JPS5845765B2 - Electrical contact materials for vacuum switches - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION A vacuum switch is a device that opens and closes electrical contacts in a container maintained at a high vacuum to turn on and off an electric circuit. The figure is a longitudinal sectional view of the vacuum switch.

In the figure, electrical contacts 3 and 4 are soldered to the tips of a fixed electrode rod 1 in a vacuum container consisting of an insulating container 9 and metal end plates 7 and 8, and a movable electrode rod 2 having a bellows 5, respectively. By opening and closing this electrical contact point of the movable electrode rod 2 by an external force, the circuit current is interrupted.

The shield 6 is provided to protect the inner surface of the insulating container 9 from the diffusion of metal vapor generated when the electrical contacts 3 and 4 are opened and closed.

The present invention relates to electrical contact materials for such vacuum switches.

In the process of decreasing the cutoff current of a vacuum switch near zero value, especially in slow-phase current cutoff with a low power factor, if a new phenomenon occurs due to a sudden drop in current, abnormal voltage will occur, threatening the insulation of connected equipment. It turns out.

Therefore, in a vacuum switch, it is necessary to lower the breaking current value and reduce the abnormal voltage.

On the other hand, in order to interrupt large currents, a contact material containing Aft@ or Cu (e), which is a highly conductive metal, is required.

Electrical contacts for vacuum switches generally consist of a metal or compound with a high melting point and low vapor pressure (hereinafter referred to as matrix material) and a metal with a relative low melting point and high vapor pressure (referred to as arc spot material).

Conventionally, when the above At or Cu is used as a mark/spot material, a metal carbide such as WC (Dungesten Carbide) is selected and used as a matrix material to be combined with it, and the cutting current is about 1A. However, there is a large variation, reaching 7 to 8 A in some cases, and it is necessary to reduce the variation in the cutting current value.

Especially when Cu and carbide are combined, the cutting current value is 2
It is difficult to get it below A.

The present invention was made in view of the above points, and an object thereof is to provide an electrical contact material which reduces the breaking current value and has less variation by adding a boride having a low work function of thermionic emission. It is.

The electrical contact material according to the present invention is heavy and At or C
15 to 50% of any one of u, 0.5 to 10% of a boride with a thermionic emission work function of 3 eV or less, one of group 4, group 5, group 6 carbide or boride is 55-8
0%, and further contains 5% or less of any one of Mo, B, or Fe-based transition metals.

The electrical contact material of the present invention will be explained below. First, the metal boride is MeB2 type (Me is metal, B is boron),
There are MeB type, MeB1□ type, etc.

MeB2 type is TiB2 jZrB2, VB2TaB
21M02B6. It is a boride of group 4, group 5, group 6 such as W2B5, and MeB6 type is CaB6SrB6, YB6
, LaB6. CeB6. These are borides of alkaline earth metals and rare earth elements, such as GdB6jT h B6.

These borides are carbide materials with a high melting point of 2000°C or higher, a microhardness of 2000 KVmJL2, and an electrical resistance of 20 μΩcrfL (at room temperature) or higher, which meets the requirements for a matrix material. Suitable as a matrix material.

In addition, many of these borides have extremely low work functions for thermionic emission, and in particular, among the MeB2 types, TaB2 has a work function of 2.89 e V, and W2B5 has a work function of 2.62.
eV, and MeB6 type generally has a small work function and C
a B6 is 2.86 e V -Y Be is 2.2 eV
, LaB is 2.7 eV, CeB6 is 2.7 eV
sG d B6 is 2.05eV, ThB6 is 2.92
It is eV.

Borides, which have a low work function for thermionic emission, easily emit electrons, so a small cutting current value can be obtained.

As mentioned above, MeB6 type boride has a melting point of 2000°C or higher, but the melting point of the element is Ca843°C5r774°
CLa920°CCe800°C, the vapor pressure of the element evaporated from the boride dissociated by the arc current is Af,
Since it is thicker than Cu, it has the effect of lowering the temperature and cut-off current value.

When boride is used as a matrix material, Mo, B, and Fe-based transition metals are effective as binding materials for sintering, and are added in an amount of 5% or less.

That is, the composition of the present invention includes 15 to 50% by weight of A1 or Cu as the arc spot material, and 0.5 to 10% of boride having a work function of thermionic emission of 3 eV or less.
%, boride or carbide as matrix material is 55~
Hiroshi 80 Also, the amount of Mos B or Fe-based transition metals as a binder is 5% or less, and vacuum switches using electrical contact materials made by mixing these and sintering are capable of interrupting large currents. At the same time, the cutting current value can be set to 1.5 A or less, and its variation can be reduced.

[Brief explanation of the drawing]

The figure is a longitudinal sectional view of the vacuum switch. 1... Fixed electrode rod, 2... Movable electrode rod, 3, 4... Electric contact, 5... Bellows, 6... Shield, 7.8...Metal end plate, 9...Insulating container.

Claims (1)

[Claims] 1. Either A1 or Cu is 15 to 15% by weight.
50%, 0.5-10% boride with a thermionic work function of 3 eV or less, and 55-so% any one of Group 4, Group 5, and Group 6 carbides or borides. An electrical contact material for a vacuum switch, further comprising one of Mo, B, and Fe-based transition metals of 5φ or less.