Voltage and Power Flow Control

Module 4 : Voltage and Power Flow Control

Lecture 19 : Power Flow Control

Power Flow control can be achieved by changing effective line parameters by connection of lumped series capacitors.

Series Compensation of lines

This involves changing the effective series reactance of lines by connecting capacitors in series with a line. Reducing line reactance also improves stability of a system (see module 2 for a discussion of large disturbance stability).

In the figure given below, the power flow in the branch with reactance 2x can be increased by compensating it with a series capacitor.

Since the amount of loading changes with time, the amount of series compensation may be varied by bypassing (shorting out) these capacitors when not necessary.

Normally a capacitor can allow for short duration over-rating for a few seconds. This allows insertion of larger capacitive reactance into a line for a short time in order to improve angular stability.

Alternatively, they may be controlled using power electronic controllers. For example, a TCR (discussed in the section on voltage control), may be connected in parallel to the series capacitor and its effective reactance may be controlled by controlling the firing angle delay. This device is called a Thyristor Controlled Series Compensator (TCSC).