The document discusses the GTO Thyristor Controlled Series Capacitor (GCSC), which consists of a fixed capacitor in parallel with an anti-parallel GTO pair. The GCSC can continuously vary the voltage across the capacitor between zero and its maximum value by controlling the turn-off delay angle of the thyristor valve. It works by closing and opening the thyristor valve in synchronism with the supply frequency. The GCSC can operate in either voltage compensating mode, to maintain a rated compensating voltage over a range of line currents, or in reactance compensating mode, to maintain a maximum rated compensating reactance at any line current.

1. GCSC - GTO THYRISTOR
CONTROLLED SERIES CAPACITOR
PRESENTED BY
LEO PAUL
CHITTILAPPILLY

2. INTRODUCTION
• Proposed by Karady & others in 1992.
• It consists of Fixed capacitor in parallel with anti parallel GTO
pair or valve.
• Thyristor valve has the capability to turn on and turn off
mechanism.
• Act as a dual of TCR.

3. BASIC SCHEME OF GCSC

4. • The GCSC controls the voltage across the capacitor (Vc) for a
given line current.
• when the GTO is closed the voltage across the capacitor is zero
• when the GTO is open the voltage across the capacitor is at its
maximum value
• The magnitude of the capacitor voltage can be varied continuously
by the method of delayed angle control
• For practical applications, the GCSC compensates either the
voltage or reactance

5. WORKING
• Closing and opening of valve is carried out in each half cycle in
synchronism with supply frequency.
• Turn off instant of each half cycle is controlled by a delay angle ᵞ
wrt peak of line current.
• Here ᵞ varies from 0 to 90 degrees.
• Line current i and Vc are shown for ᵞ =0 and at an arbitary value
of ᵞ

6. principle of turn-off delay angle control

7. • Variation of VCF is
normalized to maximum
voltage
• GCSC can be operated
in either to control
Voltage or reactance
• Fundamental
component of the series
capacitor voltage vs.
the turn-off delay angle
γ.

8. GCSC IN VOLTAGE COMPENSATING MODE
• GCSC can be operated either to compensate voltage or to compensate
Xc(ᵞ).
• In first case, GCSC is used to maintain the rated compensating voltage
in association with decrease of line current over an interval
I min ≤ I ≤I max
• n this case, Xc is selected in such a manner that Vc max/I min = Xc.
• When I is increased from I min to I max, ᵞ is also increased

9. GCSC IN REACTANCE COMPENSATING
MODE
• GCSC is used to maintain the max rated compensating reactance
at any line current up to max.
• In this case, Xc is selected in such a manner that
Vc max/I max = Xc.
• GCSC can be used to vary Xc from
0≤ Xc(ᵞ) ≤ Xc