Equipment for disconnecting the current load. Load Switch
For safe operations, including repairs andreplacement of electrical equipment, repair of a section of an electrical circuit under load, it is necessary to switch off the supply of voltage. Doing this under load is not easy due to the occurrence of an electric arc when the contacts of the device open. For the process to be safe, special equipment is used - the load switch.
What is such an apparatus?
A load switch is a device,Used to disconnect the contact group on the electrical circuit by means of a mechanical action, equipped with arc chutes. The device is high-voltage and is 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 distribution substations of urban and rural areas, as well as shop floor of enterprises.
Devices for circuits with low currents
Without a large load, the switch is used withmanual drive without an arc-out 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 for operation 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.
Device of the switch of the load
If we consider the general structure of thismechanism, regardless of the type and scope of application, the usual autogas load breaker 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 three other 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 a switchload VNA-10, operating in circuits up to 10 kV with rated current up to 630 A. This type is manufactured in different versions: with grounding knives (one or three), as well as with fuses (or without them).
They are made of plastic and contain fixed point contacts attached to the main stationary ones. 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:
- with vacuum elements.
Principle of operation of load breakers
When the device is switched on, arc suppressorsThe 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 circuit breaker, the main groups of contacts are first disconnected, and only after them the decoupling knives and fixed contacts disengage from the arc extinguishing chamber.
As the knives come out of the arc extinguishing chamber,formed at this time, 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 result, 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 constantly monitored. Then the drive is installed (front or rear - depending on the design). The traction with the forks is joined to the switch shaft by the sector lever of the actuator. The parallelism of the knives is regulated by the insulators on which the axial contacts are fixed. After 25 inclusions and shutdowns, if there were no deviations in the entry of knives into the chambers and malfunctions 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
According to the method of activation, these devices are divided into three groups:
- The first - switches with a manual drive. They are designated abbreviation VNR (load switch with manual drive).
- 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.
- And the third type - with a spring drive and meltingfuses. 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 burn out.
How does the load break switch differ from automatic?
This device only works on a nominal(calculated) tripping current and does not break the circuit at short-circuit currents. The automatic version has a disconnection (disconnection) mechanism 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.