Liquid metal self-resetting current limiter

 

The invention relates to electrical apparatus. Liquid metal self-resetting current limiter includes a dielectric sleeve of ceramic heat with a channel filled with liquid metal, piston, two contact output and heat-resistant electrode. The cross-section of a heat-resistant electrode is less than the cross-section of the channel with the liquid metal, and the running resistance of heat-resistant electrode is smaller than the running resistance of the liquid metal in the channel. The limiter has a high structural reliability and improved switching capabilities. The technical result is to increase the reliability of design and breaking capacity of the current limiter. 1 Il.

The invention relates to electrical devices and can be used for protection of electrical installations low voltage from short circuits.

Known current limiter containing the fusible element of the liquid metal located in the hub of special ceramics, and contact pin (see Degtyar Century BC, Nesterov gg Contact switching device electrical apparatus low voltage. The results of science and technology. is the instability of the protective characteristics, which is caused by wear of the channel dielectric sleeve during the arc phase of the process, which is equivalent to increasing the diameter of a fuse of the conventional fuse from cycle to cycle.

The elimination of this disadvantage is possible due to the location in the channel of the dielectric sleeve special electrode with namachivayam liquid metal surface, providing increased resistance at the site of contact of the liquid metal electrode.

From theory it is known that during the flow of electric current greatest heat generation occurs in that part of the circuit, which has a large resistance. This area (the contact electrode and liquid metal) is heated to the critical temperature (in this case up to the boiling temperature of the liquid metal) faster than other parts of the circuit, thus there is heating of the liquid metal near the butt end of the electrode and the oxide film, the evaporation of liquid metal, which leads to rupture of the circuit, arcing, with subsequent quenching. Increased contact resistance of the contact electrode, the liquid metal will determine the response time of the current limiter. Therefore, the response time is not budetchisto case of heat ceramics, the channel is filled with liquid metal, the piston and pin conclusions, one of which is executed in the form of an electrode from a material with namachivayam liquid metal surface (see and.with. No. 951449, BI No. 30, 1982). With increasing heat release occurs at the site of contact of the electrode with the liquid metal. However, when the rated current flow possible “pricing” and the destruction of the oxide films and then restore them or without. The destruction of the oxide films is also possible at the first operation in the feedback on the end surface of the electrode of an electric arc. In this case, the contact resistance can apply to almost zero. The current limiter will not perform intended functions during subsequent cycles.

Thus, a disadvantage of the known device is the low reliability.

Known current limiter with the increased stability of the protective characteristics, containing dielectric body made of heat ceramic with a channel filled with liquid metal, the piston and two electrodes; one electrode has a linear resistance greater than the running resistance of the liquid metal in the channel due to the fact that the cross section of this / of the electrode material of the liquid metal (see A. with. No. 905914, BI No. 6, 1982, prototype). With this technical solution, the electrode is a conductive circuit having a high resistance (linear electrode resistance more linear resistance of the channel with the liquid metal). Therefore, when applying a fault-current in it produces a large quantity of thermal energy. The temperature of the electrode quickly reaches a value equal to the boiling temperature of the liquid metal, than the temperature of the liquid metal. The result is warming up to the boiling point of the stretch liquid metal is in close proximity to the electrode. The resulting steam tube breaks the circuit with the subsequent emergence and extinction of the electric arc. If the energy released in the electrode during predugovore stage of the process, and also in the process of extinguishing the electric arc is not sufficient to heat the electrode above its melting temperature, the machine keeps working during subsequent cycles. Otherwise, destroyed the entire electrode or a part of it. The melting of the electrode or its part is mixing the molten metal of the electrode and the liquid metal. This leads to a resistance change analnogo destination.

The prototype, according to the formula, the cross section of the electrode may be larger or smaller than the cross section of the channel with the liquid metal. When triggered, the current limiter is wear channel with liquid metal and increase its diameter. In the case when the cross section of the electrode is larger section of the channel with the liquid metal, increasing the diameter of the channel leads to disruption of the stability of the protective characteristics. There is a reduction of running resistance of the channel with the liquid metal, thus increases the difference between the linear resistance of the electrode and the channel with the liquid metal, which increases the probability of failure of the electrode.

The disadvantage of this device is its low reliability and breaking capacity of the current limiter associated with the destruction of the electrode under the influence of the short circuit current.

Increased resistance in the place of contact of the electrode - liquid metal can be obtained by narrowing the power flow through the cross section of the electrode is smaller section of the channel, and the larger the difference, the stronger the effect of the narrowing of the lines of force of the current.

This idea is implemented in the proposed device.

The technical result is increased reliability design is granitetile current containing dielectric body made of heat ceramic with a channel filled with liquid metal, piston, two contact output and the electrode section of the electrode is smaller than the cross section of the channel with the liquid metal, and the running resistance of the electrode may be smaller than the running resistance of the liquid metal in the channel.

By reducing the cross section of the electrode is formed increased contact resistance due to the increased density of power lines at the site of contact of the liquid metal and the electrode. In this form of the electrode formed area of high resistance liquid metal near the butt end of the electrode, which leads to evaporation of liquid metal at the site of contact of the electrode with the liquid metal during the flow of a fault-current.

The electrode feel no increased exposure to heat does not heat up during predugovore stage of the process up to the boiling temperature of the liquid metal and is not destroyed when triggered.

The drawing shows the proposed device.

The device consists of a dielectric sleeve 1, reinforced outer casing 2. The dielectric sleeve 1 is made of ceramic heat. Channel dielectric sleeve 1 filled with liquid metallverken in the form of glass. The piston 4 is spring-loaded with compressed gas. The gas is in the cylinder 6. The upper contact pin 7 is connected with the fusible element of the liquid metal 3 via a heat-resistant electrode 8 having an extension at the site of contact with the contact pin 7.

The cross section of the electrode is less than the cross-section of the channel with the liquid metal at the point of contact.

Through this section of the electrode is formed increased contact resistance of the stretch liquid metal channel near the end of the electrode due to the increased density of magnetic lines of force.

The current limiter operates as follows.

Upon the occurrence of an overcurrent is heated as heat-resistant electrode 8 and the liquid metal 3. The greatest heat generation occurs in the liquid metal 3 in contact with the heat-resistant electrode 8 due to the large contact resistance. Part of the liquid metal 3 near heat-resistant electrode 8 evaporates, providing an open circuit with the subsequent occurrence of the arc between the end part of the heat-resistant electrode 8 and has not yet evaporated liquid metal 3. Under the action of the current flowing arc length increases and when the critical extinguished.

Due to evaporation of the liquid metal 3 when triggered proizv metal pressure drops and the piston 4 returns the liquid metal 3 in the channel, ensuring readiness to repeat the action.

This device differs from the known prototype increased reliability and improved switching capacity, because in this design the cross section of the electrode is less than the cross-section of the channel with the liquid metal, and the running resistance of the electrode is less than the running resistance of the liquid metal in the channel, while the prototype section of the electrode may be larger or smaller than the cross section of the channel with the liquid metal, and the running resistance of the electrode is more linear resistance of the channel with the liquid metal. Unlike the prototype, the wear of the channel with the liquid metal does not lead to the destruction of the electrode. The response time of the current limiter is determined by the cross section of the electrode, therefore, it will be stable.

Claims

Liquid metal self-resetting current limiter containing dielectric sleeve of ceramic heat with a channel filled with liquid metal, piston, two contact output and heat-resistant electrode, characterized in that the cross section of heat-resistant electrode is less than the cross-section of the channel with the liquid metal, and the running resistance of heat-resistant electrode is less than linear

 

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SUBSTANCE: proposed liquid-metal current limiter designed for use in up to 0.4 kV power networks to protect power loads against short-circuit currents has insulating bushing with axial bore receiving internal loosely mounted ball-shaped ceramic part of strict geometrical dimensions, and easy-to-manufacture narrow neck disposed at cross-sectional area of internal ceramic part, along its diameter and diameter of insulating bushing. Either side of bushing mounts contact leads, bellows being attached to one of them. Inner cavity of bellows and that of insulating bushing, as well as neck are filled with liquid metal.

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