and enter the readings in the tabular column. Further vary V1 till SCR conducts, this can be noticed by sudden drop of VAK and rise of IA readings. Note down



this reading and tabulate. Vary V1 further and note down IA and VAK readings. Draw the graph of VAK V/S IA. Repeat the same for Ig=Ig2/Ig3 mA and draw the graph. Tabular Column:

MODE 1, IG1=

VAA (volts) V AK2 (volts) I AK (mA) To find latching current: Apply about 20V between anode and cathode by varying V1. Keep the load potentiometer R1 at minimum position. The device must be in the OFF state with gate open. Gradually increase Gate voltage- V2 till the device turns ON. This is the minimum gate current (Igmin) required to turn ON the device. Adjust the gate voltage to a slightly higher value. Set the load potentiometer at the maximum resistance position. The device should come to OFF state, otherwise decrease V1 till the device comes to OFF state. The gate voltage should be kept constant in this experiment. By varying R1, gradually increase anode current IA in steps. Open and close the Gate voltage V2 switch after each step. If the anode current is greater than the latching current of the device, the device stays ON even after the gate switch is opened. Otherwise the device goes into blocking mode as soon as the gate switch is opened. Note the latching current. Obtain more accurate value of the latching current by taking small steps of IA near the latching current value. Increase the anode current from the latching current level by load pot R1 or V1. Open the gate switch permanently. The thyristor must be fully ON. Now start reducing the anode current gradually by adjusting R1. If the thyristor does not turns OFF even after the R1 at maximum position, then reduce V1. Observe when the device goes to blocking mode. The anode current through the device at this instant is the holding current of the device. Repeat the steps again to accurately get the IH. Normally IH<IL. WAVEFORMS:

MODE 2, IG2= V AA (volts) V AK (volts) I AK (mA)



OnState

Transient Characteristics

ILIH

Ig Ig IgIg=0

Forward Blocking RegionReverse Blocking RegionFBO

RBO

I

3 2 1v

vvAK

A

RESULT: 1. The break over voltages : Vb1 = -------------- : Vb2 = --------------- Latching Current (IL)= ------------------------------------ amps Holding Current(IH) = ------------------------------------- amps Δ VAK Forward Resistance Rf = ------------; Δ IA Rf = ------------------------------ CONCLUSION : We conclude from the experiment that as the gate current increases the break over voltage decreases. (ii) STATIC CHARACTERISTIC OF TRIAC. AIM: To plot the characteristics of TRIAC.



APPARATUS:

1) 0 – 50V DC Voltmeter 2) 0 – 500mA Ammeter 3) 0 – 25mA Ammeter 4) Regulated power supply 5) Resistor (1kΩ/5w) 6) TRIAC(BT136-600) 7) Rheostat

DEVICE SPECIFICATIONS: BT136-600. 1. Vdrm : 600V. 2. Itrms : 4 A. 3. Itsm : 50 A. 4. It : 12.5 A. 5. di/dt : 10 A/µs. 6. Igt : 15 mA. 7. Vgt : 1.5 V. 8. IH : 13 mA. 9. IL : 50 mA. 10. dv/dt : 10 V/µs.

CIRCUIT DIAGRAM:

V

IL

0-500mA

IG

0-25mAR

2

0 - 50V 1

2

T2T1 V

V

1R

PROCEDURE: i) V-I Characteristics: Make the connections as given in the circuit diagram including meters. Now switch ON the mains supply to the unit and initially keep V1 & V2 at minimum. Set load potentiometer R1 in the minimum position. Adjust Ig-Ig1 say 10 mA by varying V2 or gate current potentiometer R2. Slowly



vary V1 and note down VT2T1 and IL readings for every 5 Volts and enter the readings in the tabular column. Further vary V1 till Triac conducts, this can be noticed by sudden drop of VT2T1 and rise of IL readings. Note down this reading and tabulate. Vary V1 further and note down IL and VT2T1 readings. Draw the graph of VT2T1 V/S IL. Repeat the same for Ig=Ig2/Ig3 and draw the graph. To find latching current: Apply about 20V between MT1 and MT2 by varying V1. Keep the load potentiometer R1 at minimum position. The device must be in the OFF state with gate open. Gradually increase Gate Voltage V2 till the device turns ON. This is the minimum gate current (Igmin) required to turn ON the device. Adjust the gate Voltage to a slightly higher value. Set the load potentiometer at the maximum resistance position. The device should come to OFF state, otherwise decrease V1 till the device comes to OFF state. The gate Voltage should be kept constant in this experiment. By varying R1, gradually increase anode current IL in steps. Open and close the Gate voltage V2 switch after each step. If the load current is greater than the latching current of the device, the device stays ON even after the gate switch is opened otherwise the device goes into blocking mode as soon as the gate switch is opened. Note the latching current. Obtain more accurate value of the latching current by taking small steps of IL near the latching current value. Increase the Load current from the latching current level by load pot R1 or V1. Open the gate switch permanently. The Triac must be fully ON. Now start reducing the anode current gradually by adjusting R1. If the Triac does not turn OFF even after the R1 at maximum position, then reduce V1. Observe when the device goes to blocking mode. The load current through the device at this instant is the holding current of the device. Repeat the steps again to accurately get the IH. Normally IH<IL.

MODES Modes MT2 MT1 G Mode1 + - + Mode2 + - - M0de3 - + + Mode4 - + - Tabular Columns:

MODE 1, IG1=

V TT (volts) V T1T2 (volts) I T1T2 (mA)

MODE 2, IG2= V TT (volts) V T1T2 (volts) I T1T2 (mA)



MODE 3, IG3=


MODE 4, IG4= V TT (volts) V T1T2 (volts) I T1T2 (mA) WAVEFORMS:

1

Ig0

Ig Ig2

I

V

IgIg2 V10Ig

BO

V-I characteristics RESULT: CONCLUSION: We conclude that the sensitivity of the mode depends on minimum gate current required to turn on the TRIAC. We found that mode1 is most sensitive where as mode3 is least sensitive. (iii) STATIC CHARACTERISTICS OF DIAC AIM: To plot the characteristics of DIAC. APPARATUS:



1) 0-60V DC Voltmeter 2) 0-250mA AC Ammeter

3) Resistor (1kΩ/5w) 4) Regulated power supply 5) DIAC (DB-3) 6) Rheostat DEVICESPECFICATIONS: DB-3. Breakdown Voltage: 32V±10% Power: 0.5 Watts. CIRCUIT DIAGRAM:

PROCEDURE: Make the connections as given in the circuit diagram. Keep R2 at maximum resistance position and do not change this throughout the experiment. Since the device is only a switching device and its power rating is only 0.5 watts. Keep V1 potentiometer also at minimum position. Next switch ON the unit and V1 power supply. Vary V1 in steps of 5V and note down the corresponding Ammeter reading. Vary in steps of 5V up to 25 Volts. After that vary in steps of 1V. At a particular value of voltage the device conducts. This can be noticed by the sudden increase of ammeter reading. This is the device breakdown voltage. Vary V1 further and note down the corresponding V/I readings in the tabular column. Tabular Columns:

FORWARD CHARACTERSTICS V TT (volts) V T1T2 (volts) I T1T2 (mA)



WAVEFORMS:

I (mA)

~ 30vV

V - I Characteristics

RESULT : VFBO = --------------- (V) VRBO = --------------- (V) CONLUSION : We conclude that DIAC is a bi-directional device. 3) CONTROLLED HWR AND FWR USING RC TRIGGERING CIRCUIT

(i)RC FIRING CIRCUIT – HALF WAVE RECTIFIER.

REVERSE CHARACTERSTICS




AIM: To study Resistance-Capacitance triggering of SCR in half wave mode. APPARATUS: Step down transformer (230–30V) , Load resistance (100Ω rheostat), Resistance (10KΩ potentiometer, 100Ω), Power Diodes (IN 4007), SCR (TYN616),CRO. DEVICE SPECIFICATIONS: TYN 616 1. Vrrm : 600V. 2. It(rms) : 16 A. 3. It(av) : 10 A. 4. It(sm) : 160 A. 5. It : 128 A/µs. 6. di/dt : 100 A/µs. 7. Igt : 25 mA. 8. Vgt : 1.5 V. 9. IH : 40 mA. 10. IL : 70 mA. 11. tq : 70µs. 12. dv/dt : 500 V/µs. CIRCUIT DIAGRAM :

DESIGN: It can be shown empirically that RC≥ 1.3T/2≈4/ω :



T = 1/f & f = 50Hz R= R1 + R2 Vc = Vgt + Vd ; where Vc is capacitor voltage , Vd is diode voltage drop. At the instant of firing , Vc is assumed to be constant ,the current Igt must be supplied by voltage source through R, D2 and the gate cathode voltage. Therefore maximum value of R is given by : R= R1 + R2 ≤ (V- Vgt - Vd )/ Igt ; Approximate values of R & C can be obtained from the above equations. EXAMPLE : RC = (4×π×50)/2 Let Vgt = 1.5 V, Vd =0.7 V Then Vc = 1.5 + 0.7 = 2.2 V let Igt(max) =10mA R= R= R1 + R2 ≤ (V- Vgt - Vd )/ Igt ; R ≤(32-1.5-0.7)/10mA ≤2.97 KΩ; & RC≥ 1.3T/2≈4/ω C≥ 1.3T/2≈4/ωR = 1.3/(2*50*2.97*10-3) = 1.01e-6F Let C = 1µF, then Let R2 =100Ω ; PROCEDURE: i) R- Triggering Make the connections as given in the connection diagram above. Connect a Rheostat of 100 ohms/1.7A between the load points. Vary the control pot and observe the voltage waveforms across load, SCR and at different points of the circuit. We can vary the firing angle from 0° to 90° only in R triggering (you may have to disconnect the capacitor to realize R triggering alone). In this triggering the synchronized firing angle can be obtained easily and economically in the positive half cycle of the supply. But there is a draw back that the firing angle can be controlled at the most at 90°, since the gate current is in phase with the applied voltage. A resistor is connected in series with the control pot, so that the gate current does not cross the maximum possible value Igmax Draw the waveform across the load and device for different values of firing angles. ii) RC Triggering Connect capacitor to the R triggering circuit to realize RC triggering. Repeat the above procedure and draw the waveform across the load and device for different values of firing angles. Note here the firing can varied from 0° to (~)180°.



TABULAR COLUMN: Firing angle Practical Theoretical (α)=sin-1 (Vn/Vp) Vodc (Volts) Vorms (Volts) Vodc

(Volts) Vorms (Volts)

Formula Used : Vodc (theoretical) = Vm ×(1+ cos α)/(2 π) WAVEFORMS :



Waveforms across Vc , Vload , Vscr , w.r.t to source RESULT : CONCLUSION : The average O/P voltage can be varied by varying the firing angle (α).



(ii)RC FIRING CIRCUIT – FULL WAVE.

AIM: To study Resistance- capacitance triggering of SCR in full wave mode. APPARATUS: Step down transformer (230–30V) , Load resistance (100Ω rheostat), Resistance (10KΩ potentiometer, 100Ω), Power Diodes (IN 4007), SCR (TYN616),CRO. DEVICE SPECIFICATIONS: TYN 616 1. Vrrm : 600V. 2. It(rms) : 16 A. 3. It(av) : 10 A. 4. It(sm) : 160 A. 5. It : 128 A/µs. 6. di/dt : 100 A/µs. 7. Igt : 25 mA. 8. Vgt : 1.5 V. 9. IH : 40 mA. 10. IL : 70 mA. 11. tq : 70µs. 12. dv/dt : 500 V/µs. CIRCUIT DIAGRAM :

NOTE : A simple RC trigger circuit giving full-wave output voltage. Diodes D1 – D4 form a full-wave bridge rectifier. Diode Bridge: In this circuit, the initial voltage from which the capacitor C charges is almost zero. The capacitor C is set to this low positive voltage(upper plate positive) by the clamping action of SCR gate. When capacitor charges to a voltage equal to Vgt SCR triggers and rectified voltage Vd appears across load as Vo.



DEISGN : Same as for Half wave triggering PROCEDURE: Make the connections as shown in the circuit diagram above. Switch ON the unit. By varying the potentiometer on the front panel, note down the voltage waveforms across the load( 100 Ohms/2A rheostat) and also across SCR and capacitor. Infer on the control obtained with and without capacitor connected to the circuit. Draw the waveforms across load, SCR and across capacitor. TABULAR COLUMN: Firing angle Practical Theoretical (α)=sin-1 (Vn/Vp) Vodc (Volts) Vorms (Volts) Vodc


FORMULA USED : Vodc (theoretical) = Vm ×(1+ cos α)/( π)



WAVEFORMS :



RESULT : CONCLUSION : We conclude that the average voltage in FW mode is greater than HW mode. The average O/P voltage can be varied by varying the firing angle (α).



4) SCR TURN – OFF CIRCUITS USING (a) LC CIRCUIT (b) AUXILIARY COMMUTATION AIM: To rig up various turn off circuits for SCR by auxiliary commutation class D commutation. APPARATUS: Forced commutation study unit, DC power supply (0-30V/2A for Class E Commutation only), Rheostats (50 ohms / 2A) – 2Nos, CRO, Probes and connecting wires. DESCRIPTION : FORCED COMMUTATION STUDY UNIT This unit consists of two parts – (i) Power Circuit and (ii) Firing Circuit sufficient to study (a) Class A Commutation – Self Commutation by load resonance. (b) Class B Commutation – Self Commutation by LC circuit. (c) Class C Commutation – Complimentary SCR commutation. (d) Class D Commutation – Auxiliary SCR commutation. (e) Class E Commutation – with an external source of pulse for commutation. POWER CIRCUIT: This part consists of the following components to build different commutation circuits with different values of commutation components. a) 2 SCRs. b) a diode. c) 2 different values of commutation capacitors to get different value of commutation capacitance by individual, series and parallel connections and d) a commutation inductor with tappings at different points and a transistor for class E commutation. An unregulated DC power supply of 24 Volts @ 2Amps is provided to use as DC input for commutation circuits. FIRING CIRCUIT: This part generates triggering pulses to fire two SCRs connected in different forced commutation circuits. The frequency and duty cycle can be varied using respective potentiometers.



FRONT PANEL DIAGRAM:

FORCED COMMUTATION STUDY UNIT - FCU

U

POWER

TRIG - OUTPUT

CAT

T2

GATE

1T

OFFON

+

ON

ES

FIRING CIRCUIT

FREQUENCYMIN MAX

+

F

-

DUTY CYCLEMIN MAX

C1 C2

T2

1LO L2 L3

T1

DPOWER CIRCUIT

C

B

RT

E

FRONT PANEL DETAILS: 1.Power : Power ON / OFF switch to the unit with built in indicator. 2.Frequency : Potentiometer to vary the frequency of commutation from 30Hz to

250Hz approximately. 3.Duty Cycle : Potentiometer to vary the duty cycle from 10% to 90% approximately. 4.Trigger Output ON / OFF : On / Off switch for mains pulse T1

5. Gate / Cathode : Positive and negative points of trigger outputs to connect to gate and cathode of SCRs.

6.T1 : Trigger output for SCR T1 – 200 s pulse. 7.T2 : Trigger output for SCR T2 – 200 s pulse.

8.Volts dc IN : 24V @ 2A unregulated DC supply is available at these terminals for DC Source for the commutation power circuit.

9. ON : ON / OFF switch for DC supply. 10.Fuse : 2Amps glass fuse for DC power supply protection. 11. + : DC power supply point after switch and fuse. 12.D : Free wheeling diode – BYQ 28 – 200. 13.T1 & T2 : SCRs – TYN 612. 14.Tr : Transistor – TIP 122. 15. Commutation Inductance

L1 : 250H L2 : 500H L3 : 1H @ 2A 16. Commutation Capacitance

C1 : 6.8F / 100V C2 : 10.0 F / 100V



BACK PANEL DETAILS: Main socket with built in fuse holder. The fuse holder has a spare fuse along with the fuse in the circuit. If the fuse blows remove the blown fuse and replace with the spare fuse. Fuse – 1A fast blow glass fuse. DESIGN OF LC COMMUTATION CIRCUIT : TON = π[LC]1/2

Let TON = 2 msec , C = 6.8 µF. Then 2 x 10-3 = π [L x 6.8 x 10-6 ]1/2 L = 590 H PROCEDURE: Switch on the mains to unit and observe the trigger outputs by varying frequency and duty cycle potentiometer and make sure that the pulse output are proper before connecting to the power circuit. Check the DC power supply between the DC Input points. Check all the devices. Check the resistance between the Gate and Cathode of SCR’s. Check the resistance between anode and cathode. Check the diode and its polarity. Check the transistor and its polarity. Check the fuse in series with the DC input. Make sure that all the components are good and firing pulse is correct before you start any commutation experiments. (a)CLASS – A COMMUTATION: (SELF COMMUTATION BY RESONATING LOAD -LC) The current reversing property of the load will force the device commutation. L,C and R values are chosen such that the circuit is under damped. Since the commutation elements carry load current on a continuous basis, these ratings are generally high. For low frequency operation large value of L & C is required. CIRCUIT DIAGRAM:

0-3 0 V

T 1

L

CR

O U T P U T A C R O S S " R "



PROCEDURE: Make the interconnections in the power circuit as shown in the circuit diagram. Connect trigger output T1 to gate and cathode of SCR T1. Switch on the DC Supply to the power circuit and observe the voltage waveform across load by varying the frequency Potentiometer. Duty cycle Potentiometer is of no use in this experiment. Repeat the same for different values of L,C and R. TABULAR COLUMN :

WHEN L = L1 AND C= C1 R (Ω) Ton ( msec) Tc ( msec)

WHEN L = L1 AND R= R1 C (µF) Ton ( msec) Tc ( msec)

WHEN R= R1 AND C= C1 L Ton ( msec) Tc ( msec) WAVEFORMS:

T r i g g e r o u t p u t s :

T 1

T 2



Voltage across the gating pulse, Thyristor, voltge across capacitor, voltage across resistor RESULT : CONCLUSION : We conclude that the SCRs can be commutated by using LC circuit also.



CLASS – B COMMUTATION:(SELF COMMUTATION BY AN LC CIRCUIT) In this type of commutation, reverse voltage is applied to the thyristor by the over swinging of an under damped LC circuit connected across the Thyristor. Capacitor charges up to the supply voltage before the trigger pulse is applied to the gate. When the thyristor is triggered, two currents flow, a load current through the external circuit and a pulse of current through LC circuit and thyristor in opposite direction. This resonant current tends to turn off the thyristor. CIRCUIT DIAGRAM:

2 4 V

L

C

R

PROCEDURE: Make the interconnections in the power circuit as shown in the circuit diagram. Connect trigger output T1 to gate and cathode of SCR T1. Switch on the DC Supply to the power circuit and observe the voltage waveform across load by varying the frequency Potentiometer. Duty cycle Potentiometer is of no use in this experiment. Repeat the same for different values of L,C and R WAVEFORMS:



O U T P U T A C R O S S "R "

o n ly fr eq u e n cy v a ria tio n is p o s ib le

RESULT : CONCLUSION : Thus the SCR’s are commutated by LC circuit for class A and class B LC commutation circuits. (ii) AUXILIARY VOLTAGE COMMUTATION: Circuit same as Jones chopper:

1T

C

2T1L 2LLM

LOA

DDM

D1

VDC

JONES CHOPPER

CIRCUIT DIAGRAM



PROCEDURE: Make the connections as given in the circuit diagram. Connect T1 and T2 gate pulse from the firing circuit to the corresponding SCR’s in the power circuit. Initially keep the trigger ON/OFF at OFF position to initially charge the capacitor, this can be observed by connecting CRO across the Capacitor. Now switch ON the trigger O/P switch and observe the voltage wave forms at different frequencies of chopping and also at different duty cycles. Repeat the experiment for different values of load resistance, commutation inductance and capacitance. Compare the results with theoretical results. PARAMETERS AND OBSERVATIONS: 1. Voltage wave form across capacitor. 2. Output voltage waveforms (across the load) 3. Output current waveforms (Through the shunt) 4. Voltage waveforms across Thyristor. 5. Study of variation of voltage and current waveforms with the variation of duty cycle and frequency. 6. Study of effect of free wheeling diode in case of inductive loads.



5) UJT FIRUNG CIRCUIT(ACVC, HWR & FWR)

(i)UJT FIRING CIRCUIT – TWO SCRS(ACVC) AIM: To fire two SCR using UJT firing circuit. APPARATUS: Step down transformer (230–30V) , Load resistance (100Ω rheostat), Resistance (50KΩ potentiometer, 3.3KΩ, 100Ω, 220 Ω, 500V/5W), Power Diodes (IN 4007), Zener diode ,SCR (TYN616),Pulse transformer, CRO. DEVICE SPECIFICATIONS: TYN 616 1. Vrrm : 600V. 2. It(rms) : 16 A. 3. It(av) : 10 A. 4. It(sm) : 160 A. 5. It : 128 A/µs. 6. di/dt : 100 A/µs. 7. Igt : 25 mA. 8. Vgt : 1.5 V. 9. IH : 40 mA. 10. IL : 70 mA. 11. tq : 70µs. 12. dv/dt : 500 V/µs. CIRCUIT DIAGRAM :



DESIGN : Let VBB =20V; VD = 0.7V; Vc = VBB (1- e-t/RC ) Vp = η VBB + VD ; (η = 0.65) Since Vc = Vp of UJT ηVz (1- e-T/RC ) Therefore T = RC ln [1/(1-n)] T = time period of output pulse . The firing angle α is given by α = ωT = ωRC ln [1/(1-n)] ω = angular frequency. Vodc(th) = Vm (1+ cosα) /2π The leakage current drop across R1 should be small that when UJT is OFF it should not trigger i.e., VBB =I1eakage(RBB + R1+R2 )< SCR trigger voltage. and R2 = 104 /( η VBB ) width of triggering pulse is R1 C = T2 When voltage drop across C reaches Vp voltage across R is VBB – Vp . Therefore Rmax = (VBB - Vp ) / Ip

Rmin = (VBB - Vv )/Iv PROCEDURE: 2.1. Firing of SCR using UJT. Switch on the mains supply observe and note down the wave forms at the different points in the circuit and also the trigger O/Ps – T1, & T1’. Now, make the connections as given in the circuit diagram above ,using AC source, UJT relaxation oscillator, SCR and suitable load(100ohms /2A rheostat). Switch ON the mains supply, observe and note down the output waveforms across load and SCR. Draw the wave forms at different firing angles as 120, 90 & 60 degrees. In the UJT firing circuit the firing angle can be carried from 150° – 30° approximately. This is one of the simplest methods of SCR triggering. We can also fire SCR’s in the different power circuits as described earlier. 2.2. UJT Relaxation Oscillator: To study oscillator using UJT, short Cf to the diode bridge rectifier to get filtered DC output. Now we will get the equidistant pulses at the O/P of pulse transformer. The frequency of the pulse can be varied by varying the potentiometer RC. Observe and note down the waveforms at different points in the circuit. TABULAR COLUMN: Firing angle Practical Theoretical (α)=sin-1 (Vn/Vp) Vorms (Volts) Vorms (Volts)



FORMULA USED : Virms = Vm /√2 Vorms (theoretical) = Virms ×[( π- α)/(2 π) + (sin2α/2 π)]1/2

WAVEFORMS :

waveforms across rectifier (Vodc),zener (Vz), capacitor (Vc), resistor (Vr2), load(VL) ,SCR (Vscr) with respect to source for α = 90 degrees.



RESULT : CONCLUSION : We conclude that the pulses obtained from UJT can be used to fire two SCRs also with the help of a pulse transformer.



(ii)SYNCHRONIZED UJT FIRING CIRCUIT FOR HWR AND FWR TRIGGERING. UJT FIRING CIRCUIT – HALF WAVE \ AIM: To fire SCR for Half Wave using UJT firing circuit. APPARATUS: Step down transformer (230–30V) , Load resistance (100Ω rheostat), Resistance (50KΩ potentiometer, 3.3KΩ, 100Ω, 220 Ω, 500V/5W), Power Diodes (IN 4007), Zener diode ,SCR (TYN616),Pulse transformer, CRO. DEVICE SPECIFICATIONS: TYN 616 1. Vrrm : 600V. 2. It(rms) : 16 A. 3. It(av) : 10 A. 4. It(sm) : 160 A. 5. It : 128 A/µs. 6. di/dt : 100 A/µs. 7. Igt : 25 mA. 8. Vgt : 1.5 V. 9. IH : 40 mA. 10. IL : 70 mA. 11. tq : 70µs. 12. dv/dt : 500 V/µs. CIRCUIT DIAGRAM :



DESIGN: Vc = VBB (1- e-t/RC ) Vp = η VBB + VD ; (η = 0.65) Since Vc = Vp of UJT ηVz (1- e-T/RC ) Therefore T = RC ln [1/(1-n)] T = time period of output pulse . The firing angle α is given by α = ωT = ωRC ln [1/(1-n)] ω = angular frequency. Vodc(th) = Vm (1+ cosα) /2π The leakage current drop across R1 should be small that when UJT is OFF it should not trigger i.e., VBB =I1eakage(RBB + R1+R2 )< SCR trigger voltage. and R2 = 104 /( η VBB ) width of triggering pulse is R1 C = T2 When voltage drop across C reaches Vp voltage across R is VBB – Vp . Therefore Rmax = (VBB - Vp ) / Ip

Rmin = (VBB - Vv )/Iv PROCEDURE: 1.1 . Firing of SCR using UJT. Switch on the mains supply observe and note down the wave forms at the different points in the circuit and also the trigger O/Ps – T1, & T1’. Make sure that the pulse transformer O/P T1 & T1’ are proper and synchronized. Now, make the connections as given in the connection diagram above ,using AC source, UJT relaxation oscillator, SCR and suitable load(100ohms /2A rheostat). Switch ON the mains supply, observe and note down the output waveforms across load and SCR. Draw the wave forms at different firing angles as 120, 90 & 60 degrees. In the UJT firing circuit the firing angle can be carried from 150° – 30° approximately. This is one of the simplest methods of SCR triggering. We can also fire SCR’s in the different power circuits as described earlier. 1.2. UJT Relaxation Oscillator: To study oscillator using UJT, short Cf to the diode bridge rectifier to get filtered DC output. Now we will get the equidistant pulses at the O/P of pulse transformer. The frequency of the pulse can be varied by varying the potentiometer RC. Observe and note down the waveforms at different points in the circuit. TABULAR COLUMN: Firing angle Practical Theoretical (α)=sin-1 (Vn/Vp) Vodc (Volts) Vorms (Volts) Vodc




Formula Used : Vodc (theoretical) = Vm ×(1+ cos α)/(2 π) WAVEFORMS :

waveforms across rectifier (Vodc),zener (Vz), capacitor (Vc), resistor (Vr2), load(VL) ,SCR (Vscr) with respect to source for α < 90 degrees. RESULT : CONCLUSION :



We conclude that the pulses obtained from UJT can be used to fire SCR. (iii)UJT FIRING CIRCUIT – FULL WAVE AIM: To fire SCR for Full Wave using UJT firing circuit. APPARATUS: Step down transformer (230–30V) , Load resistance (100Ω rheostat), Resistance (50KΩ potentiometer, 3.3KΩ, 100Ω, 220 Ω, 500V/5W), Power Diodes (IN 4007), Zener diode ,SCR (TYN616),CRO. DEVICE SPECIFICATIONS: TYN 616 1. Vrrm : 600V. 2. It(rms) : 16 A. 3. It(av) : 10 A. 4. It(sm) : 160 A. 5. It : 128 A/µs. 6. di/dt : 100 A/µs. 7. Igt : 25 mA. 8. Vgt : 1.5 V. 9. IH : 40 mA. 10. IL : 70 mA. 11. tq : 70µs. 12. dv/dt : 500 V/µs. CIRCUIT DIAGRAM :



DESIGN : Vc = VBB (1- e-t/RC ) Vp = η VBB + VD ; (η = 0.65) Since Vc = Vp of UJT ηVz (1- e-T/RC ) Therefore T = RC ln [1/(1-n)] T = time period of output pulse . The firing angle α is given by α = ωT = ωRC ln [1/(1-n)] ω = angular frequency. Vodc(th) = Vm (1+ cosα) /2π The leakage current drop across R1 should be small that when UJT is OFF it should not trigger i.e., VBB =I1eakage(RBB + R1+R2 )< SCR trigger voltage. and R2 = 104 /( η VBB ) width of triggering pulse is R1 C = T2 When voltage drop across C reaches Vp voltage across R is VBB – Vp . Therefore Rmax = (VBB - Vp ) / Ip

Rmin = (VBB - Vv )/Iv PROCEDURE: 2.1. Firing of SCR using UJT. Switch on the mains supply observe and note down the wave forms at the different points in the circuit and also the trigger O/Ps – T1, & T1’. Now, make the connections as given in the circuit diagram above ,using AC source, UJT relaxation oscillator, SCR and suitable load(100ohms /2A rheostat). Switch ON the mains supply, observe and note down the output waveforms across load and SCR. Draw the wave forms at different firing angles as 120, 90 & 60 degrees. In the UJT firing circuit the firing angle can be carried from 150° – 30° approximately. This is one of the simplest methods of SCR triggering. We can also fire SCR’s in the different power circuits as described earlier. 2.2. UJT Relaxation Oscillator: To study oscillator using UJT, short Cf to the diode bridge rectifier to get filtered DC output. Now we will get the equidistant pulses at the O/P of pulse transformer. The frequency of the pulse can be varied by varying the potentiometer RC. Observe and note down the waveforms at different points in the circuit. TABULAR COLUMN: Firing angle Practical Theoretical (α)=sin-1 (Vn/Vp) Vodc (Volts) Vorms (Volts) Vodc


FORMULA USED :



Vodc (theoretical) = Vm ×(1+ cos α)/( π) WAVEFORMS :

waveforms across rectifier (Vodc),zener (Vz), capacitor (Vc), resistor (Vr2), load(VL) ,SCR (Vscr) with respect to source for α = 90 degrees. RESULT : CONCLUSION : We conclude that the pulses obtained from UJT can be used to fire SCR



6) GENERATION OF FIRING SIGNALS USING DIGITAL FIRING CIRCUIT AIM :To control firing angle /duty cycle using digital triggering. APPARATUS: Digital firing circuit, SCR’s( Single or any combination) loads, C.R.O, Probes etc., DIGITAL FIRING CIRCUIT: This firing circuit generates isolated trigger pulses for the phase converter, Triac and DC Chopper Power Circuits. The firing angle can be varied from 0-180° in steps of one degree and duty cycle can be varied from 0- 100% in steps of 1% using a thumb wheel switch. The firing scheme is based on ZCD, fixed frequency line synchronized clock generator, up/down counter, flip flop and pulse Transformer isolation method. FRONT PANEL DIAGRAM:

DIGITAL FIRING CIRCUIT - DFC

Z C D

GENERATORCLOCK COUNTER LOGIC

CIRCUIT

A CGND

AC Ref

180°

100%

F.A. / D.Cy

FcOscillator

TP

NT

R

TRANSFORMER

PLUSETM

ONOFF

GND

TRIGGER O/PS

T1

T2 2T '

T '1

MAINS

ISOLATION

1

2INPUT

FRONT PANEL DETAILS: 1) MAIN : Power ON/OFF switch to the unit with built-in indicator. 2) AC Ref : 10V AC reference input for synchronization. 3) GND : Ground point of the unit to observe the waveforms. 4) A : ZCD output. 5) C : Reset output for resetting the counter. 6) F.A/D.CY : Thumb wheel switch to set the firing angle from 0 to 1800 and Duty cycle

from 0 to 100% 7)1800 / 100% : Switch to select 1800 (1ph converter) or 100% (chopper) mode 8)Fc Oscillator : Carrier frequency generator-5KHz. 9)R : 10 K ohms potentiometer to vary the no. of pulses from the clock



generator 10) Clock generator : A stable oscillator to generate clock input to the counter (180 pulses or 100 pulses) 3 stage. 11) Counter : 4bit up/down programmable counter. 12) Logic Circuit : Logic and modulator circuit to get TP,TN for 1ph converter and TM, TA or chopper experiments.

Tp : Train of pulses for +ve cycle TN : Train of pulses for –ve cycle. TM : Pulse of 200 sec for main SCR. TA : Pulse of 200 sec for auxiliary SCR.

13) TM ON OFF : ON/OFF switch for main SCR14) Pulse Transformer Isolation : Pulse transformer based isolation circuit with amplifier to isolate the Logic

circuit from the power circuit. 15) INPUT 1 and 2 : Input terminals to connect logic inputs. 16) Trigger O/Ps : Pulse Transformer isolated Trigger O/Ps –to be connected to gate and cathode of SCRs. T1 and T1

1: Identical and isolated O/Ps for input-1,T2 and T21: Identical and

isolated O/Ps for input-2 BLOCK DIAGRAM:



Digital Frequency N - bit Flip - FlopLogic ckt. + ModulatorCounter (F / F)

+Driver Stage

ZCDCarrier FrequencyOscillator(~ 5 kHz)

Oscillator

Preset('N' no. of counting bits)

CLK maxmin S

A A

BB

T TFc

T

T

R ResetLoadReset

CSync.Signal (~ 8V)

SupplyDC 5V

A

¯

En

DIGITAL FIRING CIRCUIT

A

P

N

AM

PROCEDURE: - Switch ON the mains supply to the unit. Observe AC reference signal and compare it with ZCD O/P A and reset output C. Observe the carrier frequency oscillator o/p-5khz. Now set the 1800 (Converter) mode. Observe the counter O/P keep the firing angle at 179°. Adjust the potentiometer R in such a way that a very small pulse at the counter O/P is obtained. Now vary the firing angle from 1800 to 00 step by step and observe the variation in trigger O/Ps TP and TN. Connect TP and TN to 1 and 2 input of pulse Transformer isolation circuit and we will get the pulse Transformer isolated and amplified outputs at T1 & T1

1 and T2 & T21 respectively.

Connect these Trigger O/Ps to gate and cathode of SCRs for different power circuits as given in the table. Now set the 1800-100% switch to 100% mode (chopper) keep the duty cycle at 99%. Adjust the potentiometer ‘R’in such a way that a very small pulse output is obtained. Now vary the duty cycle in steps from 99% to 1% and observe the counter O/P and also observe the time variation between main pulse TM and auxiliary pulse-TA. Connect TM and TA to input 1 and 2 of pulse transfer isolation.

TABLE Experiment TRIGGER I/P’S TRIGGER O/P’S



TP TN TM TA T1 T11 T2 T2

1 1)Single Ph-half wave converter. 2)1-ph-full wave converter. 3)1-ph-half controlled bridge 4)1-ph-Fully controlled bridge 5)1-ph.AC phase control 6)Triac (short T1-T2 +ve –ve) 7)Complimentary commutation 8)Auxiliary commutation

* * * * * *

* * * * * *

* *

* *

* * * * * * * *

*

* * * * * * * *

*

Table shows the useful Trigger inputs and Trigger outputs for different experiments. WAVE FORMS:



0

1

Pe

2Wt

3

0

A

FA

F1

0

AWt

WtA

0Wt

Wt

Wt

0

C

Down

0Counting

16th pulse ofI f

N pulse

A

0Wta 2 3

0

B

Wt

0

B

Wt

Wt

Wt

0

C

0

G1

a 2 3

20

G

a+ 2

G = A,B, I1 c

G = A,B, I2 1

RESULT: CONCLUSION : 7) AC VOLTAGE CONTROLLER USING TRIAC – DIAC COMBINATION



AIM : To fire TRIAC using DIAC. APPRATUS REQUIRED : Dimmer stat ,Isolator, Lamp Load, Resistor ,Potentiometer ,Capacitor, DIAC( DB -3) ,TRIAC (BT-136), Power scope. DEVICE SPECIFICATIONS: BT136-600. 1. Vdrm : 600V. 2. Itrms : 4 A. 3. Itsm : 50 A. 4. It : 12.5 A. 5. di/dt : 10 A/µs. 6. Igt : 15 mA. 7. Vgt : 1.5 V. 8. IH : 13 mA. 9. IL : 50 mA. 10.dv/dt : 10 V/µs. DEVICE SPECFICATIONS: DB-3. Breakdown Voltage: 32V±10% Power: 0.5 Watts. CIRCUIT DIAGRAM :

DESIGN FOR AC VOLTAGE CONTROLLER :



Time Constant = T =RC + (R+R1)C T should exceed the time period of half a cycle for 50Hz mains. T =(R+R1)>=10mSec. The resistance R1 should limit the current value ,which prevents DIAC in conduction even after capacitor has discharged. Therefore, R1>VBBmax/Imax : R1>=VBDIAC/IDIAC R1>32/100ma R1>320 ohms Therefore , Let C=0.47 microfarads So, 0.00000047(320+R)=15mSec R=31900-320 =31580 ohms Choose a 100 kilo ohms potentiometer PROCEDURE: Make the connections as given in the circuit diagram. Switch ON the mains supply. Trigger the TRIAC using DIAC firing circuit. Vary the firing angle potentiometer and observe the AC voltmeter reading , waveform on the CRO & variation in lamp brightness and also note down the voltage variation across the lamp. For different positions ,we get different firing angle and for each setting note down the O/p voltage ac voltmeter reading in tabular column. Plot the graph of firing angle Vs ac load voltage. TABULAR COLUMN: Firing angle Practical Theoretical (α)=sin-1 (Vn/Vp) Vorms (Volts) Vorms (Volts) Vrms = Vm /√2 Vorms = Vm [(-)/(2) + (sin 2)/(2)]1/2

If =00; then Vorms = Vm /√2 = Virms WAVEFORMS:



waveforms across Vsupply, capacitor (VFBO), TRIAC (VTRIAC), load(VL) with respect to source for α = 90 degrees. RESULT: CONCLUSION : We conclude that power dissipation is less in case of DIAC firing circuit than UJT firing circuit. DIAC firing circuit has a better firing angle control than the UJT firing circuit. 8) SINGLE PHASE CONTROLLED CONVERTER



1) SINGLE PHASE SEMI CONTROLLED CONVERTER AIM :-To conduct a suitable experiment on half controlled(semi controlled) converter with resistive and inductive load . APPARATUS :- Dimmer-stat, isolator, rheostat, inductor (transformer/isolator)resistors ,single phase converter firing circuit, SCR converter module (power circuit module) .

SINGLE PHASE CONVERTER FIRING CIRCUIT FRONT PANEL DIAGRAM:

SINGLE PHASE CONVERTER TRIGGERING UNIT - SCT

ON / OFF

90°60°

30°

0°

120°

150°

180°TRIGGEROUTPUTS

+ - FIRING ANGLE

T1

T '1

T 2

T '2

GND1 2 3

7654

TEST POINTS

POWER



FRONT PANEL DETAILS: 1. Power :- Main ON/OFF switch with built in LED Indicator. 2. Firing angle :- Potentiometer to vary the firing angle from 180° to 0° 3. ON/OFF :- Switch for trigger output with soft start feature. 4. Test points :- To observe the signals at various points in the logic circuit for study purpose. 5. Trigger outputs :- T1 & T1

1 : For +ve Half Cycle. T2 &T2

1: For -ve Half Cycle. This unit generates four line synchronized isolated triggering pulses to fire thyristors connected in single phase (1) Half wave (2) Full wave (3) Half controlled Bridge (4) Fully controlled Bridge and (5) AC phase control power circuit. The firing circuit is based on Ramp-comparator scheme. Isolation is provided by pulse transformer. FEATURES :- 1. Work directly on 230V AC mains. 2. Gate drive current of 200mA to trigger wide range of devices. 3. Firing angle variation from 180° to 0° on a graduated scale. 4. Test points to study the logic circuit 5. Soft start and soft stop feature. 6. Neatly designed front panel. This unit along with our SCR converter modules, rectifier diode modules, single phase half controlled converter power circuit and single phase fully controlled converter power circuit can be used to conduct power electronics experiments on single phase. BACK PANEL DETAILS :- Mains socket with built in fuse holder. Fuse -500mA. A spare fuse is also provided in the fuse holder. INSTALLATION: While operating, keep the equipment in well-aerated cool place. Avoid direct sunlight on the equipment. Use a properly earth grounded outlet socket to connect to the equipment. This is so because a floating earth ground will not provide a clean AC reference to the equipment. The power input plug is situated on the back panel of the unit. Use the power cord provided along with the equipment to the power outlet socket. INPUT POWER SPECIFICATIONS:



Voltage : 215V -245V AC at 45 to 55Hz. Current : 75mA (Max continuous) @ 230V AC. 500mA (Max surge). Fuse : 500mA (Slow Blow) capsule type 20x 5mm. Situated in the lower left corner of the equipment front panel is the power ON/OFF switch with built in LED indicator. The LED glows when the switch is in ON position. A fuse protects the equipment against over voltage and any short circuit. The fuse holder is an integral part of the power inlet plug situated on the back panel. A spare fuse is provided in the fuse holder. The power cord has to be removed from the plug, before you can access the fuse holder. While replacing the fuse, pull off the holder smoothly. Refer to figure shown below: Power inlet plug Pull here Fuse holder Power inlet plug/fuse holder Remove and discard the blown off fuse and insert a new fuse in to the bay provided for it, replace back the assembly in correct direction and press it until it flushes with the surface. Now connect power cord back into the plug. Switch on the mains supply to the equipment. Observe the signals at test points, trigger outputs and their phase sequence before connecting to the thyristor in the power circuit. The built in pulse transformer based isolation between the trigger circuits and the power circuit provides isolation up to a tune of 1000V.



5V1

1K+ 12V

10 K

100K

1K

4K7

47K

-12V

100µF

OFF/ON

+ 12V

1N 4007

1N 400710K

1K

V1S

1K

0.1

100K

4K74K7

4K74K7

555

83 7

61 25

4

P

+12V4K7

414812K

0.010.01

7VS

4K7

P7V5

4K7

0.01 0.01

414812K

4K7+12V

5556215

4

3 8 7

T1 T2

T3 4148

1K

1N 4148

4K7

41482N2222

22K

1N 4007

22K

1N 40072N2222

IN 41484148

+12V

+12V

7V5

4K7

100 K

4148

1K

1K

741

3 4

67

+12V 100K3

2741

67

4

+12V

1K

T4T5

6T

15V

0.75A

15V

1N4007

1N4007

1000µF

1000µF25V

7812

7912

1000µF25V

1000µF25V 25V

+12V

GND

-12V

33 /5W

Vun 330

P/n 1K 12VBC107

SL-10010K

22PF

GATE

1K8 5V1

CATGATE

CAT

T

5V11K8

1N4007

FIRING ANGLE POT

CIRCUIT DIAGRAM

+ 15V

+ 15V

100K

(75mA) 0

+12V

-12V

T7

1N4007

1'

T1

0.1µF

0.1µF



TEST POINTS

1

2

3

Vc 4

5

6

7

8

T1 & T1

T2 & T2

TRIGGER OUTPUTS



SERVICING DETAILS SINGLE PHASE CONVERTER FIRING CIRCUIT : a) Check the 3 pin Mains Cable used along with this unit b) Check the Fuse in the Mains socket c) Check the Mains Switch d) Check the transformer e) Check the firing angle potentiometer. f) Check the ON/OFF switch g) Check the zener diodes & IN4007 diodes at the output of the pulse transformer. h) Check +12V & -12v power supply (Check 7812 &7912 regulators) i) Check BC 107 & SL 100 transistors j) Check 2N2222 transistors k) Check 741/555IC’s l) Check for any loose contacts. SINGLE PHASE SEMI CONTROLLED CONVERTER POWER CIRCUIT : SPECIICATIONS, 230V/5A The circuit arrangement of a single-phase full converter is shown in fig. During the positive half cycle, thyristor T1 and T1

1 are forward biased; and when these two thyristor are fired simultaneously at wt=, the load is connected to the input supply through T1 and T1

1 . In case of inductive loads, during the period wt (+), the input voltage is negative and the freewheeling diode Dm is forward biased. Dm conducts to provide the conductivity of current in the inductive load. The load current is transferred from T1 to Dm; and thyristor T1 IS turned off due to line or natural commutation. During the negative half cycle of the input voltage, thyristor T2 is forward biased. The firing of thyristor T2 at wt= + will reverse bias Dm. The diode Dm is turned off and the load is connected to the supply through T2 and T2

1. Figure shows the waveforms for input voltage, output voltage and Trigger Outputs. FRONT PANEL DIAGRAM:



This power circuit consists of four SCRs connected as semi- controlled bridge converter. A free wheeling diode is provided to observe the effect of free wheeling diode on inductive loads. Each device in the unit is mounted on an appropriate heat sink and is protected by snubber circuit. Short circuit protection is achieved using glass fuses. A circuit breaker is provided in series with the input supply for overload protection and to switch ON/OFF the supply to the power circuit. The front panel consists of input and output terminals. The gate and Cathode of each SCRs brought out on the front panel for firing pulse connection. Voltmeter and an Ammeter is mounted on the front panel indicates the output voltage and current. A separate full wave bridge rectifier is provided in the unit to get the DC supply for the field of DC Shunt Motors. The power circuit schematic is printed on the front panel. SPECIFICATIONS: Input Voltage :15V to 230V AC. Load current : 5 Amps maximum Fuses : 6 Amps fast blow glass fuses. Field supply : 220V ± 10%/2 Amps MCB : Two pole 6 Amps/ 230V FRONT PANEL DETAILS: Input terminals : To connect single phase input supply. Output terminals(+&-) : To connect load. Voltmeter(0 to 300V) : To indicate output voltage Ammeter(0 to 5A) : To indicate output current. Circuit breaker : 6 Amps AC power ON/OFF to the circuit and for protection . T1 & T2 : SCR – 16 TTS 12-16 A rms/1200Volts. D1 & D2 : Diodes –SPR 16PB-16A/1200V DM : Free wheeling diode –SPR 16PB-16A/1200V Field(+ and -) : Field supply for DC motor for motor control (with indicator) experiments. BACK PANEL DETAILS: Mains socket : For 230V AC mains supply to field supply bridge rectifier. Fuse holders : 2 fuses in series with input AC supply, a fuse at the output and a fuse for free wheeling diode.Fuse - 6 Amps SINGLE PHASE POWER CIRCUIT BLOCK DIAGRAM: : 230 V ,50Hz 0-230V

Isolation Transformer

Power Circuit

Load

Dimmer Stat

Firing circuit



1. Isolation Transformer: To suit single phase 230V/50Hz supply, ratio 1:1, KVA rating to suit the load rating with tapping at different voltages. Isolation of mains, phase and neutral with measurement circuit. Serves the purpose of di/dt protection of SCR’s and safe measurement of waveforms by using oscilloscope. Isolation of Electric noise with mains. 2. Power circuit: Different power circuit configurations are possible using SCR’s and diode modules. Half Wave Converter – 1SCR Half Controlled Converter _ 2 SCRs & 2 Diodes AC phase Control – 2 SCRs 3. Firing Circuit:

Each SCR of the above Power Circuit to be triggered using independently isolated outputs using single phase converter firing unit. Trigger outputs phase sequence and variation to be checked before with the power circuit. Phase sequence to be compared with the power circuits phase sequence.

PROCEDURE :-

Switch on the mains to the circuit. Observe all the test points by varying the firing angle potentiometer and trigger o/p’s ON/OFF switch. Then observe the trigger o/p’s and their phase sequence .Make sure that all the trigger o/p’ sure proper before connecting to the power circuit.. Next connections in power circuit .Use a dimmer stat with a isolator and connect it to power circuit. Connect the R-load between load points .Connect firing pulses from the firing circuit to respective SCR’s .Switch ON the MCB trigger o/p’s and note down load voltage can be seen .Repeat this same for R-L load and with and note down waveform.



TABULAR COLUMN: Firing angle Practical Theoretical (α)=sin-1 (Vn/Vp) Vodc (Volts) Vodc (Volts) Vodc (th) = Vm (1+cos ) /

Free Wheeling Diode, Resistive Load, and Resistive and Inductive load



WAVEFORMS:



RESULT:- CONCLUSION :- The output voltage at various firing angles are noted with R load and RL load and the difference with and without free wheeling diode is observed. The relevant waveforms are traced.



(ii) SINGLE PHASE FULLY CONTROLEED CONVERTER AIM: To Study the Single Phase Fully Controlled Converter on Resistance, Resistance & Inductance Loads . APPARATUS: Single Phase Converter Firing Circuit, Single Phase Fully controlled Power circuit, Rheostat (150 Ohms/5A), Inductor(150 mH/5A), Power Scope, Connecting Wires etc., SINGLE PHASE CONVERTER FIRING CIRCUIT FRONT PANEL DIAGRAM:

SINGLE PHASE CONVERTER TRIGGERING UNIT - SCT

ON / OFF

90°60°

30°

0°

120°

150°

180°TRIGGEROUTPUTS

+ - FIRING ANGLE

T1

T '1

T 2

T '2

GND1 2 3

7654

TEST POINTS

POWER

FRONT PANEL DETAILS: 1. Power :- Main ON/OFF switch with built in LED Indicator. 2. Firing angle :- Potentiometer to vary the firing angle from 180° to 0° 3. ON/OFF :- Switch for trigger output with soft start feature. 4. Test points :- To observe the signals at various points in the logic circuit for study purpose. 5. Trigger outputs :- T1 & T1

1 : For +ve Half Cycle. T2 &T2

1: For -ve Half Cycle. This unit generates four line synchronized isolated triggering pulses to fire thyristors connected in single phase (1) Half wave (2) Full wave (3) Half controlled Bridge (4) Fully controlled Bridge and (5) AC phase control power circuit. The firing circuit is based on Ramp-comparator scheme. Isolation is provided by pulse transformer.



FEATURES :- 1. Work directly on 230V AC mains. 2. Gate drive current of 200mA to trigger wide range of devices. 3. Firing angle variation from 180° to 0° on a graduated scale. 4. Test points to study the logic circuit 5. Soft start and soft stop feature. 6. Neatly designed front panel. This unit along with our SCR converter modules, rectifier diode modules, single phase half controlled converter power circuit and single phase fully controlled converter power circuit can be used to conduct power electronics experiments on single phase. BACK PANEL DETAILS :- Mains socket with built in fuse holder. Fuse -500mA. A spare fuse is also provided in the fuse holder. INSTALLATION: While operating, keep the equipment in well-aerated cool place. Avoid direct sunlight on the equipment. Use a properly earth grounded outlet socket to connect to the equipment. This is so because a floating earth ground will not provide a clean AC reference to the equipment. The power input plug is situated on the back panel of the unit. Use the power cord provided along with the equipment to the power outlet socket. Input power specifications: Voltage : 215V -245V AC at 45 to 55Hz. Current : 75mA (Max continuous) @ 230V AC. 500mA (Max surge). Fuse : 500mA (Slow Blow) capsule type 20x 5mm. Situated in the lower left corner of the equipment front panel is the power ON/OFF switch with built in LED indicator. The LED glows when the switch is in ON position. A fuse protects the equipment against over voltage and any short circuit. The fuse holder is an integral part of the power inlet plug situated on the back panel. A spare fuse is provided in the fuse holder. The power cord has to be removed from the plug, before you can access the fuse holder. While replacing the fuse, pull off the holder smoothly. Refer to figure shown below: Power inlet plug Pull here Fuse holder Power inlet plug/fuse holder



Remove and discard the blown off fuse and insert a new fuse in to the bay provided for it, replace back the assembly in correct direction and press it until it flushes with the surface. Now connect power cord back into the plug. Switch on the mains supply to the equipment. Observe the signals at test points, trigger outputs and their phase sequence before connecting to the thyristors in the power circuit. The built in pulse transformer based isolation between the trigger circuits and the power circuit provides isolation up to a tune of 1000V. Note that T1- T1

1 and T2- T21are from different secondary. Therefore T1 –T1

1 will be in phase and T2-T2

1 in the opposite phase. The table below gives the usage of the trigger output against different experiments. SL.NO EXPERIMENT TRIGGER OUTPUTS

T1 T1’ T2 T2’ 1 I –Phase half wave converter * 2 I –Phase full wave converter * * 3 I –Phase half controlled converter * * 4 I –Phase full controlled converter * * * * 5 I –Phase AC, phase control * *

5V1

1K+ 12V

10 K

100K

1K

4K7

47K

-12V

100µF

OFF/ON

+ 12V

1N 4007

1N 400710K

1K

V1S

1K

0.1

100K

4K74K7

4K74K7

555

83 7

61 25

4

P

+12V4K7

414812K

0.010.01

7VS

4K7

P7V5

4K7

0.01 0.01

414812K

4K7+12V

5556215

4

3 8 7

T1 T2

T3 4148

1K

1N 4148

4K7

41482N2222

22K

1N 4007

22K

1N 40072N2222

IN 41484148

+12V

+12V

7V5

4K7

100 K

4148

1K

1K

741

3 4

67

+12V 100K3

2741

67

4

+12V

1K

T4

T5

6T

15V

0.75A

15V

1N4007

1N4007

1000µF

1000µF25V

7812

7912

1000µF25V

1000µF25V 25V

+12V

GND

-12V

33 /5W

Vun 330

P/n 1K 12VBC107

SL-10010K

22PF

GATE

1K8 5V1

CATGATE

CAT

T

5V11K8

1N4007

FIRING ANGLE POT

CIRCUIT DIAGRAM

+ 15V

+ 15V

100K

(75mA) 0

+12V

-12V

T7

1N4007

1'

T1

0.1µF

0.1µF



TEST POINTS

1

2

3

Vc 4

5

6

7

8

T1 & T1

T2 & T2

TRIGGER OUTPUTS



SERVICING DETAILS SINGLE PHASE CONVERTER FIRING CIRCUIT : a) Check the 3 pin Mains Cable used along with this unit b) Check the Fuse in the Mains socket c) Check the Mains Switch d) Check the transformer e) Check the firing angle potentiometer. f) Check the ON/OFF switch g) Check the zener diodes & IN4007 diodes at the output of the pulse transformer. h) Check +12V & -12v power supply (Check 7812 &7912 regulators) i) Check BC 107 & SL 100 transistors j) Check 2N2222 transistors k) Check 741/555IC’s l) Check for any loose contacts. SINGLE PHASE FULLY CONTROLLED CONVERTER POWER CIRCUIT : SFC-230V/5A The circuit arrangement of a single-phase full converter is shown in fig. During the positive half cycle, thyristor T1 and T1

1 are forward biased; and when these two thyristor are fired simultaneously at wt=, the load is connected to the input supply through T1 and T1

1 . In case of inductive loads, during the period wt (+), the input voltage is negative and the freewheeling diode Dm is forward biased. Dm conducts to provide the conductivity of current in the inductive load. The load current is transferred from T1 and T1

1 to Dm; and thyristor T1 and T11 are

turned off due to line or natural commutation. During the negative half cycle of the input voltage, thyristor T2 and T2

1are forward biased. The firing of thyristor T2 and T2

1 simultaneously at wt= + will reverse bias Dm. The diode Dm is turned off and the load is connected to the supply through T2 and T2

1. Figure shows the waveforms for input voltage, output voltage and Trigger Outputs. FRONT PANEL DIAGRAM:

A +

S H CF I E L D

O N

L IN E

R E C T IF IE R~

+

~

-

1 P h . IN

N

L

-

T 1 T 2

VD m

1 P h . F U L L Y C O N T R O L L E D C O N V E R T E R P O W E R C I R C U I T

T 1 'T 2'

N

L

M C B

A M M E TE R

M E TE RV O L T



This power circuit consists of four SCRs connected as fully controlled bridge converter. A free wheeling diode is provided to observe the effect of free wheeling diode on inductive loads. Each device in the unit is mounted on an appropriate heat sink and is protected by snubber circuit. Short circuit protection is achieved using glass fuses. A circuit breaker is provided in series with the input supply for overload protection and to switch ON/OFF the supply to the power circuit. The front panel consists of input and output terminals. The gate and Cathode of each SCRs brought out on the front panel for firing pulse connection. Voltmeter and an Ammeter is mounted on the front panel indicates the output voltage and current. A separate full wave bridge rectifier is provided in the unit to get the DC supply for the field of DC Shunt Motors. The power circuit schematic is printed on the front panel. SPECIFICATIONS: Input Voltage :15V to 230V AC. Load current : 5 Amps maximum Fuses : 6 Amps fast blow glass fuses. Field supply : 220V ± 10%/2 Amps MCB : Two pole 6 Amps/ 230V FRONT PANEL DETAILS: Input terminals : To connect single phase input supply. Output terminals(+&-) : To connect load. Voltmeter(0 to 300V) : To indicate output voltage Ammeter(0 to 5A) : To indicate output current. Circuit breaker : 6 Amps AC power ON/OFF to the circuit and for protection . T1,T1

1,T2 & T21 : SCR – 16 TTS 12-16 A rms/1200Volts.

DM : Free wheeling diode –SPR 16PB-16A/1200V Field(+ and -) : Field supply for DC motor for motor control (with indicator) experiments. BACK PANEL DETAILS: Mains socket : For 230V AC mains supply to field supply bridge rectifier. Fuse holders : 2 fuses in series with input AC supply, a fuse at the output and a fuse for free wheeling diode. Fuse - 6 Amps SINGLE PHASE POWER CIRCUIT Single ph AC Input Single Phase Experiments Block Diagram

Isolation Transformer

Power Circuit

Load

Firing Circuit



1.Isolation Transformer :- To suit single phase 230V/50Hz supply, ratio 1:1, KVA rating to suit the load rating with tappings at different voltages. Isolation of mains, phase and neutral with measurement circuit. Serves the purpose of di/dt protection of SCR’s and safe measurement of waveforms by using oscilloscope. Isolation of Electric noise with mains. 2.Power circuit : Different power circuit configurations are possible using SCR’s and diode modules. Half Wave Converter – 1SCR Full Wave converter – 2 SCRs Half Controlled Converter _ 2 SCRs & 2 Diodes Fully Controlled Converter – 4 SCRs AC phase Control – 2 SCRs 3. Firing Circuit :

Each SCR of the above Power Circuit to be triggered using independently isolated outputs using single phase converter firing unit. Trigger outputs phase sequence and variation to be checked before with the power circuit. Phase sequence to be compared with the power circuits phase sequence. 4. Load :

Load connection should include an ammeter and a current shunt for current waveform measurements. Use freewheeling diodes wherever necessary. Types of Loads: - a) Resistance – ‘R’ b) Resistance and Inductive load ‘R’ & ‘L’. c) Motor and Generator. Note: In case of DC motor control, field excitation is separate. Field supply should be ON before giving armature supply. It should be switched OFF only after switching off the armature supply. Lamp load: Due to di/dt limitation of SCR’s and since the initial inrush current is 20 to 25 times more than load current in lamp loads and also since the cold resistance of the lamp is very less, lamp loads can be used with large safety factors. Precaution: Initially keep the input voltage low and firing angle at 1800.Slowly increase the voltage to the rated voltage and firing angle to 00.



CIRCUIT DIAGRAM:

INSTRUCTIONS: 1. Check all the SCRs for performance before making the connections. 2. Check the firing circuit trigger outputs and its relative phase sequence. 3. Make fresh connections before you make a new experiment. 4. Preferably work at low voltages (20-30V) for every new connections. After careful verification it can be raised to the maximum ratings. (This is to reduce damages due to wrong connections and high starting current problems). 5. The thyristor has a very low thermal inertia as compared to machine and by any overload or short circuit the SCR will immediately get damaged. Therefore do not switch ON the supply until the instructor has checked the connections. 6. While observing the waveforms of two parameters on the oscilloscope, either differential input oscilloscope should be used or special differential modules should be used with normal oscilloscope. On normal oscilloscope, observation of wave forms can be done with respect to single common point only. Ground connections of other probe must be avoided. It will lead to short circuit if ground connections of both the probes are used since they are internally shorted. In no case should oscilloscope input ground point be disconnected. This is a dangerous practice. Use 10:1 oscilloscope probe to see the waveforms at high voltages. 7. Do not make Gate & Cathode measurements when the power circuit is ON. TABULAR COLUMN: Firing angle Practical Theoretical (α)=sin-1 (Vn/Vp) Vodc (Volts) Vodc (Volts) Vodc (th) = 2Vm (cos ) /



PARAMETERS AND OBSERVATIONS: 1. Input voltage waveform 2. Output Voltage waveform (across the load) 3. Output current waveform (through the shunt) 4. Voltage waveform across thyristors (make this measurement only if isolations is used) 5. Study of variation of voltage and current waveforms with the variation of firing angle. 6. Study of effect of freewheeling diode in case of inductive loads. WAVEFORMS:

0

Wt

Wt

Wt

Wt

Vm V

V=VmSin wt

2

20

T 1

2T

Vo

VOLTAGE WAVE FORMS






RESULT: CONCLUSION: The output voltage at various firing angles are noted with R load and RL load and the difference with and without free wheeling diode is observed. The relevant waveforms are traced.



SERVICING DETAILS: Single-phase fully- controlled converter: Power circuit: - a) Check the devices – SCRs and diodes. b) Check the fuse. c) Check the MCB. d) Check for any loose contacts. e) Check the field supply bridge rectifier.



9) VOLTAGE COMMUTATED (IMPULSE COMMUTATED CHOPPER) BOTH CONSTANT FREQUENCY AND VARIABLE FREQUENCY AIM: To rig up DC Jones Chopper and to control O/P average DC Voltage both at constant frequency and variable frequency and at different duty cycles. APPARATUS: DC chopper power circuit ,DC chopper firing circuit, DC Regulated power supply (0-30V/2A), Rheostat (100hms/2A), CRO, connecting wires. DESCRIPTION : DC CHOPPER FIRING CIRCUIT: This firing unit provides triggering pulses for the Thyristors in auxiliary commuted chopper circuit configurations. It can be used for voltage commutation and current commutation chopper circuits consisting of one main load carrying Thyristor and one auxiliary Thyristor and associated commutation components. DC – Chopper firing unit should be used together with our DC-Chopper power circuit to conduct DC-DC chopper experiments on resistance, resistance and Inductance and motor load. This firing circuit can also used for other chopper circuits also. SPECIFICATIONS: Power supply : 230V/50 Hz, single phase ac mains. Output : Two pulse Transformer isolated trigger pulses for main and auxiliary Thyristors. Gate Drive current : 200 mA Auxiliary Gate pulse width :100µsec. Main Gate pulse width : Train of pulses Test points : 1 to 8 provides signals at various points of the logic circuit. Duty cycle : Variation from 10% to 90%. Frequency : Variation from 30 Hz to 300 Hz. Approximately. Control Voltage : Variation from 0 to 5V when the control switch is in INT position. External control voltage can be used by putting the switch to EXT position.




DC - CHOPPER TRIGGERING UNIT - DCT

10%

TRIGGEROUTPUTS

90%

DUTY CYCLE

Max.Min.

FREQUENCY

+ -

T MAIN

T AUX

GND1 2 3

7654

TEST POINTS

POWER

FRONT PANEL DETAILS: Power : ON/OFF switch with built-in indicator. Test points :1-7 test points for study of firing circuit. Duty cycle : Potentiometer to vary the duty cycle from 10% to 90% when the control switch is at INT position at the set frequency . Frequency : Potentiometer to vary the operating frequency of the chopper from 30Hz to 300Hz approximately. ON/OFF : Switch for main thyristor trigger pulse with soft start feature. Trigger Output TM : Main Thyristor Trigger pulse – Train of pulses. Trigger Output TA. : Auxiliary Thyristor Trigger pulse of 100 µsec. BACK PANEL DETAILS: Main socket with built in fuse holder. Fuse – 500mA.



NOTES: 1. The chopper cannot be tested without connecting the load. 2. The main thyristor T1 has to carry the resonant reversal current (along with load current) there by increasing current rating requirements. 3. The discharging and charging time of commutation capacitor are dependent on the load current and this limits the high frequency operation, especially at low load current. 4. The maximum value of the duty cycle is also limited to allow the commutation capacitor to discharge and recharge. 5. The thyristor T1 must be ON for a minimum time of tr = π(LmC) to allow the charge reversal of the capacitor and tr is fixed for a particular circuit design. This imposes minimum duty cycle limit and hence minimum output voltage. 6. The firing circuit provides the trigger pulses in the following range: Duty cycle: 10% to 90% Frequency: 30Hz to 300Hz. When the frequency is varied, the duty cycle is maintained constant at the set value. For example if the duty cycle is 50% at 50 Hz and you have now selected the frequency to vary from 50 Hz to 100 Hz, the duty cycle still remains 50% at 100Hz. The range of chopping frequency/duty cycle provided is no guarantee that any chopper power circuit will work for the full range. The limits of operation of a given power circuit depend on various factors like (a) the turn off requirement of the main thyristor (which should be less than the available turn off time) (b) the peak load current (c) the input DC voltage (d) The source and load inductance (e) The commutation circuitry – the value of C and Lm, etc., The function of firing circuit is only to provide properly sequenced and accurately timed trigger pulse in the said range. The trigger pulse for the main thyristor T1 is a continuous train of pulses for the whole of the ‘ON’ time kT (where k is the duty cycle). This train of pulses will be followed by the firing pulse for commutation thyristor, also known as Auxiliary thyristor, T2. This auxiliary trigger pulse is a single pulse whose width is approximately 100 microseconds. INSTALLATION: While operating, keep the equipment in well-aerated cool place. Avoid direct sunlight on to the equipment. Use a properly earth grounded outlet socket to connect to the equipment. This is so because a floating earth ground will not provide a clean AC reference to the equipment. The power input plug is situated on the back panel of the unit. Use the power card provided along with the equipment to the power outlet socket. INPUT POWER SPECIFICATIONS: Voltage : 215 – 245 A/C at 45 to 55 Hz. Current : 75mA (Max. continuous)@ 230V A/C. 500mA (Max. surge.) Fuse : 500mA (Slow Blow) Capsule type 20 x 5mm. Situated in the lower left corner of the equipment font panel is the power ON/OFF switch with built-in in LED indicator. The LED glows when the switch is in ON position.



A fuse protects the equipment against over Voltages and any short circuit. The fuse holder is an integral part of the power inlet plug situated on the back panel. A spare fuse is provided in the fuse holder. The power card has to be removed from the plug, before you can access the fuse holder. While replacing the fuse, pull off the holder smoothly. Refer to the figure shown below. Power inlet plug Pull here Fuse holder Power inlet plug/fuse holder Remove and discard the blown off fuse and insert a new fuse in to the bay provided for it, Replace back it the assembly in correct direction and press it until it flushes with the surface. Now connect the power card back into the plug. Switch on the mains supply to the equipment. Observe the test point’s signals, Trigger outputs and their phase sequence before connecting to the thyristors in the power circuits. CIRCUIT DIAGRAM:

741U2 741

U3

15V

FREQ100K

10K

1K

1K

4 8

7

6251

3555U1

TP1

0.01 0.47µF

62

3 P2T

100KTP3

-15V

329C10K

62

3

10K

10K

5V

1K A

5V1

29

51 8 6

71415

3101116

74LS123

4U

DUTY CYCLE

GATE

CAT

1K8

15 / 5W

330

9V

BC107

3019

220P

r

1K

1K8 5V1

1N4007 GATE

CAT

V57

330

15 / 5W9V

BC107

P7T2N3019

1KON / OFF

10K

4K7

7

6251

3

8

U5

555

DC CHOPPER FIRING CIRCUIT

5V

5V

4P4T

TP5

A

5V

33K

33K

.01

.01

5V1 (AUX)

(MAIN)



DESIGN FOR JONES CHOPPER (VGE COMMUTATED CHOPPER) Ic = Cdv/dt; -(1); Ic = capacitor current v=Voltage across capacitor for constant load current ; equation can be Ic = CVs/tc or C = tcIo/Vs tc= commutating circuit time>tq(device turn-off time) i.e,tc>tq ; so now let tc = tq + ∆t tq for TY612 is 70 µSec which is almost equal to100 µSec Let ∆t= 20 µSec Therefore tc = 120µSec Let Vs= 30v; Ic =2 A. Therefore c = 120 µSec x 2/30 = 4 x 2 µF = 8 µF. Choose C = 10 µF. Ic = VsSin (Wot)/Wo L ; Wo = 1/[LC] ½

Icp = Vs/WoL<=Io <=Vs[(C/L)] ½ , L>=[ (Vs/Io)]2 C >= [ (30/2)]2 8 x 10-6 >=1.8mH Select L= 2mH or 8mH.



WAVEFORMS:

15 T P1010V5 T P25V0 T P3

D C - C H O P P ER FIR IN G C IR C U IT - T E ST P O IN T S

5V0 T P 45V0 T P 5

0 T P 65V

T P 7

T

T A

M

JONES CHOPPER POWER CIRCUIT: 30V/2A: This unit consists of two SCR’s two diodes and L C commutation circuit to construct Jones chopper power circuit. Each device in the unit is mounted on an appropriate hear sink and is protected with an RC snubber circuit. All the components are independent and their connections are brought out to front panel. The cathode and gate of each SCR is brought out ob to separate terminals for firing pulse connection. A switch and a fuse are provided in series with the input DC Supply. The devices and components can also be used to build different chopper circuits. Integrated Thyristor Controller –ITC 08 and DC chopper firing unit DCT provided triggering pulses for this power circuit. SPECIFICATION: 30V @ 2.0 Amps.




+

+

-

DC INPUT

L

L'

C com

TM

TA DFW

D1

OUTPUT

+

-

RECTIFIER~

+

~

-

230 VAC

FIELD

SCR DC - CHOPPER POWER CIRCUIT - SDCP

MC B

FRONT PANEL DETAILS: VDC IN : Terminal to connect DC input 10V to 30V DC. ON : ON/OFF switch for the input DC supply to the power circuit. Fuse : In series with the DC input for short circuit protection –2 Amps. T1 & T2 :SCR’s – TYN 616 D1 & D2 : diodes – BYQ 28 200. C : Commutation Capacitor – 10uF/100V. L1-0-L2 : Commutation Inductor 500-0-500 Micro henry/2 Amps. CIRCUIT DIAGRAM:

1T

C

2T1L 2LLM

LOA

DDM

D1

VDC

JONES CHOPPER

CIRCUIT DIAGRAM



CONNECTION DIAGRAM:

FUSE C

T1

2T

DM

LOA

D

1DL2

ML

L1

Vdc In

SWIT

CH

JONES - CHOPPER POWER CIRCUIT 30V/2A

PROCEDURE : To begin with switch ON the DC Chopper firing unit. Observe the test point Signals and Trigger output signals by carrying Duty cycle and Frequency Potentiometer by keeping the control switch into INT position. Be sure the trigger Outputs are proper before connecting to the power circuit. Now make the interconnections in the power circuit as given in the circuit diagram. Connect DC supply from a variable DC source. Initially set the input DC supply to 10 Volts. Connect a Resistive load. Connect respective trigger outputs from the firing circuit to the respective SCRs in the Power circuit. Initially keep[ the ON/OFF switch in the firing circuit in OFF position. Switch ON the DC supply. Apply Main SCR trigger pulses by pressing the ON/OFF Switch to ON position. Observe the voltage waveforms across load. We can observe the chopped DC waveform. If the commutation fails we can see only the DC voltage. In that case switch OFF the DC supply, Switch OFF pulses and check the connections and try again. Observe the voltage across load, across Capacitor, across Main SCR and auxiliary SCR by varying Duty cycle and frequency Potentiometer. Now vary the DC supply up to the rated voltage (30V DC). Draw the waveforms at different duty cycle and at different Frequency. Connect Voltmeter and Ammeter and note down values in the table.



TABULAR COLUMNS: SL.NO V in Ton Toff Duty

cycle Vo Io

INSTRUCTIONS: 1. Check all the SCR’s for performance before making the connections. 2. Check the firing circuit Trigger output and its relative phase sequence 3. Make fresh connection before you make a new experiment. 4. Preferably work at low voltages for every new connections. After careful verification it can be raised to the maximum ratings (This is to reduce damages due to wrong connections and high starting current problems) 5. The Thyristor has a very low thermal inertia as compared to machine and by any over load or short circuit the SCR will immediately get damaged. Therefore do not switch ON the supply until the instructor has checked the connections. 6. While observing the waveform of two parameters on the oscilloscope observation of waveforms can be done with respect to single common point only. Ground connection of other probe must be avoided. It will lead to short circuit if ground connections of both the probes are used. Since they are internally shorted. In no case should oscilloscope input ground point be disconnected. This is a dangerous practice. Use 10:1 oscilloscope probe to see the waveforms at high voltages. 7. Do not make Gate & cathode measurements when the power circuit is on



PARAMETERS AND OBSERVATIONS: 1. Voltage wave form across capacitor. 2. Output voltage waveforms (across the load) 3. Output current waveforms (Through the shunt) 4. Voltage waveforms across Thyristor. 5. Study of variation of voltage and current waveforms with the variation of duty cycle and frequency. 6. Study of effect of free wheeling diode in case of inductive loads. PRECAUTIONS: 1.In case of DC motor control, field excitation is separate. Field supply must be ON before giving armature supply. It should be OFF only after switching off the armature supply. Without field supply load current is too high which is limited by armature resistance. 2.In case lamp load, due to di/dt limitation of SCR’s and since the initial inrush current is 20 to 25 times more than load current, it can be done only with large safety factor. 3.Chopper cannot be tested without connecting load. RESULT: CONCLUSION : The chopper has been verified and tested .It is found that Vo(prac) = Vo(theor)



10) SPEED CONTROL OF SEPARATELY EXCITED DC MOTOR:

SPECIFICATIONS: Input Voltage :15V to 230V AC. Load current : 5 Amps maximum Fuses : 6 Amps fast blow glass fuses. Field supply : 220V ± 10%/2 Amps MCB : Two pole 6 Amps/ 230V FRONT PANEL DETAILS: Input terminals : To connect single phase input supply. Output terminals(+&-) : To connect load. Voltmeter(0 to 300V) : To indicate output voltage Ammeter(0 to 5A) : To indicate output current. Circuit breaker : 6 Amps AC power ON/OFF to the circuit and for protection . T1,T1

1,T2 & T21 : SCR – 16 TTS 12-16 A rms/1200Volts.

DM : Free wheeling diode –SPR 16PB-16A/1200V Field(+ and -) : Field supply for DC motor for motor control (with indicator) experiments. BACK PANEL DETAILS: Mains socket : For 230V AC mains supply to field supply bridge rectifier. Fuse holders : 2 fuses in series with input AC supply, a fuse at the output and a fuse for free wheeling diode. Fuse - 6 Amps



1.Isolation Transformer :- To suit single phase 230V/50Hz supply, ratio 1:1, KVA rating to suit the load rating with tappings at different voltages. Isolation of mains, phase and neutral with measurement circuit. Serves the purpose of di/dt protection of SCR’s and safe measurement of waveforms by using oscilloscope. Isolation of Electric noise with mains. 2.Power circuit : Different power circuit configurations are possible using SCR’s and diode modules. Half Wave Converter – 1SCR Full Wave converter – 2 SCRs Half Controlled Converter _ 2 SCRs & 2 Diodes Fully Controlled Converter – 4 SCRs AC phase Control – 2 SCRs 3. Firing Circuit :

Each SCR of the above Power Circuit to be triggered using independently isolated outputs using single phase converter firing unit. Trigger outputs phase sequence and variation to be checked before with the power circuit. Phase sequence to be compared with the power circuits phase sequence. 4. Load :

Load connection should include an ammeter and a current shunt for current waveform measurements. Use freewheeling diodes wherever necessary. Types of Loads: - a) Resistance – ‘R’ b) Resistance and Inductive load ‘R’ & ‘L’. c) Motor and Generator. Note: In case of DC motor control, field excitation is separate. Field supply should be ON before giving armature supply. It should be switched OFF only after switching off the armature supply. Lamp load: Due to di/dt limitation of SCR’s and since the initial inrush current is 20 to 25 times more than load current in lamp loads and also since the cold resistance of the lamp is very less, lamp loads can be used with large safety factors. Precaution: Initially keep the input voltage low and firing angle at 1800.Slowly increase the voltage to the rated voltage and firing angle to 00. INSTRUCTIONS: 1. Check all the SCRs for performance before making the connections. 2. Check the firing circuit trigger outputs and its relative phase sequence. 3. Make fresh connections before you make a new experiment.



4. Preferably work at low voltages (20-30V) for every new connections. After careful verification it can be raised to the maximum ratings. (This is to reduce damages due to wrong connections and high starting current problems). 5. The thyristor has a very low thermal inertia as compared to machine and by any overload or short circuit the SCR will immediately get damaged. Therefore do not switch ON the supply until the instructor has checked the connections. 6. While observing the waveforms of two parameters on the oscilloscope, either differential input oscilloscope should be used or special differential modules should be used with normal oscilloscope. On normal oscilloscope, observation of wave forms can be done with respect to single common point only. Ground connections of other probe must be avoided. It will lead to short circuit if ground connections of both the probes are used since they are internally shorted. In no case should oscilloscope input ground point be disconnected. This is a dangerous practice. Use 10:1 oscilloscope probe to see the waveforms at high voltages. 7. Do not make Gate & Cathode measurements when the power circuit is ON. 8. Vary the firing and note down Vodc, Iodc and speed N in RPM TABULAR COLUMN: Firing on the Pottetiometer Deg

Firing angle Practical Theoretical N Speed in RPM

(α)=sin-1

(Vn/Vp) Vodc (Volts) Vodc (Volts)

Vodc (th) = 2Vm (cos ) / PARAMETERS AND OBSERVATIONS: 1. Input voltage waveform 2. Output Voltage waveform (across the load) 3. Output current waveform (through the shunt) 4. Voltage waveform across thyristors (make this measurement only if isolations is used) 5. Study of variation of voltage and current waveforms with the variation of firing angle. 6. Study of effect of freewheeling diode in case of inductive loads. 7. Fro various firing note the speed on the digital meter on the motor panel.



WAVEFORMS:

0W t

W t

W t

W t

V m V

V =V m Sin w t

2

20

T 1

2T

V o

V O LTA G E W A V E FO R M S






RESULT: CONCLUSION: The output voltage at various firing angles are noted with DC Motor as load and the difference with and without free wheeling diode is observed. The relevant waveforms are traced.



11) SPEED CONTROL OF UNIVERSAL MOTOR Motor Specification: 0.5HP/220V AC/DC AIM: To Control the speed of the Universal through (i) AC-DC Power converter (FCR) and (ii)AC Voltage Controller Apparatus: Universal Motor, Isolation Transformer, dimmer-stat, Fully controlled bridge rectifier (FCR), ACVC, FCR Firing Circuit.



Procedure: Make the inter connections in the power circuit as in the circuit for FCR and ACVC,. Switch on the the firing circuit and observe the trigger pulses. Make sure that the firing pulses are proper before connecting to the power circuit. Then connect the trigger output from the firing circuit to the corresponding SCR’s/TRIAC. In the power circuit initially set AC input to 30V. Switch on the MCB. Switch on the trigger. First observe the output across R load by varying the potentiometer. If the output wave form is proper then you can connect the motor and increase the input voltage to the rated value i.e., 230V gradually. Vary the firing angle and note O/P voltage and speed of the motor Table (Fully Controlled Rectifier Firing on the Potentiometer Deg


(α)=sin-1

(Vn/Vp) Vodc (Volts) Vodc (Volts)

Table (ACVC) Firing on the Potentiometer Deg


(α)=sin-1 Vn/Vp) Vodc (Volts) Vodc (Volts)



12) SPEED CONTROL OF STEPPER MOTOR: STEPPER MOTOR CONTROLLER This is Micro controller based controller circuit to accurately generates pulses to energizes the stepper motor winding in the desired sequence . Power transistor based driver circuit to driver circuit to drive the stepper motor. From this controller we can set the speed of the stepper motor in RPM, set the number of steps motor can move .We can set the direction of rotation forward and reverse direction. We can also set half step and full step mode. FRONT PANEL DETAILS: 1.Mains :Power ON/Off Switch to the unit with built-in indicator. 2.Display :Seven segment 5 digit display to display the parameter and values 3.Key board : a)Set :To set the Parameter. b)INC :To increment the set parameter values. c)DEC :To decrement the set parameter values. d)ENT :To enter the set values. e)RUN/STOP :To start and stop the stepper motor. .(Built in) 4.+v : 5v/2 amps DC supply for stepper motor.(Built in) 5.+5v :5 v for control circuit .(Built in) 6.GND :Supply ground point 7.FUSE :2 amp fast below glass fuse for short circuit protection. 8.A1,A2,B1 & B3: Outpoints to connect to the A1,A2,B1 &B3 leads of stepper motor. 9.LED’s :To indicate the status of output. BACK PANNEL DETAILS: Mains socket with built in fuse holder and a spare fuse. PROCEDURE:- Connect A1, A2, B1 and B2 leads of stepper motor to the corresponding output terminal points. And two common terminal to +V supply. Switch ON the mains supply to the unit. Check the power supplies. The unit display S – 00. Now press SET. Then the display shows rpm(revolutions per minute). If you press ENT now the speed mode is set and it displays 00. Then press INC Key to set the rpm. When the display shows rpm, if you press INC/DEC it goes to STEP mode or vice versa. After setting the Speed in rpm/ no of steps, press ENT Key. Then the parameter values is entered and it shows set direction of rotation. Press INC/DEC changes the direction of rotation. Then press ENT Key to set the direction of rotation. Then it displays Half step or Full step mode. Pressing INT/DEC will changes to HALF Step/ FULL Step mode or vice versa. Press ENT Key to set the Half step or Full step mode.



Then it displays n-set rpm if speed is selected or S-set steps if steps is selected. This is the method for setting the parameter. After this if we press RUN/STOP key the Motor stops. If we select the STEP mode the motor moves the number of set steps and stops when we press RUN/STOP key. If we press again the motor moves again and stops. Set the step mode at 1 step and half step mode and check the output status by LED indication for each step of rotation and verify with the theoretical. Repeat the same foe Full step mode also. Repeat the above for the other direction. D.C.BRUSHLESS STEPPING MOTORS The stepping motor is an electromagnetic device which converts digital pulses into discrete mechanical rotational movements. In rotary stepper motor, the output shaft of motor rotates in equal increments, in response to a train of input pulses. CHARACTERISTICS:- Construction:- Stepping Motor is basically a Motor with two phases, eight salient poles, toothed iron rotor and a permanent magnet. This rotor is known as hybrid rotor. The rotor is suspended in the stator by means of sealed ball bearings. All parts of the motors are precision machined for better performance and accuracy of steps. Step Angle: 1.8*+ or - .1* non-cumulative. Holding Torque: 2.8 Kg cm. Dynamic Torque: Dynamic torque is mainly controlled by the electronic control circuits. Torque will drop down as the speed increases. Residual Torque or Detent Torque : Because of the presence of permanent magnet in the rotor. Working Temperature and insulation Class: Temperature of stepping motors may rise 50*C above ambient. It is observed that body temperature generally stabilizes at about 85*C to 90*C for continuous duty cycle. The insulation used is of class B type which can withstand hot spot temp of 130*C. For better heat dissipation motors duly fitted with heat sinks are recommended. This reduces the temp by about 10*C to 15*C. Working of stepping motor:- The stepping action is caused by sequential switching of supply to the two phases of motor as shown in switching logic sequence table. The specified torque of any stepping motors is the torque at stand still (holding torque). This torque is directly proportional to the current to rated level within the time given for one step. This is mainly due to L/R time constant of winding. The drop in current level causes drop in torque as the speed increases. In order to improve torque at high speed it is necessary to maintain current at the rated level. Never exceed rated current of the motor. Stepping Motors differ form conventional DC Servo Motors in the following respects. 1.There is no control winding in stepping Motors. Both windings are identical. 2.The stepping rate (speed of rotation) is governed by frequency is governed by frequency of switching and not by supply voltage.



3.A single pulse input will move the shaft of motor by one step. Thus number of steps can be precisely controlled by controlling number of pulses. 4.When there is no pulses input, the rotor will remain locked in the position in which the last step was taken since at any time two winding are always energized which lock the rotor electro magnetically. 5.Steping Motors can be programmed in there parameters namely : a) Direction. b) Speed. c) Number of steps. 6.Stepping Motor is brush less so no wear & tear. 7.Load & no load condition makes no difference in running currents of the motor. GENERAL INFORMATION:- 1.Resonance – When a stepping motor is operated at its natural frequency an increase in noise and vibration occurs. This phenomenon is called as resonance. The frequencies at which this resonance occurs depends widely on the characteristic of load and it also varies from motor to motor. The change in inertial load will; change the resonance frequency. In half-step mode resonance may be reduced / avoided. 2.Ramp – Acceleration (soft start) and declaration (soft stop are essential factors of controller . Acceleration is required to run the motor at high step rates and declaration is to stop motor accurately at specified position. 3.Half Step Mode – Advantage – Smother motion ,resolution factor increases by the factor2, reduces resonance problems. Disadvantages-Loss of torque(above 40%) In half step mode we do not offer guarantee for accuracy but error automatically gets corrected on next even half step. 4. Mounting-Flange Mounting. Motor must be mounted with reference to boss and not with reference to mounting holes. 5. Synchronization-‘N’ no. of SRI.SYN. Stepper motors can be operated simultaneously at time with single controller &’N’ no. of drives. APPLICATION:- Numerically controlled Machine Tools and Machining centers: Profile cutting, Grinding, Milling and Boring Machines, Lathes, park erosion Machines, sheet Metal presses, Industrial Robots ,etc. Plastic and packaging: Mark registration ,labeling, cut to length. Graphics: Photo printing and developing ,Photo type setting printing presses, Film projectors and cameral, etc Process control and Instrumentation: Textile web control, valve controls, Material Handling systems, Assembly lines, carburetor Adjusting, In process Gauging ,chart Recorders, servo Mechanism, Electronic gear box, profile, precise RPM control, RPM control, RPM meter calibration



Medical Instrumens:- Infusion pumps, x-ray and Radioactive Machinery, Blood analyzers etc. Office Automation Equipments: Printers, plotters, Hard and Floppy Disc, Teleprinter and Typewriters, copying Machines and Accounting Machines V=4*motor voltage Rs=3*Rm(Motor resistance/phase) Suitable for slow RPM SWICHING LOGIC SEQUENCE A1 A2 B1 B2 Red Green Blue Black 0 1 0 1 0 1 1 0 1 0 1 0 1 0 0 1 Q1 Q2 Q3 Q4 Half step A1 A2 B1 B2 Red Green Blue Black 0 1 0 1 0 0 0 1 1 0 0 1 1 0 0 0 1 0 1 0 0 0 1 0 0 1 1 0 0 1 0 0 To change the direction red sequence from bottom to top Specification:- Permanent magnet, Bifilar wound Steps per Revolution:200 Two phase. Step Angle:1 .8*+0r-0.1*non cumulative. No of leads-6 3kg.cm=0.1 N .m=13.90z-in





13) SERIES / PARALLEL INVERTER

(i)SERIES INVERTER

AIM : To design the series Inverter circuit and test its working. APPRATUS REQUIRED : Series Inverter Module, Digital Millimeter , Power Supply, Patch chords . DESCRIPTION : This unit consists of power circuit and firing circuit sufficient to build and study the modified series inverter. Firing circuit: This part generates two pairs of pulse transformer isolated trigger two SCRs connected as series inverter ON/OFF switch is provided For the trigger pulses which can be used to switch ON the inverter. Frequency of the inverter can be varied from 100hz to 1Khz approximately. Power circuit : This part consists of two SCRs two diodes. A center tapped inductor with tapings and capacitors .Input supply terminals with ON/OFF Switch and a fuse is provided .All the devices in this unit mounted on a proper heat sink, snubbed circuit for dv/dt protection and a fuse in series with each device for short circuit protection. All the points are brought out to front panel for inter connection. They have to be interconnected as shown in the circuit diagram .Free wheeling diodes Can be connected across SCRs and its effect can be observed. Refer any standard text books for theoretical details. Front panel details: 1.Frequency: Potentiometer to vary the inverter frequency. 2. Trigger outputs: From 100HZ to 1KHZ approximately 3.ON/OFF: Switch for trigger outputs. 4.T1 and T2: Trigger outputs. 5.Power : Mains switch for firing circuit. 6.Vdc in: Terminals for dc input-30v/2amps Max. 7.ON/OFF: Switch for dc input 8.Fuse: Fuse for dc input 2amps Glass fuse. 9.T1 and T2: SCRs TYN612.12amps/60v 10.D1 and D2: Diodes BYW51-200 4amps/200v 11.L2 L1 Lm L1 L2: 10mH-5mH-0-5mH-10mH/2 amps 12.C1 and C1: 6.8f/100v 13.C2 and C2: 10f/100v.



CIRCUIT DIAGRAM :

DESIGN OF SERIES INVERTER : (specimen calculation) wr =(1/Lc)-(R2/4L2) f r<=fmax = 1/(tq + / wr ) let tq = 10 sec f r = 1 k hz wr = 20,408 r/sec R2 < 4L/C wr (1/Lc) 20,408 = (1/Lc) let C = 10 f so, L = 0.240mH R2 < 4L/C R2 < 96 R < 9.6 (load).



PROCEDURE: To begin with switch on the power supply to the firing circuit. Check that trigger pulses by varying the frequency. Make the interconnection s of the power circuit as shown in the circuit diagram. Now connect trigger outputs from the firing circuits to gate and cathode of SCRs T! and T2.Connect dc input from a 30v/2amps regulated power supply. Switch on the input dc supply .Now apply trigger pulses to the SCRs and observe voltage wave from across load vary the frequency and observe the wave forms of the inverter frequency increases above resonant frequency of the power circuit communication will fail. Then switch OFF the dc supply , reduce the inverter frequency and try again if you will not get the result check the input fuse and try again, if it fails again you have to check the fuses in series with devices. Repeat the same with different values of L,C and load. And also observe the wave forms with and without free diodes. The output waveform is entirely depending on load .To switch OFF the inverter. Switch OFF the input supply first and then trigger pulses. RESONANT FREQUENCY: fr=1/2 (1/LC-R*R/4L*L) TABULAR COLUMN : KEEPING RESISTANCE CONSTANT AT ---- Ω , F(Hz) Vorms (volts) KEEPING FREQUENCY CONSTANT AT ---- Hz , R(Ω) Vorms (volts)



WAVEFORMS :



RESULT : CONCLUSION : We conclude that as and when the frequency and resistance increases the Vorms also increases.



2) PARALLEL INVERTER

AIM : To design the series Inverter circuit and test its inverter working. APPRATUS REQUIRED : Series Inverter Module, Digital Millimeter , Power Supply, Patch chords . DESCRIPTION : This module consist of two units – (1) Firing circuit and (2) Power circuit. 1)Firing circuit :- This unit two pairs of pulse transformer isolated trigger pulses to trigger two SCRs connected in center tap transformer type parallel inverter. Frequency of the inverter can be varied from 75 hz to 200 hz approximately. 2)Power circuit. :- This unit consist of two SCRs, two free wheeling diodes, commutation induction. Commutation capacitor and a center transformer to be inter connected to make parallel inverter. All the points are brought out to the front panel. A switch and fuse is provided for input DC supply. All the devices are mounted on proper heat sink. Each device is protected by snubber circuit. FRONT PANEL DETAILS: 01.Frequency :potentiometer to vary the inverter frequency from75Hz to 200 Hz approximately 02.ON/OFF :Switch for trigger outputs. 03.T1 & T2 :Trigger outputs. 04.Power :Mains switch for firing circuit. 05.VDC in :terminals for DC input. 06. ON :Switch for DC input. 07. TP & TN :SCR’S 10A/600V 08. DP & DN :Diodes 10A/600V 09.L :Inductance 300 10.C :6.8 F/100V 11.Load :Terminals to connect the load :Transformer center tap point which should be connected to +ve of DC supply after fuse. 13.Fuse :2A Glass fuse. 14.Output Transformer :Primary-30V-25V-0-25V-30V. Secondary-0-30V/2Amps.



CIRCUIT DIAGRAM :

DESIGN OF PARALLEL INVERTER (specimen calculation) L acts as current source C is resonating element. Lm mutual inductance of transformer and acts as a resonating inductor. wr = (1/Lc) Quality factor = Q; let Q = 4 Q = woCR ; fo = 1 khz. Let wo = 6.280 khz Let R = 20 C = 31.8 f & (6280) 2 = 1/LC L = 0.797 mH. Choose L = 1 mH.(should be mutual inductance of transformer). The commutating components L & C are selected as follows: L = Vs tq /0.425Im & C = Im tq /1.7 Vs , Im = Current at Commutation. Vs = DC supply voltage; tq = Reverse bias time offered to SCR.



PROCEDURE : The circuit is a typical class C parallel inverter. Assume TN to be ON and TP to be turned OFF .The bottom of the commutating capacitor is charged to twice the supply voltage and remains at this value until Tp is turned on .When Tp is turned on, the current flows through lower primary ,Tp and commutating inductance L. Since voltage across c cannot raise instantaneously, the common SCR cathode point raises approximately to 2Vdc and reverse biases TN. Thus TN turns off and C discharges through L , the supply circuit and recharges in the reverse direction. the auto transformer action makes C to charge making now its upper point to reach +2Vdc Volts ready to commutate Tp, when TN is again turned on, and the cycle repeats. The major purpose of the commutating inductance L is to limit the commutating capacitor charging current during switching. Freewheeling diodes Dp and DN assists the inverter in handling various range of loads and the value of C may be reduced since the capacitor now does not have to carry the reactive current. To dampen the feedback diode currents within the half period , feedback diodes are connected to the tapings of the transformer at 25V tapings. Switch on the firing circuit .Observe the trigger outputs TP and TN by varying frequency potentiometer and by operating ON/OFF switch. Then connect input DC supply to the power circuit. Connect the trigger outputs to gate and cathode of the SCR TP and TN. Make the interconnections as shown in circuit diagram. Connect load between load terminals. Connect free wheeling diodes in the circuit. To begin with set input voltage to 15V. Apply trigger pulses to SCR and observe voltage wave forms across load. Output voltage is square wave only. Then remove the free wheeling diode connections and observe the wave forms. Then vary the load, vary the frequency and observe the waveforms. To switch OFF the inverter switch OFF DC input supply only. Switch OFF the trigger pulses will lead to short circuit. Since the parallel inverter works on forced commutation ,there is a chance of commutation failure. If the commutation fails, there is a dead short circuit in the input DC supply, which will leads to blown off the input fuse. Please check the fuse if the commutation fails. Preferably connect the input DC supply from the 30V/2A regulated DC power supply unit which has over current tripping facility there by protect the DC supply unit. If the commutation fails, switch off the DC supply first and then trigger outputs. Check the connections again. TABULAR COLUMN : KEEPING RESISTANCE CONSTANT AT ---- Ω , F(Hz) Vorms (volts) KEEPING FREQUENCY CONSTANT AT ---- Hz , R(Ω) Vorms (volts)



WAVEFORMS :

RESULT : CONCLUSION : We conclude that as and when the frequency and resistance increases the Vorms also increases.



MODEL QUESTION BANK OF LABORATORY

Expt. No. QUESTION

1

Conduct a suitable experiment to determine the V-I Characteristics of “Unidirectional four layer switch” for different gate currents. Determine break down voltage and holding current for two cases.

2

Conduct a suitable experiment to determine the V-I Characteristics of “Bi-directional four layer switch”. Determine break down voltage and holding current in 1st and 3rd quadrants and comment on its sensitivity.

3 Conduct a suitable experiment on MOSFET to verify its on – state resistance and gate threshold voltage. Plot the transfer characteristics and output static characteristics.

4 Conduct a suitable experiment to determine the V-I Characteristics o IGBT. Comment on its switching characteristics.

5 Conduct a suitable experiment to control Half Wave Rectifier using RC firing circuit and plot a graph of load voltage versus firing angle and various waveforms.

6 Conduct a suitable experiment to control Full Wave Rectifier using RC firing circuit and plot a graph of load voltage versus firing angle and various waveforms

7 Design a synchronized UJT Relaxation Oscillator circuit to turn ON the SCR and hence plot various waveforms.

8 Design a synchronized UJT Relaxation Oscillator circuit for controlling Half Wave Rectifier and hence plot a graph of load voltage versus firing angle & various waveforms.

9 Design a synchronized UJT Relaxation Oscillator circuit for controlling Full wave rectifier and hence plot a graph load voltage versus firing angle & various waveforms.

10 Conduct a suitable experiment on LC commutation circuit to prove that conduction period of SCR depends on commutating elements (R, L and C ). OR Auxiliary Commutation

11 Conduct a suitable experiment to control the speed of an AC motor/Brightness of a lamp using TRIAC–DIAC combination. Draw the graph of firing angle Vs speed/Vorms

12 Conduct a suitable experiment on half controlled/fully controlled bridge rectifier with resistive load /R-L load. Plot DC voltage Vs. delay angle graph.

13 Conduct a suitable experiment to experiment to control the speed of separately excited DC motor and plot a graph of speed versus firing angle and Vodc Vs firing. Angle.

14

Conduct a suitable experiment on Chopper to convert constant DC voltage to variable DC voltage with a duty cycle of ___________ check the result with theoretical value.

15 Conduct a suitable experiment to verify the operating principle of a single phase Series/Sarallel inverter and hence plot various waveforms of the inverter



VIVA QUESTIONS

1. What is SCR ? 2. What is TRIAC ? 3. What is DIAC? 4. What is MOSFET ? 5. What is IGBT ? 6. What is meant by commutation ? 7. What is the difference between TRIAC and DIAC ? 8. What is the difference between MOSFET and IGBT ? 9. What is the difference between UJT and BJT ? 10. How di/dt and dv/dt protection is provided for power transistors ? 11. What is the use of isolator ? 12. What is the difference between n-channel and p-channel MOSFET ? 13. What do you understand by threshold and pinch- off voltages ? 14. What is the importance of holding current ? 15. What do you understand by latching current ? 16. What is pulse transformer ? 17. What is the need of a transformer in circuits ? 18. Name few applications of MOSFETs and IGBTs . 19. List the factors that affect the turn ON turn OFF times of a power BJT . 20. Name the terminals of MOSFET . 21. What do understand by thyristor ? 22. What is snubber circuit ? 23. What is the affect of gate current on break over voltage in SCR ? 24. State the conditions to be satisfied for proper turn off of an SCR. 25. What are the different methods of commutation of SCRs ? 26. What is line commutation ? 27. What is impulse commutation ? 28. What is self commutation ? 29. How to turn off an SCR properly ? 30. What is auxiliary commutation ? 31. What is an AC voltage controller ? 32. List the different types of ACVC. 33. What are the applications of ACVC ? 34. What is controlled rectifier ? 35. Give the classifications of controlled rectifier circuits . 36. List the applications of rectifiers . 37. What is the difference between uncontrolled and controlled rectifier ? 38. What is chopper ? 39. What are the methods of chopper control ? 40. How will you classify choppers ? 41. What is the function of an inverter ? 42. List different types of inverters. 43. What is the difference between a converter and a inverter ? 44. What are the applications of inverters ? 45. What are the advantages and disadvantages of current source inverters ? 46. What is the difference between series and parallel inverter ? 47. What is the use of free wheeling diode ?



48. List the different methods of voltage control adopted in inverters . 49. What are the different types of thyristor firing circuits ? 50. What is dimmer stat ? 51. What is power electronics ? 52. What are the merits of power electronics ? 53. What are the demerits of power electronics ? 54. What are the applications of power electronics ? 55. What are the important parameters of SCR ? 56. What are the important parameters of MOSFET ? 57. What are the important parameters of IGBT ? 58. What are the important parameters of TRIAC ? 59. What are the important parameters of DIAC ? 60. What are the important parameters of power BJT ?

Note: Instruction Classes will be taken for the students to introduce and explain the laboratory experiments and use of equipments. BIBLIOGRAPHY

1. Manual by FRAX ELECTRO SYSTEMS 2. Power electronics by Mohamed Rashid. 3. Power electronics by Bhimra 4. Power electronics by Nattarasu.

Power Electronics Lab - 2011

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