GB1579474A - Insulation member for an electrical appliance - Google Patents

Abstract

Said solid insulating parts (2), which consist of a cured binder and at least one fibrous filler serving as a mechanical reinforcement, come into contact with arcs during operation in an electric appliance. In this appliance no fluorine compounds are found near the arc. The fibrous filler consists of a glass without compounds of alkaline earth metals and alkali metals, preferably of pure quartz glass which, in contrast to the glass of commercial glass fibres, remains electrically insulating up to very high temperatures and confers high mechanical strength upon the solid insulating part. <IMAGE>

Description

(54) INSULATION MEMBER FOR AN ELECTRICAL APPLIANCE (71) We, SPRECHER & SCHUH AG., a Swiss Body Corporate, of Buchserstrasse 7, Aarau, Switzerland, 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: - The invention relates to an insulation member for an electrical appliance. The member is of the type which, when fixed in an electrical appliance, experiences arcing with no fluoro compounds coming into contact with the arc. This type of member comprises a cured binder and at least one loading agent including a fibrous loading agent serving as at least the main mechanical reinforcing material.

Insulation members which come into contact with arcs in operation experience severe mechanical, electrical and thermal stresses. Insulation members of this kind are found more particularly in low-voltage and high-voltage switchgear and cutouts.

An important consideration for the working life and reliability of operation of an electrical appliance is that there must be little burning away of the insulation material as a result of arcing. It is usually possible to meet this requirement quite readily. Unfortunately, it has been found that it is rather more difficult to achieve adequate mechanical strength simultaneously with adequate resistance to arcing.

French Patent Specification 1,521,247 discloses organic and inorganic fibrous mechanical reinforcing materials. Glass and asbestos fibres are inorganic reinforcing materials. The organic reinforcing fibres can be polyamide, e.g. nylon, polyester, e.g.

terylene (Registered Trade Mark), polyacrylonitrile, polyvinyl alcohol, polyvinyl acetate or polypropylene.

The best mechanical strength is provided by glass fibre reinforcement. However, the resistance of the fibre-reinforced insulant to arcing improves when the fibres are made of an organic material instead of glass, but the mechanical strength of an insulant loaded with an organic fibre is much less than in the case of glass fibre reinforcement.

It is an object of the invention to provide a fibrous loading agent for an insulation member which is subjected to arcing and which is made of a cured binder and a fibrous loading agent required to ensure satisfactory mechanical strength during arcing and satisfactory resistance of the insulating member to arcing.

According to the present invention, there is provided an insulation member for an electrical appliance, the member when fixed in an electrical appliance experiencing arcing with no fluoro compounds coming into contact with the arc, the member comprising a cured binder and at least one loading agent including a fibrous loading agent serving as at least the main mechanical reinforcing material, characterised in that the fibrous reinforcing material, which serves as at least the main mechanical reinforcing material, is made of a glass without alkaliearth and alkali-metal compounds.

The glass may be pure quartz glass.

The starting point for the invention is that the conventional alkali-containing glass fibres with alkali-earth and alkalimetal compounds i.e., the reinforcing fibres which are very advantageous mechanically-become electrically conductive at high temperatures during arcing, so that the dielectric strength of the insulant drops very considerably; at high temperatures the ions consisting of alkali-earth and alkalimetal compounds can transport electrical charges and thus give rise to electrical conductivity. The main alkali-earth compounds in an alkali-containing glass are CaO and MgO. The alkali-earths are Ba, Be, Ca, Mg, Ra, Sr. The main alkali-metal compounds likely to be found in alkali-containing glass fibres are Na2O and K2O.

The alkali-metals are Li, Na, K, Rb, Cs, Fr.

Reinforcing fibres made of pure quartz glass remain dielectric up to very high temperatures and provide almost the same mechanical strength as alkali-containing glass fibres.

The invention will be described now by way of example only with reference to the accompanying drawings wherein: Fig. 1 is a view of an explosion pot in longitudinal section, and Fig. 2 is a plan view of an explosion pot.

Fig. 1 is a view of an explosion pot for a low-liquid-content power circuit breaker.

The pot comprises an outer insulating tube 1, discs 2 stuck into tube 1, and spacing rings 3. The discs 2 are adapted for longitudinal blowing. In use the tube 1 is secured in a circuit breaker (not shown).

With the circuit breaker in its closed state, the switch pin interconnecting the two contacts of the breaker is disposed inside bores 4 of the discs 2. When the circuit breaker contacts open the switch pin is pulled out of the explosion pot, with the result that an arc is struck axially of the explosion pot through the bores 4 of the discs 2. Evaporation of the arc-quenching liquid leads to very high pressures occurring between the discs 2. The discs 2 must be able to withstand the mechanical stresses occurring together with the high thermal stressing caused by the arc.

Once the arc has been extinguished, the surfaces of the discs 2 must provide electrical insulation for the recovery voltage.

The material of which the discs 2 are made has a high resistance to arcing-i.e., after experiencing arcing the surface is free from electrically conductive zones.

The discs 2 are made of a cured cycloaliphatic or heterocyclic epoxy resin, powdered loading agents and a fibrous loading agent of pure quartz glass fibres, the latter loading agent being embedded in the resin.

The disc material is highly resistant to arcing and its mechanical and electrical strength is satisfactory for the explosionpot discs of power circuit breakers.

An example will now be given of how an explosion-pot disc is produced from a moulding composition. The composition has the following ingredients: 35 parts by weight of an epoxy resin consisting of a mixture of 51 wt.O/o of a cycloaliphatic epoxy resin part having an epoxy content of 6 2 equivalent-kg and a viscosity of 1-5 X 105 cP 25"C, 485 wt.O/o of a hardening agent, consisting of hexahydrophthalic acid anhydride, and 05 wt.olo of an accelerator part consisting of benzyl dimethylamine; 10 parts by weight of quartz glass fibres 6 mm long; 2 parts by weight of zinc stearate; 30 parts by weight of aluminium trihydrate, and 23 parts by weight of zirconium silicate.

The ingredients are kneaded together at a temperature of approx. 75"C. The resulting doughy composition is cured in a mould at a temperature of 1700C and at a pressure of 100 kp/cm2.

WHAT WE CLAIM IS:- 1. An insulation member for an electrical appliance, the member when fixed in an electrical appliance experiencing arcing with no fluoro compounds coming into contact with the arc, the member comprising a cured binder and at least one loading agent including a fibrous loading agent serving as at least the main mechanical reinforcing material, characterised in that the fibrous reinforcing material which serves as at least the main mechanical reinforcing material, is made of a glass without alkaliearth and alkali-metal compounds.

2. A member according to Claim 1, characterised in that the glass is pure quartz glass.

3. An insulation member substantially as hereinbefore described with reference to and as shown in the accompanying drawing.

4. An insulation member substantially as hereinbefore described in the example.

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

Claims (4)

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

   The invention will be described now by way of example only with reference to the accompanying drawings wherein: Fig. 1 is a view of an explosion pot in longitudinal section, and Fig. 2 is a plan view of an explosion pot.

   Fig. 1 is a view of an explosion pot for a low-liquid-content power circuit breaker.

   The pot comprises an outer insulating tube 1, discs 2 stuck into tube 1, and spacing rings 3. The discs 2 are adapted for longitudinal blowing. In use the tube 1 is secured in a circuit breaker (not shown).

   With the circuit breaker in its closed state, the switch pin interconnecting the two contacts of the breaker is disposed inside bores 4 of the discs 2. When the circuit breaker contacts open the switch pin is pulled out of the explosion pot, with the result that an arc is struck axially of the explosion pot through the bores 4 of the discs 2. Evaporation of the arc-quenching liquid leads to very high pressures occurring between the discs 2. The discs 2 must be able to withstand the mechanical stresses occurring together with the high thermal stressing caused by the arc.

   Once the arc has been extinguished, the surfaces of the discs 2 must provide electrical insulation for the recovery voltage.

   The material of which the discs 2 are made has a high resistance to arcing-i.e., after experiencing arcing the surface is free from electrically conductive zones.

   The discs 2 are made of a cured cycloaliphatic or heterocyclic epoxy resin, powdered loading agents and a fibrous loading agent of pure quartz glass fibres, the latter loading agent being embedded in the resin.

   The disc material is highly resistant to arcing and its mechanical and electrical strength is satisfactory for the explosionpot discs of power circuit breakers.

   An example will now be given of how an explosion-pot disc is produced from a moulding composition. The composition has the following ingredients:

   35 parts by weight of an epoxy resin consisting of a mixture of 51 wt.O/o of a cycloaliphatic epoxy resin part having an epoxy content of 6 2 equivalent-kg and a viscosity of 1-5 X 105 cP 25"C, 485 wt.O/o of a hardening agent, consisting of hexahydrophthalic acid anhydride, and 05 wt.olo of an accelerator part consisting of benzyl dimethylamine;

   10 parts by weight of quartz glass fibres 6 mm long;

   2 parts by weight of zinc stearate;

   30 parts by weight of aluminium trihydrate, and

   23 parts by weight of zirconium silicate.

   The ingredients are kneaded together at a temperature of approx. 75"C. The resulting doughy composition is cured in a mould at a temperature of 1700C and at a pressure of 100 kp/cm2.

   WHAT WE CLAIM IS:- 1. An insulation member for an electrical appliance, the member when fixed in an electrical appliance experiencing arcing with no fluoro compounds coming into contact with the arc, the member comprising a cured binder and at least one loading agent including a fibrous loading agent serving as at least the main mechanical reinforcing material, characterised in that the fibrous reinforcing material which serves as at least the main mechanical reinforcing material, is made of a glass without alkaliearth and alkali-metal compounds.
2. 2. A member according to Claim 1, characterised in that the glass is pure quartz glass.
3. 3. An insulation member substantially as hereinbefore described with reference to and as shown in the accompanying drawing.
4. 4. An insulation member substantially as hereinbefore described in the example.