Improvement of Protection System YD/D 116MVA Multiple Tap Electric Arc Furnace Transformer in Nickel Processing Plant Using Adaptive Modified Firefly Algorithm

Abstract

Electric Arc Furnaces (EAF) utilize a step-down transformer to lower the voltage and deliver high current to the electrodes in the furnace for the melting process. The EAF system of PT. Vale Indonesia (PTVI) employs a transformer with two distinct vector group configurations, YD/D, and supports 35 online tap-changing steps for power control level 0-75 MW into the EAF. This configuration results in approximately 70 combinations of power capacity and impedance values, leading to variations in full-load current, short-circuit current, and transformer damage curve characteristics for a single EAF transformer. However, the existing protection scheme implemented for the EAF transformer at PTVI is limited to only two dedicated protection settings, which are insufficient to mitigate potential damage across multiple tap positions. This study proposes an optimized protection relay setting methodology tailored to the characteristics of the EAF transformer with a D/D vector group and 35 tap-position levels. The approach employs an Adaptive Modified Firefly Algorithm (AMFA) to enhance the relay protection settings by optimizing the Time Dial Setting (TDS) in relation to short-circuit current, current pickup levels, and the damage curve at each tap position D/D position. Performance evaluation confirms that the proposed protection optimization effectively safeguards the EAF transformer against fault conditions and minimizes the risk of relay misoperations across all tap positions. The proposed protection strategy was implemented and analyzed using MATLAB and validated through simulations conducted in ETAP.

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