Current Sensing System for Protection of High Power Frequency Converters

The design and test results of a current-sensing system used for the protection of frequency converters, which are used for controlling the speeds of ac induction motors, are presented. The proposed pulse current-sensing system consists of a magnetic field sensor, which is made of thin polycrystalline La-Sr-Mn-O manganite film exhibiting the colossal magnetoresistance (CMR) effect, and a microcontroller with a 12-bit A/D converter that is used for recording the fault current signal. The magnetic field generated by the high power current cable is fed using a flux concentrator to the manganite magnetic field sensor (CMR-resistor). The design of the contactless current sensor, consisting of two manganite resistors, is developed and investigated. The system is tested in the ambient temperature range of 0-45°C. The possibilities of using this method in other pulsed power systems are discussed.