Voltage sag and swell generator for the evaluation of custom power devices

Abstract

This paper describes a new economical sag/swell voltage generator suitable to the evaluations of high power custom power devices such as DVR (Dynamic Voltage Restorer) and DSTATCOM (Distribution Static Compensator). Proposed system was designed to generate the several power quality disturbances in MVA power ratings - sag, swell, under voltage, over voltage and harmonic distortions. The sag and the under voltage can be generated by voltage drop across a reactor, while its magnitude and durations can be controlled by the firing angle of TCR (Thyristor Controlled Reactor). In the case of the swell and the over voltage, we need a step-up transformer. Output of the step-up transformer is regulated by TCR to obtain nominal voltage level. At any given instant, if the firing angle of TCR is retarded or stopped, then we can obtain the swell voltage or the over voltage disturbance. Also we can generate harmonic current by controlling firing angles of TCR, while keeping the system voltage level within the specified limits. In this paper, two identical three-phase wye-connected TCRs are connected to the secondary windings of two step-down transformers, one operated from wye-wye transformer, the other from delta-wye transformer. Harmonic filters (11/sup th/ and 13/sup th/) are added to reduce the voltage distortion when TCRs are operated. Simulation results are given for several cases of voltage sag and swell generations. Design guidelines are given for the TCR. Finally, conclusions are given.