JPS5925021B2 - Electrical contact materials for vacuum switches - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Vacuum switches have recently been used as a type of power distribution equipment in place of conventional air or oil submerged switches.

Vacuum switches have a variety of uses, such as (1) those whose fault current is relatively small and are mainly used for switching normal load currents, and (2) vacuum switches that can be used in combination with power fuses to prevent accidents when an accident occurs. There are two types: (3) the current is cut off by a power fuse, and the switching of normal load current is performed by a vacuum switch; and (3) the main purpose is switching of fault current.

Examples of applications for (1) include capacitor switches and tap changers, applications for (2) include high-voltage combination starters, and applications for (3) include general power circuit breakers.

Since vacuum switches switch and close current in a vacuum, they tend to generate abnormal voltages due to current cutting when contacts are opened, and low cutting current has been particularly important for vacuum switches used to open and close high-voltage motors.

Conventionally, alloys made of tungsten and copper or copper and bismuth have been known as contacts for vacuum switches, but they are not necessarily sufficient as contacts, and materials that have low current cutting properties and are well-balanced for high-voltage contacts are desired. It is rare.

This proposal has been made in view of the above points, and is intended to provide a material with a low current cutting level and a well-balanced material for use as a contact point.

The feature of the present invention is that it is basically composed of 20 to 80% by weight of tungsten carbide, 1 to 30% by weight of iron, and the balance is silver, and has different opening/closing characteristics from conventional silver-tungsten carbide.

The following four effects are obtained by containing iron.

That is, (1) the cutting current value can be reduced while maintaining stable large current cutting performance, and the variation in the cutting value is small and stable.

(2) The toughness of the alloy is improved and cracks are reduced.

(3) It must have good workability; (4) It must be an inexpensive material.

It is. The contact material of the present invention replaces Fe with Ag-(20~
80) Since it is characterized by containing a large amount in weight%, it is not preferable to use it in general air breaker or contactor because the amount of arc increases.

The present invention has excellent characteristics against current cutting only when used in a vacuum, and can withstand large current interruptions.

In the present invention, if the iron content is 1% by weight or less, there is no significant change in performance, but it is required to be at least 1% by weight or more, and the most effective range is from 1 to 30% by weight.

Furthermore, if the iron content exceeds 30% by weight, the heat resistance decreases and melting loss increases when a large current is cut off, so it is preferable to keep the iron content below this range.

The inclusion of large amounts of iron in silver-tungsten carbide greatly reduces the electrical conductivity of the alloy.

For example, if we take the case of a 35 wt% silver-65 wt% tungsten carbide contact, in the case of no additives, it is about 35% lAC3.
35% by weight silver - 61% by weight tungsten carbide - 4% by weight iron material is 18% lAC335% by weight silver - 5
0wt% tungsten carbide - 15wt% iron material 12%
It is lAC3.

By reducing the electrical conductivity in this way, a stable arc can be supplied between the contacts when the current is cut off, and the current cutoff value can be reduced.

The performance of the material of the present invention will be shown below with reference to Examples.

Example 1 To verify the current cutoff value, AC420 was used using 20φ x 3 contacts in a vacuum with a pressure of less than 1X10-3 Torr.
V, 500 A, power factor approximately 0.5 Null circuit was opened and closed many times, and the change in cutting current value before and after was measured at AC 200 V, 30
Measurements were made by opening and closing each resistance circuit A 20 to 30 times.

Table 1 shows the average value or standard deviation σ of these current cutoff values, and the current cutoff value of iron-containing materials is considerably lower than that of additive-free materials, especially in the 50%Ag system, which increases the number of tests. It can be seen that the variation decreases with increase, indicating extremely excellent characteristics.

It was shown that the alloy of the present invention containing a large amount of iron exhibits excellent characteristics even when a large current is interrupted.

These are shown in Example 2.

Example 2 35% silver-61 with dimensions of 20φ x 3mm according to the present invention
wt% tungsten carbide - 4 wt% iron and 35 wt% silver - 50 wt% tungsten carbide - 15 wt% silver alloy
Attached to a vacuum switch that maintains a vacuum with a pressure of less than Xl0 Torr, AC6.6KV, 4.4KA power factor approximately 0
．． 3. When a cutoff test was carried out using the sequence 0-2 minutes - CO, all tests were successfully cut off without any abnormalities.

Also, the same alloy as above was heated to 3.3 to 4.4 KA under the same vacuum conditions.
A short-time energization test of 2 seconds and a Power Fuse coordination test of 40 KA energization at a limiting current peak value were conducted, but both results were satisfactory with no welding.

In other words, it was confirmed that the present alloy exhibited excellent current cutting characteristics before and after the durability test, and was able to perform its function without abnormalities even when switching on and off a small current and when passing a large current.

Also, cut-off test, short-time energization test and Power Fus
It was also confirmed that the current cutting value after any test in the e-coordination test was the same as that during the durability test, and that stable low current cutting performance was always maintained.

Another advantage of the material of the present invention is that the toughness of the alloy is improved, and chipping and cracking of the alloy during opening and closing of contacts can be prevented.

This is thought to be because, when comparing alloys with the same silver content, the addition of iron reduces the hard tungsten carbide itself, increases the sinterability of the alloy, and strengthens the bonding between particles.

This will be explained below using examples.

Example 3 One of the materials of the present invention, 5 with dimensions 20φ x 37n11L
0 wt% silver - 45 wt% tungsten carbide - 5 wt% iron and 30 wt% silver - 50 wt% tungsten carbide -2
Attach the 0% by weight iron material to a vacuum switch that maintains a vacuum at a pressure of less than 1X10'' Torr, and heat it at AC420V, 5
When a circuit with a 00A power factor of approximately 0.5 was subjected to continuous switching tests up to 250,000 times, no particular abnormality was observed in the contacts in both cases.

However, with 50 wt% silver-50 wt% tungsten carbide and 35 wt% silver-65 wt% tungsten carbide, which do not contain iron, chips of about 1.5 to 3 mm square were observed in the contact area after the test was completed under the same conditions. occured.

The material of the present invention not only has good properties in opening and closing the electric circuit described above, but also has the advantage of being highly machinable.

This means that when compared with the same silver content, in the material of the present invention, by replacing hard tungsten carbide with soft iron, machining after sintering, especially cutting characteristics, is improved, which helps extend the life of the cutting tool.

In addition, the material of the present invention contains a large amount of iron, which is cheaper than tungsten carbide.
When comparing the same silver content of conventional alloys,
The cost of the contact can be reduced, and it is of great value as an industrial material.

Claims (1)

[Claims] 1. An electrical contact material for a vacuum switch comprising 20 to 80% by weight of tungsten carbide, more than 1% to 30% by weight of iron, and the balance silver.