Load break switch is a high-voltage switching device designed for switching currents of a three-phase electrical network in nominal mode. The switching of currents by this piece of equipment, depending on the type, can be carried out remotely, including automatically or manually, from the site. 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 load break switches.
Appointment
The purpose of 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 mode currents, so it can only be installed if there is short circuit and overload protection in the circuit, which is implemented by fuses (PC, PKT, PT) or a protective device installed on the side of the power supply or on the group consumers.
In this case, the HV has a breaking capacity that corresponds to the electrodynamic resistance in case of short circuits, which makes it possible to use this electrical apparatus to supply voltage to a section of the electrical network, regardless of its current state, for example, for test switching.
Thus, subject to the presence in the overcurrent protection circuit, the considered piece of equipment can be operated as a full-fledged high-voltage protective device (oil, vacuum or SF6). And in the presence of a motor drive, it can participate in the operation of various automatic devices (AVR, APV, AChR, CHAPV), and also be controlled remotely by an automated dispatch process control system.
Application
The area of application of the switch-disconnector is mainly networks of voltage class 6 and 10 kV. The use of these switching devices is primarily due to savings: HVs are much cheaper than full-fledged high-voltage protective devices, and also require significantly less maintenance and repair costs.
Where are these pieces of equipment used? HVs are an alternative - they are used for switching currents on the high voltage side of power transformers. But only if there are fuses or protective elements of equipment in the connection circuit of the transformer, as mentioned above, at the other end of the line from the side of the adjacent supply substation or line switches from which the switchgear supplying this transformer is powered.
Load break switches are used in other low-power networks as an independent switching device. On long and branched overhead lines, devices are used for the convenience of disconnecting sections of the lines without the need to completely de-energize it. At the same time, a switch is installed at the supply substation to protect the entire line from damage.
Design
Let us consider what a load switch consists of using the example of a switching device of the type VNR-10/400
- Base (frame).
- Support insulator.
- Holders with contacts.
- Movable working knife.
- Arc extinguishing chamber.
- Fixed top contact.
- Insulating rod.
- Lever arm.
- Flexible communication.
- Grounding knife.
- Grounding shaft.
- Lock rod.
- Springs.
- Rubber gaskets.
- Shaft of working knives.
Operating principle
Let us briefly consider how load break switches work using the example of the aforementioned VNR-10/400, provided in the photo:
Structurally, this switching device is similar to a disconnector. The main difference between the disconnector and HV is that the latter has an arc-extinguishing device and a drive, which ensures faster execution of operations.
The principle of operation of the load break switch is as follows. When switched on, the moving contacts are in the arcing chamber. In the lower part of the arcing device there are additional arcing contacts. During the tripping operation, the main contacts open first, and then the arcing contacts. The electric arc formed in the process of breaking the contacts enters the arc-extinguishing chamber, where it heats the plexiglass to a high temperature, which in turn emits a large amount of gases. These gases burst out of the arc chute in a powerful stream, thereby extinguishing the arisen electric arc in a few milliseconds.