A COMPARITIVE STUDY OF AUXILIARY SIGNALS OF STATIC VAR SYSTEM FOR DAMPING SUBSYNCHRONOUS RESONANCE

Abstract

Transmission systems are being restructured to provide increased power transfer capability to accommodate a much wider range of possible generation patterns, due to the present pace of power system. The power transfer in the integrated power system is impeded by transient stability, voltage stability, and small signal stability. To enhance the power transfer capability, Series compensation has been widely used. The fast acting power electronic converters, Flexible AC Transmission System (FACTS) devices with their equally fast and efficient controlling capabilities are becoming the pillars of support of such a highly integrated power systems. FACTS devices are very effective and capable for increasing loadability, reducing system loss, improved stability of network and reduced cost of production.

However, presence of series compensation gives rise to the problems of dynamic instability and sub synchronous resonance (SSR). SSR is basically an electrical power system condition where the electrical network exchanges energy with the turbine generator at one more natural frequencies of the combined system below the synchronous frequency of the system. A number of power electronic devices have been proposed for dynamic compensation, improving system stability, directing power flows, etc. One of the power electronic devices used for reactive power compensation is a Static VAR Compensator (SVC). Such a system when connected in shunt with a power system is referred to as a static VAR System.

An idea of the thesis is to damp SSR by adding static var compensator (SVC). This thesis shows that by using different auxiliary controllers of SVC, damping performance is enhanced. The major objective is to compare various auxiliary controllers of SVC. The results are obtained by modelling a linearized system in MATLAB.

A detailed system model has been developed. The study system consists of a generator supplying power to an infinite bus over a long transmission line. IEEE type-1 excitation system is considered for the generator. The SVC of switched capacitor-thyristor controller reactor (SC-TCR) type provides dynamic voltage support at the midpoint of line. A lumped parameter T-circuit represents the network. The SVC and series compensation are located at the centre of transmission line in order to optimize the performance of these devices.

Different SVC auxiliary controllers are compared and evaluated for enhancement of dynamic stability of a series compensated power system by computing the eigenvalues of linearized system model. The performance of combined reactive power frequency controller (CRPF) and combined voltage angle and reactive power controller (VARP) has been compared and it is found that the combined voltage angle and reactive power (VARP), SVC auxiliary controller is the most effective for system damping at a given operating point. Concluding remarks of the work has been presented.