Purpose/Aim
The Trichel pulse in negative corona discharge received widespread attention, while the pulse sequence in surface discharge was rarely mentioned. The charge accumulation on the surface affects both the initiation and propagation of surface discharge, and the pulse sequence development with the applied voltage needs to be explored.
Experimental/Modeling methods
The electrodes for surface discharge were needle-plate ones, and the epoxy sample was fixed on the electrodes. A negative ramping voltage with a rising rate of 200 V/min was applied to the needle electrode. A 50 Ω non-inductive resistor was used to measure the discharge current, and a silicon photomultiplier (SiPM) was used to transfer the light signal into voltage signal simultaneously. The single sampling duration was 2 ms, and the sampling interval was 10 s.
Results/discussion
As shown in figure 1, different from previous research results, this paper found the transition of pulse sequence in surface discharge, and the transition voltage was around 8 kV. Before 8 kV, the pulse sequence showed a high-amplitude pulse accompanied by several or dozens of low-amplitude pulses, and the amplitude of the first pulse gradually increased with the applied voltage. However, the pulse sequence appeared as several hundred low-amplitude pulses when the applied voltage was higher than 8 kV, and the discharge number kept increasing with the applied voltage. The increased voltage made it easier for the accumulated surface charge to reach the discharge threshold.
Conclusions
The surface discharges showed a transition of pulse sequence at 8 kV. The discharge current amplitude kept a linear relationship with the SiPM signal amplitude.

surface discharge,discharge number,discharge current,pulse sequence