Field measurement based characterization of a current sensor for measurement and instrumentation in primary distribution feeders

Abstract

Abstract The wide applications of electronically controlled loads have introduced a high degree of harmonics and distortion in power system current and voltage waveforms. This distortion must be considered in the different stages of instrumentation when designing accurate measurement techniques. Using instrument transformers, current and voltage waveforms are obtained for measurement and/or characterization of harmonics and distortion. Therefore, to model the harmonics and distortion accurately, the frequency response of the instrument transformer must be considered and taken into account. A typical segmental coupler type current transformer is characterized using frequency domain modeling. A testing facility that includes a programmable calibrator, a transconductance amplifier, an oscilloscope, etc. was set up at Carolina Power and Light Company to produce a high current, variable frequency current source. The voltage-current relationship, mutual coupling, equivalent resistance and inductance were obtained from different frequency response tests conducted on the current sensor. Empirical formulas for the voltage-current relationship, mutual coupling, and equivalent resistance and inductance were obtained using a non-linear estimation procedure. Also, a system was devised to record actual three-phase current and voltage waveforms from a 23 kV distribution system. This paper describes the current sensor characterization, the date acquisition system, a scheme for correcting the distortion created by the sensor, and examples of typical waveforms which were recorded.