Static VAR Compensator

Overview

A static VAR compensator (SVC) is a fast, electronically controlled source and sink of reactive power used to stabilise transmission and large industrial supplies. Where a switched capacitor bank corrects power factor in coarse, slow steps, an SVC adjusts continuously and within a single mains cycle, which lets it hold the voltage at a connection point steady against rapidly varying loads such as arc furnaces, rolling mills, and traction substations. This module pairs a thyristor-controlled reactor for smooth inductive control with switched capacitors for the capacitive range, and uses an IGBT valve to do the fast switching.

How it works

The heart of the unit is the Switching Valve, a stack of IGBT Power Module power devices on individual heatsinks. The valve phase-controls the current in the Reactor Bank, three air-core reactors, so that, by varying the conduction angle each cycle, the module absorbs a continuously adjustable amount of reactive power. To supply reactive power instead, the Capacitor Bank switches in blocks of capacitance, and the valve trims the reactor between those blocks so the net output is smooth rather than stepped.

Firing the valve correctly is the job of the Control & Firing Board board. A system-on-chip runs the voltage-regulation loop using the line current from its measurement transformers, and a microcontroller turns that into precisely timed gate pulses delivered through the Gate Driver Board board. Because the IGBTs dissipate real losses, the Cooling Assembly assembly drives filtered air across their heatsinks under a Blower Motor, watched by thermal sensors.

Power flows through copper Copper Busbar runs tying the valve, reactors, and capacitors of each phase together, and the module lands on the line and the station controller through its Connectors. The whole assembly sits in a compartmented Enclosure.