Control circuit with validity-determining arrangement

Details Control circuit with validity-determining arrangement Control circuit with validity-determining arrangement

1988-01-25

1989-06-13

Pellinen, A. D.

Electricity: electrical systems and devices

Safety and protection of systems and devices

With specific current responsive fault sensor

361 87, 361 94, 340646, 340664, 323358, 324127, H02H 305, H01F 4006

Patent

active

048397709

ABSTRACT:
An arrangement is provided for checking the validity of a sensed-current signal from a current-sensing device. The sensed-current signal represents the current in a line. An associated control circuit utilizes the sensed-current signal to indicate or predict the presence of undesired overcurrent conditions. When such conditions may be present, the sensed-current signal is checked to determine if the sensed-current signal is valid; i.e., whether the sensed-current signal accurately represents the current in the line. If the sensed-current signal is invalid, no trip signal is generated to interrupt the current. If the sensed-current signal is valid, the control circuit generates a trip signal to control operation of a circuit-interrupting device. In a particular arrangement, the load on the current-sensing device is changed to determine if the sensed-current signal is valid. If the sensed-current signal is valid, the level of the sensed-current signal remains in a valid range and the overcurrent-detection circuit issues the trip signal. If the sensed-current signal is invalid, the level of the sensed-current signal changes. In response, the control circuit does not issue the trip signal and is reset to an initialized mode to monitor for a valid overcurrent condition in response to the sensed-current signal. In a specific arrangement, the current-sensing device is an iron-core transformer which saturates at high current levels. Thus, if the transformer is saturated, the changing of the load on the transformer causes the level of the sensed-current signal to change and the trip signal is not issued.

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"Digital EHV Current Transducer", by L. B. Berkebile, 1980, IEEE, 80 SM 647-8.

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