GB2326028A - A transformer housing with a ventilated base arrangement - Google Patents

Abstract

A housing for an electrical distribution transformer comprises a ventilation arrangement to the atmosphere via a base which includes a grid arrangement 201 with apertures 202 and a supporting framework 203, 204. The supporting framework 203, 204 also supports the remaining housing enclosure members. The aperture grid arrangement 201 may be formed by an array of conventional moulded plastic fork-lift pallets supported above ground level by the framework 203, 204. A plastic flooring grid 205 made from polyester reinforced with glass fibre may be applied to the base. The transformer housing may provide a cheap ground level substation which is secure and explosion proof.

Description

HOUSING FOR POWER TRANSFORMERS The present invention relates to housings for electrical power transformers, configured to allow high voltage devices to be housed in ambient conditions.

Introduction As is well known in the art, it is preferable to transfer electrical power at high voltage so as to minimise losses through electrical resistance. These voltages are far higher than those required for domestic and industrial applications, therefore at various stages throughout the distribution of electrical power it is necessary to transform the voltage to more acceptable levels.

The provision of high voltage transformers requires these transformers to be located throughout the country and, particularly in rural applications, a relatively small-sized installation may be required to supply electricity at consumer voltages. This results in transformer substations being located in ambient conditions which, being required to receive high voltage supplies, need to be located in such a way as to reduce the risk of accidental or intentional third party interference.

In order to avoid interference, it is known to locate transformers at positions above ground level, possibly supported on poles. This does not provide a satisfactory solution for large installations and, increasingly, even smaller installations are becoming considered as unsightly and therefore undesirable. Consequently, if supported at ground level, it is necessary to locate transformers and similar installations within enclosed housings.

A problem with locating transformer installations within enclosed housings is that faults may occur to high voltage devices, resulting in the build-up of pressure. Pressure may be relieved by the provision of ventilation systems but this in itself can create problems because the provision of ventilators will tend to reduce the physical integrity of the housing itself, thereby increasing the likelihood of intrusion or vandalism. A further solution has been proposed in which the roofs of housings are configured to rise under the influence of pressure, thereby allowing gaseous build-ups to be released without damaging the overall integrity of the design. Thus, it is known that if high voltage devices are placed within an airtight sealed enclosure or within an enclosure having insufficient ventilation, it is possible, under fault conditions during which gases build-up, for the intemal pressure to cause physical failure of the system which, given the dangerous nature of the design, would have serious detrimental effects.

The build-up of gases during the failure of substations has been considered by Dr Bill Baker, ex-head of research of the Electricity Council Research Centre in Capenhurst, UK. Dr Baker has evaluated that the failure of a cable box has three aspects to be considered, namely the development of an arc as a heat source, a pressure rise due this heating and the relief of pressure through the exhausting of hot air.

A fault in a cable box starts as an insulation failure with a fault current constrained within the solid insulating material. Quickly, the insulation is violated and an arc forms in free air. If unconstrained, as on an overhead line for example, the arc would extend in length until the available voltage is insufficient to maintain it and the arc is then extinguished. The arc length at this stage, just before extinction, would be larger than 2 metres at 11 kilovolts. Consequently, this extinction does not take place when constrained by a cable box, where the arc is unlikely to extend beyond 100 mm.

Initially, the arc will bum in ionised air, with a voltage drop along the arc path of about 3 volts per millimetre. During this early stage the current is high and the electrodes will be eroded resulting in the arc roots being filled with metal ions. Each kiloamp-second liberates more than 1 millimetre of solid metal and the resulting high density of metal ions reduces the arc voltage to about one volt per millimetre. The exhaust of hot gas from the substation also reduces the number of air molecules thereby increasing the mean free path of ions in the arc which in tum reduces the voltage drop along the arc.

An arc, assumed to be 100 mm long, exhibits a voltage drop of typically 300 volts. Additionally, voltage drops will occur at the cathode and anode, totalling 25 to 30 volts. Thus, with an arc current typically in the region of 13 kiloamps, a total arc power dissipation in excess of 3.5 megawatts is obtained.

The 3.5 megawatts of power are dissipated within the enclosure, typically containing about 8 m3 of air. This results in a pressure increase and it has been calculated that the pressure will increase by an additional 0.5 atmospheres. Unless this pressure is relieved sufficiently quickly, it will impact upon the housing walls and may lead to catastrophic failure.

Summary of the Invention According to a first aspect of the present invention, there is provided a housing for an electrical power transformer, configured to allow high voltage devices to be housed in ambient conditions, comprising an array of moulded base sections defining a support grid and having a plurality of base apertures; a frame for supporting said grid above ground level and for supporting an enclosure while defining ventilation apertures below said base sections, such that any gases created by devices contained within said housing are vented to atmosphere via said apertures and said ventilation apertures.

In a preferred embodiment, the base sections are fabricated from moulded plastic which may in tum take the form of conventional plastic pallets, designed for co-operation with fork-lift trucks, thereby significantly reducing the overall cost of the design.

Preferably, a plastic flooring grid is applied to the base sections and said flooring grid may be fabricated from polyester reinforced with glass fibre.

Brief Description of the Drawings Figure 1 shows a known housing for transformer substations; Figure 2 shows components of a transformer housing embodying the present invention; Figure 3 shows the components identified in Figure 2 assembled to form the housing base, with switchgear components supported thereon in addition to an external frame; and, Figure 4 illustrates the extemal walls of the housing supported by the interior structure shown in Figure 3.

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 known substation housing is shown in Figure 1, which has been built onto a concrete base after being prefabricated off-site. The housing is supported by a steel framework and electrical equipment contained therein may comprise a distribution transformer, an electrical switch and a low voltage distribution fusepillar. The possible combination of components is large and a particular solution will depend upon customer requirements.

The use of a mild steel frame results in a time consuming construction process and tend to be customised for particular transformer and associated equipment's requirements. As a result of this, there is a considerable overhead in terms of drawing office resource and a relatively large shop floor area is required at the factory in order to perform the off-site assembly process.

The housing assembly shown in Figure 1 has two mechanisms to alleviate the problems caused by the potential of pressure, as previously outlined. Firstly, the housing is provided with a ventilation grille 301, allowing a flow of air therethrough so as to maintain pressure equilibrium between the inside and the outside of the housing. The problem with ventilation grilles, as previously identified, is that they tend to reduce the overall security of the design and encourage vandalism. Consequently, if grilles are provided, they tend to be relatively small and therefore tend not to provide the required level of ventilation.

A second safety feature is built in to the device shown in Figure 1 in that roof components 302 are supported by piston type supports such that, during the build-up of gases within the enclosure, the roof is moveable to create a gap between the roof and the side walls, thereby relieving the buildup of pressure without jeopardising the integrity of the overall structure.

However, while such a feature provides a solution to the build-up of pressure within the enclosure, the overall cost of the arrangement is significantly increased which, in some circumstances, may lead to dangerous compromises being made.

The present invention provides a solution to this problem such that it is not necessary to fabricate structures with a piston type roof. Furthermore, the solution provided by the present invention actually reduces fabrication costs, both in terms of direct costs and also in terms of support costs incurred by factory resources.

Sub assemblies for a transformer housing embodying the present invention are illustrated in Figure 2. The base of the housing is configured as an array of moulded plastic base stations 201, preferably taking the form of conventional fork-lift type pallets. The pallets define a support grid having a plurality of base apertures 202.

In the arrangement shown in Figure 2, four pallets 201 are arranged in a two-by-two array upon a frame of welded mile steel angle ions 203. The welded frame has a plurality of cross supports 204 arranged to support the pallets in an array. Furthermore, the pallets are secured by bolts or similar mechanisms to the welded frame so as to retain them secure in place.

The pallets are relatively light and, by their very nature, are easily manoeuvred, even when fabricated together, by a fork-lift truck or similar device. Thus, the requirement for expensive lifting machinery, such as cranes etc, is significantly reduced thereby reducing the operating cost of factory units.

Pallets are easily integrated with tow-bar facilities for further ease of manoeuvrability either on-site or at a factory. The reduction in the weight of component parts also reduces the overall weight of the resulting substation, thereby again reducing transportation and delivery costs to site.

The pallet bases are supported in such a way as to allow the escape of pressure and possibly combustible gases downwards through the base apertures and through co-operating apertures in the lower portion of the side walls, thereby providing an integral ventilation system which is considered adequate for all transformer capacities upto a total of 15 kva.

Conventional plastic pallets, in combination with the mild steel frame shown in Figure 2, are each capable of supporting a static load of 5 tonnes.

Conventional substation equipment should not exceed a total of 3 tonnes applied to any one pallet with a typical weight of upto 10 tonnes being distributed over a plurality of pallets. All types of equipment may be supported by the pallets and it is envisaged that they will be appropriate for some equipment which is not presently suitable for concrete bases. The assembly facilitates a "just in time" approach in that the overall design is relatively modular, standardised and quickly realised.

The base provided by the pallet surfaces is enhance by the addition of grid-like flooring material 205. Polyester reinforced glass fibre flooring is preferred, such as that sold by Alligrid in the United Kingdom. Alligrid flooring again consists of a plurality of apertures defined in a grid which in tum cooperate with the base apertures defined within the pallet. Thus, the Alligrid flooring provides a uniform mounting surface while at the same time continuing to allow ventilation through the base.

Once the flooring panels 205 have been mounted onto the pallet supports 201, the transformer 301 and switchgear 302, 303 may be secured thereon as shown in Figure 3. In addition, wall supports 304 and roof supports 305 are added, onto which solid metal panels possibly corrugated, may be attached thereto, as shown in Figure 4.

The housing of Figure 4 does not require a side wall ventilator, as required by the housing of Figure 1 and neither does it require a piston supported roof.

The housing is raised at its four comers 401, so as to provide a free area 402 undemeath the housing. This free area has a mesh panel extending below the housing walls so as to prevent large objects and intruders entering below the housing floor. Thus, the wall panels define ventilation apertures through the mesh panel which in tum allow gases escaping through the base panels to further escape to atmosphere.

The expanded mesh panel 403 does not require the same level of mechanical integrity as, say, the ventilator provided in the housing wall shown in Figure1. The ventilator shown in Figure 1 provides direct access to the housing enclosure. However, the expanded mesh panel shown in Figure 4 merely provides access to a small region below the base of the transformer housing. Thus, if the physical integrity of the mesh is degraded, access into the operational components is still severely restricted by the base panels themselves.

It can be appreciated that the use of moulded base sections with apertures defined therein significantly reduces constnrction costs while allowing potentially dangerous gases to escape, while at the same time reducing the risk of third party intrusion.

Claims (5)

Claims

1. A housing for an electrical power transformer, configured to allow high voltage devices to be housed in ambient conditions, comprising an array of moulded base sections defining a support grid and having a plurality of base apertures; a frame for supporting said grid above ground level and for supporting an enclosure while defining ventilation apertures below said base sections, such that any gases created by devices contained within said housing are vented to atmosphere via said base apertures and said ventilation apertures.

2. A housing according to claim 1, wherein said base sections are fabricated from moulded plastic.

3. A housing according to claim 2, wherein said moulded plastic base sections are conventional plastic pallets, designed for co-operation with fork-lift trucks.

4. A housing according to any of claims 1 to 3, wherein a plastic flooring grid is applied to said base sections.

5. A housing according to claim 4, wherein said plastic flooring grid is fabricated from polyester reinforced with glass fibre.