30-11-2012, 04:35 PM
Automatic Control of Thyristor Controlled Series Capacitor (TCSC)
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ABSTRACT
There are two types of FACTS controllers viz. series and shunt. Series compensation reduces the transmission line reactance in order to improve Power Flow through it, while shunt compensation improves the Voltage profile. Among the FACTS devices, the TCSC controller has tremendous capability of giving the best results in terms of performance. This paper develops the control algorithm for automatic control for the developed working model of TCSC. This paper investigates the effects of TCSC on synchronous stability and voltage stability improvement. Stability of the System has been assessed using P-δ and P-V Curves. The experimental test results shows the improvement in both synchronous and voltage stability margins.
I. INTRODUCTION
A power system is a network of electrical components used to supply, transmit and use electric power. The interconnected power system is known as the grid and can be broadly divided into the generators that supply the power, the transmission system that carries the power from the generating centres to the load centres and the distribution system that feeds the power to nearby homes and industries. There are many losses while transmitting the power from generation stations to load centres. The focus is more on the occurrence of different kinds of instability. Voltage stability requirements and different techniques to improve the stability like the fixed compensation techniques and the dynamic compensation techniques. FACTS controllers which are the dynamic compensating devices which can be g used for better results.
OPERATION OF TCSC
A TCSC is a series-controlled capacitive reactance that can provide continuous control of power on the ac line over a wide range. From the system viewpoint, the principle of variable-series compensation is simply to increase the fundamental-frequency voltage across an fixed capacitor (FC) in a series compensated line through appropriate variation of the firing angle, α. A simple understanding of TCSC functioning can be obtained by analyzing the behaviour of a variable inductor connected in parallel with an FC. The equivalent impedance, Zeq, of this LC combination is expressed as The impedance of the FC alone, however, is given by -j(l/ωC).
ADVANTAGES OF TCSC
Use of thyristor control in series capacitors potentially offers the following little-mentioned advantages:
Rapid, continuous control of the transmission-line reactance
Dynamic control of power flow in selected transmission lines within the network to enable optimal power-flow conditions
Damping of the power swings from local and inter-area oscillations.
Suppression of sub synchronous oscillations. At sub synchronous frequencies, the TCSC presents an inherently resistive-inductive reactance. The sub synchronous oscillations cannot be sustained in this situation and consequently get damped.
CONCLUSIONS
The results shows that there is improvement in the both
synchronous and voltage stability margins, when TCSC
is connected in the test system. Series capacitive
compensation is thus used to reduce the series reactive
impedance to minimize receiving end voltage variation
and the possibility of voltage collapse and it can improve power flow capability of the line. It is also observed that the compensation by using this technique i.e TCSC is more effective than other compensating techniques such as mechanical switching capacitors and synchronous condensers.