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Flexible Alternating Current Transmission System - Thyristor Controlled Series Capacitor (TCSC) and Applications - Important Short Questions and Answers : Thyristor Controlled Series Capacitor (TCSC) and Applications

**THYRISTOR CONTROLLED SERIES CAPACITOR (TCSC) AND APPLICATIONS**

**1. What is meant by TCSC?**

TCSC is a ** thyristor controlled series capacitor**.
It has one parallel connected thyristor controlled inductor and a series capacitor
connected with the transmission line. It provides continuous variable
capacitive reactance and variable inductive reactance to control the
transmission line parameters.

**2.Write
down the expression for equivalent impedance, capacitive and inductive reactance
of a TCSC**.

Equivalent
impedance of a TCSC, *Zeq = -j ((1) / (ωc-1/ ωL))*

If (ωc -
(1/ ωL)) < 0 - the TCSC provides variable capacitive reactance mode. If (ωc
- (1/ ωL)) > 0 - the TCSC provides variable inductive reactance mode.

**3. What are the different modes of operation of
TCSC?**

*Bypassed-
thyristor mode*

Blocked -
thyristor mode

Partially
conducting thyristor or Vernier mode.

**4. Give short notes on Bypassed- thyristor mode.**

In this mode the TCSC module behaves like a
parallel capacitor - inductor combination. The susceptance (increase in power
flow) value of inductor is higher than the capacitor. This mode is employed for
control purposes and *initiating certain*** protective
functions**.

**5. Give short notes on Blocked - thyristor mode.**

In this mode, also known as the waiting mode, here
the *firing
pulses of thyristor*** switches are blocked**. The TCSC
behaves like a fixed series capacitor and the net TCSC

**6. Give short notes on capacitive Vernier mode.**

In this mode the TCSC provides continuously ** controllable
capacitive reactance**. It is achieved by varying the thyristor pair
firing angle in an appropriate range. A variant of this mode is the capacitive
vernier mode, in which the thyristors are fired when the capacitor voltage and
current have opposite polarity. This condition causes a thyristor controlled
reactor (TCR) current that has a direction opposite that of the capacitor
current thereby resulting in a loop-current flow in the TCSC controller. This
loop current increases the voltage across the fixed capacitor (FC), effectively
enhancing the equivalent capacitive reactance and the series compensation
level.

**7. Give short notes on inductive vernier mode.**

In this mode the TCSC provides continuously ** controllable
inductive reactance**. Here the TCSC can be operated by having a high
level of thyristor conduction. In this mode the direction of the circulating
current is reversed and the controller presents a net inductive impedance.

**8. What are the conclusions made from the TCSC
modes of operation?**

Thyristor
switched series capacitor (TSSC), which permits a *discrete control of**the
capacitive reactance.*

Thyristor
controlled series capacitor (TCSC), which offers a continuous control of
capacitive or inductive reactance. Practically TSSC is more commonly used.

**9. What are the modeling techniques involved in
TCSC?**

** Variable
reactance model **(1. Transient stability model 2. Long term
stability

An
advanced transient stability studies model

**10. What is the need for modeling of a TCSC?**

A TCSC involves continuous - time dynamics,
relating to voltages and currents in The capacitor and reactor, and nonlinear
discrete switching behavior of thyristors. So it is Very important to derive a
model for a TCSC controller to *maintain the stability of a*** power
system**.

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