What is a load switch and why is it needed?

Load switch - a high-voltage switching device designed for switching currents of a three-phase electric network in nominal mode. Switching currents with this item of equipment, depending on the type, can be carried out remotely, including automatically or manually, from the spot. This type of device is quite popular and is used in high voltage electrical networks. Next, we will consider the device, the principle of operation and the purpose of the circuit breakers.

Content:

Appointment
Application
Design
Operating principle

Appointment

The purpose of the HV is the switching of operating currents in electrical installations, that is, capacities that do not exceed the permissible (nominal) values for a particular section of the electrical network. This device is not designed to disconnect emergency currents, so it can only be installed if there is a short circuit and overload protection in the circuit, which is implemented by fuses (PC, FCT, PT) or a protective device installed on the side of the power source or on the group consumers.

At the same time, the HV has a breaking capacity that corresponds to the electrodynamic resistance during short circuits, which allows the use of this electrical apparatus to supply voltage to a section of the electrical network, regardless of its current state, for example, for a test switch-on.

Thus, provided that the overcurrent protection circuit is present, the equipment item in question can be operated as a full-fledged high-voltage protective device (oil, vacuum or gas-insulated). And in the presence of a motor drive, it can participate in the operation of various automatic devices (ATS, automatic reclosure, AChR, ChAPV), as well as be controlled remotely by an automated dispatch technological control system.

Application

The scope of application of the circuit breaker is mainly networks of voltage class 6 and 10 kV. The use of these switching devices is primarily due to savings: VN is much cheaper than full-fledged high-voltage protective devices, and also require significantly less maintenance and repair costs.

Where are these items of equipment used? VN are an alternative separators and short circuits - they are used for switching currents of the high voltage side of power transformers. But only if there is a transformer in the connection circuit, as mentioned above, fuses or protective elements of the equipment at the other end of the line from the side of the adjacent power substation or linear circuit breakers, from which the switchgear supplying this transformer is powered.

Load breakers are used in other networks of low power as an independent switching device.On long and branched overhead lines, devices are used to conveniently disconnect sections of lines without the need for complete de-energization. At the same time, a switch is installed at the power substation to protect the entire line from damage.

Design

Consider what a load switch consists of using an example of a device of a switching device of the ВНР-10/400

Base (frame).
Reference insulator.
Holders with contacts.
Movable work knife.
Arc extinction chamber.
Fixed top contact.
Insulating Rod.
Lever arm.
Flexible connection.
Grounding knife.
Ground shaft
Traction locking device.
Springs
Rubber gaskets.
Shaft of working knives.

Operating principle

Let us briefly consider how the circuit breakers work on the example of the aforementioned BHP-10/400, shown in the photo:

Structurally, this switching device is similar to a disconnector. The main difference between the disconnector from the VN is the presence of the last arrester device and drive, which provides faster execution of operations.

The principle of operation of the load switch is as follows. When the position is on, the movable contacts are in the arcing chamber. In the lower part of the arcing device there are additional arcing contacts. When performing a shutdown operation, the main contacts first open, and then the interrupter contacts. The electric arc formed in the process of breaking contacts falls into the arcing chamber, where the plexiglas heats up to a high temperature, which in turn releases a large amount of gases. These gases burst out of the arcing chamber with a powerful stream, which extinguishes the arising electric arc in a few milliseconds.

How is VN shown on single-line diagrams? The following is the legend on the diagram: