For safe work, including the repair and replacement of electrical equipment, repair of the section of the electrical circuit 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 contacts of the device open. To make the process safe, special equipment is used - a load switch.
What is such a device?
A load switch is a device used to disconnect a contact group in a section of an electrical circuit using mechanical action, equipped with arc chutes. The device is high-voltage and is located in electrical installations operating under voltage of 6 and 10 kilovolts. The load break switch is widely used for interrupting and resuming the power supply in distribution substations of urban and rural areas, as well as enterprise workshops.
Low circuit devices
No big loadthe circuit breaker is used with a manual drive without an arc extinguishing mechanism. It is used in circuits with low currents - usually in switchboards of domestic or administrative premises. An example of such devices is the VN-32 load switch. It is designed to operate in circuits 230-400 V and with a load current from 22 to 100 A. It has a different polarity - from 1 to 4 contacts.
Load Breaker Device
If we consider the general arrangement of this mechanism, regardless of the type and scope, then a conventional auto-gas load switch is a welded base frame on which three fixed contacts of the disconnector with leads for connecting the phase conductors of the cable are rigidly fixed on high-voltage insulators. These contacts are placed in arc chutes.
On the other three insulators corresponding to the fixed group, a movable group of contacts is attached, which is the contacts themselves, made of two plates, and an arc-suppressing group of knives.
An example of such a device is a load switch VNA-10, operating in circuits up to 10 kV with a rated current up to 630 A. This type is manufactured in different modifications: with grounding knives (one or three), as well as with fuses (or without).
Arc chambers
They are made of plastic and contain fixed point contacts attached to the main fixed ones. Plates of gas-generating material are installed on the sides of the chamber.
To extinguish the arc generatedwhen the circuit is broken, the following types of extinguishing are used in the respective chambers:
– autogas;
– autopneumatic;
– electromagnetic;
– SF6;
– with vacuum elements.
The principle of operation of load break switches
When the device is turned on, the arcing blades-knives enter the arc extinguishing chambers and are connected to the corresponding fixed contacts. The next to come into the connection are the main moving and fixed contacts. At the moment of disconnection in the auto-gas switch, the main groups of contacts are disconnected first of all, and only after them the arc-suppressing blades and the fixed contacts in the arc-suppressing chamber are disconnected.
As the knives exit the extinguishing chamber, the arc formed at that moment heats the gas generating material. The gas emitted by this material creates an increased pressure in the chamber and a flow between the movable knife and the liners, which blows the arc longitudinally, increasing its resistance. As a result, it goes out.
Now how to connect the load break switch. The device is installed strictly vertically, and with a mandatory check of the plumb line and level. If necessary, suitable gaskets are used. During the tightening of the bolts, the freedom of movement of the arc-extinguishing blades in the chamber is constantly monitored. Then the drive is installed (front or rear - depending on the design). The rod with forks is connected to the lever of the circuit breaker shaft by the sector lever of the drive. Blade parallelismis regulated by insulators on which axial contacts are fixed. After 25 switching on and off, if there were no deviations in the entry of knives into the chambers and disturbances in the operation of the drive, the phase wires of the cable are connected to the taps of the fixed and movable contact groups.
Types of load break switches
According to the method of actuation, these devices are divided into three groups:
- First - manually operated switches. They are abbreviated as BHP (manual load break switch).
- Second - spring-driven autogas. They are designated VNA, and their inclusion is carried out using a lever. And shutdown - cocked spring drive.
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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 thanks to the fusible links placed on its frame and the shutdown mechanism when they burn out.
What is the difference between a load break switch and an automatic one?
This device operates only on the rated (calculated) operating current and does not break the circuit at short-circuit currents. The automatic version has a disconnection (shutdown) mechanism in case of a short circuit. To operate on short-circuit currents, the switch-disconnector requires additional safety devices. For example, fusible links, as in VNP devices.
