A method for magnetic/impedance burst testing of large electric motors includes;
- providing a portable tester that provides a Signal Processor, a single-phase power source VAC, an AC to DC boost converter connected to the power source, at least one energy storage device connected to the AC to DC boost converter, a pulse width modulated drive (PWM) module connected to the at least one energy storage device, and a series of at least three switches (IPM) using switch/level boost-type PWM rectification, the IPM connected to both the 3 legs of the large electric motor and the PWM drive module, the method comprising the steps of:
- programming the PWM drive module with a desired duration of output burst pulse with the Signal Processor,
- programming the PWM drive module with an initial magnetic test angle with the Signal Processor,
- programming the PWM drive module with a test frequency for magnetic angle reversals with the Signal Processor,
- programming a Programmable Gain Amplifier with the Signal Processor to optimize a signal gain in order to prevent voltage and current signal clipping,
- controlling the PWM drive module with the Signal Processor to control the amplitude, magnetic angle and reversal frequency applied to the large electric motor,
- controlling the boost converter with the Signal Processor to limit/throttle a maximum power drawn from the single-phase power source and the power delivered to the energy storage device to maximally charge the energy storage device,
- controlling the series of switches (IPM) with a cross conduction preventer (CCP) to prevent crowbar of a DC Buss by adding dead-time to PWM signals and interlocking out unsafe PWM conditions,
- controlling the CCP with the PWM drive module to pass through only safe PWM drive conditions,
- controlling the charging of the at least one energy storage device with the boost converter to a maximum working voltage,
- sending an enable signal to the PWM drive module to begin burst output from the Signal Processor,
- sampling a stream of measured voltage and/or currents of at least one of the motor legs during burst output with a voltage transducer and a current transducer respectively, which converts from analog to a digital A/D Converter digital number with an A/D Converter,
- adjusting the PWM drive module with a set point level and measured voltage and/or current to maintain a desired burst level in order to compensate for sinking voltage of the at least one energy storage device applied to a programmed voltage and/or current level applied to a motor with the Signal Processor,
- recording the stream of digital numbers with the Signal Processor,
- calculating, at the end of each burst, rotor characteristics that include impedance, admittance, instantaneous power, voltage and currents for a previously applied magnetic test angle with the Signal Processor,
- recharging the at least one energy storage device with the boost converter until the maximum working voltage is attained,
- advancing the magnetic angle by N degrees to measure the response of each set of rotor bars that are in the line given magnetic angle and verify the response is the same for all magnetic angles with the Signal Processor,
- repeating the burst test N number of times until a full rotation of magnetic angles are tested and recorded with the Signal Processor,
- verifying, with the Signal Processor, rotor impedance versus magnetic angle of the full rotation in order to check for failure, and
- determining failure by identifying a shift in measured stator's impedance/admittance, harmonic or sub-harmonic level for any of the given magnetic angles by the Signal Processor.