Tatsuya Hirose

Partial Discharge Characteristics of Nanocomposite Enameled Wire for Inverter-Fed Motor

Recently, partial discharge (PD)-resistant enameled wires mixed with inorganic particles of nanometer order, referred to as the nanocomposite enameled wires, have been developed and verified to have longer life compared with conventional enameled wires. We investigated the fundamental characteristics on PD inception, propagation and breakdown (BD) of nanocomposite enameled wire under surge voltage conditions. Electrical and optical PD measurements were carried out for twisted pair samples with nanocomposite and conventional enameled wires. Experimental results revealed that there was no difference in PD inception voltage (PDIV) between both wires. The relationship between applied voltage and time to BD (V-t characteristics) exhibited the longer life of nanocomposite enameled wires, e.g. 2-20 times of conventional enameled wires, which was highly influenced by the applied voltage level and the repetition rate.

Partial discharge phenomena in artificial cavity in epoxy cast resin insulation system

It is crucial for proper insulation design of cast resin transformer to consider voids and delamination which might exist in cast molding because of several surface boundaries between resin and conductor. Such defects in the insulator lead to reduction of the life of the apparatus. In this report, we investigate the relation between the void size and apparent charge of partial discharge (PD) occurring in a model simulating the insulation system of cast resin transformer. It is also important to determine necessary PD detection sensitivity of PD test in a factory as well as in a field. In this paper, we also discuss the detection sensitivity by considering the relation between charge and void radius using formula derived by L.Niemyer, M.Pedersen and their colleagues in the late 1980?s to apply to the case of the cast resin transformer. Experiments were also performed to obtain PD inception voltage (PDIV) of epoxy resin slab including an artificial void with a given size. Investigation was also made on the effect of X-ray irradiation to the epoxy resin on PDIV characteristics.

Effect of X-ray irradiation on partial discharge inception and extinction voltage characteristics of cast resin transformer insulation system

In general, it is hard for discharge to be initiated in a small void existing in solid insulating material because of insufficient initial electrons. For this reason, the discharge occurs after a long delay even at a critical electric field to initiate discharge. In this study, the initial electrons are supplied by X-ray irradiation to a cavity formed in epoxy resin (ER) sample. We have investigated PD characteristics of ER with spherical void. Additionally, we investigated the effect of X-ray irradiation on PD inception voltage (PDIV) and PD extinction voltage (PDEV) of the sample with delamination. It was found that the lowest and stable PDIV was brought by the X-ray irradiation for the samples with the cavity and delamination. Furthermore, we estimated quantitatively attenuation of X-ray dose by the structure such as winding, an iron core of a cast resin transformer. Discharge time lag was estimated from X-ray dose, and compared with that measured for the ER sample with the cavity. This report also deals with the effect of X-ray irradiation on PD generating characteristics in various artificial detects of epoxy insulation system simulating insulation of winding, delamination, and void.

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.

Study of direction identification of partial discharge using multi small loop sensors

This paper describes the study on the identification location of partial discharge (PD) which occur at a faulty point in electric equipment. We identified the location of PD utilizing arrival time differences of electromagnetic wave emitted from PD between each loop sensor. An attempt is made to perform direction identification of PD source using the four small loop sensors placed in a fixed interval each other. It is found that PD direction can be identified with angle error of about plus or minus 25 degrees.

X-ray irradiation induced discharge of spherical void in epoxy resin

It is crucial for proper insulation design of cast resin transformer to consider voids and delamination which might exist in cast molding process and/or under long-term operation because of several surface boundaries between resin and conductor. Should such defects in the insulation system exist, it would lead to reduction of the life of the apparatus. In this report, we investigate the relation between the void size and apparent charge of partial discharge (PD) occurring in a model simulating the insulation system of cast resin transformer. It is also important to determine necessary PD detection sensitivity of PD test in a factory as well as in a field. In addition, we investigate X-ray irradiation induced discharge of spherical void in epoxy resin. Physical consideration of the effect of X-ray irradiation on void discharges in epoxy resin was also made. Time lag of void discharges in epoxy resin was also made with attenuation of X-ray irradiation dose considered.

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.