GB2086656A

GB2086656A - Liquid-filled circuit-breaker

Info

Publication number: GB2086656A
Application number: GB8131982A
Authority: GB
Original assignee: AEI
Current assignee: AEI
Priority date: 1980-10-24
Filing date: 1981-10-23
Publication date: 1982-05-12
Also published as: GB2086656B

Abstract

An electric circuit interrupter of the kind comprising a pair of contacts immersed in an arc-extinguishing, dielectric liquid, at least one of the contacts being movable between a closed position in which it engages the other contact and an open position in which the contacts are spaced apart, is provided with a layer of involatile liquid on the surface of the dielectric liquid. The involatile liquid is substantially immiscible with the dielectric liquid and preferably has a density of not more than 90% of the density of the dielectric liquid.

Description

SPECIFICATION Improvements in or relating to electrical circuit interrupters This invention relates to electrical circuit interrupters of the kind comprising a pair of contacts immersed in an arc extingui'shing, dielectric liquid, at least one of the contacts being movable between a closed position in which it engages the other contact and an open position in which the contacts are spaced apart from each other.

Dielectric liquids which are commonly used are electronegative liquids containing a high proportion of fluorine or chlorine such as sulphur hexafluoride, chloroalkanes. fluoroalkanes. chlorofluoroalkanes or mixtures thereof. A serious disadvantage of these compounds is that they are volatile. It is an object of this invention to provide an electrical circuit breaker in which loss of the dielectric liquid by evaporation is substantially prevented. This invention avoids the obvious but expensive methods of preventing loss by evaporation which involve sealing the liquid into the arcing chamber using hermetic seals or pressure vessels. The latter methods have the further complication that movable mechanisms, such as may be required to actuate the contacts, need to pass into the arcing chamber from the exterior which makes the construction of a completely sealed arcing chamber difficult.

According to this invention an electrical circuit interrupter of the aforementioned kind is provided on the surface of the dielectric liquid, with a layer of involatile liquid which is substantially immiscible with the dielectric liquid.

An involatile liquid within the terms of this invention is a liquid which is less volatile at room temperature than the dielectric liquid.

The invention provides a method of preventing evaporation of an arc-extinguishing dielectric liquid while permitting free passage of moveable mechanisms such as actuating linkages, to the contacts immersed in the liquid. The said involatile liquid must not contain any ionic substances which are soluble in the dielectric liquid since these would adversely affect the dielectric properties of the latter. The involatile liquid should preferably not be hygroscopic.

The solubility of the dielectric liquid in the involatile liquid must be as low as possible to minimise evaporation of the dielectric liquid.

Preferably the solubility of the dielectric liquid in the involatile liquid has a value less than 0.05% by volume.

Preferably the solubility of the involatile liquid in the dielectric liquid is less than 0.05% by volume.

Preferably an involatile liquid in accordance with this invention has a density which is a maximum of 90% of the density of the dielectric liquid.

Preferably the volume of the involatile liquid is between 5% and 10% of the volume of the dielectric liquid.

An involatile liquid may be selected in accordance with the aforementioned criteria of suitability for use with a particular dielectric liquid. An involatile liquid in accordance with the invention may be selected from the following: dimethyl siloxane, polythethylene glycol, polypropylene glycol or phosphate esters with a formula R'nR"3 nPO, where R is C6H50, R is CH3C6H40 and n is O, 1, 2 or 3.

Perfluorodecalin, perfluorooctane or any other perfluoroalkane having six to twelve carbon atoms may be provided with a surface layer of dimethyl siloxane. Dimethyl siloxane having a viscosity between 50 and 500 cSt is preferred. Perfluoroalkanes having six to 1 2 carbon atoms may also be provided with surface layers of triphenyl phosphate, tricresyl phosphate or other cresyl phenyl phosphates of the general formula R'nR"3 nPO, where R' = C6H50, R" is CH3C6H40 and n is O, 1, 2 or 3.

Perchlorofluoroalkane dielectric liquids such as trichlorotribluoroethane or any other per chlqroalkanes with two to ten carbon atoms per molecule may be effectively sealed by the provision of a surface layer of either polyethylene glycol or polypropylene glycol or a mixture thereof.

An involatile liquid layer in accordance with this invention can act as a scavenger for reactive impurities such as chlorine, fluorine or acids in the dielectric liquid. This scavenging property may be enhanced by the addition of chemical scavengers to the involatile liquid.

These scavengers must be insoluble in the dielectric liquid. Preferred scavengers are tetraphenyl tin and epoxidised oils such as that known as epoxidised Novolak.

1. An electrical circuit interrupter of the kind specified provided, in the surface of the dielectric liquid, with a layer of involatile liquid which is substantially immiscible with dielectric liquid.

2. An electrical circuit interrupter according to Claim 1 in which the volume of the involatile liquid layer is between 5% and 10% of the volume of the dielectric liquid.

3. An electrical circuit interrupter according to Claim 1 or Claim 2 in which the density of the involatile liquid layer is not more than 90% of the density of the dielectric liquid.

4. An electrical circuit interrupter according to any preceding claim in which the solubility of the dielectric liquid in the involatile liquid is less than .05% by volume.

5. An electrical circuit interrupter according to any preceding claim in which the solubility of the involatile liquid in the dielectric liquid is less than 0.05% by volume.

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Improvements in or relating to electrical circuit interrupters This invention relates to electrical circuit interrupters of the kind comprising a pair of contacts immersed in an arc extingui'shing, dielectric liquid, at least one of the contacts being movable between a closed position in which it engages the other contact and an open position in which the contacts are spaced apart from each other. Dielectric liquids which are commonly used are electronegative liquids containing a high proportion of fluorine or chlorine such as sulphur hexafluoride, chloroalkanes. fluoroalkanes. chlorofluoroalkanes or mixtures thereof. A serious disadvantage of these compounds is that they are volatile. It is an object of this invention to provide an electrical circuit breaker in which loss of the dielectric liquid by evaporation is substantially prevented. This invention avoids the obvious but expensive methods of preventing loss by evaporation which involve sealing the liquid into the arcing chamber using hermetic seals or pressure vessels. The latter methods have the further complication that movable mechanisms, such as may be required to actuate the contacts, need to pass into the arcing chamber from the exterior which makes the construction of a completely sealed arcing chamber difficult. According to this invention an electrical circuit interrupter of the aforementioned kind is provided on the surface of the dielectric liquid, with a layer of involatile liquid which is substantially immiscible with the dielectric liquid. An involatile liquid within the terms of this invention is a liquid which is less volatile at room temperature than the dielectric liquid. The invention provides a method of preventing evaporation of an arc-extinguishing dielectric liquid while permitting free passage of moveable mechanisms such as actuating linkages, to the contacts immersed in the liquid. The said involatile liquid must not contain any ionic substances which are soluble in the dielectric liquid since these would adversely affect the dielectric properties of the latter. The involatile liquid should preferably not be hygroscopic. The solubility of the dielectric liquid in the involatile liquid must be as low as possible to minimise evaporation of the dielectric liquid. Preferably the solubility of the dielectric liquid in the involatile liquid has a value less than 0.05% by volume. Preferably the solubility of the involatile liquid in the dielectric liquid is less than 0.05% by volume. Preferably an involatile liquid in accordance with this invention has a density which is a maximum of 90% of the density of the dielectric liquid. Preferably the volume of the involatile liquid is between 5% and 10% of the volume of the dielectric liquid. An involatile liquid may be selected in accordance with the aforementioned criteria of suitability for use with a particular dielectric liquid. An involatile liquid in accordance with the invention may be selected from the following: dimethyl siloxane, polythethylene glycol, polypropylene glycol or phosphate esters with a formula R'nR"3 nPO, where R is C6H50, R is CH3C6H40 and n is O, 1, 2 or 3. Perfluorodecalin, perfluorooctane or any other perfluoroalkane having six to twelve carbon atoms may be provided with a surface layer of dimethyl siloxane. Dimethyl siloxane having a viscosity between 50 and 500 cSt is preferred. Perfluoroalkanes having six to 1 2 carbon atoms may also be provided with surface layers of triphenyl phosphate, tricresyl phosphate or other cresyl phenyl phosphates of the general formula R'nR"3 nPO, where R' = C6H50, R" is CH3C6H40 and n is O, 1, 2 or 3. Perchlorofluoroalkane dielectric liquids such as trichlorotribluoroethane or any other per chlqroalkanes with two to ten carbon atoms per molecule may be effectively sealed by the provision of a surface layer of either polyethylene glycol or polypropylene glycol or a mixture thereof. An involatile liquid layer in accordance with this invention can act as a scavenger for reactive impurities such as chlorine, fluorine or acids in the dielectric liquid. This scavenging property may be enhanced by the addition of chemical scavengers to the involatile liquid. These scavengers must be insoluble in the dielectric liquid. Preferred scavengers are tetraphenyl tin and epoxidised oils such as that known as epoxidised Novolak. CLAIMS

6. an eledtrical circuit interrupter according to any preceding claim in which the involatile liquid layer is effective to scavange corrosive impurities from the dielectric liquid.

7. An electrical circuit interrupter according to Claim 6 in which a scavenger is dissolved within the involatile liquid layer.

8. An electrical circuit interrupter according to Claim 7 in which the scavenger is tetraphenyl tin.

9. An electrical circuit interrupter according to Claim 7 in which the scavenger is an epoxidised oil.

1 0. An electrical circuit interrupter according to any preceding claim in which the incolatile liquid layer contains one or more phosphate esters of formula R'nR"3 nPO, where R' is C6HsO, R" is CH3C6H40 and n is 0, 1, 2 or 3.

11. An electrical circuit interrupter according to Claim 10 in which the dielectric liquid is essentially a perfluoroalkane having six to twelve carbon atoms per molecule

1 2. An electrical circuit interrupter according to any of claims 1 to 9 in which the involatile liquid layer contains polyethylene glycol and/or polypropylene glycol.

1 3. An electrical circuit interrupter according to Claim 1 2 in which the dielectric liquid is essentially a perchlorofluoroalkane having two to ten carbon atoms per molecule.

1 4. An electrical circuit interrupter according to any of claims 1 to 9 in which the involatile liquid layer contains dimethyl siloxane.