GB2462001A

GB2462001A - Fault detection and restoration system

Info

Publication number: GB2462001A
Application number: GB0912616A
Authority: GB
Inventors: John Brailsford; Andrew Bower; Michael Lees
Original assignee: SURENET TECHNOLOGY Ltd
Current assignee: SURENET TECHNOLOGY Ltd
Priority date: 2008-07-21
Filing date: 2009-07-21
Publication date: 2010-01-27
Anticipated expiration: 2029-07-21
Also published as: GB0912616D0; GB2462001B

Abstract

A high voltage power supply control device arranged to detect a fault in, disconnect and reconnect a high voltage supply circuit, comprising; a fault passage indicator, a switch to connect or disconnect the supply; a pair of indicator units located on either side of the device to indicate the presence or absence of a fault on their respective sides; and a switch controlled by a control unit so as to only restore power to the side of the device where no fault is detected. Each indicator unit may be able to detect the indication state of adjacent devices and indicator units may be provided between phases of the supply or between a phase and earth. Indicator units may comprise a voltage transformer to which a monitoring signal is applied and may include an earth switch in parallel with the transformer which can be closed in response to fault detection.

Description

S

FAULT DETECTION AND RESTORATION SYSTEM

This invention relates to a fault detection and restoration system, particularly but not exclusively, for use with a high voltage (HV) supply system, and which is given the name HVSure for the purposes of this document.

Problems arise with HV supply systems and other like circuits in that it can be time consuming to locate and disconnect faulty sections on those circuits and restore supplies in a timely manner. Of course, such a problem can have an undesirable impact on services provided to customers.

In order to address this problem, automation of fault detection and restoration systems have been installed on HV circuits but these rely on communication circuits being available on the network to allow the transfer of status or timing information.

Such physical communication circuits (including those provided by public telephone communication companies) are expensive to install and maintain. Similarly radio systems are also expensive and, particularly in the case of licensed radio, may have a limited bandwidth available affecting the number of sites and the speed of operation.

A still further problem arises in that some schemes referred to as power line carrier schemes have difficulties communicating across circuits which are in a fault condition.

It is an object of the present invention to provide an automatic method for fault * S * disconnection and supply restoration within a HV supply circuit which does not S...

require additional communication systems between switching components to initiate * S.S 5* * and control the automatic sequence.

**.SS. * S

: According to a first aspect of the present invention there is provided a power supply control device operable to detect a fault in, disconnect and reconnect a HV

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supply circuit, said device comprising: a fault passage indicator; a HV switch operable to connect or disconnect the HV supply; a pair of indicator units provided on either side of the device, the indicator units operable to indicate the presence or absence of a detected fault on their respective sides of the device; and a control unit operable to control the HV switch so as only to restore power to the circuit on a side of the device where the absence of a fault is detected.

The use of an indicator unit in the present invention enables the restoration of supply without the use of additional communication systems between switching components.

Each indicator unit in one device may be operable to detect the indication state of the indicator unit on the near side of an adjacent device.

The control unit may monitor the indicator units to detect the occurrence of faults in addition to monitoring such units to determine whether to restore power.

The indicator units may be provided between any selected phases of the supply or between any selected phase or phases of the supply and earth In one embodiment each indicator unit comprises a voltage transformer and a signal generating device operable to apply a signal to the voltage transformer. In such an embodiment the signal generating means applies a signal to the voltage transformer to indicate that no fault is detected on that particular side of a device. Accordingly, if an indicator unit on the near side of adjacent device can detect this signal, it can be determined that no fault is present on this side of the device.

In an alternative embodiment the indicator unit may comprise a voltage S * * transformer and an earth switch in parallel therewith. In such an embodiment, the earth switch may be closed in response to the detection of a fault, thereby indicating that the fault occurred on a particular side of the device. Accordingly, by applying a voltage on to the voltage transformer and monitoring a current generated in response thereto, the status of the earth switch of the indicator unit on the near side of an adjacent device can be determined.

According to a second aspect of the present invention there is provided a HV supply circuit incorporating a plurality of devices according to the first aspect of the present invention.

The HV supply circuit of the second aspect of the present invention may incorporate any or all features of the first aspect of the present invention as desired or as appropriate.

The HV supply circuit may comprise one or more underground cables and/or one or more overhead HV lines. In the case of a HV supply circuit having overhead HV lines, these HV lines may be additionally provided with pole mounted auto-reclosers or circuit breakers on one or more supports for the HV line.

According to a third aspect of the present invention there is provided a method of supply disconnection and supply restoration for use with a HV supply circuit having a plurality of devices according to the first aspect of the present invention, said method comprising: disconnecting said HV supply circuit at one said device; S...

providing an indication using the indication units of the said device as to the presence or absence of a fault in the HV circuit on either side of said device; $S.S St * : monitoring the indicator units of adjacent devices to determine the presence or * I * S absence of a fault between the said device and adjacent devices to thereby determine * . the presence or absence of a fault between the said device and the adjacent devices; and restoring power to the circuit on a respective side of the device only when no fault is detected after sensing.

The method of the third aspect of the present invention may incorporate any or all features of the first or second aspects of the present invention as desired or as appropriate.

With this system, it is possible to automatically detect and disconnect problems on an HV distribution network and restore supply to non-faulted sections in a particularly quick and effective manner. The speed and manner of operation of the system of the present invention assists and minimises interruptions to the services provided to the customer.

With such an arrangement, it is possible to avoid the need for components of the system to communicate to control operation of the system.

If a fault is detected on one side of the device, the device may go to lockout, preventing the automatic restoration of power to the circuit on that side of the device.

The above method may only be initiated after a separate pole mounted auto-recloser or circuit breaker goes to lockout. This can prevent difficulties in the case of transient faults experienced on overhead HV supply lines.

This invention will now be described in more detail with reference to the * *I.

accompanying drawings of which: * **S S. * Figure 1 shows a schematic representation of one embodiment of a * S *S*S * * *:*. system in accordance with the present invention; * Figure 2 shows a part of the system of Figure 1 in enlarged form; S.....

S S

Figures 3-5 show in schematic form parts of the embodiment of the system in accordance with the present invention; and Figure 6 shows a schematic representation of an alternative embodiment of a system in accordance with the present invention Referring now to the Figures, there is shown in Figure 1 a schematic diagram of one form of device which implements one form of a system in accordance with the present invention.

The system shown uses the application of a suitable signal to an HV network or a component within the network in any suitable manner to indicate the relative position of the fault from the signalling point and by observation of such signals to initiate appropriate switching actions to restore supplies to non-faulted sections of the HV network.

A suitable device is incorporated in the system of the invention and provides a visible and electrical indication that a fault has been detected in a circuit or network.

Considering the system schematically represented in Figure 1 in more detail, the Figure shows schematically a section of HV network in which is incorporated a fault detection unit or system in accordance with the present invention. The fault detection unit includes a control unit which continuously monitors the signals present *::: : at the voltage transformers VT 1 and VT2 respectively and stores details of any fault * ** * indications which may be indicated on the fault passage indicator device (FPI). If the signal present at VT1 and VT2 respectively reduces to zero (which can be created by * the opening of a circuit breaker) the control unit would immediately instruct the * * opening of the HV switch provided in the system and would interrogate the most * : recent indication, if one exists, on the FPI.

The unit would apply a signal to either VT1 or VT2 dependent on the indication from the FPI to indicate the relative position of the fault, at the same time VT2 or VT1 will attempt to detect a signal to determine the position of the fault relative to the adjacent unit.. By this is meant, if the FPI indicates fault passage then a signal would be applied to VTI to indicate that the circuit up to this point is healthy.

If the FPI indicates no fault passage then a signal would be applied to VT2 to indicate that circuit beyond that point is healthy. At the same time if the FPI indicates fault passage VT2 would attempt to detect a signal to determine whether the downstream section is healthy. If the FPI indicates no fault then VT1 would attempt to detect a signal to determine whether the upstream section of network is healthy.

The restoration of electrical power begins from the source circuit breaker direction as shown in the Figure.

How the system responds depends upon the location of the fault within the circuit and there are at least four different sequences of events which may occur and these by way of example only are set out below in:

EXAMPLE 1

In this example, the fault is beyond the adjacent HVSure unit towards the Open Point and in particular the feeder sections on either side of the unit are without * : . fault. The FPI would have indicated fault passage. A signal would be applied to VT1 *5** s.. 20 to indicate that the upstream section is healthy, when this signal was detected by the * : * adjacent upstream control unit it would know that it was safe to close the HV switch to restore supplies. At the same time VT2 would attempt to detect a signal to *. determine the health of the downstream feeder section. In this case the adjacent

S * *

downstream section is healthy so a signal would be detected and the unit would know that it would be safe to close the HV switch and restore supplies.

The control unit will remove the injection signal to VT1 and will instruct closing of the HV switch to re-energise that section. The unit will receive confirmation of normal supply from VT1 and VT2 and will go to lockout requiring manual intervention to restore the unit to normal operation.. The sequence of actions for the unit has now completed its operation in these circumstances.

EXAMPLE 2

If the fault is in the feeder section between the HVSure unit and its adjacent unit towards the Open Point. The FPI would have indicated fault passage. A signal would be applied to VT1 to indicate that the upstream section is healthy, when this signal was detected by the adjacent upstream control unit it would know that it was safe to close the HV switch to restore supplies. At the same time VT2 would attempt to detect a signal to determine the health of the downstream feeder section. In this case the downstream section is faulty so no signal will have been applied and none will be detected.

*:::: The control unit will remove the injection signal from VT1, the HV switch will remain open and supplies can be restored from the source up to this point. The control unit will go to lockout requiring manual intervention to restore the unit to * : normal operation. The sequence of actions for this unit is now complete for these S. * * . . circumstances. * *5

EXAMPLE 3

If the fault is in the feeder section between the HVSure unit and its adjacent unit towards the source. The FPI would not have indicated fault passage. The control unit will apply a signal to VT2 to indicate that the downstream section is healthy, at the same time VT1 will attempt to detect a signal from the upstream unit to determine the health of the upstream feeder section. In this case the upstream feeder section is faulty so no signal will have been applied and none will be detected.

The control unit will remove the injection signal from VT2, the HV switch will remain open and supplies can be restored from the normally open point direction to this point. The control unit will go to lockout requiring manual intervention to restore the unit to normal operation. The sequence of actions for this unit is now complete for these circumstances.

EXAMPLE 4

In this example, the fault is in the section beyond the adjacent HVSure unit towards the Source i.e. the feeder sections on either side of unit are healthy. The FPI would not have indicated fault passage. The control unit will apply a signal to VT2 to indicate that the downstream feeder section is healthy. At the same time VT1 will attempt to detect a signal from the upstream HVSure unit to indicate the health of the upstream feeder section. In this case the upstream feeder section is healthy and a *: signal will be detected so the control unit knows that it is safe to close the HV switch.

I

The control unit will remove the injection signal from VT2 and instruct the HV switch to close allowing supplies to be restored through this point from the normally open point direction. Upon restoration of supplies VT1 and VT2 will detect voltage and the control unit will go to lockout requiring manual intervention to restore

S

*....S

S

the unit to normal operation. The sequence of actions for the unit has now completed its operation in these circumstances.

Clearly, from these four examples, HVSure can meet the sequencing requirements to provide disconnection of the faulted section and restoration of supply to the remaining sections.

One feature of this method is that it does not discriminate between transient and permanent faults, since the FPI cannot distinguish between them, and so will deal with transient faults as if they are permanent faults. For cable networks, this is not a major issue since transient faults are a very small proportion of the total. This is reflected in the frequent use of non-reclosing source circuit breakers for protecting HV cable networks. However, transient faults form a significant proportion of overhead line faults and would be a major problem for HVSure employing this fault sensing method. Multi-shot auto-reclose and Pole Mounted Recloser (PMR) schemes have been successfully deployed to deal with overhead line transient faults and straightforward replacement of such schemes by HYSure would seem to be a retrograde step. A more suitable approach would appear to be to incorporate HVSure into the reclose scheme which is disclosed more fully hereinafter.

Using the fault recognition system, it will be realised that the method of * 20 identifying the presence or not of a fault is readily achieved. By interpretation of the * *: FPI output arid the detection or otherwise of injected signals the location of the fault * : * * relative to the HVSure unit can be determined. Is it upstream or downstream, in either of the adjacent feeder sections or beyond an adjacent HVSure unit? Based on *: this interpretation the H'V switch will be closed or remain open. The method can be applied with similar success whether the presence of a signal is taken to indicate that the feeder section is faulty or to indicate that the feeder section is healthy. The system described in the present invention applies a signal to indicate the health of a feeder section, no signal indicating that the feeder may be faulty. This implementation is advantageous as in the event of an injected signal not being detected for some reason the system will revert to a safe state and not reenergise a potentially faulty feeder section.

In the circuit for the application and detection of suitable signals, shown in simplified form in Figure 2, the impedances of the VTs are the dominant factors.

Variations in capacitive leakage and earth return impedance between overhead and underground circuits will be relatively small by comparison. Thus, it is the applicants' belief that the fault sensing method of the invention would be reliable on both cable and overhead HV networks.

The application of the method in accordance with the present invention can be demonstrated in relation to an HV urban network which operates as hereinafter described. Such a network is usually within an urban or metropolitan area, being predominantly an underground cable system and would operate as follows: Typically, there are two primary transformers and a two-section HV *: : : : switchboard at each primary substation. The secondary winding of each transformer is connected to either side of the bus-section HV Circuit Breaker (CD), which is I...

normally closed.

The HV urban network is normally configured as a "loop-tee-loop't *:*. arrangement in an open "ring" formation. HV circuits are operated either as open rings across different sections of the same HV switchboard or as normally open interconnected feeders with other primary substations. This is shown in Figure 3.

The points at which an open switch is deployed to create the separated sections of the network are termed Normal Open Points (NOP).

Given that the urban HV network operates as a radial system with a switched alternative supply for emergency and maintenance purposes, a single fault will affect customer supplies, which can only be restored by operation of the switched alternative. In order to minimise the duration of interruptions, where economically viable, opportunity is taken to automate the HV distribution network by installing in line circuit breakers or actuators but to date these have required the deployment of communications networks.

To illustrate the application of the present invention by way of example only, a schematic representation of a Network is shown in Figure 4 with representative numbers of customer supply points at Ring Main Units (RMU) at suitable positions on the Network. An installation of HVSure on part of the network is highlighted, with a basic system with a single HVSure unit to divide one section into 2 parts arid a more complex one with two HVSure units to divide the other section into 3 parts.

The operating sequence of the HVSure schemes are described for 5 faults, 1 in each of the protected sections of the feeder, as indicated in Figure 4.

EXAMPLES

Referring to Figure 4, for a fault at A, (i.e. between CBI and SI) the sequence S.....

* . HVSure equipped source circuit breaker CB1 opens on normal delayed trip for grading with the RMU transformer HV fuses; *.. S S*

S

-12 - * During CB 1 dead time, HVSure equipped switch SI opens because No-Volts detected on both sides; * FPI at Si does not indicate fault passage, a signal is applied to VT2 to indicate that the downstream feeder section is healthy, VT1 attempts to detect a signal from the upstream HVSure unit to determine the health of the upstream feeder section; * HVSure unit at CB 1 attempts to detect a signal from the downstream HVSure unit to determine the health of the downstream feeder section; * HVSure unit at OP1 after detecting volts on one side, but not the other, attempts to detect a signal from the upstream HVSure unit to determine the health of that feeder section; * HVSure unit at CB1 determines that the downstream feeder section is faulty and remains open. HV Sure unit goes to lockout.

* HV Sure unit at OP1 determines that the upstream feeder section is healthy and issues an instruction to close restoring supplies between OP 1 and SI.

* HVSure unit at Si detects the restoration of supplies from downstream and having determined that the upstream feeder section is faulty will remain open.

HVSure unit goes to lockout; S... * S S

::..: * HVSure automatic sequence completed. S...

* 20 EXAMPLE 6

* S.*** * * Referring to Figure 4, for a fault at B, (i.e. between Si and NOP OP1) the *:*. sequence would be: *. *.* S * -13 - * HVSure equipped source circuit breaker CB1 opens on normal delayed trip for grading with the RMU transformer HV fuses; o During CB 1 dead time, HVSure equipped switch SI opens because No-Volts detected on both sides; * FPI at Si indicates fault passage, a signal is applied to VT1 to indicate that the upstream feeder section is healthy, VT2 attempts to detect a signal from the downstream HVSure unit to determine the health of the downstream feeder section.

* HVSure unit at CB 1 attempts to detect a signal from the downstream HVSure unit to determine the health of the downstream feeder section; * HVSure unit at OP1 after detecting volts on one side, but not the other, attempts to detect a signal from the upstream HVSure unit to determine the health of the upstream feeder section.

* HVSure unit at CB1 determines that the downstream feeder section is healthy and issues an instruction to close restoring supplies from CB 1 to Si; * HVSure unit at Si detects the restoration of supplies from upstream and having determined that the downstream feeder section is faulty will remain open. HVSure unit goes to lockout; S... * * .

* HVSure unit at OP1 determines that the upstream feeder section is faulty and remains open. HVSure unit goes to lockout; * S. *;.* * . * HVSure automatic sequence completed.

*:*. EXAMPLE 7 *

-14 -Referring to Figure 4, for a fault at C, (i.e. between S2 and S3) the sequence * HVSure equipped source circuit breaker CB2 opens on normal delayed trip for grading with the RMU transformer HV fuses; * During CB2 dead time, HVSure equipped switches S2 & S3 open because No-Volts detected on both sides; * FPI at S2 will indicate fault passage, a signal will be applied to VT1 to indicate that the upstream feeder section is healthy, VT 2 will attempt to detect a signal from the downstream HVSure unit to determine the health of the downstream feeder section.

* FPI at S3 will not indicate fault passage, signal will be applied to VT2 to indicate that the downstream feeder section is healthy, VTI will attempt to detect a signal from the upstream HVSure unit to determine the health of the upstream feeder section.

* VT at CB2 will attempt to detect a signal from the downstream HVSure unit to determine the health of the downstream feeder section.

* HVSure unit at OP1 after detecting volts on one side, but not the other, attempts to detect a signal from the upstream HVSure unit indicating that the feeder section is healthy.

. 20 * HVSure unit at CB2 will determine that the downstream feeder section is healthy and instruct CB2 to close, supplies restored between CBI and S2.

* HVSure unit at S2 will detect the restoration of supplies from upstream and *: ** : having determined that the downstream feeder section is faulty will remain open, HVSure sequence on S2 goes to lockout.

-15 - * HVSure unit at OP1 will determine that the upstream feeder section is healthy and instruct OP 1 to close, supplies restored between the OP 1 and S3 * HYSure unit at S3 will detect the restoration of supplies from downstream and having determined that the upstream feeder section is faulty remains open, HVSure sequence on S3 goes to lockout.

* HVSure automatic sequence completed.

EXAMPLE 8

Referring to Figure 4, for a fault at D, (i.e. between NOP OP1 and S3) the sequence would be: * HVSure equipped source circuit breaker CB2 opens on normal delayed trip for grading with the RMU transformer HV fuses; * During CB2 dead time, HVSure equipped switches S2 & S3 open because No-Volts detected on both sides; * FPI at S2 will indicate fault passage, a signal will be applied to VT1 to indicate that the upstream feeder section is healthy, VT2 will attempt to detect a signal to determine the health of the downstream feeder section.

*:::: * FPI at S3 will indicate fault passage, a signal will be applied to VT1 to indicate that the upstream feeder section is healthy, VT2 will attempt to detect S...

a signal to determine the health of the downstream feeder section.

*..... * .

* VT at CB2 will attempt to detect a signal to indicate the health of the * downstream feeder section. * . * * .*

S

**...S * . -16- * VT at OP1 will attempt to detect a signal to determine the health of the dead upstream feeder section.

* HVSure unit at CB2 will determine that the downstream feeder section is healthy and issue an instruction to close CB2 restoring supplies from CB2 to S2.

* HVSure unit at S2 will detect volts on the source side and having determined that the downstream feeder section is healthy will issue an instruction to close restoring supplies from S2 to S3. The HVSure unit will go to lockout.

* HVSure unit at S3 will detect volts on the source side but having determined that the downstream feeder section is faulty will remain open. HV Sure unit will go to lockout.

* HVSure unit at OP I determines that the upstream feeder section is faulty and remains open. HV Sure unit will go to lockout.

* HVSure automatic sequence completed.

EXAMPLE 9

Referring to Figure 4, for a permanent fault at E (i.e. between CB2 and S2) the sequence would be: * HVSure equipped source circuit breaker CB2 opens on normal delayed trip for grading with the RMU transformer HV fuses; * During CB2 dead time, flVSure equipped switches S2 & S3 open because No-Volts detected on both sides;

I

* * *1** * 1 * FPI at S2 will not indicate fault passage, signal will be applied to VT2 to indicate that the downstream feeder section is healthy, VT1 will attempt to

IIISII * *

-17 -detect a signal from the upstream HVSure unit to determine the health of the upstream feeder section.

* FPI at S3 will not indicate fault passage signal will be applied to VT2 to indicate that the downstream feeder section is healthy, VT1 will attempt to detect a signal from the upstream HVSure unit to determine the health of the upstream feeder section.

* VT at CB2 will attempt to detect a signal to indicate the health of the downstream feeder section.

* VT at OP1 will attempt to detect a signal to determine the health of the dead upstream feeder section.

* HVSure unit at CB2 will determine that the downstream feeder section is faulty and will remain open. HVSure unit will go to lockout.

* HVSure unit at OP1 will determine that the upstream feeder section is healthy and issue an instruction to close, restoring supplies from OP 1 to S3. HVSure unit will reset for normal operation as a midpoint switch.

* HVSure unit at S3 will sense the restored voltage at VT2 and having determined that the upstream feeder section is healthy issue an instruction to close. HV Sure will go to lockout.

* I-IVSure Unit at S2 will sense the restored voltage at VT2 and having * *.

20 determined that the upstream feeder section is faulty will remain open.

*:" HVSure unit will go to lockout. r

* S HVSure automatic sequence completed.

*. It will of course be realised that the HVSure schemes are able to correctly a...., restore supplies and disconnect the faulted section for HV urban networks without -18-requiring the use of communication systems. By using likely operating times for the different stages of HVSure operation (initial response to detecting a fault, fault sensing and actuator operation) timing scenarios for the overall automatic sequences demonstrate that HVSure would be able to restore supplies well within 3 minutes.

In addition to underground cable networks, the application of the method in accordance with the present invention can be demonstrated in relation to an HV rural network which operates as hereinafter described.

The HV rural network is predominantly an overhead line system, which is normally configured as an open "ring" with pole mounted HV I LV transformers directly connected. There may be lengthy single phase and three phase spurs in particularly remote locations served by overhead line circuits.

Where group demand is below I MVA the network configuration may be radial with no switched alternative (i.e. backfeed) facility. HVSure would not be effective on such configurations because of the lack of a backfeed and so these are not considered here.

To illustrate the possible application of HVSure, a representative open ring overhead network is shown in Figure 5 with an example of a pole mounted auto-recloser (PMR), in conjunction with a reclosing source circuit breaker plus an example of both group fusing and use of "smart" links to protect long spurs.

The HVSure units would be positioned at the source circuit breakers, Normal Open Point (NOP) and at one or more positions in the section, in a similar fashion to the HV urban cable networks described previously. However, there is a major difference on the fault pattern of overhead compared to cables due to the high incidence of transient faults. Overhead network design deals with these by the use of -19-source auto-reclosing and combinations of PMRs. Some schemes allow a number of reclosures and time-graded trips after the first instantaneous trip, which may result in the burning out and clearance of semi-permanent faults (e.g. caused by a small tree branch falling on the line, which may not be removed by the immediate tripping of the circuit, but could be burnt away by a repeated time-delayed trip). Such schemes also limit the effect of permanent faults by using time-graded protection on reclosure to give discriminative tripping after reclosure, resulting in the disconnection of the faulted section by means of the fuses and/or smart' links. These have been in use for many years and their deployment and operating sequences have been optimised to minimise the effects of both transient and permanent faults on overhead lines.

As indicated previously, this method of fault identification is likely to be suitable for use on overhead networks. Since this cannot discriminate between transient and permanent, treating transient faults as permanent faults, it seems clear that straightforward replacement of such schemes by HVSure would be a retrograde step. A better strategy is to use the two in combination to achieve the benefits of both i.e. the auto-reclose schemes to handle transients and HVSure to enhance the handling of the permanent faults. This can be achieved by amending the HVSure logic such that it does not begin its restoration sequences until the auto-recloser scheme has completed its cycle. This will take away one of the benefits of HVSure in that reclosing onto faults is allowed, but the benefits of further reducing Customer Interruptions (CI) and Customer Minutes Lost (CML) will be achieved.

Referring to Figure 5, a possible HVSure scheme is indicated with I-IVSure logic added to enhance the control of the source reclosing circuit breakers and PMR plus HVSure systems added to the NOP and an Air Break Isolator (ABI) as shown.

-20 -This will provide the capability of providing backfeed to either of the sections of open ring and splitting of them into two sections. There is no advantage in replacing the smart link or the fuse providing the group fusing with an HVSure unit since these are able to disconnect a permanent fault on their respective spurs in conjunction with the auto-recloser sequences, at less cost than an HVSure unit.

The proposed operating sequences for differing fault types on the network of Figure 5 would be: a) Permanent fault on the main line: * Source circuit breaker or PMR trips on instantaneous protection; * After a defined delay time, circuit breaker or PMR, as appropriate, recloses on delayed trip and trips again (depending on scheme details, further time delayed reclosures may be attempted); * Circuit breaker or PMR goes to lock-out and whole of feeder section disconnected; * HVSure sequence is activated in each unit equipped; * HVSure sequence is carried out dependent on position of fault, as per the sequences described for the cable networks above, to disconnect the faulted *: : :. section and restore supply to the remainder. The operating sequences for the * ** ** HVSure units will follow the same pattern as the cable networks above. There * : *.: 20 is no need to repeat the detailed analysis of operating sequence, since the outcomes will be the same.

*: * b) Permanent fault on the spurs protected by group fusing or smart' link: * * Source circuit breaker or PMR trips on instantaneous protection; * After a defined delay time, circuit breaker or PMR, as appropriate, recloses on delayed trip and discriminates with the fuse / smart' link to disconnect spur; * Supply restored to the remainder of feeder section; * HVSure sequence is not activated and remains enabled for any subsequent faults; c) Transient faults: * Source circuit breaker or PMR trips on instantaneous protection; * After a defined delay time, circuit breaker or PMR recloses on delayed trip and restores supply; * HVSure sequence is not activated and remains enabled for any subsequent faults.

For the analysis of the benefits of HVSure it is necessary to compare this proposed HVSure scheme against the performance of existing auto-recloser schemes and the benefits of extending these by adding HVSure, Example scenarios using real fault data demonstrate that additional benefits can be provided by adding HVSure to auto-recloser schemes in the manner described above, but these benefits are less than for deployment of HVSure on urban networks since auto.-reclosing is not used on cable networks.

* ** * The method in accordance with the present invention is also applicable to suburban (mixed) networks. In suburban areas, the HV network can be a mixture of overhead lines and underground cables. The large number of possible variations of mixed networks means that a typical or representative network is not really meaningful. However, the positioning of the HYSure units would follow the same pattern as for cable and overhead sections i.e. at the source circuit breaker, open -22 -point(s) and along the network to split it into two or more sections. The operating sequences will follow the same pattern as described in detail above for the underground cable and overhead line sections of the network and so need not be repeated here.

It will be understood that calculations based on the incidence of faults show that the major financial benefits of HVSure are in reducing the CJs and CMLs, which can be substantial. Whilst such benefits can be achieved with current generation automation schemes, HVSure can provide these benefits without incurring the costs of installing and maintaining communication systems, which can be substantial, and avoid potential unreliable operation of such schemes due to problems associated with the communication system. Following a fault, the purpose of any automation scheme is to automatically sectionalise the HV circuit and restore supply to customers supplied from those sections that are fault free. If the scheme can achieve restoration within 3 minutes, this avoids the restored customers being classified as a CI within the context of The Office of Gas and Electricity Markets (OFGEM) performance measures. This minimises the number of CIs and also by reducing the restoration times for those customers reduces the associated CMLs with that fault. An analysis of timings indicates that HVSure can achieve this 3 minute requirement and so can S...

provide this benefit in reduction of CIs.

The main reduction in CMLs is provided by reducing the Vt Restoration time by dispensing with travelling time and need to assess of supply loss situation, decide on the manual sectionalising strategy for restoration of the first group of customers.

Thus HVSure, as with any automation scheme, is expected to deliver the greatest -23 -improvement in customer minutes lost for networks that have above average numbers of customer interruptions coupled with the longest Restoration" times.

A further benefit of the arrangement of the system of HVSure is the avoidance of closing onto a fault by determining whether or not a fault has been detected on the next section of network before it is re-energised; rather than simply re-energising sections in sequence until the faulty section is re-energised, leading to interruption of supplies again, as has been the case in previous systems which do not employ communications. Thus, the network is not exposed to multiple fault current pulses reducing degradation by reducing the stress on network components providing benefits by, for example: * Reduced mechanical degradation caused by electromechanical forces; * Reducing the post fault maintenance on oil switchgear.

The basic rationale of HVSure is similar to any other HV automation scheme in that on detection of a fault the system seeks to reconfigure the network to disconnect the faulted section and restore supply to the remainder. Thus no significant safety and operational barriers would seem to exist. This view has also been expressed during discussions with staff from Distribution Network Operators *: : : (DNO) since the deployment of automation schemes is now commonplace.

* It will be understood that a viable HVSure system could be developed for HV * : 20 networks to provide automation schemes that are completely automatic and do not * : require separate communication circuits between the devices. The proposed method * * of faulted section identification is by interpretation of the operation of Fault Passage Indicators and detection of injected signals. It has previously been described how the combination of local FPI indication and remote signal detection can provide sufficient -24 -information to allow an HVSure unit to determine autonomously whether or not to close the associated HV switchgear.

A number of examples of restoration sequences of HVSure have been provided on typical cable and overhead networks for a range of deployment and fault scenarios. This confirms that the proposed HVSure schemes can restore supplies correctly by disconnecting the faulted section on a circuit and restoring supply to the remainder when an HV backfeed is available via a NOP with no requirement for a separate communications channel. Using likely operating times for the different stages of HVSure operation (initial response to detecting a fault, fault sensing and actuator operation) timing scenarios for the overall automatic sequences demonstrate that HVSure would be able to restore supplies well within 3 minutes used by OFGEM to define a CI. By optimising the operating sequence, restoration times within I minute appear feasible and this would be a valuable feature of the system if OFGEM do reduce the timing of a CI in the future.

A disadvantage of this method of fault identification is that transient faults are treated as permanent faults and a section suffering a transient fault would be disconnected. The low incidence of such faults on cable networks indicates that this * ::: : would not be a significant failing and is an improvement on non-reclosing schemes S...

whereby the whole feeder is disconnected for a transient fault. However, overhead * :*.: 20 circuits have a high incidence of transient faults and potentially provide a problem for : adoption of HVSure since straightforward replacement of the existing auto-reclose / PMR schemes by HVSure would be a retrograde step. As indicated previously, * : installing and configuring HVSure units to operate following completion of an auto-reclose sequence provides the CI and CML benefits of both schemes.

I

The embodiment described above describes an application of the invention to radial open ring circuits. In an embodiment where the FPI is capable of directional fault passage indication a near identical approach can be adopted to indicate and determine the health of individual circuit sections on closed ring circuits to disconnect the faulty section and restore supplies to healthy circuit sections.

In an alternative embodiment, the functionality can be implemented by a unit of the type shown in Figure 6, which similarly to Figure 1, shows schematically a section of HV network in which is incorporated a fault detection unit or system in accordance with the present invention. The fault detection unit in this embodiment includes a control unit which continuously monitors the signals present at the voltage transformers VT1 and VT2 respectively and stores details of any fault indications which may be indicated on the fault indicator device FPI. If the signal present at VT1 and VT2 respectively reduces to zero (which can be created by the opening of a circuit breaker) the control unit would immediately instruct the opening of the HV switch provided in the system and would interrogate the most recent indication, if one exists, on the fault indicator FPI.

The unit would also close either of earth switch 1 (ES 1) or earth switch 2 (ES2) dependent on the fault indication indicated on the FPI. By this is meant, if the S...

FPI indicates fault passage then the ES2 is closed which indicates that the fault is beyond the unit. If the FPI indicates a no fault passage, the ES1 is closed which signals or which gives the indication that the fault has occurred at a point before this * SS uni. S 55

* : As in the previous embodiment, how the system responds depends upon the location of the fault within the circuit. In this case however rather than detecting a -26 -signal on YTS 1 or VTS2 the location of the fault may be inferred by monitoring the current on VT1 or VT2, which is dependent upon whether the corresponding switch ES1 or ES2 is open or closed. Other than the detection of a particular current rather than the monitoring of a particular signal, the fault detection unit of this embodiment then operates in substantially the same manner of the embodiment of Figure 1. The embodiment of Figure 1 is generally a preferable manner of implementing the present invention as it does not require the provision of automatic switches between phases and Earth and thus has fewer concerns with respect to safety and reliability issues and may further be implemented in a smaller physical package.

In this specification the term "HVSure" refers to a system in accordance with the present invention and as shown in the drawings.

It has been recognised by the present Applicants that during the restoration of a high voltage (HV) supply system using the system of the present invention there will be a step change in the current which is drawn by a feeder. A step change will occur when any system of the kind of the present invention, operates to reconnect a section of the feeder. It is advantageous to provide means for counting and recording the number of current steps during a system restoration in order to permit *::: : identification of the feeder section in which the fault is located. Further, it is also S...

advantageous to provide means for communicating information collected by the system of the invention to a control point, by any suitable means as desired or as * : appropriate, along with a means for indicating at the control point if so required or *:*. equipped.

S *...* * S

It will of course be understood that the invention is not intended to be restricted to the details of the above embodiment which is described by way of

example only. * S. S. S S... * S S... * .

S..... * . *5 * * SS * S.

*SSSSS

Claims

-28 -Claims 1. A power supply control device operable to detect a fault in, disconnect and reconnect a HV supply circuit, said device comprising: a fault passage indicator; a HV switch operable to connect or disconnect the HV supply; a pair of indicator units provided on either side of the device, the indicator units operable to indicate the presence or absence of a detected fault on their respective sides of the device; and a control unit operable to control the HV switch so as only to restore power to the circuit on a side of the device where the absence of a fault is detected.
2. A power supply control device as claimed in claim 1 wherein each indicator unit in one device is operable to detect the indication state of the indicator unit on the near side of an adjacent device.
3. A power supply control device as claimed in claim 1 or claim 2 wherein the control unit monitors the indicator units to detect the occurrence of faults in addition to monitoring such units to determine whether to restore power.
4. A power supply control device as claimed in any preceding claim wherein the indicator units are provided between any selected phases of the supply or *:::: between any selected phase or phases of the supply and earth.

**.
5. A power supply control device as claimed in any preceding claim wherein each indicator unit comprises a voltage transformer and a signal generating * : * device operable to apply a signal to the voltage transformer.
6. A power supply control device as claimed in claim 5 wherein the signal generating means applies a signal to the voltage transformer to indicate that no fault is detected on that particular side of a device.

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7. A power supply control device as claimed in any one of claims 1 to 4 wherein the indicator unit comprises a voltage transformer and an earth switch in parallel therewith.
8. A power supply control device as claimed in claim 7 wherein the earth switch is closed in response to the detection of a fault, thereby indicating that the fault occurred on a particular side of the device.
9. A HV supply circuit incorporating a plurality of devices according to any preceding claim.
10. A HV supply circuit as claimed in claim 9 wherein the supply circuit comprises one or more underground cables and/or one or more overhead HV lines.
Ill. A HV supply circuit as claimed in claim 10 wherein any parts of the circuit having overhead HV lines are additionally provided with pole mounted auto-reclosers or circuit breakers on one or more supports for the HV line.
12. A method of supply disconnection and supply restoration for use with a HV supply circuit according to any one of claims 9 to 11, said method comprising: disconnecting said HV supply circuit at one said device; providing an indication using the indication units of the said device as to the presence or absence of a fault in the HV circuit on either side of said device; monitoring the indicator units of adjacent devices to determine the presence or absence of a fault between the said device and adjacent devices to thereby determine the presence or absence of a fault between the said device and the adjacent * : devices; and restoring power to the circuit on a respective side of the device only if no fault is detected after sensing.

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13. A method as claimed in claim 12 wherein if a fault is detected on one side of the device, the device goes to lockout, preventing the automatic restoration of power to the circuit on that side of the device.
14. A method as claimed in claim 12 or claim 13 wherein the method is only initiated after a separate pole mounted auto-recloser or circuit breaker goes to lockout. *.,I * * * *. S **** * . *** ** ***** * *S * S ** * * S S * S.S *S