1) A system for magnetic/impedance burst testing of large electric motors to determine broken rotor bar defect, the system encased in a portable tester and comprises:
- 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 module (PWM) connected to the Signal Processor, 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, wherein
- the PWM is programmed with a desired duration of output burst by the Signal Processor,
- the PWM is programmed with an initial magnetic test angle by the Signal Processor, the PWM is programmed with a test frequency for magnetic angle reversals by the Signal Processor,
- the Programmable Gain Amplifier is programmed by the Signal Processor to optimize the signal gain in order to prevent voltage and current signal clipping,
- the PWM is controlled by the Signal Processor to control the amplitude, magnetic angle and reversal frequency applied to the ACIM,
- the boost converter is controlled by the Signal Processor to limit/throttle the maximum power drawn from the single-phase AC source and the power delivered to the large energy storage device to maximally charge the energy storage device,
- the series of switches IPM is controlled by the CCP to prevent crowbar of the DC Buss by adding dead-time to the PWM signals and interlocking out unsafe PWM conditions,
- the CCP is controlled by the PWM drive module to pass through only safe PWM drive conditions,
- the charging of the at least one energy storage device is controlled by the boost converter to a maximum working voltage,
- an enable signal to the PWM drive to begin burst output is sent from the Signal Processor,
- a stream of measured voltage and/or currents of at least one of the motor legs during burst output are sampled with at least one voltage transducer and at least one current transducer respectively, which converts from analog to a digital A/D Converter digital number with the A/D Converter,
- the PWM drive is adjusted 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 the programmed voltage and/or current level applied to the large electric motors with the Signal Processor,
- the stream of digital numbers are stored within the Signal Processor,
- at the end of each burst, rotor characteristics that include impedance, admittance, instantaneous power (I squared r), voltage and currents for the previously applied magnetic test angle are calculated by the Signal Processor,
- the at least one energy storage device is recharged by the boost converter until the maximum working voltage is re-attained,
- the magnetic angle is advanced 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 wherein
- broken rotor bar defect is determined when a shift in measured stator's impedance/admittance, harmonic or sub-harmonic level for any of the given magnetic angles is identified by the Signal Processor.