Improving electrical machines operation safety by complex insulation and winding resistance periodic testing

Abstract

    One of the frequently occurring causes of manufacturing equipment forced outage and emergencies at industrial facilities is electrical machine insulation breakdown, arising due to severe conditions of operation, when the electric drive frequent start-ups and breakings lead to the intense reduce of the motor windings insulating strength. To a large extent these processes result from discrete (pulse) nature of the output voltage of the power rectifier converters (thyristor converters, stand-alone and network driven frequency converters, etc) that form the high-frequency harmonics that conduce the electric machine heating and therefore the reduction of insulation resistance of the electrical machine. One of the reasons of the electrical machine insulation breakdown is also sudden changes in ambient temperature and humidity that arise in many production areas. In these circumstances, it is necessary to carry out periodic diagnostics of the electric motors windings and other electrical equipment. It is now usually performed too rarely, mainly during maintenance works on the technological object. At the same time, many objects have production interruptions provided with the technology so that it is available to perform manual or automatic testing of electrical equipment insulation that exhibits the most obvious failures.
    This article discusses the construction principle of the electrical machine or another electrical equipment insulation complex resistance indicator.
    Resistance indicator RI is an autooscillating system, the output of which is a test signal to the controlled object. The response of this object affects the time constant of the integrator of the RI autooscillating cascade changing the frequency of its output pulses. Then, the frequency-modulated signal is sent to a binary counter which accumulates the number that is proportional to the controlled circuit resistance. After completion of the transformation cycle defined by an external clock generator, data is transferred to the memory register, the counter is reset and a conversion cycle is repeated. An experimental static characteristic of the RI is given. Controlled resistance range is from 10 kΩ to 105 kΩ. Temperature error is 3% max.Different variants of the RI inclusion for electrical equipment diagnosing are sentenced.