Electricity: electrical systems and devices – Safety and protection of systems and devices – Ground fault protection
Patent
1980-04-04
1982-03-23
Salce, Patrick R.
Electricity: electrical systems and devices
Safety and protection of systems and devices
Ground fault protection
361 47, 340652, 324 51, H02H 510
Patent
active
043216439
ABSTRACT:
An improved ground monitoring circuit for detecting the integrity and proper connection of the ground conductors in an electrical cable of an electrical power distribution system of a type that is commonly used at a surface mining site. A complete conductive loop is established between the ground conductor, or conductors, and the ground check, or pilot wire of the cable. A sensing signal at a frequency higher than the power frequency is coupled onto the ground monitoring loop. The monitoring loop includes a terminating resistor of predetermined value. The sensing signal on the ground conductor in the loop is isolated from local ground by means of an impedance element that presents a high impedance at the sensing signal but not at the power frequency. The impedance element is connected between the ground conductor of the power cable and the local ground. When successive lengths of cable are series connected, the impedance elements are connected in parallel with each other and are connected from an end of the ground conductor to the local earth ground, thereby to avoid series connections of the impedance elements in the ground conductors.
The voltage and current in the loop are separately sampled. Various comparisons of the voltage and current samples are made to detect any deviation in the resistance of the loop. Any deviations from desired conditions in the loop produce an output signal that changes the condition of a trip relay. The trip relay initiates action that ultimately opens circuit breakers to remove power from the cable.
REFERENCES:
patent: 3676739 (1972-07-01), Neuhouser
patent: 3729653 (1973-04-01), Mankoff et al.
patent: 4075675 (1978-02-01), Burkett et al.
patent: 4153923 (1979-05-01), Graf
patent: 4228475 (1980-10-01), Sherwood
AMF Incorporated
Hager Lawrence
Price George W.
Salce Patrick R.
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