SI22278A - Varistor protection against thermal destruction with protective fast disconnection shutdown - Google Patents

Abstract

Subject of the invention is a protection device for the protection of varistors featuring a fast varistor shutdown inside the circuit which protects the varistor against destruction in the case of overheating. In practice the varistors are exposed to overvoltages originating from atmospheric discharge or excessive oscillation of the network voltage which induces major currents through the varistor, its heating and if the situation persists an overheating of the varistor which leads to their thermal destruction, explosion or fire in the vicinity, should they not be adequately protected. The protective device for the varistor with fast disconnector which includes a mechanical disconnection mechanical system with terminal contact made preferably from spring sheet metal whose disconnection time is additionally reduced by adding springs into the mechanical system located in a special enclosure attached to the varistor which it protects as a special unit integrated into the varistor circuit, and in the case of overheating the varistor separates it from the network and signalises such a condition by switching a signal contact to indicate the exceptional status of the device which is subject of the invention. The protection device with fast disconnection for the protection of the varistor is due to its technical concept as a special unit generally applicable regardless of the varistor dimensions, various nominal voltage levels, while during overheating its implementation prevents a negative impact of varistor fumes and can be applied also with special versions of varistor protection as for example with two varistors operating by connecting their back with a common varistor terminal.

Description

VARISTOR PROTECTION AGAINST THERMAL DESTRUCTION WITH A QUICK DISCONTROL DEVICE

The subject of the invention is a varistor protection device with the ability to quickly disconnect the varistor from the circuit.

Products of this kind are classified in class H02H 5/04 according to the international classification.

The invention relates to the protection of a metal oxide varistor by means of a safety device with a built-in quick disconnect, which is thermally actuated upon overheating of the varistor, causing overvoltages of atmospheric origin and other possible causes of overvoltages originating from the network. Said protective device interrupts the flow that flows through the varistor and protects the varistor from destruction. The safety device is fixed to the varistor.

In practice, varistors in the network are exposed to a number of overvoltage overloads arising from various causes, the most important being atmospheric discharges. In addition to lightning strikes, the network or its surroundings are classified as dangerous causes of overheating and consequent destruction of the varistor, excessive fluctuation of the mains voltage, permanent or current defects in house installations, disturbances by large consumers (especially inductive character - motors, contactors, etc.).

If the overvoltage over the varistor operating parameters lasts too long, high currents flowing through the varistor will cause the varistor element to overheat and thus destroy it, which can cause damage to the circuit in which the varistor is integrated. A varistor that overheats to a critical limit can also cause fire and consequently great damage to its surroundings.

There are several solutions on the market that successfully protect the varistor from thermal destruction.

According to the prior art, one of the solutions to this problem is described in U.S. Pat. 5 901 027, wherein said technical problem is solved by means of a special layer which is applied to a varistor tablet and acts as a fuse.

A further solution is described by US Pat.No. 5706553, wherein the described thermal protection of the varistor is made by means of a solder by which the connection is soldered to the varistor tablet and which melts at an increased temperature.

In U.S. Pat.No. 6636403 B2 is a solution implemented with the help of a special protection system that is soldered to the varistor tablet.

All prior art systems that are mounted directly on the varistor itself or implemented as a standalone security element with a built-in varistor have several disadvantages that are eliminated by the solution of the present invention.

The protection of the varistor against thermal destruction due to overheating with the device according to the invention is characterized by shorter switching times and higher reliability of the switching than in the prior art solutions, since the switching mechanism of the guarding device for the protection of varistors is improved, made of sheet metal with spring properties, with spring included to accelerate disconnection. Said spring plate can be replaced by a plate characterized by in addition to spring properties, resistive properties up to 0.1 Ω and can also be combined with said spring. In the case of current conduction, the mentioned embodiment results in an increased voltage drop on the disconnecting mechanical system with resistive properties, which enables additional heating of the solder joint.

The protective device for the protection of varistors according to the invention also includes a special space in which a tripping mechanism is installed. In some embodiments, protecting the varistor from thermal destruction according to the prior art, the varistor vapors released during the overheating of the varistor may, in the disconnection phase, create an electric arc between the metal parts of the disconnect mechanism and the varistor contact, thus preventing a definitive disconnection in the solution according to the invention upon overheating the varistor pair cannot be adversely affected by the varistor pairs because the breaker mechanism is in a special housing.

The advantage of a protective device for protecting varistors of the invention against prior art embodiments is also in the ease of implementation, since the system is implemented as a separate unit and is not incorporated into the varistor body, which increases reliability and expands its scope.

The described solution according to the invention provides, for the purpose of implementation, applicability at any nominal varistor voltages. In some embodiments of the prior art, where the varistor is incorporated into the guard housing, it is possible to limit the usefulness with respect to the nominal voltage of the varistor Un, due to the varistor dimensions.

A further advantage of the solutions according to the invention is shown in its use in two varistors acting coupled to the back with common varistor contact. With two varistors in the given joint we protect two voltage levels or use them in an application where we want to increase the maximum discharge current, protect them from thermal destruction by using two protective devices for protecting the varistor with quick disconnect, for each varistor separately, mounted laterally.

The further advantages and applicability of the invention will become even more apparent to the average person skilled in the art and accompanying drawings.

Figure 1 Displays a safety device for protecting varistors attached to the body of a varistor Figure 2 Displays a disconnect mechanism with a spring in tension Figure 3: Displays a disconnect mechanism without a spring in tension Fig. 4: Disconnect mechanism in a disconnected state

Figure 5: Side view of the attachment of a varistor protection device by quick detachment to the varistor body by means of a fastener

Figure 6: Demonstrates the use of a quick-release varistor protection device in the case of two back-coupled varistors

The quick-release varistor protection device 7 is attached to the body of the varistor 2 as shown in Figure 1 and includes the housing cover of the device 6, made generally of non-conductive material, a contact contact 4, a signal contact 5, a disconnect mechanism mounted in the body Device housings 1. The housing housing cover 6, also made of non-conductive material, is generally mounted on the body of the housing 1 as shown in Figure 1.

The tensioning disconnecting mechanism, as shown in Figure 2, is mounted in a space formed by the body of the housing of the device 1 and includes a connection contact 4 inserted into the body of the housing of the device 1, soldered on one side with a low temperature solder 10 to the varistor contact 8 , which enters the body of the housing of device 1 through a prepared slot in said body of the housing of device 1, and a spring 3 which is attached at one end to the body of the housing of device 1 and the other to the connecting contact 4.

The signal contact 5 shown in Figure 2 is attached to the body of the housing 1 and is designed so that the upper, curved portion extends into the body of the housing 1 and said curved portion of the contact 5 forms a contact surface 12

When the varistor body 2 is heated, heat is transferred through the varistor contact 8 to the solder 10, which is heated and at a predetermined temperature, said terminal contact 4 melts due to the melting of the solder 10 and consequently the junction between said varistor contact 8 and the terminal contact 4, due to the spring properties of the material of which the spring contact 4 is made, triggers and jumps into space, the spring 3 accelerating the disconnection, immediately disconnects the electrical connection and disconnects the varistor from the mains and consequently the varistor no longer heats up. In the event of disconnection, the terminal contact 4 is jerked to the extreme position defined by the contact surface 12 of the signal contact 5, as shown in Figure 4, the electrical contact is made through the contact surface 12, the current flows through the signal contact 5 and signals to the users of the device that a state of emergency has occurred and the device needs to be inspected and reinstalled with a varistor protection device 7.

In less demanding applications, a non-spring 3 disconnect mechanism is used, as shown in Figure 3. The operation of the disconnect mechanism is identical to that already shown and described.

A quick-release varistor protection device 7 is secured to the body of the varistor 2 by means of a fastener 11 that is resistant to temperatures higher than the temperature of the destroyed varistor. as shown in Figure 5.

Two varistors coupled to the back that can protect two voltage levels or use them in an application where we want to maximize the maximum drain current are protected by two safety devices 7, as shown in Figure 6, attached to the side of two varistors with mounting means 11 and with a single grounding contact 9.

Claims (8)

PATENT APPLICATIONS A quick-release varistor protection device, characterized in that the disconnect mechanism mounted in a special housing includes a connecting contact, preferably made of a spring plate, extending at one end into the body of the housing and is fastened in a soldering state to varistor contact. A quick-release varistor protection device according to claim 1, characterized in that it is constructed as a stand-alone unit, which is attached to the varistor body. A quick-release varistor protection device according to claim 1, characterized in that said connection contact, at a predetermined varistor temperature, moves to interrupt the circuit and disconnect the varistor from the mains and trigger an emergency signal. 4. Fast-disconnect varistor protection device according to claim 1, characterized in that the disconnection rate of said contact is increased by the addition of a spring to the disconnecting mechanical system. 5. A quick-release varistor protection device according to claim 1, characterized in that the signal contact signaling the emergency state of the varistor protection system is inserted into a space formed by a special housing of the varistor protection system. A quick-release varistor protection device according to claim 1, characterized in that the voltage-limiting contact of the disconnect mechanism is soldered to the varistor contact by a low-temperature solder. A quick-release varistor protection device according to claim 1, characterized in that the housing is designed to allow lateral attachment to the body of the varistor. 8. A quick-release varistor protection device according to claim 1, characterized in that its housing is composed of two parts that form an enclosed space.