Electricity: electrical systems and devices – Safety and protection of systems and devices – Ground fault protection
Patent
1994-06-15
1996-09-24
Gaffin, Jeffrey A.
Electricity: electrical systems and devices
Safety and protection of systems and devices
Ground fault protection
361 45, H02H 300
Patent
active
055596576
ABSTRACT:
An earth fault circuit breaker (10) for use in a circuit including an AC power supply and a load (11), which circuit breaker comprises a current-to-voltage converter (12) having two transformers for monitoring the current before and after flowing through the load, a leakage current/voltage detector (13A) for processing the outputs (E1 & E2) of the transformers to produce a resultant voltage, a voltage comparator (16) for comparing the said resultant voltage with a predetermined reference voltage to determine if there is a difference between the two transformer outputs, which is caused by an earth fault appearing at the load, and a switching driver (14) for disconnecting the load from the power supply in response to such a difference between the two transformer outputs exceeding the predetermined reference voltage, wherein each transformer has first and second primary windings (P1 & P2) arranged to be connected to opposite sides of the load and the two transformers are arranged to provide outputs at their respective secondary windings (S), corresponding to the normal load current (I2), in a substantially anti-phase relationship. The circuit breaker (10) may optionally include another voltage comparator (21) to detect overload current by monitoring the output of either one of the transformers.
REFERENCES:
patent: 3864581 (1975-02-01), Satyanarayana
patent: 5177657 (1993-01-01), Baer et al.
Gaffin Jeffrey A.
Lam Sheir C.
Medley Sally C.
Tam Pui Y.
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