Low voltage insulation system endurance against electronic waveform and cable length

The application of electronic synthesised waveforms to electrical machines can introduce additional noise, losses and reduce the machine reliability. The adverse effects of applying these waveforms can may be minimised or avoided by incorporating suitable integrated design attributes into the machine, controller and installation. Electrical machines have evolved to accommodate electronic synthesised waveforms even though less than 10% are currently used with electronic controllers. In contrast it is not always the practice for electronic drive companies to consider the effect that a new product, which has differing waveform shapes-harmonic content, peak voltages, dv/dt´s-has on the machine, electrical distribution system and local environment. This paper describes some tests undertaken by an electronic controller manufacturer in collaboration with Brook Hansen in 1994 to provide a measure of reduced risk prior to the introduction of their new electronic products. The work relates to the effect on motor insulation life of a new large controller that incorporated a new waveform shape that exhibited higher dv/dt and PWM switching frequency than the previous range. The 1994 typical values for dv/dt and peak voltage were 500 V/μs and 1 kV respectively. The evaluation doubled the dv/dt to 1000 V/μs with only a small increase to the peak voltage. The principle of the evaluation is presented to provide awareness to designers since waveform dv/dt´s have now increased by an order of magnitude