SFC_Working_Principle.pptx

sfc working of gas power plant

1. Presentation on SFC Working Principle

2. Basics of SFC Operation December 21, 2022 Footer text 2 SFC outputs power to the generator stator to create a magnetic field in the stator. The exciter magnetizes the generator rotor. The SFC creates a rotating magnetic field in the stator to pull the rotor. Stator magnetic field is adjustable and determines the speed of the rotor.

3. What is a Static Frequency Converter December 21, 2022 Footer text 3 A frequency converter (frequency changer) is an electronic or electromechanical device that converts alternating current (AC) of one frequency to alternating current of another frequency. The device may also change the voltage, but if it does, that is incidental to its principal purpose. Traditionally, these devices were electromechanical machines called a motor-generator set (rotary frequency converter). With the advent of solid state electronics, it has become possible to build completely electronic frequency converter.

4. How does a Frequency Converter work A frequency converter usually consists of a rectifier stage (producing direct current) which is then inverted to produce AC of the desired frequency. The inverter may use thyristors, IGCTs or IGBTs. If voltage conversion is desired, a transformer will usually be included in either the ac input or output circuitry and this transformer may also provide galvanic isolation between the input and output ac circuits. December 21, 2022 Footer text 4

5. What is the purpose of SFC in a Gas Turbine A gas turbine compressor does not supply enough air for the machine to be self-sustaining until it reaches approximately 60 per cent of its rated speed. Therefore the gas turbine must be accelerated to the speed at which it can produce enough power itself to continue acceleration.  Gas Turbine need starting equipment to accelerate from standstill and follow a preset speed-time profile as required by the ignition and start-up procedure. Once the Gas Turbine can deliver enough torque, further acceleration up to the synchronous speed is accomplished by the turbine itself and the starting equipment is no more necessary. When it comes to larger machines, it is common to use SFC, using the synchronous machine as a motor. December 21, 2022 Footer text 5

6. Single Line Diagram for SFC starting of GT Generator December 21, 2022 Footer text 6

7. Operation of an SFC Inverter December 21, 2022 Footer text 7 The output of the SFC uses SCR’s to switch A C current flow to the Generator Stator windings. An analogy of a SCR is a switch. The switch is either open or closed, same as the SCR being ON, switch closed or OFF, switch open. The switches close in the sequence shown. At anytime there are 2 switches closed. SFC converter with switches

8. Operation of an SFC Inverter December 21, 2022 Footer text 8 Switches 3 & 4 closed In this view switches 4 and 3 are closed. A C current flow is into phase A winding and out of phase C winding. The current creates a magnet in the machine stator iron. The poles of the magnet are shown with the N and S indicating North and South pole Magnet created in the Stator. As the switches closing sequence continues the magnet will begin to rotate

9. Operation of an SFC Inverter December 21, 2022 Footer text 9 Switches 4 & 5 closed s Switches 5 & 6 closed Switches 6 & 1 closed

10. SFC Starting Sequence December 21, 2022 Footer text 10 Start Command given from MARK VIe . After approximately 25 s delay, Ventilators of reactor and thyristors starts. (1s difference between these operations). There are 3 nos of ventilators in all, third one is for transformer cabinet. 6.6KV MV breaker gets closed and SFC transformer (3.2MVA 6.6KV/1.5KV) is charged. Internal disconnector switch 89SFC1 (GT-1) / 89SFC2 (GT-2) is closed . External disconnector switch 89SS1 (GT-1) / 89SS2 (GT-2) is closed . Internal 1SKV (Q570) breaker is closed. Rotor brush lift off device position is detected and thyristor pulses given. Excitation starts simultaneously. An excitation current is given, the feedback of which is received at MARK VIe (250 A DC initial set point). Excitation transformer (rating 415V/ 80V) supplies the excitation voltage which is converted to 60V DC in Excitation panel and fed to generator rotor through brushes. Simultaneously, current is injected in stator of the synchronous machine and it starts to rotate as a synchronous motor.

11. SFC parameters Excitor Regulation Modes December 21, 2022 Footer text 11

12. December 21, 2022 Footer text 12 Thank you