Influence of the Gap Distance on the Repetition Rate and Apparent Discharge Power in Corona Discharges
M. Soltany, J.-R. Riba, P. Canalda, S. Bogarra Department of Electrical Engineering, AMBER High-Voltage Laboratory, Universitat Politècnica de Catalunya, Campus of Terrassa, Terrassa Spain 2026-06-27

Abstract

Testing for corona discharges is a major step in design and development of high-voltage equipment. Apparent discharge power is considered an important indicator of insulation stress, as it relates to discharge magnitude and pulse repetition rate. This study investigates the effect of gap distance, applied voltage and electrode geometry on apparent discharge power, based on the principles of IEC 60270. Partial discharge (corona) measurements were performed under controlled laboratory conditions and at a fixed pressure, using two common configurations: rod-plane and sphere-plane. The gap distance between the test object and the ground plane was varied, and voltages corresponding to 110% and 120% of corona inception voltage (CIV) were applied. The results presented in this work demonstrate that apparent discharge power decreases significantly with an increase in the gap distance, with the most dramatic change occurring at small gaps. Furthermore, the impact of electrode geometry on apparent discharge power is analyzed, with spherical electrodes producing significantly higher levels than rod electrodes under identical voltage conditions.

Key words: Corona discharges, apparent discharge power, apparent charge, discharge repetition rate.

References

[1] IEC, IEC 60270: 2025 High-voltage test techniques - Charge-based measurement of partial discharges. Geneve,
Switzerland: International Electrotechnical Commission, 2025.

[2] J.-R. Riba, “Linking digital image intensity to carrier density in low-pressure corona discharges,” Sensors Actuators A Phys., vol. 359, p. 114474, 2023.

[3] J.-R. Riba, C. Abomailek, P. Casals-Torrens, and F. Capelli, “Simplification and cost reduction of visual corona tests,”
IET Gener. Transm. Distrib., vol. 12, no. 4, pp. 834–841, Feb. 2018.

[4] S. Machmudah et al., “Phytochemical compounds extraction from medicinal plants by subcritical water and its
encapsulation via electrospraying,” Alexandria Eng. J., vol. 61, no. 3, pp. 2116–2128, Mar. 2022.

[5] M. Soltany, J.-R. Riba, and S. Bogarra, “On the scaling of digital cameras to quantify the intensity of corona discharges,” Measurement, vol. 265, p. 120343, Mar. 2026.

[6] Eberhard Lemke et al., “Guide for electrical Partial Discharge Measurements in compliance to IEC 60270,”
Electra, vol. 241, no. Technical Brochure 366, pp. 61–67, 2008.

[7] R. Haller, J. Hornak, P. Martinek, and J. Hlavacek, “Simple Calibration Method for Improving the Comparability of PD
Measurement Results at HVDC Conditions,” Lect. Notes Electr. Eng., vol. 599 LNEE, pp. 1249–1256, 2020.