GB2175448A

GB2175448A - Switchgear

Info

Publication number: GB2175448A
Application number: GB08608861A
Authority: GB
Inventors: George Graham Williams
Original assignee: Associated Electrical Industries Ltd
Current assignee: Associated Electrical Industries Ltd
Priority date: 1985-04-22
Filing date: 1986-04-11
Publication date: 1986-11-26
Also published as: CN86102745A; GB8608861D0; GB8510203D0

Abstract

An interlock mechanism for switchgear incorporating a circuit breaker and disconnector operable by manual controls 11,1 and located within a housing with an openable access cover has a cam system preventing movement of the disconnector when the circuit breaker is closed, and preventing opening of the access cover when the disconnector is in the "On" or "Earth" positions. The circuit breaker handle 11 carries a cam 7 that operates an interlock 5 to engage a notched cam 3 on the disconnector handle 1 and so prevent its simultaneous operation. The disconnector cam 3 operates a pair of interlocks 15/16 to latch a cover handle 26 in closed position when the disconnector is not "Off". Further mechanisms eg. 39 are provided to control trip mechanisms. <IMAGE>

Description

SPECIFICATION Switchgear This invention relates to switchgear of the kind incorporating an enclosure having an access opening fitted with an openable cover and, within the enclosure, means for transmitting movement to a circuit breaker and to a disconnector from respective manual control means located outside the enclosure, and relates especially, though not exclusively, to flameproof switchgear in which the circuit breaker is provided by a vacuum interrupter.

In such forms of switchgear the disconnector has at least one movable contact connected to a contact of the circuit breaker and operable to connect it to a busbar contact ("On" position) or earth contact ("Earth" position), or an "OFF" contact in which it engages neither the busbar or earth contact.

An object of the invention is to provide a form of interlock system for preventing operation of the disconnector, or the opening of the access cover when it would be unsafe to do so.

According to the invention an interlock mechanism for switchgear of the kind referred to comprises a first cam movable with the circuit breaker manual control, a second cam movable with the disconnector manual control, a first interlock member movable by the first cam and engageable with means preventing movement of the disconnector when the circuit breaker is set to the "Closed" position, and at least one further interlock member movable by the second cam to prevent opening of the access cover when the disconnector is in either the "On" or "Earth" positions.

The first interlock member is preferably urged into a recess in the second cam by the first cam when the circuit breaker is "Closed", but is withdrawn therefrom on movement of the first cam into the circuit breaker "Open" position.

Preferably also the first interlock member is operative to prevent the first cam from being returned to the circuit breaker "Closed" position unless the second cam is fully in the "On", "Off" or "Earth" positions of the disconnector.

Preferably the mechanism incorporates two said further interlock members both engageable in recesses in the second cam when the disconnector is in the "Off" position, and stop means which secure these interlock members against movement when the access cover is opened, so as to prevent the disconnector being moved to the "On" or "Earth" position.

In such a case one or other of the further interlock menibers is arranged to be acted upon by the second cam when the cam is moved to the disconnector "On" or "Earth" positions, to engage a respective recess in a cover-operating handle to prevent the opening of the access cover.

In addition movement of the second cam into the disconnector "Earth" position inhibits the operation of an undervoltage trip of the circuit breaker.

Preferably the mechanism includes locking means operative on a respective interlock member when the second cam has been moved into the disconnector "Earth" position, and the first cam has been moved into the circuit breaker "Closed" position, so as to prevent tripping of the circuit breaker. The locking means is preferably also operative to prevent the return of the first cam into the circuit breaker "Open" position.

One form of switchgear interlock mechanism in accordance with the invention will now be described by way of example with reference to Figures 1 to 7 of the accompanying drawings, in which Figure 1 represents a front view of the in interlock mechanism, Figures 2 and 3 represent exploded views of parts of the interlock mechanism, and Figures 4 to 7 illustrate the various operating conditions of the mechanism in diagrammatic form.

The switchgear incorporates a circuit breaker in the form of a vacuum interrupter, and a disconnector (or isoiator), manually operable by means of respective handles 11, 1 located outside a flameproof enclosure (not shown) accommodating means for transmitting movement of the handles to the interrupter and disconnector respectively, together with the interlock mechanism.

The vacuum interrupter (also not shown) has one contact connected to the movable contact of the disconnector, which has three positions namely an "On" position in which it engages a contact connected to a busbar or feeder cable as the case may be, an "Earth" position in which it engages an earth contact and an "Off" (or "Open") position in which it engages neither the feeder nor the earth contact.

In Figures 1 and 2 the disconnector handle 1 is shown in the "Off" position of the disconnector.

The interlock assembly is supported mainly between a pair of mounting plates A, B (Figure 1) arranged to be secured within a housing (not shown). The circuit breaker operating handle 11 is carried by an operating shaft 10 (Figure 2) supported by a bushing (not shown) and carrying a lever 8 suitably coupled to the movable contact of the vacuum interrupter through a link mechanism shown only in part at 9. The shaft 10 also carries a cam 7 which acts against a boss 6 at the lower end of an interlock plate 5 whose function will be described later.

The disconnector handle 1 is similarly carried by a shaft 2 on which is mounted a quadrant gear 2.2, forming part of the disconnec tor operating mechanism, and a cam plate 3, having three notches 3.1, 3.2, 3.3 separately engageable with a further boss 4 at the upper end of the interlock plate 5 in different positions of the handle 1, as will subsequently be described.

The interlock plate 5 is slidable vertically in guides 25, and on each side of the plate there is located an interlock bar 15, 16 respectively, also slidable vertically. The interlock bars 15, 16 are biased upwards by a pair of levers 12 mounted on respective pivots 14 and carrying pins 13 which fit into slots 17 (see Fig 3) formed in the outer edges of the bars 15, 16.

The pins 13 also carry rollers 23 which engage in the two outer notches 3.1, 3.3 of the cam plate 3 when the handle 1 is in the central, i.e "Off" position shown in Figure 1, being held resiliently in engagement with the notches by means of a spring 30, the ends of which engage the forward ends of the pins 13, which are normally inclined slightly downwards from the pivots 14 as shown.

If the interrupter handle 11 is in the "On" position as illustrated in Figure 1, and also Figures 6 and 7, the lower boss 6 of the interlock plate 5 rests on the profile of the cam 7, while the upper boss 4 lies within one of the notches 3.1, 3.2, 3.3 of the cam plate 3, depending upon the position of the disconnector handle 1. The cam plate 3, and hence the disconnector handle 1 cannot then be turned, so that operation of the disconnector is prevented when the circuit breaker is "Closed".

If, now, the interrupter handle 11 is turned anticlockwise from the "Closed" position of Figure 1, into the "Open" position as shown In Figures 4 and 5, the lower boss 6 of the interlock plate 5 drops into the notch 7.1 in the cam 7, while the upper boss 4 disengages from the notch 3.2 in the cam plate 3. The disconnector can then be operated, and switched into either the "On" position, as in Figures 5 and 6, or the "Earth" position as shown in Figure 7.

Should, however, the disconnector be left partway between two of its three positions, the interlock plate 5 cannot be lifted into its upper positions with the upper boss 4 intruded into a notch of the cam plate 3 so that the cam plate 7 cannot be turned to operate the circuit breaker.

As previously mentioned, when the disconnector handle 1 is in the "Off" position as shown in Figure 1, the rollers 23 engage in two outer notches 3.1, 3.3 of the cam plate 3, but if the plate is turned the rollers 23 will be displaced downwards, thereby depressing the pins 13, and causing the levers 12 to be pivoted downwards about the pivots 14.

Downward movement of the pins 13, which extend into the slots 17 in the interlock bars 15, 16, causes the latter to be forced downwards.

Further movement of the cam plate 3 into either the "Earth" or "On" position, permits one or other of the rollers 23 to engage within the central notch 3.2 of the cam plate, and the respective interlock bar 15, 16 to rise, although the other one remains depressed.

Now'the enclosure accommodating the interlock mechanism has an access opening closed by a cover which is held in position by a lock which can be released by movement of a handle 26 (Figure 3) having a pair of recesses 27 into which the lower ends of the interlock bars 15, 16 project when the bars are depressed. Accordingly when the disconnector handle 1 is moved into the "Earth" or "On" position the appropriate bar 15 or 16 will engage the respective recess.27, thereby preventing movement of the access cover handle 26 and hence the opening of the cover.

If, however, with the disconnector handle 1 in the "Open" or "Off" position, the access cover is opened, outward movement of the cover handle 26 will allow two spring-loaded plungers 28, 29 to protrude from the interlock mechanism housing to lie beneath bosses 31, 32 at the rear of the interlock bars 15, 16.

The disconnector handle cannot therefore be moved to either the "On" or the "Earth" position until the access cover is again closed.

Protruding through the top of a cover (not shown) of the interlock assembly cover is a lifting block handle 35 attached to a lifting block (not shown) inside the assembly. Raising this handle causes two spring-loaded stop plungers 36 to extend from the front of the assembly one on each side of the disconnector handle 1. The stop plungers 36 can be extended with the disconnector handle 1 in either the "Off" or the "Earth" position. An interlock rod 37, however, engages the disconnector handle 1 when the latter is in the "On" position and prevents the plungers 36 being extended with the handle in this position. The plungers 36 can therefore keep the disconnector handle 1 fixed in either the "Off" or "Earth" position and this position can be maintained by means of a padlock through the lifting block handle 35. It is sometimes desirable to be able to operate the disconnector from the "Off" position to the "On" position, but to be unable to place it in the "Earth" position. Incoming or ring main units, where it is desirable to prevent earthing of a live cable, are such cases. In this case the lifting block handle 35 can have three possible positions namely "Up", "Midway" and "Down", with the right hand one of the stop plungers being shorter than the left hand plunger.

Thus with the lifting block handle 35 in the "Down" position the disconnector handle 1 can be moved to any position. With it in the "Midway" position the disconnector handle 1 can be moved from the "Off" position past the shorter one of the plungers 36 to the "On" position, but cannot be moved past the longer plunger to the "Earth" position. However with the lifting block handle 35 in the "Up" position no movement of the disconnector at all is possible.

Depression of the interlock bar 16, on movement of the disconnector handle 1 into the "On" position, as previously explained, also depresses a block 38, which engages in a recess 38A in the bar 16 and consequently a pushrod 39 to which the block 38 is secured. This releases the armature of the undervoltage trip of the circuit breaker.

Depression of the other interlock bar 15, on movement of the disconnector handle 1 into the "Earth" position brings a cut-out 41 in the bar in a position to receive a boss 42 carried by a pivoted lever 43. However this is prevented by the cam 7 if the interrupter operating handle 11 is in the "Open" position. If, on the other hand, the interrupter operating handle 11 is moved to the "Closed" position the cam 7 is moved clear of the cut-out 41 and the boss 42 can be moved into the cutout on rotation of a locking knob 44 through 1800 into a "Locking" position as in Figure 7.

The boss 42 cannot be released from the cutout 41 until the locking knob 44 is returned to the original position, and this ensures that the bar 15 is retained in the depressed condition in which it prevents tripping of the circuit breaker.

Rotation of the knob 44 also causes an interlock lever 46 to turn about a fixed pivot pin 47. This carries a boss 49, which is permanently engaged in a block 50 carried by the left hand push rod 48 to be depressed, together with the push-rod itself, and this prevents all electrical tripping of the mechanism.

Moroever downward movement of the interlock lever 46 means that a ledge 51 partway along the lever 46 will now obstruct movement of the interrupter cam 7. This ensures that the handle 11 is held in the "Closed" position, so that manual, as well as electrical, tripping cannot take place.

The locking knob 44 can be padlocked in the "Locking" position therbey rendering the circuit breaker untrippable for maintenance purposes.

It will therefore be seen that the interlock mechanism provides a number of safety features as follows: 1. It prevents operation of the disconnector if the circuit breaker is in the "Closed" position, but allows the disconnector to be operated to any one of the "On" "Off" or "Earth" positions if the circuit breaker is in the "Open" position.

2. It prevents operation of the circuit breaker if the disconnector is left partway between any of its three positions, but allows the circuit breaker to be operated to either the "Open" or "Closed" position when the disconnector is fully in the "On", "Off" or "Earth" position.

3. It renders the undervoltage trip operative, provided the disconnector is in the "On" position, but with the disconnector in the "Earth" position the undervoltage trip cannot operate.

4. It prevents manual or electrical tripping of the circuit breaker if the disconnector is in the "Earth" position, the circuit breaker is "Closed" and the locking knob 44 is set in the "Locking" position.

5. It prevents the access cover from being opened if the disconnector is in either the "On" or "Earth" position.

6. It prevents the disconnector from being operated to either the "On" or "Earth" position while the access cover is open.

7. It enables all or certain movements of the disconnector to be prevented by means of a lock, regardless of the position of the circuit breaker.

Claims

1. An interlock mechanism for switchgear of the kind referred to comprising a first cam movable with the circuit breaker manual control, a second cam movable with the disconnector manual control, a first interlock member movable by the first cam and engageable with means preventing movement of the disconnector when the circuit breaker is set to the "Closed" position, and at least one further interlock member movable by the second cam to prevent opening of the access cover when the disconnector is in either the "On" or "Earth" positions.

2. An interlock mechanism according to Claim 1 wherein the first interlock member is urged into a recess in the second cam by the first cam when the circuit breaker is "Closed", but is withdrawn therefrom on movement of the first cam into the circuit breaker "Open" position.

3. An interlock mechanism according to Claim 2 wherein the first interlock member is operative to prevent the first cam from being returned to the circuit breaker "Closed" position unless the second cam is fully in the "On", "Off" or "Earth" positions of the disconnector.

4. An interlock mechanism according to Claim 1, 2 or 3 incorporating two said further interlock members both engageable in recesses in the second cam when the disconnector is in the "Off" position, and stop means which secure these interlock members against movement when the access cover is opened, so as to prevent the disconnector be ing moved to the "On" or "Earth" position.

5. An interlock mechanism according to Claim 4 wherein one or other of the further interlock members is arranged to be acted upon by the second cam when the cam is moved to the disconnector "On" or "Earth" positions, to engage a respective recess in a cover-operating handle to prevent the opening of the access cover.

6. An interlock mechanism according to Claim 5 wherein movement of the second cam into the disconnector "Earth" position inhibits the operation of an undervoltage trip of the circuit breaker.

7. An interlock mechanism according to any preceding Claim including locking means operative on a respective interlock member when the second cam has been moved into the disconnector "Earth" position, and the first cam has been moved into the circuit breaker "Closed" position, so as to prevent tripping of the circuit breaker.

8. An interlock mechanism according to Claim 7 wherein the locking means is also operative to prevent the return of the first cam into the circuit breaker "Open" position.

9. An interlock mechanism for switchgear of the kind referred to substantially as shown in and as hereinbefore described with reference to Figures 1 to 7 of the accompanying drawings.

10. Switchgear incorporating an interlock mechanism according to any preceding Claim.