GB1572589A

GB1572589A - Electrical connections in or associated with metal clad electrical sub stations

Info

Publication number: GB1572589A
Application number: GB432578A
Authority: GB
Original assignee: Pirelli General Cable Works Ltd; Pirelli General Cable Works
Current assignee: Pirelli General Cable Works Ltd; Pirelli General Cable Works
Priority date: 1978-02-02
Filing date: 1978-02-02
Publication date: 1980-07-30

Description

(54) ELECTRICAL CONNECTIONS IN OR ASSOCIATED WITH METAL CLAD ELECTRICAL SUB STATIONS (71) We, PIRELLI GENERAL CABLE WORKS LIMITED, a British Company of Thavies Inn House, 3-4 Holborn Circus, London EC2N 2QA, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed to be particularly described in and by the following statement: - This invention relates to electrical connections in or associated with metal clad electrical sub stations.

Developments in electrical sub stations in recent years have included the use of electro-negative insulating gas such as sulphur hexafloride (SAG) to fill metal enclosures which house electrical switchgear.

Electrical connections are necessary between different parts of the sub station, for example to a transformer or to an incoming cable or to an air-insulated bushing for connection to an overhead line. Sometimes these connections are 10 metres or more in length and in the past have been made by extensions of rigid busbars used in the construction of the metal clad sub station itself, or sometimes by oil-filled cables where this has proved cheaper (which is usually the case where the length exceeds 10 or 20 metres).

SF,, has also been used to fill metal cable boxes which are attached to transformers and contain electrical connections between incoming cables and the transformers.

There are disadvantages in bringing oilfilled cables into a sub station and in particular into the gas-filled metal enclosures themselves. Firstly, there is the increased risk of fire, by reason of the presence of the cable oil, and secondly there is the risk of gas from within the metal enclosures diffusing into the oil of the cable.

According to this invention, there is provided an electrical connection associated with a metal clad electrical sub station, said electrical connection comprising a gas-filled cable having one end connected by a stop joint to an oil-filled cable and its other end entering a gas-filled metal enclosure of the sub station and connected to an electrical installation therein.

This invention also provides an electrical connection in a metal clad electrical sub station, said electrical connection comprise ing a gas-filled cable having its opposite ends entering respective gas-filled metal enclosures of the sub station and connected to electrical installations therein.

The gas-filled metal enclosure which the gas-filled cable enters may house electrical switchgear or it may comprise the gas-filled metal cable box of a transformer.

With said electrical connection in asset ciated with the metal clad sub-station, there is no risk of gas diffusing into the cable oil and the oil-filled cable may terminate sufficiently far from the gas-filled enclosures to avoid the risk of fire from the oilfilled cable itself.

Within the gas-filled enclosure, the gasfilled cable is electrically connected to a conductor of the housed installation, and the termination of this end of the gas-filled cable need be completed only by a stress control member.

Within the stop joint, the insulation on the gas cable side need comprise only the gas itself.

Embodiments of this invention will now be described by way of examples only, with reference to the accompanying drawings, in which: Figure 1 shows a termination of a gasfilled cable within a metal enclosure; Figure 2 shows an alternative termination within a metal enclosure; and Figure 3 shows a stop joint between an oil-filled cable and a gas-filled cable.

In one embodiment of electrical connection in accordance with this invention, as sociated with a metal clad sub station a gas-filled cable has one end connected by a stop joint to an oil-filled cable. The other end of the gas-filled cable enters a gasfilled metal enclosure of the sub station and is connected to an electrical installation therein.

Figure 1 shows an end of a flexible gasfilled cable 1 entering a gas-filled metal enclosure 2, housing electrical switch gear.

The cable comprises a standard conductor 3, an extruded insulation 4, for example of ethylene propylene rubber (EPR) or crosslinked polyethylene, and a metal sheath 5, shown as corrugated aluminium but alternatively reinforced lead. The cable also comprises inner and outer screening layers bonded to the inner and outer surfaces of the insulation, of which the outer screening layer is shown at 6. An outer protective jacket (not shown) is applied over the metal sheath to protect against corrosion.

The metal sheath is filled with electronegative gas, preferably SF6, under pressure and in time this gas permeats the insulation and screening layers.

The cable sheath is secured and sealed to the metal enclosure, around an aperture through which the cable enters the enclosure, by a wiped joint 7. The cable conductor 3 is secured to a bus-bar 8 of the housed electrical switchgear and a stress shield 9 concentrically surrounds the conductor 3 and bus-bar 8 over their zone of connection. A simple metal trumpetshaped stress control shield 10 is applied over the insulation 4 and is connected to the cut-back outer screen 6. The enclosure 2 is filled with the same gas as the cable, the interior of the cable being in communication with the interior of the enclosure.

Referring to Figure 2, there is shown an alternative termination of the gas filled cable within the metal enclosure, wherein the simple metal trumpet-shaped stress control shield of Figure 1 is replaced by a moulded rubber stress cone which fits frictionally over the cable insulation and is provided with an appropriate surface 10a formed of semi-conducting rubber.

Referring now to Figure 3, the stop joint between gas-filled cable 1 and oilfilled cable 11 comprises a bushing 12 of insulating material, such as epoxy resin, cast about a metal connector 13. The conductors of the respective cables are secured directly to the opposite ends of the metal connector 13. The joint further comprises two casing halves 14, 15 which are sealed at their opposite ends to the bushing 12 and to the respective cable sheaths. Within the casing half 14 for the oil-filled cable, the insulation is remade by paper at 16 and this casing half is filled with cable oil. The casing half 15 for the gas-filled cable is filled with SF6 and no other insulation is needed. However, a stress shield 17 is disposed concentrically around the cable conductor and joint connector 13 at their zone of joining and a simple metal trumpetshaped stress cone 18 is fitted over the cable insulation and connected to the outer screen of the cable.

In practice, the stop joint will be installed underground a safe distance from the sub station. The gas-filled cable may connect either to a metal enclosure for switchgear, as shown in Figures 1 and 2, or to the gasfilled cable box of a transformer or other equipment.

Cables with extruded insulation are readily available for voltages of 132/150kV and the use of SF6 gas filling and metal sheath to exclude moisture allows higher stresses so that the gas-filled cables proposed should withstand at least 132kV and possibly up to 230-275kV.

In another embodiment of electrical connection in accordance with this invention, in a metal clad sub station, a gasfilled cable has its opposite ends entering respective gas-filled metal enclosures of the sub-station and connected to electrical installations therein.

WHAT WE CLAIM IS: 1. An electrical connection associated with a metal clad electrical sub station, said electrical connection comprising a gasfilled cable having one end connected by a stop joint to an oil-filled cable and its other end entering a gas-filled metal enclosure of the sub station and connected to an electrical installation therein.

2. An electrical connection in a metal clad electrical sub-station, said electrical connection comprising a gas-filled cable having its opposite ends entering respective gas-filled metal enclosures of the substation and connected to electrical installations therein.

3. An electrical connection as claimed in claim 1 or 2, in which the or each cable end entering a metal enclosure is provided with a stress control member.

4. An electrical connection as claimed in any preceding claim, in which the gasfilled cable comprises a conductor having extruded insulation and a metal sheath filled with the gas under pressure.

5. An electrical connection as claimed in claim 4, in which the gas filled cable comprises an outer screening layer bonded to the insulation.

6. An electrical connection as claimed in claim 1 or any one of claims 3 to 5 appended to claim 1, comprising a connector to the opposite ends of which are connected the respective cable conductors, the insu

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. sociated with a metal clad sub station a gas-filled cable has one end connected by a stop joint to an oil-filled cable. The other end of the gas-filled cable enters a gasfilled metal enclosure of the sub station and is connected to an electrical installation therein. Figure 1 shows an end of a flexible gasfilled cable 1 entering a gas-filled metal enclosure 2, housing electrical switch gear. The cable comprises a standard conductor 3, an extruded insulation 4, for example of ethylene propylene rubber (EPR) or crosslinked polyethylene, and a metal sheath 5, shown as corrugated aluminium but alternatively reinforced lead. The cable also comprises inner and outer screening layers bonded to the inner and outer surfaces of the insulation, of which the outer screening layer is shown at 6. An outer protective jacket (not shown) is applied over the metal sheath to protect against corrosion. The metal sheath is filled with electronegative gas, preferably SF6, under pressure and in time this gas permeats the insulation and screening layers. The cable sheath is secured and sealed to the metal enclosure, around an aperture through which the cable enters the enclosure, by a wiped joint 7. The cable conductor 3 is secured to a bus-bar 8 of the housed electrical switchgear and a stress shield 9 concentrically surrounds the conductor 3 and bus-bar 8 over their zone of connection. A simple metal trumpetshaped stress control shield 10 is applied over the insulation 4 and is connected to the cut-back outer screen 6. The enclosure 2 is filled with the same gas as the cable, the interior of the cable being in communication with the interior of the enclosure. Referring to Figure 2, there is shown an alternative termination of the gas filled cable within the metal enclosure, wherein the simple metal trumpet-shaped stress control shield of Figure 1 is replaced by a moulded rubber stress cone which fits frictionally over the cable insulation and is provided with an appropriate surface 10a formed of semi-conducting rubber. Referring now to Figure 3, the stop joint between gas-filled cable 1 and oilfilled cable 11 comprises a bushing 12 of insulating material, such as epoxy resin, cast about a metal connector 13. The conductors of the respective cables are secured directly to the opposite ends of the metal connector 13. The joint further comprises two casing halves 14, 15 which are sealed at their opposite ends to the bushing 12 and to the respective cable sheaths. Within the casing half 14 for the oil-filled cable, the insulation is remade by paper at 16 and this casing half is filled with cable oil. The casing half 15 for the gas-filled cable is filled with SF6 and no other insulation is needed. However, a stress shield 17 is disposed concentrically around the cable conductor and joint connector 13 at their zone of joining and a simple metal trumpetshaped stress cone 18 is fitted over the cable insulation and connected to the outer screen of the cable. In practice, the stop joint will be installed underground a safe distance from the sub station. The gas-filled cable may connect either to a metal enclosure for switchgear, as shown in Figures 1 and 2, or to the gasfilled cable box of a transformer or other equipment. Cables with extruded insulation are readily available for voltages of 132/150kV and the use of SF6 gas filling and metal sheath to exclude moisture allows higher stresses so that the gas-filled cables proposed should withstand at least 132kV and possibly up to 230-275kV. In another embodiment of electrical connection in accordance with this invention, in a metal clad sub station, a gasfilled cable has its opposite ends entering respective gas-filled metal enclosures of the sub-station and connected to electrical installations therein. WHAT WE CLAIM IS:

1. An electrical connection associated with a metal clad electrical sub station, said electrical connection comprising a gasfilled cable having one end connected by a stop joint to an oil-filled cable and its other end entering a gas-filled metal enclosure of the sub station and connected to an electrical installation therein.

lation in the joint for the gas-filled cable comprising the gas alone.

7. An electrical connection substantially as herein described with reference to the accompanying drawings.