GB2316239A - Converting pole mounted transformers into pad mounted transformers - Google Patents

Abstract

A ground or pad mounted transformer device 110 comprises a transformer housing and a transformer from a pole mounting arrangement 105. The housing contains a liquid and at least one opening into which is inserted a conductive connection and an insulating bushing. One end of said connection is linked to the transformer whilst the other end is linked to a supply cable via a fuse. A method of deriving such a transformer device is also disclosed. Drainage of the said liquid (possibly a cooling oil) to a level below the opening in the housing before the installation of the connection and insulation bushing, which is arranged to seal the said opening, may be involved in said method. The fuse may be housed separately from the transformer or may be arranged to be inserted within the insulating bushing of the transformer.

Description

Title: CONVERTING POLE MOUNTABLE TRANSFORMERS The present invention relates to converting pole mountable type transformer assemblies wherein said assemblies inciude a transformer unit and a housing arranged to house said transformer unit in a liquid environment including an access aperture to allow said transfomer unit to be electrically connected to a supply cable.

INTRODUCTION It is known in the electrical supply industry to transmit electricity over relatively large distances at relatively high voltages. Over main distribution trunks, electricity may be distributed at one hundred and thirty two, sixty six, thirty three or eleven thousand volts, whereafter supply cables supply electricity to consumers at potentials in the hundreds of volts, usually with a three phase option or a single phase option.

When significant currents are required to satisfy high-power demand, relatively large transformers may be provided to give voltage reduction for supply cables. Such systems are usually mounted at ground level within housings thereby providing electrical insulation and denying casual access to internal components. Similarly, insulating assemblies are provided within the transformer housing so as to allow authorised access to the.

unit.

In addition to large transformer installations, it is sometimes necessary to install relatively small transformers so as to provide relatively remote locations, requiring relatively low power loads, to be connected to national distribution networks conveying electricity at relatively high voltages. Under these circumstances it is not possible to justify the expense of large ground mounted systems and in order to satisfy this demand, transformer systems have been designed which are suitable for mounting up poles. In this way, given that the transformer is placed at a position well away from casual traffic, the level of insulation provided on the transformer itself may be significantly reduced. In particular, noninsulated wires to the transformer may be employed.

Consequently, such transformers are only suitable for remote locations such as up poles, and special precautions must be taken when such devices are installed or are being modified.

Pole mounted transformers are becoming less attractive for many reasons. Firstly, the cost of maintaining these transformers is relatively large, given the efforts that must be made to locate transformers up poles.

Secondiy, pole mounted transformers are now seen as less desirable from an environmental point of view and many organisations responsible for the installation and supply of electricity services are under pressure to replace pole mounted transformers with ground mounted equivalents. However, known ground mounted equivalents are significantly different from pole mounted transformers therefore when a replacement of this type needs to be made, existing pole mount technology effectively becomes redundant. However, in many situations, previously installed pole mounted transformers will include highly serviceable and, theoretically, reusable components, including the transformer windings themselves which, made of high grade copper, often constitute the highest value component of the assembly as a whole.

SUMMARY OF THE INVENTION According to a first aspect of the present invention, there is provided a method of converting a pole mountable type transformer, wherein said transformer includes a transformer unit and a housing arranged house said transformer unit in a liquid environment, including access holes to allow said transformer unit to be electrically connected to a supply cable, comprising steps of removing said liquid from said housing to the level of said access hole; inserting sealingly connectable insulating means, wherein said insulating means has an internal terminal contact connectable to said transformer unit and an external terminal; inserting a fuse into a fuse mounting, wherein said fuse has a first terminal and a second terminal; connecting said external terminal to said first terminal; and connecting said second terminal to said supply cable, whereafter said transformer is suitable for use as a pad mountable type transformer for application at ground level.

In a preferred embodiment, a pole mounted transformer is removed from a pole and cooling oil is partially drained therefrom.

Preferably, the sealingly connectable insulating means are inserted within the housing after ceramic insulating means have been removed therefrom.

According to a second aspect of the present invention there is provided a ground mounted transformer arranged to supply electricity via supply cables comprising a transformer unit; a housing arranged to house said transformer unit in a liquid environment; insulating means inserted within an aperture provided within said housing, having internal terminal contacts connected to said transformer unit and external terminal contacts; and fuses electrically connected between said external terminal and said supply cable, wherein said transformer unit and said housing are modified pole mounted units previously having noninsulated and non-fused primary connections.

The fuses may be retained in a separate housing connectable to the transformer unit by insulating means.

However, in a preferred embodiment, the fuses are supported by the insulating means. The insulating means may comprise a first block insertable within the housing and a block extension for providing space or the fuses. Consequently, the size of the extension may be varied to accommodate fuses of varying lengths.

Preferably, the fuses connect to bushing wells which may in turn connect with load break or dead break connectors.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 shows an installation where a transformer is provided to supply electricity to a remote location; Figure 2 details the transformer shown in Figure 1; Figure 3 shows an alternative embodiment to the transformer shown in Figure 2, including a sub-assembly for receiving fuses; Figure 4 shows the transformer of Figure 3, with a cover applied to protect the sub-assembly shown in Figure 3; Figure 5 details the fuse sub-assembly identified in Figure 3, including fuses and a support for said fuses; and Figure 6 details the fuses and fuse supports identified in Figure 5.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention will now be described by way of example only with reference to the previously identified drawings. A remote farm house 101 is shown in Figure 1, to which a three phase electrical supply at 415 volts is provided from a national distribution grid. Electricity to the farm house 101 is presently being supplied by overhead distribution cables 102 arranged to supply a voltage of eleven kilo volts (11KV) to a step-down transformer, which in turn provides the application power via underground supply cables 103.

The overhead cables 102 are not insulated, primarily so as to provide air cooling, resulting in non insulated input lines 104 being supplied to a step-down transformer 105. Cables 104 are shielded from a metal housing of transformer 105 via ceramic insulators 106 and the whole assembly is mounted on poles 108, by means of supports 107.

For the purposes of this example, it is assumed that transformer 105 is to be replaced with a ground mounted assembly and examples of ground mounted transformers are shown at 109 and 110.

Transformer 109 is a conventional three phase compartmental type pad ground mounted transformer of the type supplied by Cooper Power Systems. The transformer provides many advantages over the existing pole mount transformer, particularly in terms of it's versatility and safety. Unlike the pole mount transformer presently in place, the pad mount transformer may be isolated from the mains supply to facilitate reconfiguration of the transmission lines. Furthermore, transformer 109 includes substantially more isolating assemblies such that modifications may be made in safety without technicians being presented with live non-insulated cables etc.

However, as an alternative to the provision of a pad mount transformer 109, the particular installation shown in Figure 1 is to be replaced with a modified pole mount transformer, similar to pole mount transformer 105.

Pad mount transformer 110 has been converted from a pole mount transformer, substantially similar to pole mount transformer 105. The conversion process allows a pole mountable type transformer (105) to be converted into a pad ground mountable type transformer (110) for application at ground level. The pole mountable transformer includes a transformer unit and a housing arranged to house the transformer in a liquid environment, usually oil, so as to facilitate transformer cooling. The housing includes an access aperture to allow the transformer unit to be electrically connected to high voltage input cables. The procedure is particular suitable for converting pole mounted transformers identified as ESI 35-1 in the United Kingdom.

A conversion process would be initiated by the existing transformer being removed from the pole, such as pole 108.

Using established techniques for making modifications to live transmission wires, input cables 107 are severed and the pole mounted transformer is removed from it's mount, whereafter modifications may be made to the pole or, preferably, total removal of the pole may be effected. If a pole is retained, insulating cables are attached to the live transmission cables so as to provide input cables to the ground mounted system.

After removal from the pole, oil from the transformer hosing is removed, to the level of the access aperture. The ceramic insulating members are then removed so as to allow an insulating connecting means to be inserted into the orifices. The insulating member includes an internal terminal which is in turn connected to the transformer primary windings. A fuse is inserted into a fuse mounting and the external terminal of the insulating means is electrically connected to a first terminal of said fuse. Thereafter, a second terminal of the fuse is connected to a high voltage input cable 103.

In this way, the modified transformer, derived essentially from an existing pole mounted transformer, is modified so as to ensure that insulating connections are provided to the transformer inputs. Furthermore, the system includes fuses so as to ensure that overload protection is providedfor the primary input side of the transformer.

Pole mounted transformers are typically arranged to provide electrical energy rated at between sixteen to two hundred kilo volt-amps (kVA), while known ground mounted transformers are usually rated at between three hundred to one thousand kVA. A modification of the type identified above, allows a pole mounted transformer to be converted, thereby facilitating ground mounted installations of relatively smaller systems.

Transformer assembly 110 is detailed in Figure 2. Ceramic bushings 106 have been replaced by load break bushings 201, configured to receive load break elbow connectors 202. Insulated cables 203 connect load break connectors 202 to similar connectors 204, configured within a fuse mounting box 205.

High voltage input cables 206 are received by fuse assembly box 205 via connectors 207, similar to connectors 204.

In this way, electrical input power is supplied to the transformer 109 via the fuse assembly 205, allowing protected high voltage power to be directed into the transformer housing via connectors 202. Output supply cables 208 supply power to a consumer, such as 101, from the secondary winding of the transformer, as is known in the art. The transformer housing contains oil and the oil level may be inspected via an inspection gauge 209.

An alternative embodiment is shown in Figure 3 in which a transformer housing 301, similar to housing 109, is modified, to accommodate a conversion assembly 302 supported directly by the housing 301. A conversion aperture is cut within the housing 301 and connection pins extending from the conversion assembly 302 are strapped to the primary winding of the transformer unit.

The conversion assembly 302 includes bushing connectors 303 arranged to connect with load break elbow connectors 304 which in turn receive input power through insulated cables 305.

Transformed electricity is then supplied to supply cables substantially similar to those shown in Figure 2.

The example detailed above, load break bushings and elbow connectors have been specified. These allow the system to be disconnected while under load. In an alternative embodiment, dead break devices may be employed, primarily designed for systems where disconnection and reconnection will only take place when the transformer is not loaded.

During transportation of the transformer unit shown in Figure 3, the exposed bushings 303 are protected by a bushing cover 401 and a padlock 402. At arrival on site, the bushing cover 401 is removed and the input power cables are connected to bushings 303 as shown in Figure 3. Assemblies similar to conversion assembly 303 are employed in the arrangement shown in Figure 2, each arrangement ensuring that the protection fuses are located in line with the input power lines, before input voltages are applied to the primary windings of the transformer.

Conversion assembly 302 is detailed in Figure 5. The assembly is inserted through conversion aperture 501 of the transformer housing, is reinforced by a reinforcing web 502 having a plurality of threaded studs 503 extending therefrom.

A moulded support 504 or "monoblock" is received within conversion aperture 501 having connector pins 505 extending on both sides of the base wall of the moulded support and sealed therein to prevent the escape of oil from within the transformer housing. The inner end of pin 505 is provided with a screw thread allowing the pin to secure a connection strap, the opposite end of which is connected to a phase connection of the primary winding of the transformer. The outer end of pin 505, on the inside of the moulding, is chamfered.

The arrangement is substantially similar to the connector arrangement described in United Kingdom Patent Publication 2 252 682. The moulded support is formed from an electrically insulating material such as fibreglass reinforced epoxy resin, and is provided with a total of three pins for each of the three phases.

Pins 505 are arranged to electrically connect with respective high voltage fuses, such as type OEFN59 supplied by Cooper Bussmann. These fuses typically have an outer diameter of 75mm and a total length, including connection pins, of 360mm. A first connection pin 507 of fuse 506 is arranged to be electrically connected to pin 505. Connection pin 505 includes four blades 508 each spring loaded by a respective spring such that the blades 508 are displaced outwardly, against the action of their respective springs, as they engage with connecting pins 507 of fuses 506.

Moulded support 504 includes a restraining flange 509 having holes 510 therein engageable with studs 502. In order to ensure that an oil-tight seal is provided between the conversion aperture and the restraining flange, a sealing gasket 511 is located over studs 502, whereafter flange 510 is secured to said studs via nuts 512. Each hole 510 includes a recess so as to ensure that nuts 510 do not protrude beyond the surface flange 509, thereby providing a flush surface for receiving a second sealing gasket 513.

Moulded support 504 is received within the transformer housing and secured to studs 502. Given the length of available high voltage fuses, such as fuse 506, it is not possible to retain the whole of the fuse within the housing, therefore it is necessary for part of the fuse to extend beyond the housing and be supported by an appropriate sub assembly.

The total length of fuses 506 are accommodated by means of a support extension 514 arranged to be secured to restraining flange 509 by means of bolts 515, which engage through holes 516 of a support extension flange 518. The support extension 514 includes three fuse support apertures 519, arranged to line up with similar aperture within the moulded support 504. These apertures are formed within a support extension block 520, extending from the support extension flange 517, the depth of which may be modified to accommodate larger fuses. For example, fuses having a rating in excess of eighty amps will require a deeper support extension block.

The fuses 506 are restrained within apertures 519 by means of bushing wells 521, such as type 800-35 supplied by Cooper Power Systems. Each bushing well 521 is arranged to receive a respective load break bushing 522, such as type 800-36 supplied by Cooper Power Systems. These load break bushings 522 are connectable to respective load break elbow connectors, such as type 500-10 supplied by Cooper Power Systems.

The load break elbow connectors 523 are fully shielded plug-in termination's which may be attached to or removed from load brake bushings 522 while the transformer input is live. In this way, modifications may be made to the transformer assembly, in terms of its connection to input sources and supply cables, without disrupting operation of the remaining network. The rear face of extension flange 518, which communicates with gasket 513, and identified by arrow 524, is detailed in Figure 6. The fuses 506 are restrained within insulating covers 601 and supported by bushing wells 521.

Claims (12)

1. A method of converting a pole mountable type transformer, wherein said transformer includes a transformer unit and a housing arranged to house said transformer unit in a liquid environment, including access holes to allow said transformer unit to be electrically connected to a supply cable, comprising steps of removing said liquid from said housing to the level of said access holes; inserting sealingly connectable insulating means, wherein said insulating means has an internal terminal contact connectable to said transformer unit and an external terminal; inserting a fuse into a fuse mounting, wherein said fuse has a first terminal and second terminal; connecting said external terminal to said first terminal; and connecting said second terminal to said supply cable, whereafter said transformer may be used as a pad-mountable type transformer for application at ground level.

2. A method according to claim 1, wherein a pole mounted transformer is removed from a pole and cooling oil is partially drained therefrom.

3. A method according to claim 2, wherein said sealingly connectable insulating means are inserted within said housing after ceramic insulating means have been removed therefrom.

4. A ground mounted transformer arranged to supply electricity via supply cables, comprising a transformer unit; a housing arrange to house said transformer unit in a liquid environment; insulating means inserted within an aperture provided within said housing, having internal terminal contacts connected to said transformer unit and extemal terminal contacts; and a fuse electrically connected between said external terminal and said supply cable, wherein said transformer unit and said housing are modified pole mounted units previously having noninsulated and non-fused primary connections.

5. Apparatus according to claim 4, wherein said fuses are retained in a separate housing connectable to said transformer unit via said insulating means.

6. Apparatus according to claim 4, wherein said fuses are mechanically supported by said insulating means.

7. Apparatus according to claim 6, wherein said insulating means comprises a first block insertable within said housing and a block extension to provide space for said fuses.

8. Apparatus according to claim 7, wherein the size of said extension is variable to accommodate fuses of varying length.

9. Apparatus according to claim 8, wherein said fuses connect to bushing wells.

10. Apparatus according to claim 9, wherein said bushing wells receive bushes which in turn connect with load break or dead break connectors.

11. A method of converting a pole mountable type transformer substantially as herein described with reference to the accompanying drawings.

12. A ground mounted transformer substantially as herein described with reference to Figures 2 or Figures 3 to 6.