SOLID STATE LOAD PROTECTION SYSTEM HAVING GROUND FAULT SENSING

摘要

A solid state load protection system whereby the current supplied to a load is monitored enabling ground fault sensing to be used. A current sensor is utilized so as to produce an output current which is proportional to the current in the electrical circuit. Attached to the current sensing function is a resistive load which converts the current produced by the current sensing function to a voltage which is also proportional to the current utilized by the motor. Attached between two resistors which comprise the resistive load is a ground fault resistor which has its remaining end connected to the neutral leg of the current transformers of the current sensing function. The ground fault sensor monitors the voltage across the resistors in the resistive load and the current in the neutral leg of the current sensors. A ground fault condition is indicated when a current in the neutral leg of the current sensor is detected and thereby causes voltages across each of the resistive load resistors to be unequal to each other. If this condition is in excess of a predetermined level, for a predetermined period of time a trip signal to the output function is initiated, in turn causing a light-emitting diode to conduct and indicating a ground fault condition. The output function upon receiving a trip signal causes a second light-emitting diode to conduct and also de-energizes a contactor through which a current source is connected to a load.