Electricity: electrical systems and devices – Safety and protection of systems and devices – Ground fault protection
Patent
1980-05-29
1982-03-02
Eisenzopf, Reinhard J.
Electricity: electrical systems and devices
Safety and protection of systems and devices
Ground fault protection
363125, H02H 316
Patent
active
043181511
ABSTRACT:
An earth leakage protection device comprises a core balance current sensing transformer 1 having a secondary winding 2 in which a fault signal is generated in response to leakage from AC supply lines forming primary windings of the transformer 1, an operational amplifier OA1 for amplifying the fault signal, a precision rectifier circuit 8 comprising a pair of operational amplifiers OA2 and OA3 for performing full wave rectification of the amplified fault signal, a delay circuit 9 in the form of a two stage RC network which delays the rectified signal according to an IDMT characteristic, and a trigger circuit 10 in which the delayed signal is compared with a preset reference signal by an operational amplifier OA4 to provide a control signal which actuates a sagety device in the AC supply lines via a relay 11 when the reference signal is exceeded. Within its operating range the device actuates the safety device much more slowly for lower leakage currents than for higher currents, and since it is operative on both halves of the AC leakage current signal the device provides reliable protection against the possibility of dangerous electric shocks while avoiding spurious tripping.
REFERENCES:
patent: 3512045 (1970-05-01), Tipton et al.
patent: 3786356 (1974-01-01), MacPhee
patent: 4135129 (1979-01-01), Johnston et al.
Electronics, vol. 47, No. 16, pp. 104-105, Aug. 8, 1974, "Full Wave Rectifier Needs Only Three Matched Resistors", J. Graeme.
New Electronics, vol. 12, No. 9, p. 8, May 1, 1979, "Wide Range Full-Wave Rectifier", Donoghue.
Eisenzopf Reinhard J.
Trident Equipment Limited
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