Sun Yaohong

An experimental investigation of repetitive nanosecond-pulse breakdown in air

A compact, repetitive pulsed power system has many applications, but some basic aspects of the breakdown characteristics need further investigation. The purpose of this paper is to investigate the breakdown characteristics of dry air with repetitive nanosecond pulses. The variables affecting the discharge conditions, including the applied pulse voltage, pulse repetition frequency, gap distance and gas pressure, are investigated. The relationship between the breakdown time lag, the repetitive stressing time, and the number of applied pulses to breakdown with pulse repetition rate, E-field strength and pressure are obtained, and the breakdown characteristics and mechanism are also discussed. It is suggested that activated neutral species and residual ions should be taken into account, and repetitive nanosecond-pulse breakdown is characterized by the accumulation effect.

Experimental Study on Statistical Characteristics of Surface Flashover under Nanosecond Pulse in Transformer Oil

The insulator strength of the oil-immersed equipment is usually limited by surface flashover across the oil-solid surface. At the same time, the distributions of failure strengths have some statistical characteristics. In this paper, the flashover voltage electric strengths of several PMMA test samples are measured in transformer oil under nanosecond pulse voltage. Normal distribution is introduced to describe the statistical characteristics of the experimental data. The plot of the flashover dielectric strength on Weibull paper can also demonstrates the two-parameter Weibull distribution. The parameters of the distributions are presented and the more favorable distribution is discussed with the view of obtaining consistent results for the surface dielectric strength

Analysis of sound characteristics produced by high voltage discharges under DC and pulsed voltages

The mechanism of audible noise caused by corona discharge of UHV transmission lines is not well resolved. The sound characteristic produced by discharge is the foundation to analyze the intrinsic relation of audible noise and corona discharge. The experiment of sing point corona discharge under DC voltage was developed and the sound pressure produced by corona discharge was measured. The sound pressure in time domain was measured by capacitor microphone. The research results indicate the corona discharges in DC voltage are composed of a series of single discharge pulses. The rising edge and pulse width of single discharge pulse have relation to discharge voltage and electrode polarity. The corona discharge produces the sound pressure with a microsecond pulse lagging behind the single discharge pulse in their waveforms. The time delay between current pulse and sound pulse is mainly caused by sound propagation time from discharge spot to measurement spot. The nanosecond pulsed discharge platform was set up to study the relation of discharge parameter and sound characteristic. The sound pressure waveforms in different discharge parameters were obtained. Experiment results showed that pulsed discharge produce the similar sound pressure with corona discharge. The pulsed discharge platform could be used to study the mechanism of audible noise caused by corona discharge.

High-power and high repetitive rate charging techniques of laser power supply

Based on the demands of TEA CO2 laser, high power, high-precision and high repetitive rate charging technologies of capacitor charging power supply was discussed in the paper. Capacitor charging power supply adopted series resonant circuit has constant current and “fixed voltage steps” charging characteristics which were analyzed in the paper in theory. Because of the constant current charging characteristic, parallel operation of capacitor charging power supply adopted series resonant circuit was studied in simulation. The simulating result indicated that the power supply can operate in parallel directly. Based on this conclusion, two 30kW/7kV capacitor charging power supplies were developed and parallel operating experiments were carried out using the two power supplies. The experimental results also verified that the parallel operating mode is feasible. Influences on stability of the lasers output energy caused by the charging power supply were analyzed. Based on the “fixed voltage steps” charging characteristic, the voltage accuracy of laser system was analyzed emphatically and the solution was proposed. The 16kW/30kV capacitor charging power supply with 100Hz repetitive charging rate was developed and the control scheme of charging voltage accuracy was verified feasible through the prototype tests.

Transformer Oil Breakdown under Nanosecond Pulse

The dielectric strength of transformer oil has been measured in the nanosecond regime under single pulse conditions. The dielectric strength of transformer oil with different DC breakdown field has been tested under nanosecond pulses. The results indicate that when the DC breakdown field of transformer oil increases the pulse breakdown field of transformer oil also increases, but the voltage rate of rise falls. The breakdown characteristics of transformer oil under pulses with different widths have been studied. The influence of electrode materials for transformer oil breakdown characteristics has been investigated. The breakdown voltage of transformer oil in aluminum electrodes is the lowest. The gap distances are ranged from 0.15mm to 1mm. The pulse generator provides less than 10 ns rise time and a 300kV peak amplitude voltage. The breakdown electric fields are measured by the umbrella probe and a 1GHz bandwidth oscillograph