Error in the measurement of partial discharge pulses according to the frequency response of HFCT sensors

The measurement of partial discharges (PD) in HV installations by means of high-frequency current transformers (HFCT) is being extended progressively in recent years, as they are affordable non-invasive sensors that can be easily installed. Several manufacturers provide in their data sheets the technical characteristics considered most relevant. However, there is no formal definition of these characteristics and/or minimum requirements to be met for such type of sensors, nor objective procedures to measure and quantify them. A new European EMPIR Project [1] aims to develop a characterization procedure for PD measuring systems. The main objective of this article is to analyze some of the most relevant characteristics of an HFCT sensor and to present test-setups to be used for obtaining them, especially its frequency response, as well as its EMC immunity, and their impact on the measured PD signals.