GB1588828A - Sulpur hexafluoride gas-insulated electrical equipment - Google Patents

Description

(54) SULPHUR HEXAFLUORIDE GAS-INSULATED ELECTRICAL EQUIPMENT (71) We, WESTINGHOUSE ELECTRIC CORPORATION, of Westinghouse Building, Gateway Center, Pittsburgh, Pennsylvania, United States of America, a corporation organised and existing under the laws of the State of Pennsylvania, United States of America, 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: Sulphur Hexafluoride Gas-lnsulated Electrical Equipment This invention relates to sulphur hexafluoride gas-insulated equipment.

Gas-insulated substations are made much more compact and use much less space because the switchgear and transmission lines in the substation are insulated with pressurized SF6. Since pressurized SF6 is a far better insulator than air, the distance between electrical conductors can be made much smaller. Much of this equipment, particularly the transmission or bus lines, is enclosed in steel casings to contain the pressurized SF6 gas. The electrical conductors are mounted on insulators, usually of epoxy, inside the steel enclosures.

Occasionally flashovers (i.e., arcing) occur between the steel enclosure and the electrical conductors. The flashover may be harmless and may not have damaged the insulators or it may crack or degrade the epoxy insulators. Detectors of various types have been placed on the equipment to determine when and where a flashover has occurred. However, none of these detectors are capable of determining whether or not the insulator was damaged in the flashover. If the insulator was not damaged, the equipment can be permitted to continue functioning, but if the insulator was damaged, the equipment must be disassembled and the insulator replaced, which is a very costly operation. It would therefore be very useful and valuable to be able to determine whether or not the insulator was damaged in the flashover.

The invention consists in SF6 gas insulated equipment incorporating a device for detecting overheating and arcing comprising ionizing means for ionizing said SF6 gas and measuring means for measuring the electric current across said ionized SF6 gas.

It has been found that detection of insulator damage in SF6 gas insulated electrical equipment can be accomplished by continuously or periodically ionizing a portion of the SF6 gas and measuring the electrical current across the ionized gas. When an insulator is damaged in a flashover, it emits particles or aerosols into the SF6 gas. These particles combine with the ionized gas and lower the electrical current across it thereby revealing their presence. If the insulator was not decomposed during the arcing, particles will not be present and the electrical current will not drop.

By experiment, it has been determined that the decrease in electrical current due to the presence of particles in the SF6 gas is more than sufficient to provide a clear signal of their presence.

The detection system of this invention can be used with any SF6 gas insulated electrical equipment including switchgear, circuit breaker, bus lines, transmission lines, and various other equipment commonly found in gas insulated substations.

In order that the invention can be more clearly understood, a convenient embodiment thereof will now be described, by way of example, with reference to the accompanying drawing which is an isometric view, partially in section, of a compressed gas insulated transmission line to which has been fitted a certain presently preferred embodiment of a detection system according to this invention.

In Figure 1 a transmission line 1 comprises a metal sheath 2 filled with SF6 gas 3 under pressure. In the center of metal sheath 2 is an electrical conductor 4. The conductor is held in the center of the metal sheath by insulator 5, generally of an epoxy resin. Insulator 5 is preferably coated with a resin 6 containing a compound that, at a temperature between 60 and 250"C, produces particles which combine with ionized SF6 to decrease it mobility. The resin in coating 6 is also preferably an epoxy so it will adhere to the epoxy insulator 5. A conduit 7 passes through sheath 2. A fan 8 continuously draws some of the SF6 gas into conduit 6 and circulates it through ion chamber monitor 9, valve 10, then through conduit 11 back into transmission line 1. Ion chamber monitor 9 is a commercial device which ionizes the SF6 gas with alpha radiation, generally from thorium 232, and measures the current flow across the ionized gas. The amount of gas ionized is small and it is deionized in generating the current flow. In the event that particles are drawn into the monitor, combining with the SF6 ions thereby decreasing their mobility and lowering the current flow, monitor 9 can automatically open valve 10, diverting the SF6 through particle collector 12 thence back to transmission line 1 through conduits 13 and 11.

Suspended particles and aerosols are collected in particle collector 12 and can be analyzed to determine their composition.

Since different compounds decompose to produce different particles, the use of a different compound on each insulator, or on a group of insulators, permits one to determine which insulator was subjected to overheating or arcing.

A description of compositions suitable for coating the insulators can be found in U.S.

Patent Nos. 4.056,005; 3,973,438; 3,979,353; 4,046,733; 4.04(i,943; 3,995,489; 3,957,014; 4,016,745; 3,955,417; and 3,973,439. The compound in these compositions which emits the particles may be cast directly into the epoxy insulator in which case the coating can be eliminated.

Althougll it is preferable to monitor the SFo gas insulated electrical equipment continuously for arcing, under some circumstances it may be more economical to simply test the SF, gas periodically or only when arcing is suspected, and to attach the detection system to the equipment onlv at those times. Also, when the volume of SF6 gas being monitored is relativelv small. it may not be necessary to use a fan or pump to circulate the gas through the ion chamber monitor. On the other hand, if the transmission line is several hundred feet long, it may be necessary to position a particle detection system every ten feet or so along the line.

The invention will now be illustrated with reference to the following Examples: EXAMPLE I A 2 inch by 2 inch piece of quartz-filled cast epoxy resin of the type used for electrical insulation was placed in a stainless steel boat within a 1 inch stainless steel tube.

Sulfur hexafluoride gas was passed over the sample at flow rate of 6 1/mien. A phase controlled temperature regulator and programmer controlled the temperature in the boat and the temperature in the boat was measured by mounting a hot junction Chromel Alumel thermocouple within a small hole in the boat. The output of the thermocouple and the detector were monitored on a two pen potentiostatic recorder. A 6"%/mien.

heating rate was maintained in each experiment after the insertion of the epoxy sample in the boat. The threshold temperature at which considerable particulation occurred was taken from the chart produced by the recorder. The occurrence of particulation was detected using a Generator Condition Monitor sold by Environment One Corporation, a commercial ion chamber monitor. A sharp drop in electrical current across the ionized SF6 gas occurred when the temperature of the epoxy resin reached 197"C.

EXAMPLE 2 Example 1 was repeated except that instead of using a piece of epoxy resin as the sample, a grease sold by Dupont under the trademark "Krytox 240-AD" was used instead. The grease was a mixture of about 20% (by weight) telomer of polytetrafluorethylene and about 80% perfluoroalkyl polyether. A sharp drop in electrical current was recorded when the grease reached 195"C.

EXAMPLE 3 Example 1 was repeated using the same type and size piece of epoxy resin, but instead of heating it gradually the resin was placed between two electrodes 2 inches apart and arced at 100 KV with an impulse generator. A drop in current flow was recorded immediately after arcing. The sample was damaged by the arcing.

EXAMPLE 4 Example 1 was repeated except that the sample was prepared from the following composition: Parts by Weight p-toluene sulfonic acid ... ... ... . . 20 epoxy resin made from 200 phr linseed fatty acids, ... ... 200 phr styrene, and 300 phr diglycidyl ether of Bisphenol A. Sold by Westing house Electric Corporation as "B-276" Varnish (See Example 1 of U.S. Patent 2,909,497 for detailed description) ... ... ... 50 6% solution in low boiling hydrocarbons of cobalt napthenate ... 1.0 24% solution in low boiling hydrocarbons of lead naphthenate 0.25 toluene . ... ... ... ... 50 Samples were prepared by brushing the above composition onto t by 3 inch aluminium and copper sheet l/l6 to 1 inches thick. The samples were dried to form coatings 1 inches thick, then placed in an oven at 60"C overnight to determine if they were stable and would function after aging. The sample was tested as described in Example 1. A drop in current flow was recorded when the sample temperature reached 116 to 1200C.

EXAMPLE 5 Example 4 was repeated except that chromium acetylacetonate was used in the epoxy resin composition (instead of ptoluene sulfonic acid). A drop in current occurred at a sample temperature of 181 to 185"C.

EXAMPLE 6 Example 4 was repeated except tellurium diethyldithiocarbonate was used in the epoxy resin composition (instead of p-toluene sulfonic acid). A drop in current occurred at a sample temperature of 159 to 164"C.

EXAMPLE 7 Example 1 was repeated except that various pieces of resins each about 2 inch by 9 inch square were used instead of the piece of epoxy resin. The following table gives the resins used and the temperature of the resin when the drop in current was recorded.

Polytetrafluoroethylene 496 to 500"C Polyimide . 547 to 551"C Polystyrene 375 to 3790C Polysulfone . 440 to 4450C WHAT WE CLAIM IS:- 1. SF6 gas-insulated electrical equipment incorporating a device for detecting overheating and arcing comprising ionizing means for ionizing said SF6 gas and measuring means for measuring the electric current across said ionized SF6 gas.

2. A device according to Claim 1 including means for circulating with SF6 gas to the ionizing means.

3. A device according to Claim 2, wherein the SF6 gas insulated electrical equipment is part of a compressed gas insulated substation.

4. A device according to Claim 1, 2 or 3, wherein the ionizing means and the measuring means together comprise an ion chamber monitor.

5. A device according to 'Claim 4, wherein the SF6 gas insulated electrical equipment is a compressed gas insulated transmission line and a plurality of the ion chamber monitors are positioned along said transmission line.

6. A device according to any of Claims 1 to 5, wherein the SF6 gas is ionized with alpha radiation.

7. A device according to any of Claims 1 to 6, wherein the surfaces of the SF6 gas insulated electrical equipment which are exposed to the SF6 gas are coated with a resin containing a compound which can pro duce particles which lower the electrical current across the ionized gas when said compound is heated to a temperature between 60 and 250"C.

8. A device according to any of Claims 1 to 6, wherein said SF6 gas insulated electrical equipment includes an epoxy insulator containing a compound which can produce particles which lower the electrical current across said ionized gas when said epoxy insulator is subjected to arcing.

9. A device according to Claim 1, wherein the SF6 gas insulated electrical equipment is a circuit breaker.

10. SF6 gas-insulated electrical equipment incorporating a device for detecting overheating and arcing and substantially as described therein with particular reference to the accompanying drawing.

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

Claims (10)

**WARNING** start of CLMS field may overlap end of DESC **. Parts by Weight p-toluene sulfonic acid ... ... ... . . 20 epoxy resin made from 200 phr linseed fatty acids, ... ... 200 phr styrene, and 300 phr diglycidyl ether of Bisphenol A. Sold by Westing house Electric Corporation as "B-276" Varnish (See Example 1 of U.S. Patent 2,909,497 for detailed description) ... ... ... 50 6% solution in low boiling hydrocarbons of cobalt napthenate ... 1.0 24% solution in low boiling hydrocarbons of lead naphthenate 0.25 toluene . ... ... ... ... 50 Samples were prepared by brushing the above composition onto t by 3 inch aluminium and copper sheet l/l6 to 1 inches thick. The samples were dried to form coatings 1 inches thick, then placed in an oven at 60"C overnight to determine if they were stable and would function after aging. The sample was tested as described in Example 1. A drop in current flow was recorded when the sample temperature reached 116 to 1200C. EXAMPLE 5 Example 4 was repeated except that chromium acetylacetonate was used in the epoxy resin composition (instead of ptoluene sulfonic acid). A drop in current occurred at a sample temperature of 181 to 185"C. EXAMPLE 6 Example 4 was repeated except tellurium diethyldithiocarbonate was used in the epoxy resin composition (instead of p-toluene sulfonic acid). A drop in current occurred at a sample temperature of 159 to 164"C. EXAMPLE 7 Example 1 was repeated except that various pieces of resins each about 2 inch by 9 inch square were used instead of the piece of epoxy resin. The following table gives the resins used and the temperature of the resin when the drop in current was recorded. Polytetrafluoroethylene 496 to 500"C Polyimide . 547 to 551"C Polystyrene 375 to 3790C Polysulfone . 440 to 4450C WHAT WE CLAIM IS:-

1. SF6 gas-insulated electrical equipment incorporating a device for detecting overheating and arcing comprising ionizing means for ionizing said SF6 gas and measuring means for measuring the electric current across said ionized SF6 gas.

2. A device according to Claim 1 including means for circulating with SF6 gas to the ionizing means.

3. A device according to Claim 2, wherein the SF6 gas insulated electrical equipment is part of a compressed gas insulated substation.

4. A device according to Claim 1, 2 or 3, wherein the ionizing means and the measuring means together comprise an ion chamber monitor.

5. A device according to 'Claim 4, wherein the SF6 gas insulated electrical equipment is a compressed gas insulated transmission line and a plurality of the ion chamber monitors are positioned along said transmission line.

6. A device according to any of Claims 1 to 5, wherein the SF6 gas is ionized with alpha radiation.

7. A device according to any of Claims 1 to 6, wherein the surfaces of the SF6 gas insulated electrical equipment which are exposed to the SF6 gas are coated with a resin containing a compound which can pro duce particles which lower the electrical current across the ionized gas when said compound is heated to a temperature between 60 and 250"C.

8. A device according to any of Claims 1 to 6, wherein said SF6 gas insulated electrical equipment includes an epoxy insulator containing a compound which can produce particles which lower the electrical current across said ionized gas when said epoxy insulator is subjected to arcing.

9. A device according to Claim 1, wherein the SF6 gas insulated electrical equipment is a circuit breaker.

10. SF6 gas-insulated electrical equipment incorporating a device for detecting overheating and arcing and substantially as described therein with particular reference to the accompanying drawing.