This document discusses two types of variable impedance series compensators: the thyristor-controlled series capacitor (GCSC) and the thyristor-switched series capacitor (TSSC). It explains that the GCSC uses thyristors to control the voltage developed across a fixed capacitor, creating a variable reactive impedance. The TSSC uses thyristors to control the current in a fixed inductor from a constant voltage source, creating a variable reactive admittance. It also covers the operating control schemes for each device and discusses the phenomenon of sub-synchronous resonance.

1. Variable impedance type series
compensators
By: G A Chougule
EE, SITCOE

2. Index
• GTO Thyristor-Controlled Series Capacitor
(GCSC)
• Thyristor-Switched Series Capacitor (TSSC)
• Operating control schemes for GCSC & TSSC
• Sub Synchronous Resonance

3. GTO Thyristor-Controlled Series
Capacitor (GCSC)

4. Analogues
GCSC
• Supplied from current source
• Thyristor valve is stipulated to
close at voltage zero
• Its controlled by turn off delay
γ wrt crest of line current,
which decides the blocking
interval ζ
• Controls voltage developed by
constant current source across
fixed capacitor – Variable
reactive impedance
TCR
• Supplied from voltage source
• Thyristor valve is stipulated to
close at current zero
• Its controlled by turn on delay
α wrt crest of line current,
which decides the conduction
interval σ
• Controls current in fixed
inductor from constant voltage
– Variable reactive admitance

9. Thyristor Switched Series Capacitor
TSSC

11. Operating Control Scheme GCSC

12. Operating Control Scheme TSSC

13. Sub Synchronous Resonance (SSR)

15. Thank You