Online monitoring method based on magnetic field for stator insulation lifetime tests

Abstract

In this paper, an online monitoring method of insulation faults based on the stator magnetic field for insulation life tests is developed. In recent years, a trend towards higher operating voltages, higher switching frequencies, and shorter voltage rise times has been observed for low-voltage motors, mainly driven by increasing electromobility. An insulation system must withstand these requirements over the entire operating range and the required service life. Significant over-dimensioning of the insulation is not justifiable, since this has a negative impact on the utilization or the efficiency of the machine. Lifetime tests are therefore required for dimensioning the insulation. For this purpose, end-of-life (EOL) tests are usually carried out. Here, different damage patterns occur, which are distinguished during the analysis. In addition to the EOL test, insulation faults can be detected by monitoring the magnetic field of a stator during the operating time (“online”). An early shutdown often prevents the drive from further damage. In this paper, five methods to evaluate the magnetic field are presented. The operation is investigated using a 2D FEM simulation (sinus excitation) and a network simulation (PWM excitation) and evaluated through measurements on a 4 kW PM external rotor stator. Subsequently, an application of the method on a test rig setup with continuous monitoring of the insulation system is presented. The test setup serves as a basis for future investigations on the influence of voltage rise time, switching frequency, and DC link voltage on insulation faults to estimate the lifetime of insulation systems of electrical machines.