Equipment for disconnecting the current load. Load Switch

For safe operations, including the repair and replacement of electrical equipment, repair of the electrical circuit section under load, it is necessary to disconnect the power supply. Doing this under load is not easy due to the occurrence of an electric arc when the contacts of the device are opened. For the process to be safe, special equipment is used - the load switch.

What is such an apparatus?

A load breaker is a device used to disconnect a contact group on a section of an electrical circuit by means of a mechanical action equipped with arcing chambers. The device is high-voltage and located in electrical installations operating at a voltage of 6 and 10 kilovolts. The load switch is widely used to stop and resume power supply in the distribution substations of urban and rural areas, as well as the shops of enterprises.

Devices for circuits with low currents

Without a heavy load, the circuit-breaker is used with a manual drive without an arc-suppression mechanism. It is used in circuits with small currents - usually in distribution boards of household or administrative premises. An example of such devices is the load breaker VN-32. It is designed to work in circuits 230-400 V and with a load current of 22 to 100 A. It has a different pole - from 1 to 4 contacts.

Device of the switch of the load

If we consider the general arrangement of this mechanism, regardless of the type and scope of application, the conventional gas-pressure switch is a welded base frame on which three fixed contacts of the disconnector with terminals for connecting the phase conductors of the cable are rigidly fixed to the high-voltage insulators. These contacts are placed in the arc chutes.

On the other three insulators corresponding to the fixed group, a mobile group of contacts is formed, which is the contacts made of two plates and an arc-quenching group of knives.

An example of such a device is the BNA-10 load breaker, operating in circuits up to 10 kV with a rated current of up to 630 A. This type is manufactured in different versions: with grounding knives (one or three), and fuses (or without them).

Arcs interrupters

They are made of plastic and contain fixed point contacts attached to the main stationary. On the sides of the chamber are plates made of gas-generating material.

To extinguish the arc that occurred when the circuit is broken, the following types of cancellation are used in the respective chambers:

- autogas;

- auto-pneumatic;

- electromagnetic;

- gas-insulated;

- with vacuum elements.

Principle of operation of load breakers

When the device is turned on, the arc-extinguishing knife plates enter the arc extinguishing chambers and are connected to the corresponding fixed contacts. Next, the main movable and fixed contacts come into contact. At the time of disconnection in the gas-oil circuit breaker, the main groups of contacts are first disconnected, and only after them the decoupling knives and fixed contacts are disengaged in the arc extinguishing chamber.

As the knives leave the quench chamber, the arc formed at this moment heats the gas generating material. The gas released by this material creates in the chamber an increased pressure and flow between the movable knife and the liners, which extends the arc lengthwise, increasing its resistance. As a consequence, it goes out.

Now, how to connect the load break switch. The device is installed strictly vertically, with mandatory checking of the plumb and level. If necessary, suitable gaskets are used. During the tightening of the bolts, the freedom of the arc-cutting blades in the chamber is continuously monitored. Then the drive is installed (front or rear - depending on the design). The pull rod is connected to the switch shaft by the sector lever of the drive. The parallelism of the knives is regulated by insulators on which axial contacts are fixed. After 25 inclusions and shutdowns, if there were no deviations in the entry of knives into the chambers and disruptions in the operation of the drive, the phase conductors of the cable are connected to the outlets of the fixed and movable groups of contacts.

Types of load break switches

By the method of activation, these devices are divided into three groups:

1. The first - switches with manual drive. They are abbreviated as VNR (load switch with manual drive).
2. The second - with a spring drive autogas. They are designated BHA, and their inclusion is carried out with the help of a lever. A trip - a spring loaded drive.
3. And the third type - with a spring drive and fuses. This type is referred to as GNP. Its feature is that it can work as a short-circuit protection due to the fuse-links inserted on its frame and the shut-off mechanism when they are burned out.
   

How does the load break switch differ from the automatic?

This device only operates on the rated (calculated) tripping current and does not break the circuit at short-circuit currents . The automatic version has a mechanism for disconnection (tripping) in case of a short circuit. To activate the load circuit breaker, additional safety devices are required. For example, fuse-links, as in devices like GNP.