AU628379B2 - Cable earth fault indicator - Google Patents

Description

628379 Form COMMONWEALTH OF AUSTRALIA PATENTS ACT 1952-61 COMPLETE SPECIFICATION

(ORIGINAL)

Class Application Number: Lodged: Int. Class Complete Specification Lodged: Accepted: Published: 'Prfority Related Art: 0 Name of Applicant: Address of Applicant: Actual Inventor: e.

Adtess for Service PROOF ENGINEERING (PTY) LIMITED 4 Kruger Street, Denver, Johannesburg, Africa Transvaal, Republic of South LESLIE GADSEN HETIWSON, PHILIP MARKS and CLIVE ROGER WHITBURN $~YlDWA tMeXQ rmXKatermark Patent Trademark Attorneys 50 QUEEN STREET, MELBOURNE, AUSTRALIA, 3000.

Complete Specification for the invention entitled: CABLE EARTH FAULT INDICATOR The following statement is a full description of this invention, including the best method of performing it known to us 1 Field of the Invention The invention lies in the field of electrical power supply wherever that-power may be supplied by cable. A particular area of interest is in underground mining because of the extensive use of electrical power supplied by cable, often with the cable relatively vulnerable, and because of the relatively hazardous conditions prevailing in underground mining. Another area of interest, for example, is in *@*the reticulation of electricity to consumers by a public utility in urban, peni-urban and rural areas.

The invention is in general applicable to any other area in which electrical power is supplied by cable.

The Prior Art SElectrical power is used extensively in mining for lighting, pumping, ventilation, hoists and as the main source of energy to drive machinery with which to extract the ore and undertake other mining Soperations. Various voltages are used such as 525 volts, 1000 volts, 3,3 kV, 6,6 kV and 11 kV and power is taken from the surface substation by means of cables to the numerous areas of utilisation underground.

In hazardous areas, in particular, for example in mines such as coal mines, flame proof cable couplers are used to connect lengths of cable together in a convenient manner in order to extend the electrical network as mining progresses as well as to facilitate replacement of cable sections which are damaged either by mechanical agents or by the agency of electricity.

Such cable reticulations are typically protected by overload or earth fault activated breakers located at the points of supply and substations in the supply network. In collieries the modern trend Sis to use cables which have individual earth screens around each conductor so that practically all electrical faults are limited to 060S phase to earth type faults, the level of fault current being limited to manageable levels by means of an earthing resistor in the neutral of the power transformer in the three phase system. This reduces the

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S: risk of incendiary sparking which might cause fires or explosions in fiery mines, typically methane in coal mines because of the low earth fault current (1 to 2 amps). This also minimises damage at the em 0 point of fault, in fact it is likely that no visible damage will result.

0 A major problem still exists, however, in that it becomes very difficult to find the location of a fault so that the fault can either be repaired or the faulty section of cable replaced. This represents a major problem since the location of an electrical fault in a section of cable can in many instances take an excessively long period leading to production down-time in the mine with accompanying high costs due to loss of revenue not to mention the maintenance and repair time cost and expenditure involved. It has been found that this delay has such serious consequences for production that it tends to encourage the dangerous (and illegal) practice of closing on to the fault (that is holding the tripped fault breakers closed) until the fault is "burned out". This burns the cable sufficiently severely to make the visual location of the fault in an extensive reticulation system possible.

The invention 0° o The insight leading to the present invention is the recognition of a need for an indicator which will provide a quick and easy indication which can be used to lead to location of the position of the fault in an extensive cable network.

o• In accordance with this invention there is provided an earth fault r. indicator device adapted to provide a visual indication of either the presence or the absence of a fault condition and accommodated in an adaptor which may be interposed between the two halves of a cable o coupler, providing continuity of conduction of load currents in the cable and monitoring the pJ:esence or absence of an earth fault condition in the load currents, which condition is relayed by the indicator.

The indicator will be actuated under earth fault conditions to indicate the presence of an earth fault and will be reset to indicate the absence of an earth fault upon the restoration of a healthy power i supply in the cable.

As an optional extra it shall also be possible to include a partial discharge detector to detect incipient faults tracking of the insulation). This device can be caused to operate the indicator alternatively to operate its own indicator coloured amber to provide an early warning alarm of an impending fault either inside or in the vicinity of the coupler.

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C 0 66o.0. Since the adaptor may be interposed at all the cable couplers in a cable network, when there is an earth fault at some point in that network it merely becomes necessary to inspect the indicators along the course of the network from the point of supply progressing past Sthose indicators which show the presence of an earth fault until the Sfirst indicator is found showing an absence of the earth fault whereupon the location of the earth fault is identified as being between the last two indicators inspected.

The preferred embodiment of the invention comprises the case where the 5G56*5 adaptor is a component existing normally independently of the cable couplers but so designed and adapted that a cable coupler may be opened and then reconnected with the adaptor interposed.

It is a fortunate circumstance that the cable couplers commonly, in many areas almost universally, employed are of quite standardised proportions and dimensions, complying with standard specifications ili_ which are compulsory, for example, in the case of use in fiery mines.

This makes it possible to supply such an adaptor in standardised proportions and dimensions which will be almost universally applicable. One may accordingly apply the earth fault indicators not only during laying down of new cable networks but also in existing cable networks which use standard couplers.

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o* OOO Fbwever, in accordance with an alternative embodiment of the invention the idicatoris provided mounted in or on one of a coupler pair, for example, either the male or the female part of a coupler pair. In fact in such a case the indicator may for practical purposes be wholly incorporated in a coupler part so as, in accordance with the So o o invention, not to make out an independent component at all.

Although superfluous the indicator could also be provided in both parts of a coupler pair.

Where the couplers are of the flame proof type an adaptor which will be interposed between the couplers with earth fault indicator will, of course, also be designed to fully comply with the flame proof requirements which are met by the coupler.

The invontion will be more fully described by way of examples with reference to the accompanying drawings, in which Figure 1 is a view of a coupler pair with an adaptor interposed prior i to closing the couplers with adaptor, Figures la, Ib and Ic show variants in design of coupler pairs and Id a cast joint type, 9 Figure 2 is a view of a pair of couplers in which an adaptor with indicator is incorporated in one part of the couplers, Figure 3 is a functional schematic of the operation of the device, and Figure 4 is a schematic plan of a cable network employing the S f invention.

As shown in figure 1 the invention comprises an adaptor 1 having an indicator face 2, sockets in its face 3 and pins 4 on its opposite S face.

This adaptor is interposed between the two parts 5 and 6 of a standard coupler for cables 7 and 8. The adaptor 1 matches the coupler so that instead of the parts 5 and 6 being directly coupled together in the normal way the adaptor is simply interposed, its sockets 3 receiving the pins 9 of the coupler 5 instead of these entering sockets in the face 11 of part 6 and the adaptors pins 4 entering the sockets in the part 6. Where the coupler is a flame proof design this quality is preserved by use of suitable flanges and i L _L.i ~r l Il l- SW S

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rebates and by preserving the facilities f6r bolting coupler parts together, for example at the flanges The indicator face 2 can be any instrument or appliance which gives an appropriate indication whether by means of a flag, flap-face indicator, light or other. The indicator will, of course, be carefully sealed and protected from mechanical damage so far as possible especially for use in mines.

Figure la shows another bolt up configuration, with loose pins 19, figure lb a screw connected configuration and figure lc a restraint plug in type. Comparable parts are given the same reference numerals as were used in figure i. Figure ld shows a cast joint type in which the indicator has been partially embedded in the joint.

Figure 2 shows the provision of an adaptor 1' which is incorporated as part of the coupler part Other parts are analogous and the same reference numerals are used. It will be seen though that the pins 9 plug directly into sockets in the face 11 of the coupler part 6. The coupler part 5' may thus be supplied as a modified coupler part still fitting the female coupler part 6 but incorporating the indicator means. Alternatively the adaptor 1 as shown in figure 1 may be semipermanently attached to the coupler part 5 to form the unit shown in the left hand part of figure 2.

Figure 3 shows the three phase conductors R, Y and B with a core 8 1balance transformer 12 housed in the adaptor unit 1 and encircling all three conductors. In the case of an out of balance resulting from an earth leakage on one or more of the conductors the out of balance signal is transmitted to the level detector 13 which then gives an actuation signal to the indicator 2. This signal also activates a flip flop circuit 20 to connect the level detector 13 to mnnitnr th sP.nsor 14. The indicator 2 is preferably of bistables type such that it will remain in the state giving indication of the presence of a fault until a resetting signal is supplied to it. Such a resetting signal can be arranged to arise when a load current is restored to one S of the conductors, which will be detected by a sensor 14, for example a transformer, which sends a signal which is gated in accordance with a predetermined threshold to reset the indicator to show an absence of fault condition upon the restoration of a healthy supply and restore the flip flop.

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Figure 4 shows in simplified manner the use of the indicator in a S cable network. The substation 15 suprlies power to a network established by a plurality of cables 16 which are interconnected by connectors 17 which incorporate an indicator adaptor as shown in figures 1 or 2. Where an earth fault arises at 18 all of the indicators 17 are activated so as to indicate the presence of an earth fault except for the indicators 17' where there is no earth fault indication. This will show the maintenance team that the fault lies in the cable section 16' which then can be replaced quickly.

Claims (9)

1. An earth fault indicator device adapted by means of a visual indicator in the device to provide a visual indication of either the presence or the absence of a fault condition and accommodated in an adaptor which is adapted to be interposed between the two halves of a cable coupler of a high voltage 3-phase cable used in mining or industrial applications by being provided with male elements adapted to couple with female elements 1 0 of the one haif of the cable coupler and female elements adapted to couple with male elements of the other half of the cable coupler, the device providing continuity of conduction of load currents in the cable irrespective of the presence or absence of earth faults and monitoring the presence or absence of an earth fault condition in the load currents and to provide the visual indication thereof. 1~ r/lg Prj ~2_~FT\~j -CI x THE CGAIMS DEFINING THE INVETION ARE AS FOLLOWS.- 1. An earth fault indicator device adapted to prov e a visual indication of either the presence or t absence of a fault condition and accommodated in a aptor which may be interposed between the two halve a cable coupler, providing continuity nor of conductio fAload currents in the cable and monitoring the pr nce or absence of an earth fault condition in the load .rntwhich condition is rlayed by the indieator.

2. An earth fault indicator device as claimed in claim 1, which further includes, as an optional extra a partial discharqe detector to detect incipient faults.

3. An earth fault indicator device as claimed in claim 2, adapted to operate its own indicator coloured amber to provide an early s a*or a sppy tice pi -4e warning alarm of an impending fault either inside or in the vicinity of the coupler.

4. An earth fault indicator device as claimed in any one of claims 1 to 3, in which the adaptor is a component existing normally independently of the cable couplers but so designed and adapted that a cable coupler may be opened and then reconnected with the adaptor interposed.

An earth fault indicator device as claimed in any one of claims 1 to 3, in which the adaptor .is provided mounted in or on one of a coupler pair.

6. An earth fault indicator device as claimed in claim 5, which is wholly incorporated in a coupler part so as not to make out an independent component at all.

7. An earth fault indicator device as claimed in any one of claims 1 to 6, for couplers of the flame proof type designed to fully comply with the flame proof requirements which are met by the coupler.

8. An earth fault indicator device substantially as herein described and as illustrated in the accompanying drawings.

9. A method of locating the position of an earth fault in a cable S network which comprises inspecting indicators as claimed in any one of the preceding claims and which have been included in the cable along the course of the network from the point of supply progressing past those indicators which show the presence of an earth fault until the first indicator is found showing an absence S. ,SS of the earth fault whereupon the location of the earth fault is identified as being between the last two indicators inspected. A cable network which incorporates indicators as claimed in any one of claims 1 to 8. DATED this 13th day of September 1989. PROOF ENGINEERING (PTY) LIMITED WATERMARK PATENT TRADEMARK ATTORNEYS QUEEN STREET MELBOURNE. VIC. 3000.