Ground fault desensitization circuit for electronic breaker
AssigneeSquare D Company
InventorsHenry J. Zylstra, Harley W. Jansen
Life of this patent
Estimating the term…
Abstract
A desensitizing circuit for the electronic fault sensing system of high amperage molded case circuit breaker to prevent a ground fault signal from tripping the breaker in the event of current transformer saturation or the response of a downstream breaker to the ground fault signal.
Claims20
A circuit breaker having interruption means operable for interrupting a plurality of line conductors with each conductor having a respective current transformer for sensing the current in the respective line conductor and for deriving a signal corresponding to the overcurrent present in the respective line conductor the improvement comprising:
- ground fault means for detecting a ground fault current in any one of said conductors and for thereafter operating said interrupting means to interrupt said line conductors,
- a desensitization circuit responding to a signal above a first predetermined level derived from any of said conductors,
- and means in said desensitization circuit for preventing said ground fault means from operating said interruption means for a predetermined time period in response to the detection of said signal exceeding a first predetermined value for preventing interruption of said line conductors during the detection of said ground fault current.
A circuit breaker having interruption means operable for interrupting a plurality of line conductors with each conductor having a respective current transformer for sensing the current in the respective line conductor and for deriving a signal corresponding to the overcurrent present in the respective line conductor the improvement comprising:
- ground fault means for detecting a ground fault current in any one of said conductors and for thereafter operating said interrupting means to interrupt said line conductors, said ground fault means includes a differential transformer, a pair of operational amplifiers each having one input connected to a common supply voltage, a variable resistance connecting the output of said differential transformer to the input of one of said amplifiers and a voltage dropping resistor connected in partial shunt with said variable resistance for enabling said operational amplifier to respond to a ground fault current by switching the output of the other operational amplifier to operate said interruption means,
- a desensitization circuit responding to a signal above a first predetermined level derived from any of said conductors, and
- means in said desensitination circuit for preventing said ground fault means from operating said interruption means in response to the detection of said signal exceeding a first predetermined value for preventing interruption of said line conductors during the detection of said ground current.
A circuit breaker having interruption means for interrupting a plurality of line conductors with each conductor having a respective saturable current transformer for sensing the current in the respective line conductor to derive a signal corresponding to the overcurrent present in the respective line conductor and having a differential transformer connected in the outputs of said current transformer for deriving a ground fault voltage the improvement comprising:
- a pair of tandemly connected operational amplifiers with one amplifier adapted to switch outputs in response to a change in the output of the other amplifier and having an RC circuit for holding the output of said one amplifier switched for operating said interrupting means to interrupt said line conductors in response to periodic changes in the output of said other amplifier within a predetermined time,
- a variable resistance connecting the output of said differential transformer to the input of said other amplifier to change the output of said other amplifier in response to a selected voltage provided by said differential transformer,
- a second pair of amplifiers with one of said amplifiers of said second pair of amplifiers receiving said signal from said current transformers for switching the other amplifier of said second pair in response to said signal reaching one predetermined level,
- and a unidirectional circuit connected between the output of said other amplifier of said second pair and the input of the other amplifier of said first pair for preventing said other amplifier of said first pair from changing outputs in response to a switch in the output of said other amplifier of said second pair for preventing operation of said interruption means.
A circuit breaker having interruption means operable for interrupting a plurality of line conductors each providing a predetermined continuous current, with each conductor having a repsective current transformer for sensing the current in the respective line conductor and for deriving a signal corresponding to the overcurrent present in the respective line conductor, the improvement comprising:
- ground fault means for detecting a ground fault current in any one of said conductors and for thereafter operating said interrupting means to interrupt said line conductors,
- a desensitization circuit responding to a signal above a first predetermined level derived from any of said conductors,
- and means in said desensitization circuit for preventing said ground fault means from operating said interruption means for a predetermined time period in response to the detection of said signal corresponding to an overcurrent having a value at least equal to six times the predetermined continuous current for preventing interruption of said line conductors during the detection of said ground fault current.
Dependencies are inferred from the claim text.