Nano-crystalline magnetic core pulse CT development and assessment for partial discharge measurements

The measurement and monitoring of some important parameters characteristic for the equipment health evolution, from the moment of leaving the manufacturing company and throughout the active life, is contained in the standards in the field and followed carefully by the organizations that use the equipment. The paper deals with issues related to the accurate measurement of Partial Discharges (PD) level in the electrical insulation and, in particular, to the sensors used for this purpose. Lately, inductive current sensors are more and more used instead of the classical measuring impedances of RLC type provided in the standards in force, but the adequacy of their characteristics to the phenomena under study is not experimentally verified. The design of some dedicated wide band pulse current transformers (PCTs) with high sensitivity which, unlike those usually used, have a high permeability nano-crystalline magnetic core is analyzed. Their behavior is studied in the time and frequency domains for determining the sensitivity and the frequency band adapted to be used for Phase Resolving Partial Discharge Analysis (PRPDA). The response of PCTs achieved by authors is compared with the response of other commercial PCTs and with the response of some classical measuring impedances, by using current pulses produced by professional PD calibrators. It is described their application for PD measurement at power transformers.