THYRISTOR CONTROLLED BRAKING RESISTOR

MALAVIYA NATIONAL INSTITUTE OF TECHNOLOGY JAIPUR

SUBMITTED BY:Roopmati Meena

2012UEE1460Deepesh Haldania

2012UEE1043

Basic Concept•It’s shunt connected thyristor switched linear resistor. •The best location for a TCBR is near a generator that would need braking during transient instability conditions. Transformer tertiary at or near the generator bus would be desirable.

TCBR can be connected either in star or delta formation although delta connection would be more convenient since the ground path would not be needed.

Functions of TCBR

• Prevent transient instability during the first power system swing cycle, by immediately taking away the power that would otherwise be used in accelerating the generator. 

• Enhance damping to prevent dynamic instability involving low frequency oscillations between interconnected ac systems.

• Facilitate synchronizing a turbine-generator.

Transient State Stability

Conti….

Speed Deviation• The resistor is switched on when the filtered speed

deviation of a particular oscillation to be damped is positive, and the TCBR is switched off when the speed deviation is negative.

• Since the resistor only consumes power and does not supply power, it helps to serve as a brake when the speed is higher than normal but doesn’t counter increase in speed when the speed is lower than normal.

The speed deviation signal is essential to the correct exploitation of the TCBR.

Power system Swing Oscillation• The speed deviation derived from the turbine-generator

plant can be filtered through a low-pass filter to derive the low-frequency signal for controlling the low-frequency oscillations.

• It is seen that these pulses are wide, corresponding to the low-frequency time period.

Conti…• Figure shows the load pulses corresponding to the

unfiltered speed deviation input. It is evident that such a signal will essentially result in damping the low-frequency oscillation until the low-frequency swing is small enough for the unfiltered signal to frequently cross the zero line.

• It is seen that because a thyristor will turn off only when its current reaches zero, the TCBR conduction will last for about a half-cycle longer with decreasing power during that extended period beyond time tB1.

SWITCHING TECNIQUES

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