This document provides an overview of the thyristor controlled series capacitor (TCSC). It begins with the basic TCSC scheme and equations showing how the variable inductive reactance XL can change the capacitive reactance XC. It then discusses the impedance characteristics of the TCSC and how the capacitor voltage is reversed by the thyristor controlled reactor (TCR). Next, it examines the TCSC operating in the capacitive and inductive regions and how it can provide phase advance or retard. The document also covers the attainable voltage-current characteristics and harmonic voltage generation in the TCSC. It describes the functional internal control schemes and concludes with notes on design considerations.

1. Thyristor Controlled Series
Capacitor (TCSC)
Prepared By : Karansinh Parmar

2. Flow of Presentation
• Basic TCSC scheme with equations
• The impedance vs. delay angle ∝ characteristic of the TCSC
• Capacitor voltage reversal by TCR
• TCSC in the capacitive & the inductive region under steady state
• Phase advance & retard
• Attainable V-I characteristics of the TCSC
• Harmonic voltages generation in TCSC
• Functional internal control schemes of the TCSC
• Conclusion
• Reference

3. Basic TCSC scheme with equations
Fig.:- Basic TCSC scheme
• Steady state impedance of TCSC is that
for a parallel tuned L-C circuit.
• Fixed capacitive reactance XC & variable inductive reactance XL .
• Change in XC with change in XL .
• Change in XL with change in ∝.

4. The impedance vs. delay angle ∝ characteristic of the
TCSC
Fig.:- XC vs. α characteristics of TCSC
• Impedance of the controlled
reactor XL (∝) varied.
• Parallel resonance
• Two operating ranges:
• (1)
(2)

5. Capacitor voltage reversal by TCR
Fig.:- (a) Line current & corresponding capacitor voltage
(b) Equivalent circuit of TCSC at firing angle ∝
(c) The resulting capacitor voltage & related TCR current

6. TCSC in the inductive & the capacitive region
under steady state
Fig.:- Capacitor voltage & current
waveforms, along with TCR votage &
current waveforms , Steady state
operation of TCSC in the capacitive
region.

7. Continue….
Fig.:- Capacitor voltage & current
waveforms, along with TCR votage
& current waveforms , Steady state
operation of TCSC in the inductive
region.

8. Continue…
• Charge reversal
• Components of steady state
compensating voltage across series
capacitor:
 Uncontrolled component Vco
 Controlled component VCTCR
Fig.:- Composition of idealized TCSC waveform

9. Phase advance & Retard
Fig.:- Increase of capacitor voltage by advancing the voltage reversal from ∝= 𝜋 𝑡𝑜 ∝= 𝜋 −∈.

10. Continue…
Fig.:- Decrease of capacitor voltage by retarding the voltage reversal from ∝= 𝜋 𝑡𝑜 ∝= 𝜋 +∈.

11. Attainable V-I characteristics of the TCSC
Fig.: Attainable V-I (compensating voltage vs, line current) char. Of TCSC when operated in voltage control (a1)&
reactance control (b1) modes, and the associated losss vs. line current char. (a2 & b2 respectively).

12. Continue…
Fig.:- Compensating reactance vs. Line current characteristics of the TCSC

13. Harmonic voltage generation in TCSC
Fig.:- Dominant harmonic voltages generated by TCSC at an XL/XC
ratio of 0.133.
• Effect of harmonics on TCSC
components
• Most important 3rd,5th & 7th
harmonics voltages
• 7th order harmonics
• Lower order harmonics
• Narrowing uncontrolled
capacitive band to a smaller
size for dynamic stability.

14. Functional internal control schemes of the TCSC
• Two types of internal control schemes:
Based on the synchronization to the fundamental comp. of the
line current.
Based on the prediction of the capacitor voltage zero crossing.
 The main consideration of TCSC internal control scheme to
ensure immunity to subsynchronous resonance.

15. Continue…
Fig.:- Functional internal control scheme based on the synchronization to the fundamental
comp. of the line current.

16. Continue…
Fig.:- Functional inernal control scheme based on the prediction of the capacitor
voltage zero crossing.

17. Conclusion
• Impedance of TCR does not significantly alter TCSC operation as it
is sufficiently smaller compared to capacitive reactance.
• Smaller XL is helpful in controlling period time of compensating
voltage & providing well-defined charge reversal.
• Smaller reactor L is also advantageous in protetive bypassing heavy
surge current during system fault.
• Smaller XL increases current harmonics generated by TCR.
• TCSC is usually applied to long, high impedance lines so line
current harmonics will be lower tan the ambient system.

18. Reference
Book:- “Understanding FACTS”
-By N.G.Hingorani & L.Gyughi

19. Thank you