GB2107527A

GB2107527A - Take off cabinets for distribution transformers

Info

Publication number: GB2107527A
Application number: GB08224714A
Authority: GB
Inventors: John Denis Cullen
Original assignee: Associated Electrical Industries Ltd
Current assignee: Associated Electrical Industries Ltd
Priority date: 1981-10-07
Filing date: 1982-08-27
Publication date: 1983-04-27
Also published as: GB2107527B

Abstract

A transformer take-off cabinet (2) for use with a power distribution transformer having load break moulded connectors (21, 24) for connecting the transformer to a high voltage electrical supply, has a low voltage distribution unit (13), and fuse links (14) connecting the transformer output terminals to an off-load disconnector located in separate chambers (7, 9) only accessible through respective doors (8, 12), the door (12) to the fuse link chamber (9) being openable only after disconnection of all the associated load break connectors (21, 24) whence a key can be reached which enables a lock (17) of the door (12) to be released. <IMAGE>

Description

SPECIFICATION Distribution transformers and take off cabinets therefor This invention relates to power distribution transformers, and more especially to cabinets, known generally as transformer take off cabinets, which are attachable to the tanks of such transformers.

A transformer take off cabinet, as at present constructed, accommodates a low voltage (LV) distribution unit having a plurality of fused disconnectors energised through bus-bars from the output windings of the transformer to which it is attached, via an off-load disconnector, the fused disconnectors providing protection and a means of isolating the out-going distribution cables.

The present practice is for protection of the transformer, the LV disconnectors and LV busbars to be provided by high voltage oil fuse links accommodated in a HV oil fuse switch on the supply side of the transformer.

Moulded connectors having a suitably high make and break facility have recently been developed, but because these load break connectors do not provide fuse protection for personnel working on the distribution unit they do not provide a satisfactory alternative to the oil fuse switches on distribution transformers employing conventional take off cabinets.

According, therefore to the present ivention, a transformer take off cabinet for use with a power distribution transformer having load break moulded connectors for connecting the transformer to a high voltage electrical supply, has a first chamber accommodating a low voltage distribution unit accessible through a first door, and a second chamber accommodating low voltage fuse links between the transformer output terminals and corresponding terminals of the off-load disconnector, the second chamber being accessible only through a second door, and the second door being openable only after disconnection of all the associated load break connectors.

In such an arrangement personnel working on the LV distribution unit will be protected by the fuse links which are contained in a separate restricted chamber which can be fully insulated from the distribution unit chamber Furthermore access to the restricted second chamber can only be achieved when the load break connectors have been disconnected from the transformer, and conductors within the chamber are no longer "live".

The cabinet may be associated with an interlock system which prevents opening of the second door until disconnection of all the load break connectors.

Alternatively the second door may be securable in the closed position by a lock which is openable by a key which only becomes accessible on disconnection of the load break connectors. Means may be provided for preventing reconnection of the connectors until return of the key to its original position, the key being removable from the cabinet only when said second door is closed and locked.

The first door may be provided at the front of the cabinet as in known transformer take off cabinets, the second chamber being located above the first chamber and the second door being provided at the top of the cabinet, conveniently in the form of a hinged or removable roof.

One embodiment of the invention will now be described by way of example with reference to Figs 1 to 3 of the accompanying schematic drawings, in which Figure 1 represents diagrammatically and not to scale a front view, partly broken away, of a transformer take off cabinet in accordance with the invention, Figure 2 represents, also in diagrammatic form a sectional side view of the cabinet, and Figure 3 shows part of a transformer tank with the cabinet attached thereto.

Referring to the drawings, a transformer tank 1 has attached to it a sheet metal takeoff cabinet 2 incorporating, in known manner, a distribution unit 3 carrying a plurality of fused disconnectors 4, only some of which are shown, connected to respective bus-bars 5 through an off-load disconnector 6.

The distribution unit 3 is housed within a chamber 7 of the cabinet, accessible through a door 8 at the front of the cabinet.

At the top of the cabinet there is located a further chamber 9 having an instrument panel 10 at the front and separated from the distribution unit chamber 7 by an insulating partition 11, the second chamber 9 being accessible only through the top of the cabinet, after swinging back the roof 12, and removal of a vent screen 1 3.

The upper chamber 9 houses three low voltage fuse links 14, one for each phase of the supply, connected to respective bus-bars 5 passing downwards at the rear of the chamber 7 to the off-load disconnector 6. The other end of the fuse links 1 4 are connected to respective low voltage output terminals 1 5 of the transformer through further bus-bars 16.

The roof 1 2 is normally locked in the closed position by any suitable form of lock, represented diagrammatically at 1 7 openable only by a special key (not shown).

This is normally housed in a repository as at 19 (Fig. 3) which is only accessible when the removable parts 21 of all three moulded load break connectors, at the terminations of the high voltage supply cables 23 are removed from the fixed parts 24 of the disconnectors forming the high voltage terminals of the transformer, to completely de-energise the transformer.

The fuse links 14 to provide protection for personnel having access to all equipment housed within the chamber 7, for example when working on the LV distribution unit 3 which is housed within it, and as the fuse links are contained in a separate chamber 9 fully insulated from the chamber 7 the risk of accidental contact with any "live" conductors on the transformer side of the fuse links is virtually avoided.

The repository 1 9 for the key may be such that the removable parts 21 of the load break connectors can only be replaced when the key 18 is returned to the repository, and conveniently in such a case the key is only removable from the take-off cabinet 2 when the roof 1 2 of the cabinet has been closed and locked.

Instead of the lock and key, the cabinet 2 and load break connectors may be associated with an interlock system which, with the connectors in position, prevents the roof from being opened so as to enable access to the chamber 9 to be obtained only on disconnection of the connectors.

Claims

1. A transformer take off cabinet for use with a power distribution transformer having load break moulded connectors for connecting the transformer to a high voltage electrical supply, said cabinet having a first chamber accommodating a low voltage distribution unit accessible through a first door, and a second chamber accommodating low voltage fuse links between the transformer output terminals and corresponding terminals of the offload disconnector, the second chamber being accessible only through a second door, and the second door being openable only after disconnection of all the associated load break connectors.

2. A transformer take off cabinet according to Claim 1 having associated with it an inter-lock system which prevents opening of the second door until disconnection of all the load break connectors.

3. A transformer take off cabinet according to Claim 1 wherein the second door is securable in the closed position by a lock which is openable by a key which only becomes accessible on disconnection of the load break connectors.

4. A transformer take off cabinet according to Claim 3 including means for preventing reconnection of the connectors until return of the key to its original position, the key being removable from the cabinet only when said second door is closed and locked.

5. A transformer take off cabinet according to any preceding Claim wherein the first door is disposed at the front of the cabinet, the second chamber is located above the first chamber and the second door is disposed at the top of the cabinet.

6. A transformer take off cabinet according to Claim 5 wherein the second door comprises a hinged or removable roof panel.

7. A transformer take off cabinet substantially as shown in and as hereinbefore described with reference to Figs 1 and 3 of the accompanying drawings.

8. A transformer having a take off cabinet according to any preceding Claim.