Separators and short-circuits: purpose, design, principle of operation

To reduce the cost of equipment in the high-voltage substation, short-circuits and separators on the high-voltage side are used instead of circuit breakers. Such a system, of course, is outdated and inferior to many a more reliable protection option, but it is still used at substations with a voltage of 35 kV and above. In this article, we will consider the principle of operation, purpose and design of separators and short-circuits.

Operating principle

A transformer is a device that is an electromagnetic device with 2 (or more) windings. This apparatus is mainly designed to convert alternating current from one voltage to another. Energy transformation occurs due to the magnetic field. Transformer booths in the main part are used to conduct electricity to tremendous distances, with all this they separate and send it to receivers, rectifiers, amplifiers of various types devices. The main component of the above device is a wire with windings. For high-quality work in transformers, short-circuits and separators are installed, which regulate the serviceability of the apparatus.

Briefly about the short-circuiter

Short-circuiter – is a device that creates an unnatural short circuit. Where are such devices used? First of all, the device is installed in transformers. It is used to ensure that a faulty transformer is disconnected after a short circuit has been created during relay protection actions the line that feeds. After that, both the transformer and the line are disconnected from the mains.

How does a short-circuiter work? The device operates on 2 or 1 pole, depending on the voltage. Installations with 35kV operate with two poles, and with a voltage of 110kV or more, one pole is used. You can visually consider the photo and the short circuit diagram in order to understand what it consists of.

Short circuit diagram of KZ-35: (1 - steel box; 2 - support insulator; 3 - immovable contact; 4 - moving grounded knife (contact); 5 - shaft).

The short-circuiting gear has a spring that is responsible for turning on the moving knife to the immovable contact, which is currently energized. The protection relay gives an impulse to start the drive, but is manually disabled. In order to avoid arcing and breakage of the device, it is necessary to increase the speed of the knife. In such designs, the short-circuiter turns on in 0.15 - 0.5 s.

Briefly about the separator

The separator is a kind of disconnector that quickly disconnects the network without current, when the command goes about it. It can be distinguished from the disconnector thanks to a spring-type actuator on the separator. The inclusion of this device is carried out manually. The separators can also have a grounded leg on one side or on both. Consider in the photo and diagram below what the separator consists of:

Separator circuit OD-220: (1 - 2-column disconnector with a knife that rotates; 2 - columns; 3 - actuator in the form of springs).

After reviewing the diagram, let's see how the separator works. It disconnects the circuit (no current) or the magnetizing current, but it is impossible to disconnect the short-circuit current that appeared during the start of the short-circuit. And through this nuance, there is a blocking in the OD and short circuit circuits, which does not allow the separator to turn off, provided that a current passes through the transformer. Where is this device used? In a transformer box, to stabilize its work.

Also, so that the separator does not disconnect, a current relay is introduced into the structure, which is connected directly to the current transformer located in the short-circuit. After disconnecting the line, the relay will close the contact and the capacitor, which will lead it to work. Further, thanks to the capacitor 2, a shutdown will be triggered.

Collaboration

If the design is of an open type, then the operation of the above-mentioned devices is unstable (up to failure to work), since they are sensitive to frost and ice. For this reason, closed gas chambers have been developed. The gas can escape and, under this condition, it is recovered from the cylinder, which is attached to the chamber shell. The pressure in such chambers is constantly regulated by a manovacuum meter.

The short-circuiter contains a porcelain contact chamber and 2 electrodes with a single break of 0.9 cm. There is an output for attaching the bus conducting current in the immovable contact. Flexible links connect the contact together. The contact chamber is filled with gas at a pressure of 0.3 MPa. The gas in the chamber is non-combustible, and this poses no danger in an explosion or fire. Based on this, arc extinguishing devices are meaningless in design. The bottom contact is similar to a rod with a cylinder in the form of a screen and is of the female type.

The collaboration scheme looks like this:

where:

• Q - switch;
• QR - separator;
• QN - short-circuiter;
• T1, T2 - power transformers;
• TA1, TA2, TA3 - current transformers;
• YAT - disabling the separator;
• YAC - inclusion of a short-circuiter.

This system, the combination is almost analogous to a high voltage switch. In an emergency situation inside the protected area, a power transformer acts as a protective element, which, with the help of some processes, de-energizes all consumers of this transformer.

Also, during the time when there is no current supply, the separator is turned off to prevent its own rupture from the influence of the current. Such a system is used in networks with high currents. As we said above, the OD-KZ system is cheap, but in our time it is already outdated and is being replaced by newer switches. You can learn more about this issue by watching the video:

Overview of the OD-KZ system

Advantages and disadvantages

Opened separators and short-circuits do not work very well in adverse weather conditions. Because of this, a certain structure with a contact system was created, placed in a chamber with SF6 gas.

A 35 kilowatt installation uses 2 poles. More powerful (110 kilowatts or more) use one pole. Typical short-circuits operate for a very long time and therefore it is more advisable to use a device based on a powder charge. Blasting it sets the knife in motion.

It is important to know that when monitoring the condition of the devices, first of all, you need to check the insulation on all parts.

That's all that I wanted to tell you about the principle of operation, design and purpose of short-circuits and separators. We hope the information was useful and understandable for you!

We also advise you to read:

• How electricity is transmitted at a distance to consumers
• How to identify a short circuit in the network
• Protective equipment in electrical installations with voltages above 1000 Volts