Abstract: An automatic current overload protection circuit for electrostatic precipitator power supplies of the type utilizing a ferroresonant transformer. A low voltage tertiary winding in association with the transformer provides an output voltage to a sensing circuit for inhibiting current flow into the primary of the transformer when the tertiary voltage falls below a predetermined threshold. Another output voltage developed in association with the high voltage secondary winding of the transformer is also utilized to independently inhibit current flow into the primary of the transformer when the secondary voltage falls below a predetermined threshold. A time delay may be provided to permit operation of the overload protection circuit only in the event of a sustained overload current condition.

Abstract: A circuit for controlling the duty cycle of a two-stage electrostatic precipitator power supply. The circuit includes a switching device connected in series with the primary winding of the power supply transformer and a circuit operable for controlling the switching device. A capacitive network, adapted to monitor the current in the primary winding of the power supply transformer, is provided for operating the control circuit. Under normal operating conditions, i.e., when the current in the primary winding of the power supply transformer is within normal limits, the capacitive network operates the control circuit to allow current flow through the power supply transformer primary winding in a normal manner.