VFD

- Y.Rama Krishna

WELCOME

Natural draught system Induced draught system Forced draught system Balanced draught

system

DRAUGHT SYSTEM

“The difference between the atmospheric pressure and the pressure existing in the furnace is called Draught”.

FANS

An essential auxiliary equipment of the boiler.

Supply air for the combustion in the furnace. (FD Fan)

Evacuates the flue gases formed from the combustion. (ID fan)

Evacuation wouldn’t be possible with out using FANS

“Machines moving the gaseous fluids with a pressure ratio up to 1.15 are know as FANS”

Speed control Inlet guide vane control Damper control Blade pitch control

Types Of Controls Employed For The Fans

MAINTAINS THE DESIRED BALANCED DRAUGHT AND

NEGATIVE PRESSURE REQUIREMENT OF A FURNACE

WITH THE HELP OF F.D. FAN

IMPORTANCE of ID FAN

REGULATION

The fan is adapted to changing operating conditions by means of •Adjustable inlet dampers.•Varying the fan speed

Variable Fan Speed•Two speed drive motor with inlet guide vanes•Variable Speed Hydraulic Coupling•Variable speed drives (stepped/step less variation)•Frequency Controlled Variable Speed Drive

Inlet Damper Control• Actuator

VARIABLE TORQUE

BASIC VFD (LCI-VFD) SYSTEM

LCI -Load Commutated InverterVFD -Variable Frequency Drive

SYNCHRONOUS MACHINE

RATING

6-PULSE 12-PULSE

KW 1488 3895

RPM 390 545

Volts (L-L) 1804 2X2300

PF 0.85 0.85

Exc Volts 240 345

Exc Amps 48 64

Stator YY , 10 pole, A.C.

Rotar 8 pole, D.C.

ISOLATION TRANSFORMER

The transformer provides isolation from the ac system bus.

Provides the correct voltage at the terminals of the rectifier i/p.

Internal impedance of the transformer limits the magnitude of any downstream bus faults.

Transformer rating:-

KVA = 3000 CH-1 Δ/ΔVolts HV/LV = 11/2.3 KV CH-2 Δ/YAmps HV/LV = 157.5/753.1

RECTIFIER I/P - CONSTANT a.cO/P- VARIABLE d.c

THYRISTOR FIRING

1 -- 2 2 -- 3 3 -- 4 4 -- 5 5 -- 6

6 -- 1

1 -- 2

RectifierO/p

INVERTER

INVERTER SWITCHING

i2

1

6

5

4

3

LCI Drive

SPACE VECTOR MODULATION

Inverter o/p

LINE NOTCHES & BUMPS

POWER MODULES 2.3 kV FOR VFD

Gate driver module

HPTK MODULE (Gate driver)

Voltage Regulator For Exciter

FIELD EXCITER MODULE

Overall Functional VFD Diagram

2-channel VFD

LINING-UP AND ISOLATION OF ID FAN

LINING-UP1. Charge the cooling water to fan bearings.2. Charge the cooler from water side & ensure the flow in

view glass. 3. Charge the motor cooling water and observe the FLOW4. Line up the lube oil system5. Normalize the power supply of inlet / outlet gates.6. Normalize the supply of IGV.7. Normalize the fan main breaker.8. Check LOP s availability & interlock.9. Release the EPB. (always at the LAST)

STARTING1. Ensure no alarm persists on the source & load Breakers.2. Check all the permissive available.3. Check no fault is persisting.4. Close the SOURCE breakers from OWS.5. Ensure closing of the breakers from Local.6. Close the Load Breakers.7. Wait till the Drive attains a constant speed.8. Then increase the speed as per requirement.9. Use IGV & SPEED control to maintain DRAUGHT.

ISOLATION

1. Ensure that fan is in stopped condition.2. Press EPB.3. Electrically isolate the main breaker.4. Earthing to be done as per the requirement.5. Ensure that inlet / outlet gates are in closed condition.6. Isolate the supply of inlet and outlet gates.7. Isolate IGV supply.8. Isolate LOP-1 & 2 motor power supply after ensuring that fan at standstill.9. Isolate cooling water to Oil coolers,Bearings,Motor coolers.10.Isolate the oil cooler from oil side.

ADVANTAGES OF USING V.F.D.

1. FAST RESPONSE2. HIGH ACCURACY3. HIGH EFFICIENCY4. LOW MAINTENANCE5. NO SUPPLY FLUCTUATION6. SOFT START7. INCREASE IN MOTOR LIFE

FURTHER APPLICATIONS

The success of VFD to the ID fan in the power plant opens new channels for its application in the power plant auxiliaries like

1. MDBFP2. FD FAN3. PA FAN4. GAS TURBINE STARTER5. COMPRESSOR DRIVES6. CENTRALISED AC SYSTEMS

CONCLUSIONS

•Reduction in auxiliary power consumption approximately by 10% at peak generation and by 15% at 60% generation.

Lower order Harmonics can be eliminated by using PWM

Fuzzy Logic, Neural Networks and Genetic Algorithms can be implemented for optimized control.

SUGGESTIONS

REFERENCES

1. NTPC ET course material.2. NPTI training module3. Customer training manual, LCI VFD vol & II -BHEL4. Power Electronics -P.S Bimbhra, Khanna pub.5. Power Electronics converters, applications and design -N.Mohan, Undeland,Robbins6. VFD article, Kilowatt Classroom7. PWM Current Source Converter Induction Machine Drive -Alfons Klönne, Friedrich W. Fuchs Christian-Abrechts-University of Kiel -Power Electronics and Electrical Drives,

8. A Variable Step-Size C-MEX S-Function for Reduced Simulation Times of Variable Speed Drives, Alan Mullane, Gregor Gregor¡ci¡c, Gordon Light body and Robert Yacamini Department of Electrical Engineering, University College Cork, IRELAND

START PERMISSIVES FOR VFD CH-1

ID FAN

1. VFD Source Breaker Not Disturbed AND2. VFD Source Breaker ON AND3. No VFD CH-1 Alarm Persisting AND4. VFD CH-1 Ready AND5. VFD CH-1 Start Permissive Available AND6. (VFD CH-2 ON) OR (Reg Damper Position Min(<2%) AND Fan I/L & O/L Gates Closed) AND7. Fan Either LO P/P ON AND

contd…

8. Fan LO Press OK (>0.8 KSC) AND9. LO Temp. after Cooler Not High (<75 °C) AND10. Fan Motor Brg. Temp. Not High (<85°C) AND11. Fan Brg temp. Not High (< 90°C ) AND12. Fan Motor Winding Temp. Not High(<120 °C ) AND13. Fan VFD Auxiliary Supply OK AND14. FG path Available OR Other ID Fan ON AND

ID FAN

PROTECTIONS FOR VFD CH-1

VFD CH-1 Fault Condition ORMotor Brg. Temp V High (TD 5 sec) >90°C ORFan Brg Temp V High (TD 5 sec) >110°C ORMotor/Fan Brg. Vib V High (TD 15 sec) >9 mm/sec ORPost Purge Trip from FSSS ORBoth ID Fan ON AND FD Fan-A Tripped ORFan ON (>01 min) AND O/L Gates Closed ORFan ON (>01 min) AND I/L Gates Closed ORVFD CH-2 Fault Condition