Electricity: measuring and testing – Fault detecting in electric circuits and of electric components – Of ground fault indication
Reexamination Certificate
1998-10-26
2001-10-16
Brown, Glenn W. (Department: 2858)
Electricity: measuring and testing
Fault detecting in electric circuits and of electric components
Of ground fault indication
Reexamination Certificate
active
06304089
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to an apparatus and a method utilizing a ground-check monitor for detecting a discontinuity in the ground conductor of the leg or either arm of Y-configured trailing cables supplying power to two loads, i.e. one load at the end of each arm of the Y.
BACKGROUND OF THE INVENTION
In the mining industry, portable power cables, referred to as trailing cables, are used to supply power to equipment such as pumps, drills, shovels, and mining machines. A trailing cable includes three phase conductors, a ground conductor (also referred to as a ground wire), and an insulated ground-check wire (sometimes referred to as a pilot wire) which is used to monitor continuity of the ground wire. In most jurisdictions, continuity of the ground conductor in a trailing cable must be monitored in order to ensure that, in the event of a ground fault, a predictable ground-fault current will flow and thereby allow coordinated ground-fault protection to be reliably achieved.,
At the junction box of the equipment receiving power from a trailing cable, a termination device is connected between the ground-check wire and the ground wire. At the other end of the trailing cable (i.e. the location of the power source) the ground-check and ground wires are connected to terminals of a ground-check monitor which measures and monitors the electrical characteristics between these terminals. The termination device used with a given ground-check monitor is matched, by its circuit characteristics, to that particular monitor type. In operation, the ground-check monitor permits the trailing cable to be energized (i.e. powered) only if the circuit characteristics associated with the termination device are detected; otherwise, if either the ground wire or the ground-check wire is broken, if the ground-check wire is shorted to ground, or if the termination device is removed, the ground-check monitor will not detect such characteristics and will cause the cable to be de-energized. Typically the termination device is a diode or zener diode.
In some applications, power is supplied to two pieces of equipment from one remote power supply. It is desirable to use one long trailing cable to feed a splitter box which feeds two separate cables to supply power to the two pieces of equipment (loads). This configuration of the trailing cable is sometimes referred to as a Y-configuration (or T-configuration). However, if a termination device associated with the ground-check monitor is connected across the ground-check and ground wires at the end of each cable connecting the loads to the power source (i.e. so as to monitor the ground wire of each arm) a problem will be created. In such a configuration, the electrical characteristics produced by each of the parallel termination devices corresponds to the normal characteristics of the termination device which the monitor is designed to detect and, therefore, the ground-check monitor would detect such characteristic and fail to cause power to be removed if either termination device is removed.
The problem of how to monitor the ground wires of all sections of such a branched trailing cable has to date been addressed by expensive and complicated circuit installations. Such installations utilize either a second ground-check monitor at the splitter box to monitor the ground-check wire in the circuit of the second load or a multiplexer at the splitter box to switch the monitor between the ground-check wires of each of the two load circuits. Therefore, there is a need in the industry for a solution to this problem which is economical yet reliable from a safety perspective.
SUMMARY OF THE INVENTION
In accordance with the invention there is provided a combination of two termination devices for connection in parallel between the ground-check and ground conductors of the two arms of a Y-configured trailing cable supplying power to two loads. Also in accordance with the invention there is provided a method of detecting a discontinuity in the ground-check loop of the leg or either arm of a Y-configured trailing cable supplying power to first and second loads (wherein the ground-check loop of each arm includes the ground-check conductor, the termination device and the ground conductor). A discontinuity in the ground conductor of the cable, which may be due to any of a number of conditions (i.e. if either the ground wire or the ground-check wire is broken, if the ground-check wire is shorted to ground, or if the termination device is removed), is detected by a monitor at the power source whenever the monitor fails to detect a predetermined electrical characteristic between the ground-check and ground conductors. A first termination device and a second termination device are provided. The configuration of the devices is such that, individually, each produces an electrical characteristic across the ground-check and ground conductors which does not satisfy the predetermined electrical characteristic. However, the first and second termination devices together, connected in parallel, produce an electrical characteristic across the ground-check and ground conductors which does satisfy the predetermined electrical characteristic.
The predetermined electrical characteristic may be a zener-diode characteristic. Similarly, each of the first and second termination devices may, individually, produce a zener-diode characteristic with one of the zener-diode characteristics being switched on and off at a predetermined frequency.
REFERENCES:
patent: 2685684 (1954-08-01), Atkinson et al.
patent: 3676739 (1972-07-01), Neuhouser
patent: 3697809 (1972-10-01), Self
patent: 3699392 (1972-10-01), Lee et al.
patent: 3727205 (1973-04-01), Scourtes
patent: 3771020 (1973-11-01), Smith
patent: 3886409 (1975-05-01), Scarpino
patent: 3891894 (1975-06-01), Scarpino
patent: 3895264 (1975-07-01), Kirilloff
patent: 3944914 (1976-03-01), Simmonds
patent: 4011483 (1977-03-01), Meadows
patent: 4075675 (1978-02-01), Burkett et al.
patent: 4110807 (1978-08-01), Neuhouser
patent: 4149208 (1979-04-01), Fiorentzis
patent: 4153923 (1979-05-01), Graf
patent: 4225793 (1980-09-01), Philipsen
patent: 4228475 (1980-10-01), Sherwood
patent: 4321643 (1982-03-01), Vernier
patent: 4389694 (1983-06-01), Cornwell, Jr.
patent: 4415850 (1983-11-01), Sherwood
patent: 4609865 (1986-09-01), Goodman et al.
patent: 4621199 (1986-11-01), Bailey
patent: 4639719 (1987-01-01), Pappano et al.
patent: 5270896 (1993-12-01), McDonald
Dudiak Joseph J.
Paulson Garry E.
Paydli Rodney J.
Vangool Michael P.
Brown Glenn W.
Cassan Lynn S.
LandOfFree
Parallel termination apparatus and method for ground-check... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Parallel termination apparatus and method for ground-check..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Parallel termination apparatus and method for ground-check... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2607564