WO1992010772A1

WO1992010772A1 - An arrangement for use with high voltage equipment

Info

Publication number: WO1992010772A1
Application number: PCT/GB1991/002196
Authority: WO
Inventors: Alan Duncan Atkins; Ray John Grimewood
Original assignee: Focas Ltd
Current assignee: Focas Ltd
Priority date: 1990-12-11
Filing date: 1991-12-11
Publication date: 1992-06-25
Anticipated expiration: 1993-06-11
Also published as: GB9026878D0; AU9047691A

Abstract

The present invention relates to an arrangement for use with high voltage equipment comprising a fibre optic cable (6) on which are located a high voltage electrode (13a) and a low voltage electrode (13b) wherein the fibre optic cable (6) constitutes an insulator thereby enabling connection of high voltage equipment to a point at lower voltage.

Description

AN ARRANGEMENT FOR USE WITH HIGH VOLTAGE EQUIPMENT

The present invention relates to an arrangement and method for use with high voltage equipment, in particular, an arrangement and method comprising fibre optic cables.

The demand for control of sensors and electronics which are situated at high voltage potentials has increased greatly. In the past, such control has been achieved by radio links and more recently by optical methods. By high voltage equipment is meant equipment rated at 1 kV or above and may be as high as 1000 kV. The use of fibre optic cables in association with high voltage conductors is already known. The first optical links comprised large porcelain housings filled with a fluid or semi-fluid substance through which the fibre optic passed from a high potential to a low potential. More recent developments have used composite insulator structures, i.e an insulator constructed with a grp core (a hollow or solid rod) with a polymeric sheath as an external covering. With such an arrangement the fibre optics are passed into the unit (normally a factory made unit which is spliced or connected to existing fibre optics in the field) either in the centre of the tube or on the surface of the grp. The resulting insulator is either rigid or semi-rigid and has a finite length of tyoically 5 m for a 400 kV unit. This type of ir._ulator also typically has "fibre optic pigtails" extending from both ends inside conduits (metal at the high potential end to act as an electrical stress-free area) . These conduits normally connect onto splice boxes or optical/electronic interfaces. Unfortunately, the aforementioned arrangements are only suitable where the actual length of the insulator matches the design height of the structure to which it is to be connected. In low voltage situations and/or situations where the link from the high voltage conductor to the earth must be very long, for example, from an overhead line to a suitable ground point the normal composite insulator structure is too short and impractical. In the case of an overhead line the fibre optic cable is usually helically wrapped around the line and at a given distance from a station will have to leave the line for connection to a lower potential or a ground point.

For this reason, the applicants designed and have used a flexible high voltage fibre optic termination for wrapped fibre optic cable systems. Typically, a fibre optic cable will comprise a substantially non-tracking outer jacket, a non-metallic strength member, one or more fibre optic elements and a compatible protective filler. The purpose of the filler is to eliminate or at least inhibit the formation or existence of significant elongate voids or a significant transmission of moisture within the structure in the event of puncture of the outer jacket. The track resistant outer jacket is constructed to survive the various hazards found in high voltage environments such as leakage current, corona, electrical discharge and voltage surges. The flexible high voltage fibre optic termination is used typically with overhead lines and involves passing the fibre optic cable through a flexible hollow high voltage insulator in the form of a tube, which at its bottom end has an earthed point before the cable is either spliced to another similar cable returning back onto the overhead line or enters an underground duct. Sometimes the cable is spliced onto an underground cable depending on end requirements. The hollow insulator allows the voltage difference between the high voltage and low voltage points to drop over its length and can be provided with sheds and/or a convoluted surface to increase creepage distance. In order to ensure that all air is excluded from inside the insulator it is filled with a "gel" which prevents electrical discharge. The hollow insulator is provided because the fibre optic cable, having a typical diameter of less than 8mm, is too fragile to suspend from an overhead line without additional protection.

Although the flexible high voltage fibre optic termination can be used from distribution voltages of 10 kV up to 180 kV, the insulator is commonly only 5 long even for a 10 kV system which electrically only requires 150 mm cable length and an additional 250 mm cable length for creepage distance (typically 25mm per Kv) . Clearly, use of a 5 m cable in situations where a 0.4 m cable would suffice is impractical and expensive.

The important factor in making a high voltage insulator is the physical distance between the high voltage (phase) wire and the low voltage connection on the support pole or tower at, for example, a switch gear/transformer station. Therefore, problems arise when a high voltage insulator is required on or near a high voltage overhead line or bus bar to a unit at ground potential. Although it is possible to utilise the flexible high voltage fibre optic termination described, this would be extremely - A -

expensive for most voltages and over-engineered.

Therefore, it has long been considered desirable to solve the problem of expense, to reduce operations in the field and to design an arrangement which would suit most dimensional requirements.

According to the present invention, there is provided an arrangement for use with high voltage equipment comprising a fibre optic cable on which are located a high voltage electrode and a low voltage electrode wherein the fibre optic cable constitutes an insulator thereby enabling connection of high voltage equipment to a point at lower voltage.

Preferably, the positions of the electrodes on the cable are variable.

Preferably, fibre optic cable is provided with an outer jacket such that the diameter of the cable is substantially 10 - 20 mm.

Preferably, the outer jacket is insulating and substantially non-tracking.

Preferably, the electrodes include a porcelain sleeve section for location around the cable.

Preferably, one or more sheds for deflecting water/rain are located on the cable.

Preferably, the sheds are provided on an integral sleeve construction.

Preferably, the arrangement is used with an optical current transformer (OCT) wherein the outer jacket of the fibre optic cable is stripped back over the portion of its length which passes into the main optical insulator link to the OCT.

Preferably, the difference in voltage between the high voltage electrode and the low voltage electrode lies within the range 1 to 500 Kv.

Preferably, the fibre optic cable is provided with one or more non-conductive strength members.

The present invention also provides a method of connecting high voltage equipment to a point at a lower voltage comprising the steps of locating a high voltage electrode and a low voltage electrode on a fibre optic cable such that when the cable is connected between the high and lower voltages, the fibre optic cable constitutes an insulator.

A preferred embodiment of the present invention will now be described in detail, by way of example only, with reference to the accompanying drawings of which:

Figure 1 is a cross-sectional view of a fibre optic cable according to the present invention;

Figure 2 is a schematic view of a fibre optic cable provided with water/rain deflecting sheds;

Figure 3 shows details of an electrode suitable for use at the high voltage or low voltage positions on the fibre optic cable depicted in Figure 2;

Figure 4 depicts a variation on the electrode arrangement in Figure 3;

Figure 5 is a schematic view of an arrangement according to the present invention in use on a high voltage device on a overhead line or bus bar. In Figure 1 a cross-sectional view of a fibre optic cable generally indicated by reference numeral 6 is shown. The fibre optic cable 6 comprises four optical fibres 1, four fillers 3, a non-conducting strength member 2, water blocking 4 and an outer track-resistant jacket 5. The fibre optic cable is of normal construction except that the thickness of the track-resistant jacket 5 is increased to give an overall diameter of typically 10 to 20 mm. This would require a jacket thickness of between 2mm to 10mm. The cable may also have an externally convoluted surface which serves to increase surface area and thus extend the creepage path length. Previously, the fibre optical cable would have had an overall diameter of at most 8mm. This was a result of the balance between the cable being lightweight for use on overhead lines and the cable being sufficiently robust to withstand wear and tear during use.

Figure 2 is a schematic view of a fibre optic cable 6 upon which rain/water deflecters 7 normally referred to as "sheds" have been mounted. Typically, the sheds 7 are mounted closer to the top of a fibre optic cable length but could be spaced out evenly along the cable length. The sheds 7 serve both to shield the cable 6 from water and to further increase the creepage path length. They will typically be of the same material as the outer jacket 5 and could be vulcanised or heat shrunk to the outer jacket 5. The sheds can either be separate from each other or provided on an integral sleeve.

Figure 3 is a detailed view of an electrode suitable for use at the high voltage end or the low voltage end of a fibre optic cable. The electrode is shown mounted on the fibre optic cable 6 where it connects to the high voltage device/sensor. The electrode comprises a collar 9a which co-operates with a hollow threaded cylinder 9b, both of which are free to move along the length of fibre optic cable

6. Located between the collar 9a and the cylinder 9b is a gland 8 which makes a secure clamp on the fibre optic cable when the collar 9a is threaded onto cylinder 9b. The cylinder 9b is provided with a fitting flange 11 which serves to locate the terminal against the casing of the high voltage device/sensor. The terminal will be secured in position on the casing of the device/sensor by means of a back nut 10 inside the casing which will thread onto the end of the threaded cylinder 9b which extends into the casing. The terminal is assembled by passing the fibre optic cable 6 into the rounded front end of the collar 9a, positioning the gland 8 around the cable 6 and threading the cylinder 9b into the collar 9a. The arrangement will then be pushed into a hole in the high voltage device/sensor and a back nut 10 added to secure the electrode. The collar 9a will then be tightened and the gland 8 will be squeezed onto the cable 6 to prevent slippage occurring.

Thus, it can be seen that the electrode can be moved along the fibre optic cable 6 to positions which facilitate the best physical position of the complete installation, subject to minimum recommended arcing distances.

Figure 4 depicts a variation on the electrode arrangement 5 in Figure 3. The electrode further comprises a porcelain sleeve 20 having a flange 21 which sits against the end of cylinder 9b. Cylinder 9b is extended to form a recess for gland 8 and an abutment 22 for flange 21. The electrode is assembled by first pushing the porcelain sleeve 20 into the wider end of collar 9a and pulling it through the opposite end of collar 9a as far as it will go. The gland 8 is then inserted and the cable 6 pushed through the assembled parts. The cylinder 9b will then be threaded inside collar 9a and the arrangement located on the casing of the high voltage device or the lower voltage point as described in connection with Figure 3. The porcelain sleeve 20 will serve to control leakage currents which will be dissapated over its surface.

Figure 5 is a schematic view of a typical arrangement in place between a high voltage device and ground. The high voltage electrode 13a is connected to the casing of the high voltage device 15 which is on an overhead line 14. The high voltage device 15 includes an optical/electronics interface

16. The fibre optic cable 6 is provided with sheds 7 to deflect water and rain. The sheds 7 can be located at given positions along the length of fibre optic cable 6, depending on the particular situation. The sheds 7 will be secured in position on the cable once their locations are determined. The electrode 13b is connected to the tower extension 12 from the support pole or tower 19. This is the earth point and there is a lead 18 to earth which extends down the support pole or tower 19. There is also a lead from the earth point to a ground duct 16 leading to the electronics, etc.

High voltage device 15 could be any optical or electrical measuring/sensing system. It is more typically an electrical sensing device with an optical interface for converting electrical signals into optical signals.

The arrangement would typically comprise 3 m of 5 cable extending from the high voltage device followed by a 1.5 m section with sheds mounted upon it and a 10 m tail section. Therefore, the insulator could be adapated to suit situations which required a length of fibre optic cable from 1.5 m to just under 14.5 m.

10

It is envisaged that the present invention could be used with an optical current transformer (OCT) , an optical thermometer, an optical voltage transformer or any other optical sensor located at a high voltage.

15

An OCT comprises three different parts, the current transducer in a high voltage circuit, an interface unit and an optical fibre system connecting the transducer to the interface. The OCT is designed

20 for use in an outdoor environment and accordingly, is very robt . A typical application would be for the supervision and protection of EHV series capacitor banks where the OCT will sit on the series capacitor platform and measure current at different points on

25 the EHV platform. In such an application there will be a demand for a suitable link from the OCT to ground. The platforms have main optical insulator links running from the platform deck to ground which are approximately 5 - 8m long. There is also an

30 optical platform link running from the main optical phase link to the OCT which could be at 70Kv higher than the platform deck itself. Accordingly, it can be seen that an arrangement according to the present invention would be suitable for replacing the

35. platform link and connecting the OCT to ground. Usually, the main optical insulator link which runs from ground to the platform has between 10 to 20 fibres running inside it. The insulator will normally be provided with "pigtails" (inside conduits) of 2 - 10 m long at each end of the insulator. The "pigtails" will then be spliced or connected to a receiving unit on the ground and to platform links on the platform. With the present invention it would be possible to use a single unit running from the OCT via the optical platform link and the main optical insulator link to the receiving unit without the need for splices. This could be achieved by cutting back the thick outer jacket of the fibre optic cable where it would enter the main optical insulator. Those fibres which emerged from the bottom of the insulator would be protected by a conduit as at present.

Thus, it can be seen that the fibre optic cable 6 with a suitable trac -resistant outer jacket can, along part of or all of its length, actually function as a high voltage insulator.

The present invention removes the need for an outer high voltage insulator by making the fibre optic cable act as the insulator. Accordingly, it is far more adaptable to varying dimensions not being restrained by the finite length of the known arrangement. The present invention is a unitary arrangement which is capable of carrying optical signals from a high voltage device/sensor to a lower potential.

Claims

1. An arrangement for use with high voltage equipment comprising a fibre optic cable on which are located a high voltage electrode and a low voltage electrode wherein the fibre optic cable constitutes an insulator thereby enabling connection of high voltage equipment to a point at lower voltage.

2. An arrangement as claimed in Claim 1 wherein the positions of the electrodes on the cable are variable.

3. An arrangement as claimed in Claim 1 or Claim 2 wherein the fibre optic cable is provided with an outer jacket such that the diameter of the cable is substantially 10 - 20 mm.

4. An arrangement as claimed in Claim 3 wherein the outer jacket is insulating and substantially non-tracking.

5. An arrangement as claimed in any preceding claim wherein the electrodes include a porcelain sleeve section for location around the cable.

6. An arrangement as claimed in any preceding claim wherein one or more sheds for deflecting water/rain are located on the cable.

7. An arrangement as claimed in Claim 6 wherein the sheds are provided on an integral sleeve construction.

An arrangement as claimed in any preceding claim for use with an optical current transformer (OCT) wherein the outer jacket of the fibre optic cable is stripped back over the portion of its length which passes into the main optical insulator link to the OCT.

9. An arrangement as claimed in any preceding claim wherein the difference in voltage between the high voltage electrode and the low voltage electrode lies within the range 1 to 500 Kv.

10. An arrangement as claimed in any preceding claim wherein the fibre optic cable is provided with one or more non-conductive strength members.

11. A method of connecting high voltage equipment to a point at a lower voltage comprising the steps of locating a high voltage electrode and a low voltage electrode on a fibre optic cable such that when the cable is connected between the high and lower voltages., the fibre optic cable constitutes an insulator.

12. A method as claimed in Claim 11 further comprising the step of making the positions of the electrodes on the cable variable.

13. A method as claimed in Claim 11 or Claim

12 wherein the fibre optic cable is provided with an outer jacket which gives the cable an overall diameter of substantially 10 - 20 mm.

14. A method as claimed in any of Claims 11 to

13 comprising the step of stripping the outer jacket of the fibre optic cable back over part of its length and passing the stripped portion throμgh the main optical insulator link to an optical current transformer.

15. An arrangement for use with high voltage equipment substantially as herein described and as illustrated in the accompanying drawings.

16. A method of connecting high voltage equipment to a point at lower potential substantially as herein described with reference to the accompanying drawings.