Vfd Training 2p3kv

POWER MODULES FOR VFD

VARIABLE FREQUENCY DRIVES

(VFD)


Introduction

• Variable Frequency Drives (VFD) are

used for speed control of AC motors

• Load Commutated Inverters ( LCI)

concept used for controlling

Synchronous Motor


FEATURES OF LCI

1. Speed control of Synchronous motor

2. Provides smooth speed control

3. Fuse less design

4. Thyristors are used as switching device


RATINGS

a. 1.2 kV modules

b. 2.3 kV modules

c. 4.2 kV modules

Generally 1.2 kV modules are used in

210 MW boilers, 2.3 kV for 500 MW

boilers.


Configuration:

Source side converter consists of 6 power modules in 3 phase bridge configuration to get DC.

Load side converter consists of 6 power modules in 3 phase bridge configuration to get Variable Frequency Variable Voltage


Power module consists of :

a. Thyristors as switching device

b. Heatsinks to dissipate heat generated in device

c. Snubber resistor and capacitor to protect device against overvoltages

d. Sharing resistors for equalising the voltage across series connected thyristors.

e. Pulse transformer to supply gate pulses to thyristor and to provide isolation between control and power circuit.


Construction:

1.2 kV module• Two thyristors are used in series.• Snubber provides protection to thyristor against

over voltages.• Reactor limits rate of rise of On state current• HPTF module gives firing pulses to thyristors

and also indicates healthiness of thyristors.









anode+

cathode-

p1 n1 p2 n2

J1 J2 J3

Ig

Three-terminal thyristor:



Transient V I characteristics of Thyristor


Three-terminal thyristor:

0-1: Forward blocking / OFF state J1,J3: forward, J2: reversed biased 2-3: Forward conduction / ON state J1, J2, J3: Forward biased0-4: Reversed biased J1,J3: reverse, J2: forward biased 4-5: Breakdown

OFF

ON

anode+

cathode-

p1 n1 p2 n2

J1 J2 J3

switching (dV/dI=0)

forward break-over voltage

holding voltage










General mounting arrangement








Thyristor stack : 1.2 kV





HPTF module


Construction:

2.3 kV module • Three thyristors are used in series.• Snubber provides protection to thyristor against

over voltages.• HPTK module gives firing pulses and indicates

healthiness of thyristors.• NTDA module indicates healthiness of thyristors• XPTN module gives attenuated voltage for

control


POWER MODULE 2.3 kV


THYRISTOR STACK 2.3 kV




Snubber : 2.3 kV




HPTK module



XPTN Module


Synchronous Field Exciter module

Features:• Six thyristors in ac controller configuration.• Snubber provides protection to thyristor against

over voltages.• NHVL module gives firing pulses to thyristors

and also indicates thyristor healthiness• Voltage attenuator and current feedback





Field Exciter Module



THANK YOU

Documents

Vfd Training 2p3kv