For safe work, including repair and replacement of electrical equipment, repair of a section of an electrical circuit that is under load, it is necessary to turn off the voltage supply. It is not easy to do this under load 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 an apparatus?
A load switch is a device used to disconnect a contact group in a section of an electrical circuit using mechanical stress, equipped with interrupter chambers. The device is high-voltage and is located in electrical installations operating under voltage of 6 and 10 kilovolts. The load switch is widely used to cut off and resume voltage supply in distribution substations in urban and rural areas, as well as in workshops of enterprises.
Devices for low current circuits
Without heavy load, the circuit breaker is used with a manual drive without an arcing mechanism. It is used in circuits with low currents - usually in switchboards in domestic or office buildings. An example of such devices is a VN-32 load switch. It is designed to operate in 230-400 V circuits and with a load current of 22 to 100 A. It has a different pole - from 1 to 4 contacts.
Load switch device
If we consider the general structure of this mechanism, regardless of the type and scope of application, then a conventional autogas load switch is a welded base frame on which three fixed disconnector contacts with leads for connecting phase conductors of the cable are rigidly fixed to high-voltage insulators. These contacts are placed in arcing chambers.
On three other insulators corresponding to the fixed group, a movable group of contacts is mounted, which is the contacts themselves, made of two plates, and an arcing group of knives.
An example of such a device is a VNA-10 load switch operating in circuits up to 10 kV with a rated current of up to 630 A. This type is made in various modifications: with grounding knives (one or three), as well as with fuses (or without them).
Arcing chambers
They are made of plastic and contain fixed point contacts attached to the main fixed ones. On the sides of the chamber are plates made of gas-generating material.
In order to extinguish an arc arising from an open circuit, the following extinguishing types are used in the respective chambers:
- autogas;
- autopneumatic;
- electromagnetic;
- gas-insulated;
- with vacuum elements.
Principle of operation of circuit breakers
When the device is turned on, the extinguishing plates-knives enter the arc quenching chambers and are connected to the corresponding fixed contacts. The next to come to the connection are the main movable and fixed contacts. At the moment of disconnection in the autogas switch, the main groups of contacts are disconnected in the first place, and only after them the arcing knives and fixed contacts are disconnected in the arc extinguishing chamber.
As the knives exit the quenching chamber, the arc formed at this moment heats the gas-generating material. The gas released by this material creates an increased pressure in the chamber and a flow between the movable knife and the inserts, which longitudinally blows the arc, increasing its resistance. As a result, it goes out.
Now about how to connect the load switch. The device is installed strictly vertically, and with a mandatory plumb and level check. If necessary, suitable gaskets are used. While tightening the bolts, the freedom of movement of the extinguishing knives in the chamber is constantly monitored. Then the drive is installed (front or rear - depending on the design). The rod with forks fits into the lever of the switch shaft with the sector lever of the drive. The parallelism of the knives is regulated by insulators, on which axial contacts are fixed. After 25 on and off, if there were no deviations in the entry of knives into the chambers and irregularities in the operation of the drive, the phase wires of the cable are connected to the taps of the fixed and mobile contact groups.
Types of load breakers
By the method of driving these devices are divided into three groups:
- The first is hand-operated switches. They are designated by the abbreviation VNR (load switch with manual drive).
- The second is autogas with spring drive. They are designated VNA, and their inclusion is carried out using the lever. And shutdown - cocked spring drive.
- And the third type - with a spring drive and fuses. This type is referred to as GNP. Its peculiarity lies in the fact that it can work as protection against short-circuit due to the fusible inserts placed on its frame and the shutdown mechanism when they burn out.
What is the difference between a load switch and an automatic switch?
This device works only at the rated (calculated) tripping current and does not break the circuit at short-circuit currents . The automatic option has a disconnection (shutdown) mechanism in the event of a short circuit. To operate on short-circuit currents, the load switch requires additional safety devices. For example, fusible inserts, as in devices such as GNP.