SU951449A1 - Liquid metal self-recuperating current limiter - Google Patents

Description

(54) LIQUID-METALLIC SELF-REDUCING

CURRENT LIMITER

one

The invention relates to electrical apparatus and can be used to limit and disconnect short-circuit currents in low-voltage electrical networks.

Known current limiters containing a fusible element of liquid metal, located in a tube of special ceramics 1.

The disadvantage of these devices is the instability of the protective characteristics. This is due to the wear of the inner diameter of the ceramic tube under the action of an electric arc when triggered. The inner diameter of the tube of known devices increases after each actuation, which is equivalent to an increase in the diameter of the fusible element. Therefore, the response time at a constant magnitude of the fault current varies with each subsequent cycle.

The closest to the invention to the technical essence is a current limiter, which contains a dielectric case of heat-resistant ceramics with a channel, filled with liquid metal and contact leads, one of which is made with an insulated side surface 2.

However, the high resistance of the electrode causes a high heating temperature both in the normal mode and 5 in the operation mode. Hence, a large loss of power and the need to make the electrode refractory. At very high current values, the electrode may be destroyed. This indicates a limited switching capacity of the device.

The aim of the invention is to increase the switching capacity, reduce power loss and simplify the design of the device.

15

The goal is achieved by the fact that the electrode is made of a material with a nonwettable liquid metal surface.

In this case, the resistance of the electrode may be less than that of the prototype. BUT

Claims (2)

20, an increase in resistance at the point of contact of an electrode-liquid metal is achieved due to transient resistance, which is of great importance in case of poor wetting. The drawing shows the proposed device. The device consists of a ceramic tube 1, reinforced by an outer casing 2. The tube is filled with liquid metal 3, the pressure of which is given by a piston 4 located in the lower contact cap 5 and a spring-loaded compressed gas in cylinder 6. The upper contact cap-7 is connected to fusible a liquid metal element by means of an electrode 8 made of a material with a non-wetting surface, for example, graphite, with a liquid metal. The current limiter works as follows. When an emergency current occurs in the circuit, the metal column and the electrode are heated. The greatest heat release occurs at the point of contact of the electrode with the liquid metal due to the high transition resistance. A portion of the liquid metal near the electrode evaporates to form a vapor lock. The magnitude of the emergency current decreases sharply. An electric arc arises between the electrode and the still not evaporated part of the liquid metal. Under the action of a flowing current and an electric arc, the length of the channel with the evaporated metal increases. When the critical length is reached, the arc quenches. The excessive pressure inside the tube is reduced due to an increase in the volume of the internal cavity filled with liquid metal due to the drop down of the spring-loaded piston. The damaged electrical circuit is then broken by another switching device synchronized with the current limiter. After condensation of metal vapors, the pressure in the cavity with the liquid metal decreases and the piston returns the liquid metal to the tube, ensuring readiness for re-action. The outer jacket serves to prevent the ceramic tube from bursting due to the high pressure inside it when triggered. The wear of the ceramic tube in this device under the action of the arc does not significantly affect the protective characteristic, since the current and the response time are determined by the magnitude of the contact-resistance of the electrode-liquid metal contact. Wear of the end part of the electrode does not change the area of contact with the liquid metal and the magnitude of the transient resistance. This device is advantageously different from the prototype, since it has an electrode with less resistance at the same length. This allows to reduce power losses in the nominal mode, to simplify the design due to the fact that there is no need to perform the electrode to increase its heat resistance, and also makes it possible to increase the switching capacity, which in the prototype is limited by the heat resistance of the electrode. The invention of the Liquid metal self-healing current limiter containing a dielectric body of heat-resistant ceramics with a channel filled with liquid metal, grit and contact leads, one of which is made in the form of an electrode with an isolated side surface, characterized in that, in order to increase switching capacity and reduce losses power, this electrode is made of a material with a non-wettable metal surface. Sources of information taken into account during the examination 1. V. Degr and G. G. Nesterov. Contact devices of Low-voltage Electrical Apparatus. Results of science and technology VINITI Academy of Sciences of the USSR, ser. Electrical apparatus. 1980, No. 2, p. 98. Bible. 234. 2. USSR author's certificate in application number 2905174, cl. H 01 H 29/30, 1979. // // f ///