Observations of X-ray in 4-meters long laboratory sparks under positive lightning impulse

In this paper, the observation of X-rays in 4-meters long laboratory sparks is presented for the first time. In this study, a total of 20 standard positive lightning impulse voltages (1.2/50 µs) with measured peak voltages between 3.0 to 3.2 MV were applied across 4-m long horizontal air gap of sphere-sphere configuration with 50-cm spheres. The results show that most of the X-ray emission were detected at about 1–2 µs after the applications of the lightning impulse voltage during the rising part of the voltage or at around the peak of the voltage. Compared to previous shorter gaps studies, the longer air gaps seem leads to a delay in X-ray occurrence time. X-rays appeared at about 1–2 µs after the applications of lightning impulse voltage which is slightly delayed compared to some of the previous shorter gap's studies. This study also finds an increase in the X-ray emission rate and deposited energies of X-rays in the case of higher applied peak voltages. Higher applied peak voltages seemed to change the X-rays appearance time as well. Additionally, multiple peaks X-rays pulses were observed near to the peak of the voltage in this study.