A proposed method for evaluating the frequency response of 22 kV outdoor current transformers for harmonic measurements in renewable energy plant applications

Abstract

With an increase in renewable energy plants connected to the national grid of South Africa the monitoring and assessment of power quality is becoming more important for utilities and independent power producers (IPPs). For the IPPs the results are used to determine their compliance to the relevant grid codes. One of the many electro-magnetic compatibility factors to be considered in this process of proving compliance, is the harmonic emissions of these plants. With inductive current transformers being in the center of the measuring circuit it is important to ensure that the frequency response of these instrument transformers, and the errors involved, are quantified. This paper considers a proposed method to determine the frequency response of outdoor current transformers, using results from tests conducted on two 22 kV outdoor current transformers. It also compares the results of two tests conducted on the same current transformers, with and without the fundamental current. The results thereof are discussed, and a conclusion is drawn regarding the measured results and future work.