The backward discharge induced by residual charge has attracted considerable attention, but the complex mechanism requires further investigation. This article analyzes the surface discharge and the residual surface charge accumulation characteristics in atmospheric air under a positive impulse. The photographic figure method, the dust figure method, and the electrostatic probe method are employed, allowing the residual charge distribution to be quantitatively determined. One main forward discharge is observed at the impulse front and several subsequent backward discharges are observed at the impulse tail. The propagation length of the forward streamer is closely related to the voltage at the moment of discharge. A model illustrating the evolution process of surface forward and backward discharges as well as the corresponding residual charge accumulation characteristics is established. The residual surface charge plays a significant role in the development of the streamer discharge. The backward discharge is incurred by the positive charge that is deposited by the previous forward discharge. 

Surface forward and backward discharges and corresponding residual charge accumulation characteristics under positive impulse

Influence of N2 pressure on surface discharge characteristics of PEEK under positive repetitive square voltage

The micron metal particles are inevitably produced in long-term operation condition of high voltage direct current SF6 insulated apparatus, which could frequently cause the surface discharge. Degradation of long-term surface discharge will be a severe threat to the insulation strength. Aiming at this problem, the surface charge accumulation and flashover voltage of epoxy itself before and after discharge degradation by particles were compared in this paper. The composition after degradation was measured by EDS and FTIR. The microstructure was observed by SEM. The roughness was measured as well. The trap distribution was measured by SPD. The mechanism of degradation and its effect on insulation characteristics were analyzed. The results show that the surface charge accumulation increase three times after degradation. Additionally, flashover voltage decreases 19% after degradation. The smoothly surface after degradation decrease the trap energy level for 14%, which might be the change reason of surface charge accumulation and flashover voltage. This paper can offer as a reference for the effect of micron metal particles on insulation degradation in SF6 gas insulated equipment.

Insulation degradation affected by micron metal particles attached on epoxy surface: charge accumulation and flashover voltage

Streamer-to-precursor transition in N2–SF6 mixtures under positive repetitive submicrosecond pulses

The working voltage of the high-voltage high-power electronic devices is the positive periodic square waveform (PPSW) voltage, which is much different from the conventional AC or DC voltage. For the composite insulation structure of devices, it is important to analyse the transient electric field under the PPSW voltage. However, the existing investigations are often conducted under the electrostatic field due to the high frequency of the PPSW voltage. Thus, the transient characteristics of the electric field are missed. To obtain some qualitative conclusions, this paper focusses on the theoretical analysis of the transient characteristics of electric field for the composite insulation structure under the PPSW voltage. First, the formula of the electric field intensity and the interfacial charge density are derived analytically. Second, the influence of the cycle and the duty cycle on the transient characteristics are investigated. Third, the maximum of the electric field intensity and the interfacial charge density in the positive square waveform steady-state are discussed in detail. Besides, the engineering calculation methods for obtaining these maximum values are also suggested. Lastly, an actual model is employed to testify the validity of the analytical analysis. This work is significant for the numerical calculation of the transient electric field of composite insulation structure under the PPSW voltage in engineering. 

https://onlinelibrary.wiley.com/doi/pdfdirect/10.1049/hve2.12203

Transient electric field of the combined insulation structure under positive periodic square waveform voltage: Analytical analysis and application

In this study, the surface discharge current pulses of polyetheretherketone (PEEK) material under positive repetitive square voltage in a nitrogen atmosphere are measured. The influences of different voltage amplitudes and frequencies on the detail parameters of forward discharge and backward discharge current pulses are statistically analysed. The results show that as the square voltage amplitude increases, the current pulse amplitude, fall time and pulse width of both forward and backward discharge current increase, and the rise time does not change significantly. As the voltage frequency increases, current pulse amplitude, fall time and pulse width of both forward and backward discharge current decrease, and the rise time does not change significantly. Due to the independence of the discharge at different repetitive cycles, the specific discharge process in one cycle is analysed in detail to explain the influence mechanism of the voltage amplitude and frequency on the discharge current. By mean of the Richardson–Schottky and the Cavallini relaxation model, the relationship between discharge voltage ratio and surface charge, and the decay process of surface discharge are analysed. Furthermore, the influences of amplitude and frequency of the positive repetitive square voltage on the PEEK surface current pulses are explained qualitatively.

https://ietresearch.onlinelibrary.wiley.com/doi/pdf/10.1049/hve.2019.0292

Influence of frequency on the surface discharge characteristics of PEEK under positive repetitive square voltage

In this paper, the surface discharge current pulses of PEEK (polyether-ether-ketone) under positive repetitive square voltage are measured The effects of voltage rise time and fall time on pulse parameters of discharge current, instantaneous voltage of discharge and time-lag of discharge are analyzed in detail The results show that the amplitude of discharge current and the instantaneous voltage of discharge decrease, and the time-lag of discharge and the dispersion of time-lag increase with the increase of voltage rise time With the increase of voltage fall time, the amplitude of discharge current decreases and the instantaneous voltage of discharge, the time-lag of discharge and the dispersion of time-lag increase To analyze the influence mechanism of voltage rise time and fall time on surface discharge, the accumulation of surface charge under repetitive square voltage is regarded as a periodic process Besides, the correlation between forward discharge and back discharge in the process of discharge is analyzed, and the development of discharge is analyzed by using the time-lag theory Furthermore, the relationship between instantaneous discharge voltage and voltage slew rate is revealed, and the surface charge accumulation processes under different voltage rise times and fall times are compared to reveal the influence mechanism of rise time and fall time on the surface discharge under positive repetitive square voltage

Influence of Rise Time and Fall Time on Surface Discharge Characteristics of PEEK Under Positive Repetitive Square Voltage

The invention discloses a power transmission line corona discharging point positioning system. The positioning system comprises a positioning device, a data collection device and a computer; the positioning device is an antenna array composed of four time-domain testing systems; the first, the second and the third time-domain testing systems are respectively located on three vertexes of a virtualisosceles right triangle, the second time-domain testing system is placed at the right-angle vertex, and the fourth time-domain testing system is placed at a reverse extension line of an angle bisector of the right-angle; each time-domain testing system comprises an antenna, a sampling resistor, voltage probes, an insulation board and a ground metal board; the insulation board is placed above theground metal board, and the antenna is connected to the insulation board; the sampling resistor is connected between the antenna and the ground metal board, and voltage probes are connected at two ends of the sampling resistor; the computer obtains a location of the power transmission line corona discharging point by adopting time delay information at different locations of the antenna. Through the positioning system disclosed by the invention, the corona discharging points of the power transmission line can be accurately positioned.

Power transmission line corona discharging point positioning system and positioning method thereof

In this article, the effects of air humidity and salinity on the discharge characteristics of a short rod-plane gap under negative dc voltage are investigated experimentally. The discharge of the rod-plane gap was recorded using a measuring resistance, photomultiplier tube, and ultraviolet imager. The experimental results show that corona discharge of rod electrode can be observed in the rod-plane gap when the relative humidity is lower than 70%, and furthermore, partial discharge of water molecules in the air can also be observed in the rod-plane gap when the relative humidity is higher than 70%. The partial discharge inception voltage (PDIV) decreases with the increase of air humidity and salinity, and the corona discharge inception voltage (CDIV) increases slightly with the increase of humidity. The average discharge current increases with the increase of applied voltage and humidity. The repetition rate of the optical pulse and the Trichel pulse increases with the increase of applied voltage. The discharge repetition rate of water molecules in the air can be estimated from the repetition rate difference between the optical pulse and the Trichel pulse. The amplitude of the Trichel pulse in clean air is higher than that in the salty air, while the repetition rate of the Trichel pulse in clean air is lower than that in the salty air, which is due to the charging of NaCl particles during discharge.

Influence of Humidity and Salinity on the Discharge Characteristics of a Short Rod-Plane Gap Under Negative DC Voltage

In this paper, the positive corona discharge in rod-plane gap was measured by non-inductive resistance, photomultiplier and ultraviolet imager. With the increase of applied voltage, different positive corona discharge modes are distinguished according to the difference of optical and electrical characteristics. The positive corona discharge develops from streamer discharge to glow discharge at low humidity, and the discharge of water molecules in air can be detected before streamer discharge when the relative humidity is higher than 80%. Humidity has little effect on the inception voltage of streamer discharge, while the inception voltage of glow discharge increases with the humidity. As for the positive corona discharge in salty air, the streamer discharge will never develops into the glow discharge but develops directly to a spark if the air humidity is somewhat high. The physical mechanism of positive streamer discharge and glow discharge are analyzed, and the evolution of space charge distribution during positive corona discharge are obtained by simulation. The glow discharge is characterized by the presence of negative ion sheath around the anode. The increase of humidity and salinity in air reduces the migration rate of negative ions, which is not conducive to the establishment of glow discharge. 

Xiangrui Meng

Papers

Influence of frequency on the surface discharge characteristics of PEEK under positive repetitive square voltage

Influence of Rise Time and Fall Time on Surface Discharge Characteristics of PEEK Under Positive Repetitive Square Voltage

Power transmission line corona discharging point positioning system and positioning method thereof

Influence of Humidity and Salinity on the Discharge Characteristics of a Short Rod-Plane Gap Under Negative DC Voltage

Influence of Humidity and Salinity on the Transformation of Positive Corona Discharge Modes in Rod-Plane Gap