Development of Test System for Motor Insulation

Abstract

Abstract Modern pulse width modulated (PWM) inverters found in variable speed motor drives, while enhancing energy efficiency, introduce rapid switching transients and voltage overshoots that significantly increase electrical stress on motor insulation. The rapid switching triggers partial discharges (PDs) within the insulation, accelerating material degradation and ultimately causing insulation and motor failure. This thesis presents the design and validation of a programmable test platform that subjects motor winding insulation to electrical stresses commonly found in modern PWM drives. The system was implemented as a LabVIEW program that with the utilization of a PCI-6541 National Instrument (NI) digital I/O card controls multiple fast high voltage push-pull switches to generate arbitrary PWM signals in order to study PDs. To enable the NI card to deliver suitable current to control the switches, gate drivers were implemented. The software allows for save and load of test profiles, continuous or finite waveforms generation, and for stopping test sequences automatically if the current through the device under test (DUT) exceeds a user defined limit. Validation of the system was done through experimental testing with signal pulse widths ranging from 50 μs to 1 s. Tests were performed for three and four-level signals that confirm accurate generation for signals with pulse widths above 500 μs and demonstrates the viability of NI I/O cards for generating square waveforms. The testing results indicate that the primary limitations of the system are imposed by the push-pull switching devices rather than the software. To enhance the system’s testing capabilities, the use of faster switching components are proposed. Furthermore, future improvements could include the development of a custom PCB layout and a more refined user interface.