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Firing angle of a TCR

Firing angle of a TCR - Sadhan Vol 30 Part 1 February 2005...

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S¯adhan¯a Vol. 30, Part 1, February 2005, pp. 57–67. © Printed in India Harmonics and voltage stability analysis in power systems including thyristor-controlled reactor M UZUNOGLU Yildiz Technical University, Electrical–Electronics Faculty, Electrical Engineering Department, 34349 Besiktas, Istanbul, Turkey e-mail: [email protected] MS received 28 October 2003; accepted 5 May 2004 Abstract. In this study, non-sinusoidal quantities and voltage stability, both known as power quality criteria, are examined together in detail. The widespread use of power electronics elements cause the existence of significant non-sinusoidal quantities in the system. These non-sinusoidal quantities can create serious har- monic distortions in transmission and distribution systems. In this paper, harmonic generation of a static VAR compensator with thyristor-controlled reactor and effects of the harmonics on steady-state voltage stability are examined for various opera- tional conditions. Keywords. Harmonics; stability; thyristor-controlled reactor. 1. Introduction It is not only required to meet the demand for electrical energy but also to improve its quality. Today, power quality studies are becoming a growing concern. The present paper focuses on two parameters affecting power quality – harmonics and voltage stability. Static VAR compensators (SVCs) are applied on transmission systems to improve voltage control and system stability during both normal and contingency system conditions. Most SVCs use a thyristor-controlled reactor configuration to provide continuous control of the reactive power compensation level. The thyristor-controlled reactor (TCR) produces harmonic currents because thyristors only allow conduction in the reactor for a portion of the cycle. Harmonic current magnitudes vary as the firing angle of the thyristors is varied. A comprehen- sive harmonic study includes evaluation of possible harmonic concerns over the full range of firing angles and possible system conditions. Generally, harmonic filtering is accomplished with capacitors connected in parallel with the TCRs. For transmission applications, the filters might include tuned filters at the fifth and seventh harmonics along with a high pass filter for higher order components. Use of a static compensator with a thyristor-controlled reactor (TCR) has been known to be an effective and reliable means to ensure power system voltage stability. This device is essentially a variable reactor that can adjust its reactive power consumption. The adjustment is realised through the firing angles of thyristors that normally operate in partial conducting 57
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58 M Uzunoglu states, and thereby produce harmonics (Miller 1982). The generated harmonics depend criti- cally on the control characteristics of a static VAR compensator (SVC) with a fixed-capacitor thyristor-controlled reactor (FC-TCR). However, this makes the firing angles dependent on the network load flow conditions and harmonic voltage distributions (Xu et al 1991). Poor
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