Takahisa Ueno

Novel dual Marx Generator for microplasma applications

Micrometer size plasmas, or microplasmas, find applications in pollution control, reduction, and prevention. The required nonthermal plasmas can be generated by either an electron beam or an electric discharge. The pulse widths and voltages necessary to generate these nonthermal plasmas are 10/sup -10/-10/sup -8/ s, and 10/sup 3/-10/sup 4/ V, respectively, depending on the application. The required energy is typically in the low 10/sup -3/ J range. This paper presents a novel circuit design to generate high-voltage pulses with variable pulse widths and pulse rise and fall times in the low 10/sup -9/ s regime. The circuit employs two parallel Marx Generators utilizing bipolar junction transistors (BJTs) as closing switches. The BJTs are operated in the avalanche mode to yield fast rise times. The design allows for positive or negative polarity pulses, and can easily be changed to yield higher or lower output voltage.

Effects of Output Peaking Capacitor on Underwater-Streamer Propagation

This paper describes the effects of an output peaking capacitor on the propagation of an underwater streamer. A pulsed-power modulator using a magnetic-pulse-compression circuit was employed to generate 20-30-kV pulses with 2-mus pulsewidth. A point-to-plane electrode setup with 2-cm gap in tap water was used. A copper line with 0.43-mm tip diameter was used as the discharge electrode, and an aluminum plate was set in water and connected to ground. Underwater-streamer propagation was visualized by an intensified-charge-coupled-device camera with a high-speed gate. An optional output peaking capacitor was connected in parallel to the electrodes to get pulses with different rise time and higher peak voltage and current. Thin and well-distributed channels were observed when the peaking capacitor was used. In contrast, the number of streamer channels was small, and each of them was thick and bright when the peaking capacitor was removed from the circuit. It is concluded that the peaking capacitor has a favorable effect on the generation and propagation of the underwater streamer.

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.

Dynamic Characteristics of Laser-Assisted Discharge Plasmas for Extreme Ultraviolet Light Sources

This paper reports the dynamics of laser-assisted discharge plasmas for extreme ultraviolet (EUV) sources. A pulsed laser was focused on the tin cathode surface to form vapor jet across 5 mm long anode–cathode gap where pulsed power was applied later on. Comparison of time-resolved pinhole EUV imaging and high speed visible photography reveals that intensive EUV is emitted only from the neck of the hot plasma, which starts showing up near the laser spot on the cathode and moves away from the cathode. This movement of the neck plasma results in the enlargement of the EUV emissive region acting as its source.

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.

Round-robin test of repetitive partial discharge inception voltage measurements on complete winding of 4 kW random-wound motor

Measurements of repetitive partial discharge inception voltage (RPDIV) based on IEC 60034-18-41 using a stator coil winding of 4 kW random-wound motor have been performed in round-robin test (RRT) in Japan. A commercially available impulse power supply and a PD sensor were commonly used in the RRT. The present paper reports not only test procedure and results of RRT but also additional experimental data to clarify the mechanism of PD phenomena in the RRT.

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.

Recent progress in round-robin test of repetitive partial discharge inception voltage measurements on complete winding of 4 Kw random-wound motor

This paper presents the results of round-robin test (RRT) of repetitive partial discharge inception voltage (RPDIV) measurements with a stator coil winding of 4 kW random-wound motor. Nine independent laboratories in Japan participated in the RRT in order to validate evaluation procedures described in IEC 60034-18-41. The results provided new insights into RPDIV measurements with complete windings such as ambient humidity and pre-discharge effects.

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.