73084736 Electrical Machines II Lab Manual

EE 706

ELECTRICAL MACHINES LABORATORY II

2006 Scheme

July 5, 2010

ACKNOWLEDGEMENT

This manual is the result of contributions from the following staff members.

Ms. Sheena K. M.Mr. Anith KrishnanMr. Naveen T. R.Mr. Jobiraj C.Mr. Manoj M. S.Mr. Gireesh G.Mr. Vaishak L. S.

INTRODUCTION

A few words about the lab.

INSTRUCTIONS

• All students should wear shoes.

• Male students should tuck in their shirts.

• Female students should tie up their hair properly.

• Students should not lean on the work bench.

• Do not switch on the supply before the circuit is verified by the concerned lab faculty.

• Use of mobile phone inside the laboratory is strictly prohibited.

All the students are to strictly abide by the instructions given here and any additionalinstruction given during the lab session, failing to which he/she will have to face disciplinaryaction.

Contents

Load test on SCIM. 1

No load and blocked rotor test on SRIM. 4

Load test on single phase induction motor 9

Alternator regulation by direct loading. 11

Alternator regulation by indirect method 13

V curves and inverted V curves of synchronous motor 18

No load and blocked rotor test on SCIM. 21

Lab Manual: Electrical Machines Laboratory II (EE 706) 2006 Scheme

Experiment No.: 1

LOAD TEST ON SQUIRREL CAGE INDUCTION MOTOR

Aim:

To study the performance of the machine when loaded and to plot the following charac-teristics of a squirrel cage induction motor.

η Vs o/pN Vs o/pIa Vs o/pcos φ Vs o/p%s Vs o/p

Machine details:

Refer name plate of the machine.

Precautions:

1. All the connections should be tight.

2. The autotransformer should be in minimum position initially.

3. The motor should be on no load at the time of starting.

Procedure:

1. Make the connections as shown in the circuit diagram.

2. After taking care of the precautions, switch on the supply.

3. Adjust the autotransformer till rated voltage is applied across the motor terminals.

4. Note down all the meter readings in no-load condition.

5. Increase the load in steps until the ammeter reads the rated current and note downall the meter reading for each applied load.

6. Reduce the load to zero, bring the autotransformer to the minimum position andswitch off the supply.

Division of Electrical Engineering, S.O.E., CUSAT 1


Circuit Diagram:

440V, 50Hz 3Observation Table:

Sl. V1 A1 W1 W2 N S1 S2 i/p T o/p cos φ %s ηNo. (V) (A) (W) (W) (rpm) (kg) (kg) (W) (Nm) (W)123456



Equations and Calculations:

Voltage V = . . . . . . V

Current I = . . . . . . A

W1 = . . . . . . W

W2 = . . . . . . W

I/P power = W1 + W2 = . . . . . . W

Speed N = . . . . . . rpm

S1 = . . . . . . kg

S2 = . . . . . . kg

Torque T = (S1 − S2)rg = . . . . . . Nm

O/P power =2πNT

60= . . . . . . W

Power Factor cos φ = . . . . . .

Slip s =Ns − N

Ns

× 100 = . . . . . . %

Efficiency η =O/P

I/P× 100 = . . . . . . %

Here r is the radius of the break drum and g is the acceleration due to gravity.

Result:



Experiment No.: 2

NO LOAD AND BLOCKED ROTOR TEST ONSLIP-RING INDUCTION MOTOR

Aim:

To conduct no load and blocked rotor test on slip-ring induction motor and to draw itsequivalent circuit and circle diagram.

Machine Details:


Precautions:

1. The autotransformer should be in minimum position while switching on the supply.

2. The motor should not be on load while starting.

Procedure:

No-load test


2. Adjust the autotransformer gradually such that the rated voltage is applied to thestator.

3. Note down all the meter readings under no-load condition.

4. Reduce the autotransformer to minimum position.

5. Switch off the supply.

Blocked rotor test


2. Adjust the autotransformer till the rated current flows through the stator.

3. Take all the meter readings.





Circuit Diagram:

440V, 50Hz, 3Figure 1: Circuit diagram for no-load test.

440V, 50Hz, 3Figure 2: Circuit diagram for blocked rotor test.

30V DCFigure 3: Measurement of stator resistance.



Observation Table:

No-load test

Sl. V0 I0 W1 W2 W0

No. (V) (A) (W) (W) (W)123456

Blocked rotor test

Sl. Vsc Isc W1 W2 Wsc

No. (V) (A) (W) (W) (W)123456

Stator Resistance

Sl. V I Ra = 12× V

I

No. (V) (A) (Ω)123456




From no-load test

Supply voltage V0 = . . . . . . V

Circuit current I0 = . . . . . . A

No-load power W0 = W1 + W2 . . . . . . W

cos φ0 =W0√3V0I0

= . . . . . .

Magnetising current Iµ = I0 sin φ0 = . . . . . . A

Working current Iw = I0 cos φ0 = . . . . . . A

R0 =V0

Iw

= . . . . . . Ω

X0 =V0

Iµ

= . . . . . . Ω

From blocked rotor test

Supply Voltage Vsc = . . . . . . V

Circuit current Isc = . . . . . . A

Power consumed Wsc = W1 + W2 = . . . . . . W

Z01 =Vsc

Isc

= . . . . . . Ω

R01 =Wsc

3I2sc

= . . . . . . Ω

X01 =√

Z201 − R2

01 = . . . . . . Ω

From stator resistance test

DC resistance Rdc =1

6

6∑Sl.No.=1

Ra = . . . . . . Ω

AC resistance Rac = 1.2 × Rdc = . . . . . . Ω

Rest of the parameters can be calculated as

R′2 = R01 − Rac = . . . . . . Ω

X1 = X ′2 =

X01

2= . . . . . . Ω



R0 X0

R1 X1 R′2

X ′2

R′2

(1s − 1

)

Figure 4: Equivalent Circuit.

Figure 5: Circle Diagram.

Result:



Experiment No.: 3

LOAD TEST ON SINGLE PHASE INDUCTION MOTOR

Aim:

To conduct load test on a single phase induction motor and to plot the following charac-teristics.

η Vs o/pN Vs o/pIa Vs o/pcos φ Vs o/p%s Vs o/pT Vs o/p

Machine details:


Precautions:

1. All the connections should be tight.


Procedure:

1. Close DPST and start the motor on no load at rated voltage.

2. Note down all the meter readings at no load.

3. Gradually apply the load in steps till the ammeter reads rated current. Note downall the meter readings for each load.

4. Gradually decrease the load to zero and switch off the supply.

Circuit Diagram:

230V, 50Hz A.C. SWDivision of Electrical Engineering, S.O.E., CUSAT 9


Observation Table:

Sl. V1 A1 W1 N S1 S2 T o/p cos φ ηNo. (V) (A) (W) (rpm) (kg) (kg) (Nm) (W)123456


Voltage V = . . . . . . V

Current I = . . . . . . A

I/P power = W1 = . . . . . . W

Speed N = . . . . . . rpm

S1 = . . . . . . kg

S2 = . . . . . . kg

Torque T = (S1 − S2)rg = . . . . . . Nm

O/P power =2πNT

60= . . . . . . W

Power Factor cos φ = . . . . . .

Efficiency η =O/P

I/P× 100 = . . . . . . %

Here r is the radius of the break drum and g is the acceleration due to gravity.

Result:



Experiment No.: 4

ALTERNATOR REGULATION BY DIRECT LOADING

Aim:

To determine the regulation of a 3φ alternator by direct loading and to plot the followinggraphs.

Machine Details:


Precautions:

1. The field rheostat of D.C. motor should be kept at minimum position and that ofthe alternator should be at maximum position while starting the experiment.

2. All the switches should be in open position before giving the supply.

Procedure:

1. Wire up the circuit as shown in the circuit diagram.

2. DC supply is given to the prime mover by closing DPST and is started using thestarter.

3. By varying the field rheostat, the prime mover is made to run in the rated speed ofthe alternator.

4. Close SPST to energize the field of alternator.

5. Adjust the alternator field rheostat so as to get rated voltage across the alternatoropen circuited terminals.

6. Close TPST switch (the alternator is now connected to the load).

7. Add some load to the alternator. This causes the terminal voltage to change (it candecrease or increase).

8. Adjust the alternator field rheostat such that the rated voltage is applied across theload. Note down the ammeter readings.

9. The entire load is now thrown off the alternator by bringing the TPST switch to theopen position.

10. The open circuit or no-load voltage (E0) is noted.

11. Repeat 7-10 until the ammeter reads the rated current of the machine.

12. De-energise the alternator field and switch off the supply.



Circuit Diagram:

220V D.C. DPST TPSTObservation Table:

Sl. VL IL If E0 RegulationNo. (V) (A) (A) (V) (%)123456


Voltage across the load VL = . . . . . . V

Load current IL = . . . . . . A

Field current If = . . . . . . A

% Regulation =E0 − VL

VL

× 100 = . . . . . . %

where E0, VL, IL and If are per-phase values.

Result:



Experiment No.: 5

ALTERNATOR REGULATION BY INDIRECT METHOD

Aim:

To pre-determine the regulation of a 3φ alternator by indirect methods at different loads(1

4, 3

4and full load) for various power factors (0.8 lead, 0.8 lag, upf) and draw the regulation

vs. load current curve by conducting suitable tests.

Machine Details:


Precautions:

1. All the switches should be in open position before switching on the supply.

2. The field rheostat of D.C. motor should be kept at minimum position and that ofthe alternator should be at maximum position while starting the experiment.

Procedure:

OC Test





5. By adjusting the alternator field rheostat, increase the alternator field current insteps and note down If and open circuit voltage E0.

6. Repeat the above step till the voltmeter reads 1.25 times the rated voltage of themachine.


SC Test



3. Close SPST switch such that the alternator is now short-circuited.





6. By adjusting the alternator field rheostat, increase the alternator field current insteps and note down If and the armature current Ia.

7. Repeat the above step till the ammeter reads 1.25 times the rated current of themachine.


Circuit Diagram:

OC Test

220V D.C. DPSTSC Test

220V D.C. DPST TPSTDivision of Electrical Engineering, S.O.E., CUSAT 14


Resistance measurement30V DCObservation Table:

OC Test SC TestSl. E0 If Sl. If Ia

No. (V) (A) No. (V) (A)1. 1.2. 2.3. 3.4. 4.5. 5.6. 6.

Resistance Measurement

Sl. V I Rdc

No. (V) (A) (Ω)123456



Sample Graph:

V0from OC Test (V) Iafrom SC Test (A)Equations and Calculations:

EMF Method

Synchronous Impedance Zs =E0

Isc

= . . . . . . Ω

AC resistance of armature Ra = 1.2 × 1

6

6∑Sl.No.=1

Rdc = . . . . . . Ω

1. Lagging p.f.

E0 =√

(V cos φ + IRe)2 + (V sin φ + IXs)2

2. Unity p.f.E0 =

√(V + IRe)2 + (IXs)2



3. Leading p.f.E0 =

√(V cos φ + IRe)2 + (V sin φ − IXs)2

MMF MethodThe students are expected to complete this section by themselves and write it in thelaboratory record.

Result:



Experiment No.: 6

V CURVES AND INVERTED V CURVES OFSYNCHRONOUS MOTOR

Aim:

To obtain V and inverted V curves of the given synchronous motor.

Machine Details:


Precautions:

1. Synchronizing switch should be in open position.

2. The synchronous machine field regulator should be in maximum resistance positionat the time of starting.

3. The DC machine field regulator should be in minimum resistance position at thetime of starting.

4. DPST and SPST switch should be in open position before giving supply to the circuit.

5. DPDT switch should be position 1-1 when supply is switched on.

Procedure:

1. Close the DPST switch and start the DC machine by cutting down the starter resis-tance.

2. Adjust the field regulator of DC motor and drive the synchronous machine in syn-chronous speed.

3. Close TPST switch and note down the supply voltage level using voltmeter Vs.

4. Close SPST switch and increase the field current of the synchronous machine suchthat the terminal voltage becomes the same as supply voltage i.e., VL=Vs.

5. Observe the manner in which the lamps (across the synchronizing switch) are glowing.

6. If the 3 sets of lamps become bright and dark one after another (indicating wrongphase sequence) bring the TPST switch to open position.

7. Bring the field rheostat of the synchronous machine to minimum position.

8. Open SPST switch and interchange any two terminal connection on the TPST switch.Follow steps 4 and 5.

9. If the 3 sets of lamps become bright and dark simulataneously, the phase sequence iscorrect.

10. Reduce the rate of flickering of synchronizing lamps as low as possible by adjustingthe DC motor field energizing rheostat.



11. Close the synchronizing switch at the middle of the dark period of the lamps.

12. Open DPDT switch. The synchronous machine will now work as synchronous motorand the DC machine will work as a self-excited DC shunt generator.

13. For this no load position, the exciting field current of synchronous motor is variedin steps till the ammeter reads the rated line current. The meter readings are noteddown for each field current.

14. Put the switch to 2-2 position and apply a constant load by using loading rheostatRL.

15. Vary the field current and note down the field current and armature current. Repeatthe same for different loads.

Circuit Diagram:

220V D.C. DPST 415V, 50Hz 3(0‐300V) MC(0‐20A) MCObservation Table:

No Load Load Current = . . . . . .ASl. Ia If I/P

cos φIa If I/P

cos φNo. (A) (A) (W) (A) (A) (W)1.2.3.4.5.6.




Armature Current Ia = . . . . . . A

Field Current If = . . . . . . A

Power Factor cos φ =I/P√3VLIa

= . . . . . .

Result:



Experiment No.: 7

NO LOAD AND BLOCKED ROTOR TEST ONSQUIRREL CAGE INDUCTION MOTOR

Aim:

To conduct no load and blocked rotor test on squirrel cage induction motor and to drawits equivalent circuit and circle diagram.

Machine Details:


Precautions:

1. The autotransformer should be in minimum position while switching on the supply.


Procedure:

No Load Test


2. Adjust the autotransformer gradually such that the rated voltage is applied to thestator.

3. Note down all the meter readings under no-load condition.



Blocked rotor test

1. After taking care of the precautions, switch on the supply with the rotor blocked.

2. Adjust the autotransformer till the rated current flows through the stator.

3. Take all the meter readings.





Circuit Diagram:

440V, 50Hz 3Figure 6: Circuit diagram for no-load test.

440V, 50Hz 3Figure 7: Circuit diagram for blocked rotor test.

30V DCFigure 8: Measurement of stator resistance.



Observation Table:

No-load test

Sl. V0 I0 W1 W2 W0

No. (V) (A) (W) (W) (W)123456

Blocked rotor test

Sl. Vsc Isc W1 W2 Wsc

No. (V) (A) (W) (W) (W)123456

Stator Resistance

Sl. V I Ra

No. (V) (A) (Ω)123456


73084736 Electrical Machines II Lab Manual

Documents

blocked rotor

rated current

w1 w2 wsc

cos ire

load test

alternator

close spst

close tpst