Experience in Measuring Switching Overvoltages Under Operating Conditions

This article discusses alternative methods for measuring switching voltages without the use of classical voltage dividers under operating conditions. Fast transient overvoltages in power systems often arise from switching operations, such as the opening and closing of disconnectors, posing serious threats to the insulation of high-voltage equipment, such as bushings and transformer windings. This study examines three cases of broadband measurements of high-frequency switching overvoltages in operational settings without relying on dedicated voltage dividers: measuring wires of an overhead line, a substation bus, and during power transformer switching. Measurements on the overhead power line wire yielded inaccurate results, while voltage measurements on the substation bus require adjustments. The most reliable measurements were obtained during power transformer switching, where the capacitance of the primary insulation at the input is utilized as the upper arm of the voltage divider. These findings can be instrumental in studying and measuring switching overvoltages, as well as in updating regulatory documents.