GB2338601A

GB2338601A - Electrical equipment interlock

Info

Publication number: GB2338601A
Application number: GB9812678A
Authority: GB
Inventors: Trevor Brian Marshall
Original assignee: Switchgear & Instrumentation L
Current assignee: Switchgear & Instrumentation L
Priority date: 1998-06-12
Filing date: 1998-06-12
Publication date: 1999-12-22
Anticipated expiration: 2018-06-12
Also published as: GB9812678D0; GB2338601B

Abstract

An equipment cabinet and a switchgear for high voltage applications are described comprising a first cubicle 14 for receiving a first equipment cradle having a retractable tongue 36 projecting outwardly from a side thereof; a second cubicle 12 adjacent the first for receiving a second equipment cradle having a retractable tongue projecting outwardly from a side thereof; an interlocking mechanism comprising at least one wall 28 having a channel 38 therethrough in which is mounted a shuttle bolt 42, the length of the shuttle bolt 42 relative to that of the channel 38 being such that when a first cradle is received in the first cubicle 14, the tongue 36 of the first cradle is able to engage in the channel 38 causing the shuttle bolt to travel towards the second cubicle 12 to prevent the tongue of any second cradle received in the second cubicle 12 from engaging in the channel 38.

Description

1 0 1 EQUIPMENT CABINET WITH INTERLOC 2338601 The present invention

relates to an equipment cabinet with an interlock, particularly, but not exclusively for high voltage applications, such as switchgear, for example switchboards or controlgear.

Switchboards are a type of switchgear. For the purposes of this description, the term Iswitchgearl should be taken to also include control gear, for example for use with contactors for the supply of power.

In high voltage switching operations, supply voltages of many kilovolts are applied to conductors connecting equipment together. Before carrying out work on these conductors, it usually must be ensured that they are at a harmless voltage, and will remain so during the works.

It may be insufficient to simply disconnect the high supply voltage, as a dangerous voltage may be retainedin the conductors by their inherent capacitance. There is also the risk that a conductor may inadvertently become 'live,, raised to several kilovolts, while it is being worked on.

For example it may still be connected to equipment, 25 previously powered up to a high voltage, which by its inherent capacitance or for some other reason, has retained a voltage on it. Such may be the case in event of a fault in the switchgear, or any associated equipment, or in the case of a person unknowingly applying a high voltage to the conductor, or associated equipment, that is being worked upon.

1 2 It would be safer to provide an earth switch, to provide a low resistance path from the conductor being worked on to an earth, for the duration of the works. Such an earth switch is actuated if working on, or adjacent to, the conductors or other potentially live equipment. In this way, one can be sure that the conductor being worked upon is at a safe voltage, and that it will remain at a safe voltage throughout the duration of the works.

Automatic engagement of an earth switch could result in the connection of the conductor to earth being made whilst it and equipment connected to it are powered by high voltages. A large potentially damaging current would then be drawn. Indeed, the currents are so large that failure of this nature can be instantaneous and explosive. Such is the risk involved, that elaborate electrical or mechanical interlocking mechanisms have been proposed particularly for high voltage applications, for example 1kV to tens of kV, to prevent the earth connection being made whilst equipment is still connected to the conductor. Electrical interlocking is of no concern here, however, the mechanical interlocking mechanisms proposed typically involve rotating shafts, or push/pull shafts and cables which are prone to mechanical breakdown and are open to tampering by unwary users.

Accordingly, the invention aims to provide an equipment cabinet having a mechanical interlock, which alleviates these problems and in particular is more resistant to tampering.

The invention also aims to provide an equipment cabinet 3 with a mechanical interlock which is relatively simple to manufacture.

The present invention provides an equipment cabinet for high voltage applications comprising:

a first cubicle for receiving a first equipment cradle having a retractable tongue projecting outwardly from a side thereof; a second cubicle adjacent the first for receiving a second equipment cradle having a retractable tongue projecting outwardly from a side thereof; an interlocking mechanism comprising at least one wall having a channel therethrough in which is mounted a shuttle bolt, the length of the shuttle bolt relative to that of the channel being such that when a first cradle is received in the first cubicle, the tongue of the first cradle is able to engage in the channel causing the shuttle bolt to travel towards the second cubicle to prevent the tongue of any second cradle received in the second cubicle from engaging in the channel.

Preferably, the length of shuttle bolt is less than that of the channel and more than that of half the channel.

Preferably, the interlocking mechanism comprises an adjacent pair of walls of the cubicles having opposing aligned sub channels therethrough forming the channel.

Preferably, the length of the shuttle bolt is less than the 1 1 4 combined length of the sub channels and larger than that of either single sub channel.

Preferably, the one or more walls comprises a pillar.

Preferably, a first equipment cradle is provided having at least one retractable tongue projecting outwardly from a side thereof.

Preferably, a second equipment cradle is provided having at least one retractable tongue projecting outwardly from a side thereof.

Preferably, the or each tongue is resiliently mounted so as 15 to project from the side of the cradle in a relaxed condition.

Preferably, the or each tongue is spring-loaded so as to project from the side of the cradle under the influence of the spring whereby the or each tongue is retractable into the cradle by working against the spring.

Preferably, at least one lateral dimension of the shuttle bolt is less than a corresponding lateral dimension of the entrance to the channel whereby the shuttle bolt is retained within the channel.

Preferably, at least one or each tongue is substantially planer.

Preferably, the shuttle bolt is substantially planer.

1 Preferably, the shuttle bolt is mounted so that its plane is substantially vertical.

Preferably, at least one equipment cradle is adapted to transfer equipment mounted on it towards the rear of a respective cubicle only if tongues projecting from opposite sides of the cradle are engaged in channels of the cubicle.

Preferably, there is provided a switch gear in which the first cubicle is adapted for receiving a circuit breaker for passing power to or from at least one busbar; the second cubicle is adapted for receiving an earth truck for earthing at least one busbar whereby when a circuit breaker cradle is engaged by means of one or more tongues in the one or more channels of its respective cubicle, the earthing truck cradle is prevented from being so engaged.

Preferably, a third cubicle is provided for receiving a second circuit breaker and having a shuttle bolt interlocking mechanism between the second circuit breaker cradle and the earthing truck cradle.

Preferably, a fourth cubicle is provided for receiving a second earthing truck the second circuit breaker cradle and the second earthing truck cradle having a shuttle bolt interlocking mechanism therebetween.

Preferably, a fifth cubicle is provided for receiving a third circuit breaker, the third circuit breaker cradle and the second earthing truck cradle having a shuttle bolt interlocking mechanism therebetween.

6 Brief Description of the Drawinas

The present invention will be described in accordance with certain embodiments, given by way of examples only, with reference to the accompanying diagrams, in which:

Figure 1 shows a front elevation of a medium voltage equipment cabinet for use as a switchgear according to a preferred embodiment of the invention; Figure 2 shows a side sectional view through a circuit breaker cubicle Figure 1; Figure 3 shows a schematic sectional top view through the switchgear of Figure 1 along line II-II of Figure 2; Figure 4 shows a single line diagram illustrating the connections between the circuit breakers and earth trucks of the switchgear in Figure 1; Figure 5 shows a single line block diagram of the circuit of Figure 4; Figure 6 shows a plan view of an equipment cradle for use in one of the cubicles of Figure 1; Figure 7 shows a front elevation of the cradle of Figure 6 along line AA with the handles 32 removed; Figure 8 shows a plan schematic view of an equipment cradle illustrating in particular the means by which tongues 36 are locked out as equipment 49 is moved towards an engaged position to the rear of the equipment cradle.

7 Figure 9 shows a schematic front elevation of the cradle of Figure 8.

Figure 10 shows a schematic close-up of the mechanical interlocking mechanism between adjacent cubicles of the equipment cabinet.

In Figure 1, an electrical equipment cabinet 10 comprises five cubicles 12 to 20. First incomer A cubicle 12 houses a first circuit breaker CBi in mid-section 24 for connecting a power supply to first incomer busbars A for supplying busbars A or B. Upper section 22 includes a chamber through which busbars A pass carrying a three phase supply (not shown). The lower section 26 houses a small transformer for measuring the current being derived from the busbars.

Adjacent incomer A cubicle 12 is busbar earth A cubicle 14 which houses earthing truck ET1 in its mid-section. An adjacent bus-section cubicle 16 houses circuit breaker CB2 in its mid-section 24. Next busbar earth B and transition cubicle 18 houses earthing truck ET2 in its mid-section 24.

Finally, incomer B cubicle 20 houses circuit breaker CB3 for connecting a power supply to second incomer busbars B to supply busbars A or B. Thus, each mid-section of each cubicle houses a piece of electrical equipment. The electrical connections between these items will be described later. Each piece of equipment can be moved in and out of position on an equipment cradle 30 by means of handles 32. Handles 32 are 8 spring-loaded so that the cradle can be latched into position as will be described later. Handles 32 are able to slide to the left and right in the figures pulling against springs as they move towards the centre of their respective cradle.

Each cubicle has side walls 28 in the form of pillars with opposing aligned channels 38 passing through adjacent walls of adjacent cubicles. Tongues or projections 36 of 10 cradles 30 are receivable in respective channels 38 of adjacent cubicles. A shuttle interlock mechanism 40 prevents equipment in adjacent cubicles from being inserted at the same time. Thus, earthing truck ET1 cannot be inserted at the same time as either circuit breaker CB1 or circuit breaker CB2 and vice versa. Similarly, earthing truck ET2 cannot be inserted at the same time as circuit breaker CB2 and circuit breaker CB3 and vice versa.

In Figure 2, a side sectional view of cubicles 12, 16 or 12 is shown in which a busbar chamber 90 contains horizontal busbars 94 which pass through upper sections 22 of cubicles 12, 14, 16, 18 and 20. Connections 92 and 98 connect the busbars to circuit breakers CB1, CB2 or CB3. Busbars 94 are divided into two sections, busbars A and B, by circuit breaker CB2. The circuit breakers are mounted on cradles which have wheels 66. Each cradle can be wound into a service position, in which the circuit breaker is connected, or an isolated position in which the circuit breaker is disconnected, as indicated by the arrows. Power is passed from the circuit breaker to connection 102 via current transformer bushing 100. An earth connection 120 is connected by earth switch 110 when mechanical interlock 9 is released indicating that circuit breaker is in an isolated position. Mechanical interlock 130 is contained entirely within an individual cubicle and will not be described further.

Figure 3 shows circuit breakers CB1, CB2 and CB3 which have been wound into a service position with conductors 64 contacting conductors 62 of current transformer bushings 100. This is achieved on cradles 30 which have separable rear and front portions. The rear portion of each cradle moves forwards or backwards with respect to the front portion as threaded bar 48 is rotated when projections or tongues 36 of the front portion of cradle 30 are braced in channels 38 of walls 28. Threaded bar 48 is rotated by a mechanism mounted on the front panel of the cradle (not shown).

When tongues 36 of a first cradle are inserted in channels 38 of side walls 28, so the rear portion of cradle can be moved into a service position, the tongues engage respective shuttle bolts 42 situated in channels 38. The shuttle bolt 42 is moved towards and into the channel of an adjacent side wall 28 of an adjacent cubicle. The presence of shuttle bolt 42 in this adjacent channel, wedged against tongue 36 of the first cradle prevents a tongue 36 of the second cradle in the adjacent cubicle from engaging in the channel 38 of the side wall of that cubicle. Accordingly, the cradles of earth trucks ET1 and ET2 are prevented. if circuit breakers CB1, CB2 or CB3 are in a service position, from securely engaging in channels 38, in the side walls and so have nothing to brace against. Thus, even if threaded bar 48 were wound, the front portion of cradle 30 would not be fixed in position and therefore the rear portion carrying the earth truck is not able to be moved into an engaged position.

Figures 4 and 5 show circuit diagrams for the switchgear of Figure 1. As described previously, circuit breaker 1 and earth truck 1 are not engageable simultaneously. Any power supply (not shown) supplying power to equipment via the switchgear is isolated from section A and section B of the incoming busbars 94 by opening the appropriate circuit breaker CBi before earth truck ET1 is engageable to earth the busbars. The two are prevented from being engaged simultaneously by the mechanical interlock of the invention. otherwise any power supply connected to the circuit circuit prevent breaker earthed.

breaker may be earthed inappropriately. Similarly, breaker CB2 is interlocked with earth truck ET1 to a power supply (not shown) connected to circuit CB3 from being earthed when earth truck ET1 is Figure 6 and 7, 8 and 9 show in more detail the cradle for carrying equipment such as the circuit breakers and busbar earthing trucks. Springs 44, connected between the sides of the cradle and the handles 32, pull handles 32 towards the outer sides of cradle 30 so that tongues 36, which are also connected to handles 32, project from the sides of cradle 30 under the influence of the springs. To retract tongues 36 into the cradle, so allowing the cradle to be properly mounted in the cubicle, handles 32 must be moved inwards towards the centre of the cradle. As can be seen in Figure 8, a winding mechanism 46 on the front panel enables equipment 49 to be wound in or out on a rear 11 portion of the cradle by rotating threaded bar 48. As soon as winding starts, or in order for winding to begin, a section 47 occupies the space between bars 50, which are connected to handles 32 and tongues 36, so preventing these from being retracted. Thus, on winding equipment 49 towards a service position from an isolated position, tongues 36 are locked outwards and can no longer be retracted. Accordingly. tongues 36 cause the shuttle bolt 42 to occupy the channel in a side wall of a neighbouring cubicle, preventing a cradle from being engaged in position.

Figure 10 shows the shuttle bolt interlock mechanism 40 in more detail. Here, mechanism 40 includes shuttle bolt 42 which has been pushed into side wall 28 of cubicle 12 by tongue 36 of an equipment cradle (not shown) in cubicle 14.

Thus, side 36B of tongue 36 pushes against side 42B of shuttle bolt 42 preferably at least until side 42A of shuttle bolt 42 is adjacent to channel entrance 38A of channel 38 of side wall 28 of cubicle 12. Once tongue 36 is latched in a projected position, when cubicle 14 is wound in, shuttle bolt 42 cannot be retracted into side wall 48.

The shuttle bolt 42 is hidden within walls or pillars 28 and thus is largely inaccessible to a user. Preferably, though this is not shown, the width or height of shuttle bolt 42 is greater than that of the channel entrances 38A so preventing the shuttle bolt from being inadvertently ejected from channel 38. Typically, tongue 36 has smaller lateral dimensions than shuttle bolt 42 to pass through the reduced size entrance of channels 38. Since the shuttle bolt 42 and channels 38 are encased almost entirely within 12 side walls 28, they are virtually inaccessible.

Typically, the equipment cabinet or switchgear will be provided as a single unit of two or more adjacent cubicles fixed together with one or more shuttle bolts between cubicles already mounted in position. Indeed adj acent cubicles may simply be separate compartments of a single equipment cabinet. It should also be understood that whereas two adjacent walls or pillars, having opposing aligned channels formed therethrough, are provided, a single wall or pillar with a single channel may be provided, into the open ends of which projecting tongues 36 may engage. It should be also understood that the term wall is intended to include a structure such as pillar which does extends only partially between the front and rear of the cabinet. Side walls 28 may be solid, or hollow as shown. In the case of a hollow arrangement, it is preferred though not necessary, for channel 38 to be formed from an enclosure through which shuttle bolt 42 passes. Alternatively, channel 38 may comprise simply a shelf along which shuttle bolt 42 travels. Preferably, the shelf has side walls to guide shuttle 42 as it travels towards channel entrance 38a. Preferably, the tongue 36 is planer for example arranged so that its width is narrower than its height. It may be provided with means for abutting the end of shuttle bolt 42, for example an enlarged end.

Thus, the invention provides a simple mechanical interlock which is inaccessible to the user and which because of its simplicity is less prone to mechanical breakdown.

13

Claims

CLAIMS is 1. An equipment cabinet for high voltageapplications comprising:

a first cubicle for receiving a first equipment cradle having a retractable tongue projecting outwardly from a side thereof; a second cubicle adjacent the first for receiving a second equipment cradle having a retractable tongue projecting outwardly from a side thereof; an interlocking mechanism comprising at least one wall having a channel therethrough in which is mounted a shuttle bolt, the length of the shuttle bolt relative to that of the channel being such that when a first cradle is received in the first cubicle, the tongue of the f irst cradle is able to engage in the channel causing the shuttle bolt to travel towards the second cubicle to prevent the tongue of any second cradle received in the second cubicle from engaging in the channel.
2. An equipment cabinet according to claim 1, in which the length of shuttle bolt is less than that of the channel and more than that of half the channel.
3. An equipment cabinet according to claims 1 or 2 in which the interlocking mechanism comprises an adjacent pair of walls of the cubicles having opposing aligned sub channels therethrough forming the channel.
4. An equipment cabinet according to claim 3 in which the length of the shuttle bolt is less than the combined 14 length of the sub channels and larger than that of either single sub channel.
is An equipment cabinet according to any preceding claim in which the one or more walls comprise a pillar.
6. An equipment cabinet according to any preceding claim comprising a first equipment cradle having at least one retractable tongue projecting outwardly from a side thereof.
An equipment cabinet according to any preceding claim comprising a second equipment cradle having at least one retractable tongue projecting outwardly from a side thereof.
8. An equipment cabinet according to claim 6 or 7 in which the or each tongue is resiliently mounted so as to project from the side of the cradle in a relaxed condition.
9. An equipment cabinet according to claim 8 in which the or each tongue is spring-loaded so as to project from the side of the cradle under the influence of the spring whereby the or each tongue is retractable into the cradle by working against the spring.
10. An equipment cabinet according to any preceding claim in which at least one lateral dimension of the shuttle bolt is less than a corresponding lateral dimension of the entrance to the channel whereby the shuttle bolt is retained within the channel.

is
11. An equipment cabinet according to any preceding claim in which at least one or each tongue is substantially planer.
12. An equipment cabinet according to any preceding claim in which the shuttle bolt is substantially planer.
13. An equipment cabinet according to claim 12 in which the shuttle bolt is mounted so that its plane is substantially vertical.

is
14. An equipment cabinet according to any preceding claim in which at least one equipment cradle is adapted to transfer equipment mounted on it towards the rear of a respective cubicle only if tongues projecting from opposite sides of the cradle are engaged in channels of the cubicle.
15. A switchgear comprising an equipment cabinet according to any preceding claim in which the first cubicle is adapted for receiving a circuit breaker for passing power to or from at least one busbar; the second cubicle is adapted for receiving an earth truck for earthing at least one busbar whereby when a circuit breaker cradle is engaged by means of one or more tongues in the one or more channels of its respective cubicle, the earthing truck cradle is prevented from being so engaged.
16. A switchgear according to claim 15 comprising a third cubicle for receiving a second circuit breaker and 16 having a shuttle bolt interlocking mechanism between the second circuit breaker cradle and the earthing truck cradle.
17. A switchgear according to claim 16 comprising a fourth cubicle for receiving a second earthing truck the second circuit breaker and the cradle and the second earthing truck cradle having a shuttle bolt interlocking mechanism therebetween.
18. A switchgear according to Claim 17 comprising a fifth cubicle for receiving a third circuit breaker, the third circuit breaker cradle and the second earthing truck cradle having a shuttle bolt interlocking mechanism therebetween.
19. An equipment cabinet for high voltage application substantially as described herein with reference to and/or as illustrated in the accompanying drawings.
20. A switchgear for high voltage applications substantially as described herein with reference to and/or as illustrated in the accompanying figures.