| 摘要 |
The minimum instantaneous voltage output of a phase resistor connected to receive the rectified phase and neutral currents of three wye-connected current transformers, magnetically coupled to respective phase conductors of a three phase electric power circuit, is proportional to the peak current of the phase conductor carrying the center magnitude phase current. A voltage proportional to this minimum instantaneous voltage is measured and stored by a capacitor each cycle. The peak instantaneous voltage output of a ground resistor connected to receive the full wave rectified output of three, parallel-connected current transformers, also coupled to respective phase conductors of the power circuit, is proportional to the peak ground current of the electric power circuit. A voltage proportional to the voltage output of the ground resistor is applied to the base of a NPN transistor, and the voltage stored by the capacitor is applied to the emitter of this transistor, to turn on this transistor every time the peak ground current exceeds a preselected percentage of the center magnitude phase current. The momentary turnon of this transistor at least once every current cycle activates a timing circuit, which after a predetermined time, initiates tripping of a circuit interrupter. |
