Satoshi Hiroshima

Evaluation of novel impulse voltage generator for detecting partial discharge

The Inverter surge is a high-voltage phenomenon that is generated by the overlap returning wave by impedance mismatching to an inverter and load like cables and motors. The inverter has been available by advancement of control system of electrical instrument, such as the industrial motor. The increase of current changing rate with the advance of power semiconductor causes the surge voltage to rise, increasing the number of failure events. The evaluation technology by partial discharge (PD) measurement is important because the mechanism leading to breakdown by the inverter surge is a cause of PD. In this study, a repetitive impulse voltage generator has been developed which is used in detecting PD in the inverter surge. We report the result that repetitive impulse voltage was applied to confirm the insulation dignity of inverter-fed motor insulation using the repetitive impulse voltage generator.

Development of repetitive voltage impulse generator and automatic repetitive PD inception voltage measurement system for testing inverter-fed motor insulation

In this study, a repetitive impulse voltage generator has been developed for detecting RPDIV (Repetitive Partial Discharge Inception Voltage) and RPDEV (RPD Extinction Voltage) of motorette test specimen designated in IEC60034-18-41-TS in the inverter surge. The fabrication of a generator is also described using a high-power semiconductor module and a variable amplitude DC power source. A design methodology for the impulse generator for partial discharge test is developed. The developed generator can generate a given number of voltage impulses with rise time of larger than 200 ns and arbitrary pulse width at less than 10 kHz of repetitive frequency and variable rate of applied voltage rise. Automatic PD measuring system including the repetitive voltage impulse generator was also developed. The system allows automatic data acquisition of RPDIV and RPDEV defined according to IEC61934TS as well as conventionally defined PDIV and PDEV. We report the result that repetitive impulse voltage was applied to confirm the insulation dignity of inverter-fed motor insulation using the repetitive impulse voltage generator.

Partial Discharge Resistant Aging Mechanism of Nanocomposite Enamel Wires under Repetitive Surge Voltage Condition

This paper discusses the partial discharge (PD) resistant mechanism of nanocomposite enamel wires under repetitive surge voltage condition for inverter-fed motors. We focused on the reduction of deterioration depth and the surface condition of nanocomposite enamel wires after repetitive surge voltage application with successive PD. Experimental results revealed that the longer lifetime of breakdown of nanocomposite enamel wires compared with the conventional wires would be brought about not only by the filled nano materials, but also by their byproduct on the enamel surface under repetitive PD generation. The erosion of nanocomposite enamel layers was suppressed in depth by the byproduct and dispersed in the longitudinal direction along the enamel surface, which could contribute to the longer lifetime of breakdown than conventional wires.

Repetitive impulse voltage generator development and waveform analysis for testing insulation dignity of inverter-fed low voltage motor

The authors have developed a repetitive impulse generator which meets conditions required by IEC/IS 60034-18-41 for inverter-fed low voltage motor. This paper deals with experimental and analytical investigation on impulse voltage waveform generated with our developed impulse generator under the voltage application to a low voltage inverter-fed motor. A relatively good agreement is obtained between the experimental and analytical waveforms.

Effects of motorette structure and vanish treatment on repetitive partial discharge inception voltage measurement test in inverter surge insulation

The Inverter surge is a high-voltage phenomenon that is generated by the overlap returning waves by impedance mismatching among an inverter, cable and motor. The inverter has been available by advancement of control system of electrical instrument, such as the industrial motor. Insulation performance evaluation technology by partial discharge (PD) measurement is important because the mechanism leading to breakdown by the inverter surge is a cause of PD. In this study, a design methodology for the impulse generator for partial discharge test is developed. In addition, we measure repetitive PD inception voltage (RPDIV) at phase to phase, phase to ground and turn to turn in a motorette sample using automatic RPDIV measuring system and developed repetitive impulse voltage generator. As a result, it is found that generated voltage and current waveform varies depending on the motorette structure. It is also found that RPDIV of the motorette differs with and a without a varnish treatment. The repetitive impulse voltage is applied to confirm the insulation dignity of inverter-fed motor insulation.

Off-line and on-line detection of PD in inverter-fed random-wound motor considering IEC technical specifications

In the inverter-fed motor, the surge voltages with fast rise time and high voltage peak may cause partial discharge (PD) which potentially damages the electrical insulation system. Offline tests with an impulse generator are executed under the IEC technical specifications of TS60034-18-41 (2006) and TS61934 (2011) for insulation systems of low-voltage motors fed from inverters, which are required of PD free in their expected service lives. On-line tests are executed during operation of an actual motor fed from a PWM inverter, since the PD properties may differ from the off-lines ones. This paper mainly discusses the detection sensitivity of PD for off-line and on-line tests using the PD detector at motor terminal. Firstly, effects on PD signal at the motor terminal in the stator windings under surge voltage are examined, when PD signal propagates through some coils after generating PD in the twisted pair that is connected to the motor winding purposely. In our test conditions, it is confirmed that PD signal propagating through the motor winding to the motor terminal can be detected correctly. Secondly, effects of noises on detection sensitivity are examined. It is concluded that the residual surge noise signals from an inverter or an impulse generator can be excluded using the high-pass filter of the appropriate selected frequency, then PD signals can be easily recognized, even for on-line tests. Finally, the transient noises hardly have effect on the PD detection of offline tests under an IEC-TS61934, since the time range required for the PD distinction of off-line tests is extremely shorter than of power frequency tests. These testing results and considerations may be useful for the standardizations of the IEC TS60034-18-41 and TS 61934 in the near future.

Sensitivity characteristics of partial discharge electromagnetic sensor located in stator core

Repetitive partial discharge inception voltage (RPDIV) measurement is indispensable for inverter-fed motor when testing according to IEC 60034-18-41 IS. Our previous study showed sensitivity comparison between kinds of electromagnetic (EM) sensors and a partial discharge (PD) measuring device in an actual motor core. This paper deals with an influence of the position and distance of EM sensor on the sensitivity of detected EM wave to quantitatively evaluate RPDIV. Results revealed that the detected signal attenuation is affected by not only the distance between the PD source and the sensor location but also the existence of the actual core. Furthermore, RPDIV provided by a loop sensor located at 135° around the circumference direction from the bottom of the core was estimated by 10% higher than that determined with a reference LS located just above the PD source which was placed at the bottom of the core. Namely, it is indicated that employing EM wave sensor to detect PD can result in estimating higher RPDIV than actual one. In other words, a correction is necessary for estimating precise RPDIV by multiplying a given factor depending on the size of the core and the location of the EM sensor to measure RPDIV.