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Deep investigations and reliability analysis of twisted pairs or motors fed by frequency drives
New IEC standards, IEC 60034-18-41 and IEC 60034-18-42, have been issued to define the procedures for testing partial discharge inception voltage and the long-term performance (endurance) of Type I and Type II insulation systems used in rotating machines fed from voltage converters. Voltage impulse generators are required at least to test turn insulation, but they would be recommended for any testing under power electronics supply because of their capability to simulate the real electrical stress conditions. More generally, any type of electrical insulation system when subject to impulsive voltage waveform during life should be carefully evaluated in terms of partial discharge and endurance behaviour. This is why voltage impulse generators able to provide impulses with controlled amplitude and frequency are needed to face this new testing challenge.
The use of power electronics to supply induction motors is widely spreading out due to significant advantages in terms of speed and torque control of electrical machines.The most common are ASD (Adjustable Speed Drives) systems, lead by PWM (Pulse Width Modulation) techniques.Unfortunately, it has been proved that this kind of power supply can cause overstress on electrical insulation in comparison to the sinusoidal 50/60 Hz voltage supply, thus decreasing drastically life and reliability of controlled motors.The reliability of winding insulation, as it occurs for other insulation systems, can be investigated by Partial Discharge (PD) analysis.In order to reproduce the same stress conditions on the insulation materials of the conductor’s windings of induction motors, TechImp Systems has developed a new complete system dedicated to tests on twisted pairs or other specimens, under high voltage square waveforms conditions.The off-line testing apparatus is composed by a high voltage square wave generator, whose amplitude, frequency, duty cycle and rise time are selectable by the user.
60034-18-41: Partial discharge free electrical insulation systems (Type I) used in rotating electrical machines fed from voltage converters – Qualification and quality control tests60034-18-42: Partial discharge resistant electrical insulation systems (Type II) used in rotating electrical machines fed from voltage converters - Qualification testsIEC/TS 61934: Electrical insulating materials and systems – Electrical measurement of partial discharges (PD) under short rise time and repetitive voltage impulsesIEC 62068: Electrical insulating materials and systems – General method of evaluation of electrical endurance under repetitive voltage impulses