Evaluation and current-response based identification of insulation degradation for high utilized electrical machines in railway application

Abstract

In order to investigate insulation degradation of high voltage traction drives, series of measurements on form wound coil specimens have been done. These stator bars have been aged by different accelerated aging cycles until the failure of the insulation is determined by voltage exposure tests. After every aging cycle the dissipation factor (tan ) and capacitance (C) of the insulation system is recorded. With these non destructive diagnostic measurements, the correlation between the indicator values (tan , PI, C) and the degradation of the insulation strength until a breakdown can be investigated. Furthermore, an online insulation condition monitoring method for traction drives is proposed. In this method the inverter is used as a source of excitation with a simple switching pattern. The current transducer's transient response at step excitation is used to evaluate a change of the insulation system. The drive system containing machine, cabling and inverter can be represented with a complex network of electrical, also parasitic components like resistances, inductances and capacitances. Insulation degradation within the machine also changes these components as investigated at the accelerated aging tests, and thus the tendency can be used for the monitoring method.

The Impact of Thermal Degradation on Properties of Electrical Machine Winding Insulation Material

“…The most influent factors and interactions were identified as those having the highest estimated effects: the voltage V, the temperature T, their interaction, and the T². Finally, in [27] the authors experienced a 20% capacitance drop of their tested windings after 5 thermal cycles. In the same work, they proposed a method, which is based on the monitoring of the current transients after step voltage excitation applied by the inverter and was applied on a high voltage induction motor.…”

Impact of SiC semiconductors switching transition speed on insulation health state monitoring of traction machines

“…The affected frequency range depends on the size of the machine and position of the fault capacitor. Previous investigations in [4] on the test machine showed that the highest-frequency component of interest for the estimation of the insulation state is up to 1 MHz. On the basis of the root mean square deviation between the 'healthy' and 'degraded' trace for every equidistant frequency point within a defined frequency range, an indicator is calculated to assess the severity of the insulation degradation.…”

“…The main causes for machine breakdown have been analysed in [1][2][3][4][5][6][7]. The fast rise times of voltage pulses applied by modern standard switching devices like insulated gate bipolar transistors (IGBTs) and beyond that, by using upcoming wide-bandgap semiconductors [SiC-metal-oxide-semiconductor field effect transistors (MOSFET)/diode combinations] as presented in a later section, result in low switching losses, but ultra-high dv/dt-rates in combination with impedance mismatch (machine against cabling and surge).…”

Degradation Monitoring of Insulation Systems Used in Low-Voltage Electromagnetic Coils under Thermal Loading Conditions from a Creep Point of View

“…Thus, they claimed that the capacitance can be used as an aging indicator of the winding insulation. Zoeller et al [ 36 , 37 , 38 ] proposed a method for stator insulation defect detection in traction-drive machine windings by evaluating the current response after a voltage step excitation, which is based on the fact that parasitic winding capacitance changes as the insulation degrades. Nussbaumer et al [ 13 ] proposed a method to monitor changes in the insulation health state by evaluating high-frequency machine properties.…”