GB2229871A - Electric power distribution - Google Patents

Abstract

An installation for distribution of power to a plurality of substations, 1 to 6, includes at least one substation served by an incoming and an outgoing feeder conductor 7, 7 which can be connected to each other by a single switch 8, and alternative coupling means 9, 10 both adjacent the switch 8 but on its opposite sides provide for connecting a load circuit 11 either to the incoming feeder conductor 7 or to the outgoing feeder conductor 7. This is less expensive than the customary practice of providing three switches per phase at each substation, but nevertheless allows temporary reconnection of all the load circuits to be made in a reasonable time in the event of a fault in a feeder cable. For example, if a fault occurs in a ring main at a point 19 between substations 1 and 2 the switches 8 thereat are opened to isolate the faulty segment and the alternative connections 12A are made to coupling 9 at substation 1 and to coupling 10 at substation 2. The coupling means may comprise a flexible cable 15 terminated in a slip-on connector which can be plugged into connection points 9 or 10 on respective tee connectors (13), (Fig 2). The switch 8 may be a vacuum switch rated "load break/fault make", and may be remotely controlled. The arrangement may be applied to radial or ring circuits. <IMAGE>

Description

ELECTRIC INSTALLATIONS This invention relates to electric installations and especially (but not exclusively) to feeder installations of the kind used by electric utilities (Area Electricity Boards in current United Kingdom practice) to distribute power to a number of final step-down transformers each outputting: supply voltage to a group of domestic and/or other small consumers.

Feeder installations may be ring mains or they may be connected as radial circuits, but in the latter case they are usually so organised that in case of a fault preventing normal operation, power may be supplied from an alternative source or by an alternative route. In either case, however, the faulty part of the feeder installation must be isolated before power can be restored. Current practice is to achieve this by the use of three switches for each phase at each load substation. One switch connects each of the incoming and outgoing feeder conductors to a common connection point, and the third connects that common connection point to the transformer or other load.This permits either of the feeder conductors to be isolated from the substation by means of the its own switch, while the third switch is required to isolate the load from the feeder conductors without breaking the connection between them.

It is an object of the invention to reduce the cost of such installations without detriment to the facilities provided.

In accordance with the invention, an electric installation for distribution of power to a plurality of substations includes at least one substation served by an incoming and an outgoing feeder conductor; a single switch which, when closed, connects the said feeder conductors to each other; and alternative coupling means both adjacent the said switch but on its opposite sides for connecting a load circuit either to said incoming feeder conductor or to said outgoing feeder conductor.

Preferably all the substations are equipped as defined, but when an existing installation is modified it will usually be convenient to retain existing switching arrangements at existing unaltered substation.

In the intended operation of the installation, a fault affecting one of the feeder conductors initially leads to disconnection of the whole installation by the normal protective circuit breaker at the power source.

The faulty conductor can be quickly identified using pulse-echo or other well-known techniques. Assuming that the faulty conductor is connected to a substation equipped according to the invention, it is isolated at that substation by opening the switch there, and by whatever action is appropriate at the substation at its other end. In the case of a radial circuit installation a temporary link will be required to restore supply to any substation thereby disconnected; in the case of a ring main installation power will remain available at each substation from one side of the interrupted ring or the other. At the substation equipped in accordance with the invention, a load circuit may possibly remain isolated, depending on which side of the switch it is connected.It will be reconnected by transferring it to the connection means on the opposite side of the switch (either by a live-line technique or by using a short manual supply break); all consumers are now temporarily connected while the faulty feeder conductor is isolated.

It is preferably earthed for extra safety and restoration work then proceeds. On completion of restoration work, all that needs to be done to restore normal operation at the substation is to re-close the switches: there is no need to transfer back the load circuit connection.

Since the switch will be opened only when the circuit is dead, it need not have the capacity to break fault current (or even normal load current) and they may therefore be relatively compact and inexpensive; preferably they are, however, capable of 'making' onto a fault without damage as on rare occasions a restoration may be defective or there may have been two faults of which only one was initially detected. Vacuum switches rated "load break/fault make" at the current capacity of the ring are particularly suitable. Remotely controlled switches can be used if desired.

We prefer to connect the load circuit to alternative connection points on the two sides of the switch by means of a cable having at least a degree of flexibility terminated by a "plug-in" connector of a design appropriate to the voltage of the installation; preferred plug-in connectors conform to at least the interface requirements of Standard ESI 12-22 and/or U.S.

Standard ANSI 386 and/or Electricité de France Standard HN 52-S-61.

Screened moulded "slip-on" connectors of the kind sold by our subsidiary BICC Components Limited under the trademark BIMOLD are suitable for the usual llkV/2-400A distribution ring mains widely used in the United Kingdom. Other connector types that can be used include unscreened moulded types sold by Yorkshire Switchgear Limited under the trademark Dyscon and by Raychem Limited and the metal-clad ones sold by AEG Kabel as types AGT20/40 and AGW 20/400; those sold by Karl Pfisterer K-G under the trademark Connex can also be used, but do not conform to any of the above standards and are incompatible with the others. In outdoor locations, a suitable protective cover will be needed for weather protection.

The invention will be further described by way of example with reference to the accompany drawings in which Figure 1 is a diagrammatic representation of an AC ring main in accordance with the invention and Figure 2 is a more detailed diagram of a sub-station forming part of the installation of figure 1.

Figure 1, for simplicity, shows only a single phase of the ring main; usually there will be three phases and there may be provision for separate or combined neutral and earth conductors.

As seen in this Figure, the ring main serves a number of sub-stations 1 to 6 and is itself supplied with power by any appropriate source 26, say through primary distribution transformers 27, 28 and whatever protective equipment 29, 30 is appropriate to the circumstances. For the phase shown in the diagram, a ring 18 is formed by a number of feeeder conductors 7 and normally-closed switches 8, one in each substation, which interconnect the adjacent feeder conductors.

Each sub-station also includes, in this example, a final distribution transformer 11 supplying a respective group of subscribers (not shown); and alternative connection points 9 and 10 for the transformer are provided, in each sub-station, on opposite sides of the respective switch 8.

Figure 2 shows one of the sub-stations, say number 1, in rather more detail.

The switch 8 is preferably a vacuum switch, a suitable design of which (for an llkV 400A sub-station) is available from GEC Industrial Controls Limited. The feeder conductors 7,7 are connected to opposite sides of the switch 8 by respective tee connectors 13, suitably being "slip-on" connectors of the kind sold in the United Kingdom by BICC Components Limited under their trade mark BIMOLD and in other countries by Amerace Corporation or its affiliates/licensees.

Each of these tee connectors provides one of the connection points 9,10 to which the final distribution transformer 11 may alternatively be connected by means of a cable 15 terminated with a matching BIMOLD elbow connector, or other suitable connector 12.

The operation of the ring main will be illustrated by supposing that a fault has occurred at the point 19 in the ring conductor segment 7 extending from substation number 1 to sub-station number 2. This will immediately trip protective circuit breakers or other protective apparatus 29 and 30 and cut off supply to the whole ring and all six groups of consumers. As soon as the fault has been located, the switches 8 in substations numbers 1 and 2 are opened, isolating the fault from the remainder of the ring.

The next step is to transfer the plug-in connection 12 in sub-station no.1 from connection point 10 to connection point 9, and that in sub-station no.2 from connection point 9 to connection point 10, as shown in dotted lines (reference 12A); the length of feeder conductor 7 containing the fault at 19 is thus isolated not only from the ring but also from any load circuits, and it will normally be earthed at both ends for maximum safety during the necessary restoration work. As soon as earthing is complete, power can be restored to all consumers by re-setting the protective equipment 29 and 30, if necessary at a reduced current rating, without waiting for completion of the restoration work.When the restoration work is finished, the earth connection is removed and the only other action needed is to re-close the two switches 8 in sub-stations numbers 1 and 2, so re-establishing the ring 18, and possibly to re-set the trip values of the protective equipment 29 and 30 to the original settings.

In a possible development of the technique (which would require changes to supply regulations and practice at present effective in the United Kingdom) the switches 8 could be remotely controlled. The appropriate two switches 8 could then be operated to isolate a faulty segment and power temporarily restored to at least some consumers (in the example, excluding those served by substations 1 and 2) immediately the location of the fault was established and without waiting for personnel to arrive at the two substations concerned. A short interruption to supply to the whole ring would then be needed while the loads at substations 1 and 2 were transferred to the other side of respective switch 8 and the faulty feeder earthed (unless a live-line technique were available); subsequent operations would be exactly as previously described.

Claims (11)

1. An electric installation for distribution of power to a plurality of substations including at least one substation served by an incoming and an outgoing feeder conductor; a single switch which, when closed, connects the said feeder conductors to each other; and alternative coupling means both adjacent the said switch but on its opposite sides for connecting a load circuit either to said incoming feeder conductor or to said outgoing feeder conductor.

2. An installation as claimed in claim 1 in which all the substations are equipped as defined.

3. An installation as claimed in claim 1 or claim 2 in which the said feeder conductors constitute a ring main.

4. An installation as claimed in any one of the preceding claims in which the or each said switch is capable of making onto a fault without damage but incapable of breaking fault current.

5. An installation as claimed in any one of the preceding claims in which the or each said switch is a vacuum switch rated "load break/fault make".

6. An installation as claimed in any one of the preceding claims in which the or each said coupling means comprises a cable having at least a degree of flexibility terminated by a plug-in connector.

7. An installation as claimed in claim 6 in which the said plug-in connector conforms to at least the interface requirements of European Standard ESI 12-22 and/or U.S. standard ANSI 386 and/or Electricité de France Standard HN 52-S-61.

8. An installation as claimed in claim 6 or claim 7 in which the plug-in connector is a moulded screened "plug-in" connector.

9. An electric installation for distribution of power to a plurality of substations substantially as described with reference to the accompanying drawings.

10. The method hereinbefore described of managing and repairing a fault in a feeder conductor in an installation claimed in any one of the preceding claims.

11. A method of managing and repairing a fault in a ring main installation in accordance with anyone of claims 3-9 substantially as described with reference to the drawings.