Study of current transformer performance during transient conditions and development of a selection criterion in protection applications

Abstract

The optimum selection of current transformers is one of the most crucial requirements of correct protection functioning of power systems. In the case of CT selection, protection engineer has to pay attention on transient behavior as well as steady state performance of current of transformers. Transient performance of current transformers varies with system parameters and current transformer parameters. System parameters vary with fault level and inductance to resistance ratio (L/R) at fault location. In Sri Lankan power system, these parameters rapidly vary due to network development. Type of selected protection relay, type of protection function and switchgear arrangement make huge influence on current transformer selection. This dissertation focuses on developing a current transformer selection criterion with analysis of current transformer transient performance and protection application. The developed selection criterion is mainly focused on protection relay based selection and generalized CT selection. In addition to analysis of the current transformer transient performance, PSCAD software is used for current transformer performance simulation on fault conditions and a case study is used to validate the developed selection criteria.