Motor-Starting Lamp Flicker on Open-Delta Transformer Banks

When a motor is started through a transformer bank that serves both power and lighting loads, there is a dip in voltage on the lighting circuits. A digital computer study has been made of the voltage on the lighting phase during motor starting for the open-delta connection of transformer secondary windings. Equivalent circuits have been developed for the general case of the open-delta transformer connections having legs of different kilovolt-ampere ratings.