Для безопасных работ, включающих в себя ремонт и replacement of electrical equipment, repair of a part of an electrical circuit under load, it is necessary to disconnect the supply voltage. Do this under load is not easy due to the occurrence of an electric arc when the device contacts open. To ensure that the process is safe, special equipment is used - a load switch.
What is such a device?
A load switch is a device,used for disconnection of the contact group on the section of the electric circuit by means of mechanical action, equipped with arcing chambers. The device is high-voltage and is placed in electrical installations operating under voltage of 6 and 10 kilovolts. The switch disconnector is widely used for stopping and restarting the supply voltage in the distribution substations of urban and rural areas, as well as workshops of enterprises.
Low Current Devices
Without heavy load, the switch is used withhand-operated without arc mechanism. It is used in circuits with low currents - usually in the distribution boards of household or administrative premises. An example of such devices is the HV-32 load switch. It is designed to work in 230–400 V circuits and with a load current from 22 to 100 A. It has different poles - from 1 to 4 contacts.
Breaker device
If we consider the general device of thismechanism, regardless of the type and scope of application, the usual auto gas load 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 fixed on high-voltage insulators. These contacts are placed in the arc chambers.
On the other three insulators, corresponding to a fixed group, a movable group of contacts is mounted, which are the contacts themselves, made of two plates, and an arc-extinguishing group of knives.
An example of such a device is a switchVNA-10 loads 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 blades (one or three), as well as with fuses (or without them).
Arc chambers
They are made of plastic and contain fixed point contacts attached to the main fixed. On the sides of the chamber there are plates made of gas-generating material.
To extinguish the arc that occurred when the chain is broken, the following types of quenching are used in the respective chambers:
- autogas;
- auto-pneumatic;
- electromagnetic;
- gas-insulated;
- with vacuum elements.
The principle of operation of the load switches
When turning on the device arc-suppressingplate-knives enter the arc quenching chambers and are connected to the corresponding fixed contacts. The next come in the connection of the main moving and fixed contacts. At the moment of shutdown, the main groups of contacts are disconnected in the autogas switch of the load, and only after them the arc-extinguishing knives and the fixed contacts in the arc quenching chamber are uncoupled.
As the knives come out of the arc quenching chamber,formed at this moment, heats the gas-generating material. The gas released by this material creates an increased pressure in the chamber and the flow between the movable knife and the inserts, which longitudinally blows the arc, increasing its resistance. As a result, it goes out.
Now how to connect a load switch.The device is installed strictly vertically, and with obligatory checking by a plumb and level. If necessary, suitable gaskets are used. During the tightening of the bolts, the freedom of movement of the arc-extinguishing knives in the chamber is constantly monitored. Then install the drive (front or rear - depending on the design). Thrust with forks docked with the lever shaft of the switch sector lever arm. The parallelism of knives is regulated by insulators, on which axial contacts are fixed. After 25 inclusions and shutdowns, if there were no deviations in the presence of knives in the chambers and no malfunctions in the drive, the phase conductors of the cable are connected to the taps of the fixed and movable groups of contacts.
Types of load switches
By way of actuation, these devices are divided into three groups:
- The first one is hand operated switches. They are denoted by the abbreviation VNR (load switch with a manual drive).
- The second - with a spring drive autogas. They are designated VNA, and their inclusion is carried out using a lever. A shutdown - cocked spring drive.
- And the third type - with spring drive and fusiblefuses. This type is referred to as GNP. Its peculiarity lies in the fact that it can work as a protection against short circuits thanks to the fusible inserts placed on its frame and the shut-off mechanism at their burnout.
What is the difference between a load switch and an automatic switch?
This device only works on nominal(calculated) operation current and does not produce an open circuit at short-circuit currents. The automatic version has a mechanism of disconnection (shutdown) during a short circuit. To operate on short circuit currents, the load breaker requires additional safety devices. For example, fusible inserts, as in devices like GNP.
