Controlling the on-load tap changer control of a step-down transformer taking into account the operating parameters of the electric-arc steelmaking facility

The paper presents the main results of developing and researching a new principle for controlling the step-down transformer on-load tap changer (OLTC), which coordinates the OLTC operation with the electrical parameters of the electric-arc steelmaker, compensators installed in the high-power and ultrahigh-power EAF power supplies, and the mains. The proposed principle consists in pre-determining the operating voltage ranges on the mains-transformer primary side for all OLTC tap positions taking into account the existing of both the electric-arc steelmaking facility and the mains. The static VAR compensator (SVC) control system is improved by adding a block for finding the mains-transformer OLTC tap position number so as to use new position-switching algorithms. The problem of optimizing the OLTC tap-position switching in mains-transformers supplying power to electric-arc steelmaking facilities under significant mains-voltage deviations is analyzed on the basis of evidence from three Russian steelworks companies. We herein discuss the particularities selecting the mains-transformer OLTC positions in two SVC control modes, one consisting in keeping zero consumption of reactive power from the mains, and the other one consisting in maintaining a coordinate voltage in the common EAF and SVC connection point. The effect of the proposed solutions is found from the results obtained by means of mathematical modeling of electric-arc steelmaking facilities in MATLAB Simulink. We discuss the options for further improvement of principles for coordinating the operation of automatic transformer-voltage regulators (AVR) with the parameters of steelmakers, compensators, and mains.