High-voltage disconnectors: purpose, device, classification

For switching on power lines, high-voltage switches and disconnectors are used. The former are used for operational switching under load, and the latter are used for disconnecting the circuit without load or with low load. They are used together and installed in a chain in series. In this article, we will explain what a high voltage disconnector is, what it is intended for and where it is used.

Purpose and scope

The high-voltage disconnector is a switching device that allows a line to be disconnected with a visible break. The need to create a visible gap is due to the fact that when using vacuum, oil or gas switches, it is not always it is possible to make sure that the contacts are completely disconnected, since they are usually located in a tank with an arcing medium (oil, SF6, vacuum).

In case of malfunctions of high-voltage switches, it can happen that two phases are disconnected, and the third is not, or in a different configuration the circuit remains energized. In the future, when carrying out repairs or maintenance of power lines, workers will be energized.

Therefore, a disconnector is installed in series with the switch. If you describe it in simple terms, then a high-voltage disconnector is a large switch, the device of which creates an open high voltage circuit. Where are such devices used?

High-voltage disconnectors are used everywhere on transmission lines from low and medium voltage, for example, 6 or 10 kV, up to high-voltage lines of 750 kV.

In addition to ensuring the disconnection of the line with a visible break, the BP is also used for switching:

• neutrals of transformers;
• grounding reactors (if there is no earth fault);
• magnetizing current of transformers from 6 to 500 kV;
• charging current of air and cable power lines, bus systems and the like;
• ring currents (6-10 kV networks).

Switching of 10 kV circuits with a current of up to 15 A is also allowed, as well as remote disconnection of one of the 220 kV disconnectors and more, if it is bridged by at least one more disconnector. For example, when using a quadrangle scheme on a substation.

Basic types

To begin with, consider what is the classification of high-voltage disconnectors:

• By characteristics (rated voltage, current);
• By location (external and internal);
• By design.

Structurally, they can also differ:

• By the number of poles;
• By the movement of the knife (rotary, swinging, chopping type);
• By the type of drive (operational dielectric rod, lever system, using electricity, pneumatics and hydraulics).

Device and principle of operation

High-voltage disconnectors do not have arc extinguishing means, therefore, when disconnected under load arc can lead to interphase short circuit.

In the figure below, you see a lever-operated high-voltage disconnector.

Notice in the figure there are two drives - one for disconnecting the blades in the line and the other for driving the grounding blades (top). In some cases, two levers are combined in one drive - one for grounding, and the other for power. At the same time, they are included in different directions so that their simultaneous inclusion is excluded, such as the PRNZ, which is shown below. It is installed on the support at the bottom and is connected through a dielectric rod with the disconnector knives.

In the video below, you see how a disconnector on a 735 kV power transmission line works, pay attention to how strong the arc is.

Outdoor HV disconnectors must be more robust and withstand high mechanical loads. For example, when opening in case of icing, in the figure below you see such a device on a 6 kV support, you also see a pull from the bottom of the manual drive.

To control the electrical drive of the disconnector, control cabinets are used, they are located on the ground, for switching large devices requires great effort, therefore, one such cabinet is installed on each pole (phase).

So how does a high voltage disconnector work? Generally speaking, to answer this question, it consists of:

1. Frames.
2. Insulators.
3. Contact knives.
4. Drive.

The video below clearly shows the design of the disconnector:

The device may differ depending on the type of disconnector.

Before making the switch

Switching is done only after receiving the appropriate order. First, they check whether the switch is turned off in this circuit, then conduct an external inspection of the insulators for cracks and chips - if they do not perform operations.

They also check the condition of the locking devices and drives. In case of visible damage, if possible, act on the drives carefully and with the permission of the person who issued the order. There should also be no jumpers and bypass switching devices.

When using the manual drive, the disconnectors are switched on with a quick and confident movement, but without impact. If an arc arises when the live parts approach, they are not pulled back to avoid its lengthening and overlap of adjacent phases. When the contacts are fully closed, the arc will disappear. Disconnect with a slow motion, without jerking. The first movement is a trial one, to check the integrity of the rods. After that, the circuit is opened, if an arc arises at the same time, it is quickly turned back on, and is not performed until the reasons for its formation are clarified.

That's all we wanted to tell you about high-voltage disconnectors. Now you know the main types and types of these devices, what they are intended for and where they are used. We hope the information provided was useful and interesting for you!

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