Current sensing system for protection of high power frequency converters

Abstract

We present the design and test results of the current sensing system for protection of frequency converters, which are used for control of the speed of AC induction motors. Proposed pulse current sensing system consists of magnetic field sensor made from thin polycrystalline La-Sr-Mn-O manganite film exhibiting colossal magnetoresistance (CMR) effect, and microcontroller with 12-bit A/D converter for fault current signal recording. The magnetic field generated by high power current cable was fed using flux concentrator to the manganite magnetic field sensor (CMR-resistor). The design of contactless current sensor consisting of two manganite resistors was developed and tested. The system was tested in 0-45 ºC ambient temperature range and was able to protect frequency converters of AC induction motors at threshold current value higher than 10 A.