EXPERIMENTAL DETERMINATION OF ELECTROMAGNETIC INTERFERENCE LEVELS IN SECONDARY CIRCUITS OF INSTRUMENT TRANSFORMERS UNDER LIGHTNING STRIKE CONDITIONS

The results of an experimental study on the level of electromagnetic interference in the secondary circuits of voltage and current measuring transformers during the simulation of a direct lightning strike to lightning rods located on the territory of an operational substation are presented. Attention is focused on the issue of overvoltages caused by the dissipation of lightning currents through the grounding system and their impact on the insulation of secondary circuit cables. It is shown that the resulting voltages under such conditions may exceed the permissible limits defined by regulatory standards, including IEC 61000-2-5, by several times, reaching tens of kilovolts while the allowable level is 4000 V. A method for simulating lightning current on a live power facility using an aperiodic impulse generator is discussed, which allows the reproduction of pulse front and duration with parameters 1.2/50 µs at an amplitude of 1000 V. The proposed method was tested at a 330/35/10 kV substation for various current circuit configurations and lightning rod locations. Measurement results of current and voltage in secondary circuits are provided along with recalculated values based on a probable lightning current. It is demonstrated that the highest overvoltages occur in circuits grounded in the main control panel. The obtained results help assess the risk of insulation breakdown due to direct lightning strikes and justify the implementation of additional protective measures. The developed approach can be further applied to improve methods for evaluating and ensuring electromagnetic compatibility of energy infrastructure facilities, particularly in the context of digitalization and SmartGrid deployment.