Experimental Study of Non-Design-Basis Electromagnetic Interference and the Risk of False Operation of Relay Protection at a 500 kV Substation

Cascading failures in power systems worldwide are often triggered by short-circuit (SC) faults accompanied by intense high-frequency (HF) electromagnetic transients that can generate non-design-basis electromagnetic interference (EMI) and increase the risk of maloperation of microprocessor-based relay protection and automation (RPA) devices. This paper presents an on-site simulation method for determining the level of HF antiphase EMI in RPA control circuits, based on reproducing the HF component of the short-circuit current using a pulse generator with test current injection into the grounding system. The method was validated at the operating 500 kV Shymkent substation of KEGOC JSC (Republic of Kazakhstan): pulsed electromagnetic disturbances in secondary circuits were measured at the 500 kV and 220 kV switchyards while simulating the HF component of the single-phase-to-ground short-circuit current. It was experimentally established that the level of induced antiphase interference is determined by the impulse resistance of the grounding system and the attenuation coefficient of the disturbance into secondary circuits, and in a number of the investigated circuits the levels rescaled to the HF component of the fault current exceed the 1 kV immunity test level of microprocessor-based devices. The measured impulse resistance of the equipment grounding was 1.8–7.2 Ω, the attenuation coefficient was 2.1–12.7, and the rescaled differential-mode interference reached 1.9 kV (1.5–2.2 kV, taking into account an uncertainty of ±20%). Since the reaction of the terminals was not recorded, these results indicate an increased risk of RPA maloperation due to non-design-basis EMI during short circuits and justify the need to account for this factor when designing grounding systems and configuring relay protection settings.