Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
  • H01B3/00—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties
  • H01B3/18—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of organic substances
  • H01B3/20—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of organic substances liquids, e.g. oils

Definitions

• the present invention relates to switchgear, and in particular relates to fluid-insulated tap-changers.
• Fluid-insulated tap-changers are employed for light-duty switching in a variety of applications, such as distribution transformer installations, underground railways and the like, where repeated on-load switching of currents of up to about 500A at voltages of typically a few kV is required.
• a tap-changer may perform 20,000 to 30,000 make and break cycles annually, and a working life of a minimum of 20 years is normally expected.
• tap-changer electrodes are subject to considerable wear in use, and for the same reason the dielectric fluid in a tap-changer quickly becomes contaminated with carbon and other arcing products, which in turn tend to cause the electrodes to wear more rapidly.
• fluid-insulated tap-changers are distinguished from fluid-insulated switchgear in general by the requirement to renew their dielectric liquid at frequent intervals throughout their working life and also by the requirement that the dielectric liquid employed should be compatible with an absolute minimum of electrode wear.
• the problem of electrode wear is less severe in heavy duty switchgear for example, even though such switchgear may switch currents of perhaps several kA at several tens of kV.
• BS148 petroleum oil has the following disadvantages; a) it is highly inflammable b) it can have poor lubricating properties c) it can freeze at -20°C and d) being a natural petroleum product the molecular structure can contain various aromatic structures of questionable toxicity or carcinogeneticy. Also in operation in a tap-changer or switch, petroleum oil evolves large quantities of hydrogen and other flammable gases, and produces large quantities of colloidal carbon which requires periodic removal.
• a liquid insulated tap-changer incorporates a dielectric liquid which includes as a major constituent one or more monomeric or polymeric esters of the general formula: wherein R' are the same or different alkyl groups having five to ten carbon atoms, and R are independently H or Me or Et or or (in the case that the ester is polymeric)
• the dielectric liquid may comprise a single said ester or a mixture of such esters.
• each R is or one R is ethyl and the other R is CH 2 -0-C-R'.
• R' is preferably hexyl (C 6 ), heptyl (C 7 ) or octyl (C 8 ).
• R' may be a straight chain or a branched chain alkyl group.
• Preferred esters for use in accordance with the invention are esters (particularly tetra-esters) of pentaerythritol (C (CH 2 OH) 4 ) and heptanoic or octanoic (particularly the n-heptanoic and n-octanoic) acid.
• Esters of trimethylol propane are also suitable, particularly when the acid is heptanoic or octanoic acid.
• esters trimethylol-propane triheptanoate, trimethylol-propane tricaprylate and pentaerythritol tetrapelargonate and listed their viscosities, boiling points, electrical loss tangents (tan6), resistivities, permittivities, electrical breakdown strengths, fire points and autoignition temperatures.
• esters in accordance with the invention when used as dielectric liquids in tap-changers, significantly reduce contact erosion in comprison with tap-changers which utilise petroleum oil (which has previously been considered the best dielectric fluid for tap-changers). Furthermore the esters of the present invention form only a small fraction of the carbon produced by petroleum oil in tap-changers, and the carbon produced by the esters of the present invention is less colloidal and separates more readily to leave a cleaner system. Thus, by using the esters of the present invention in tap-changers the overall life of the tap-changer may be increased and the required maintenance may be reduced.
• the fire point was determined by the method specified in the Institute of Petroleum handbook No. 36/63
• the pour point was determined by the method specified in the Institute of Petroleum Handbook No. 15/67 (ASTM Designation D97-66)
• the type testing involved 20,000 make and break operations in a 33kV 500 amp High Speed Resistor Transition Tap-Changer.
• esters produced from different batches of acid may be necessary in order to achieve the desired pour point, fire point, viscosity or other characteristics.
• the precise composition is not critical, but it should be noted that the electrical properties, especially the loss tangent and the resistivity, improve with increasing molecular weight and increasing symmetry of the ester molecule.

Landscapes

• Chemical & Material Sciences (AREA)
• Oil, Petroleum & Natural Gas (AREA)
• Physics & Mathematics (AREA)
• Spectroscopy & Molecular Physics (AREA)
• Organic Insulating Materials (AREA)
• Lubricants (AREA)

Applications Claiming Priority (2)

Publications (2)

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Family Applications (1)

Country Status (3)

Cited By (4)

Citations (2)

• 1985
  • 1985-05-17 GB GB858512488A patent/GB8512488D0/en active Pending
• 1986
  • 1986-05-16 DE DE8686303735T patent/DE3662016D1/de not_active Expired
  • 1986-05-16 GB GB08611961A patent/GB2175311B/en not_active Expired
  • 1986-05-16 EP EP19860303735 patent/EP0202878B1/de not_active Expired

Patent Citations (2)

Non-Patent Citations (1)

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