Thyristor Controlled Three Winding Transformer as a Static Var Compensator

摘要

This paper details the design of a thyristor controlled three winding partial core resonanttransformer specially designed for testing generator insulation. The tertiary winding of thistransformer is closed through a Thyristor Controlled Reactor (TCR). Firing angle control of ananti- parallel connected pair of thyristors provides continuous variation of reactive power.Modelling of the three winding transformer in PSCAD/EMTDC reveals the design criteria andperformance of the proposed scheme. Automatic control of thyristor valves will be achieved bysensing the reactive power in the primary winding, i.e. low voltage winding. The exactmagnitude of the firing angle for the thyristors at which the primary winding supplies only realpower for overcoming losses and attains almost unity power factor, will be determined by a PIcontroller. Thus, only the real component of current is required from the supply. Nearly all thereactive power of the iron core and TCR counterbalances the leading VArs produced by thegenerator insulation. Fine tuning of thyristor firing angles avoids any over or undercompensation of the system. Consideration is also given to keeping total harmonic distortion(THD) and overall power quality on the high voltage side within standard limits.