Oil circuit breakers device and principle of operation, what are the advantages and disadvantages – ElektrikExpert.ru

In this material, we will talk about oil switches, their device, principle of operation, scope, advantages and disadvantages, varieties and much more.

What are oil switches, purpose, where they are used

Oil circuit breakers are high-voltage electrical equipment used for switching networks from 6 kV, switching on and off electric motors, transformers, as well as entire sections and bushings of high-voltage substations.

This switch has three poles. Each pole, in turn, consists of tires and the switch itself.

When the device is turned off, an electric arc is formed. Its quenching takes place in a pot in which a dielectric is poured – transformer oil.

Oil circuit breakers (MV) are used in electrical substations located at industrial enterprises, as well as in settlements.

General device, how they work

MV consists of the following main elements:

1. Power contact group. It includes a movable stem and a fixed socket into which it is inserted. The arc is extinguished in a tank with transformer oil.
2. porcelain insulators. With their help, current-carrying parts are isolated from the housing and from each other.
3. Tank filled with transformer oil. Due to the latter, the electric arc is extinguished.
4. Block control contacts that are connected in one group.
5. Drive unit. Installed manual and automatic, based on the solenoid coil.
6. Springs. The contacts of the oil switch are opened due to the compression energy.

When voltage is applied to the solenoid coil, the core retracts, starts the lever mechanism, which connects the moving contacts (pins) to the fixed socket. Thus, the oil circuit breaker is automatically switched on.

It can also be turned on manually. To do this, you need to apply force to the solenoid through a special lever.

It is necessary to act on the lever until the mechanism is fixed by a special latch with a characteristic sound. Work must be done in overalls and shoes, in electrically insulating gloves.

Device types (classification)

There are two types of oil switches:

1. Tank.
2. Low oil.

According to the principle of operation of the arc extinguisher, they are divided into devices:

1. With auto blow. The gas-oil mixture moves due to the energy generated from the electric arc.
2. With oil blast. Special hydraulic mechanisms supply oil under pressure to the contact separation point.
3. With quenching in oil magnetically.

Tank switches, device, principle of operation 

The tank circuit breaker is one or more large tanks with transformer oil in which the arc is extinguished when the MW is turned off.

The tank circuit breaker structurally consists of tanks filled with transformer oil, a system of contacts and a control unit. The arc is extinguished directly in the tank(s).

The oil in the tank, in addition to extinguishing the arc, performs the function of an insulating substance.

These types of circuit breakers are mainly used in 35-220 kV distribution installations, most often they are large and installed in open substations.

Their principle of operation is the same as that of low-oil ones: as noted above, the formation of an arc occurs when the contacts open, and it is extinguished due to the gas-oil mixture, while a high temperature is released and the oil evaporates.

Tank switches can have both manual and automatic drives. In the second case, the inclusion is carried out using a solenoid coil.  

Single tank with open arc

The simplest design of an oil circuit breaker. It consists of one large tank, the arc is extinguished in it by means of a double break of contacts.

This type of circuit breaker has a standard structure and consists of contact blocks (movable, fixed, arcing), a tank with transformer oil, porcelain insulators, plates, a traverse, springs and a shaft.

Six porcelain insulators pass through the MV cover and end with copper brackets. The latter are fixed working contacts.

Moving contacts are placed on the traverse and driven by an insulating rod.

The magnetic switch is turned on when the traverse is in the upper position. At this point, the spring is compressed and the contacts are closed.

The switch is connected to a latch that holds it in the on position. When disconnected, the latch is released, the spring is released, the contacts open. In this case, at each pole, the circuit opens at two points. An arc is formed that burns no more than 0,1 s.

This type of switches is one of the simplest in design and operation, unpretentious and inexpensive.

With arc chute

Oil circuit breakers with an arc chute are superior in terms of breaking capacity and reliability.

This is achieved just by the presence of an arc chute. The latter is located inside the tank in oil.

The design of this type of MV is more complex: there are current transformers, a heating element, and an oil drain device.

The arc is extinguished in the arc chute. The peculiarity of the process lies in the fact that the magnitude of the pressure that occurs during extinguishing is much higher than what is observed in the MW without an arc chute.

Higher pressure reduces the diameter of the arc, resulting in faster extinguishing of the arc.

Low-oil switches (pot), device, principle of operation

This type of MV is designed to turn on / off consumers of electrical energy in normal mode, or in emergency situations. Shutdown occurs in manual and automatic modes.

Let’s consider the device of the oil switch on the example of VMG-10.

It consists of the following main elements:

1. The metal case on which the poles are mounted.
2. Pots with transformer oil. These are three poles isolated from each other by means of air and insulators, and located on one common frame.
3. Movable rods and fixed contacts.
4. porcelain insulators. With their help, the pots are isolated from the metal case.
5. Traverse.
6. Oil buffer.
7. Insulating barriers.
8. Spring.
9. Shaft.
10. Levers. By means of the lever mechanism there is an inclusion/switching off of MV.

The principle of operation of this type of oil switch is to extinguish the electric arc that occurs when the contacts are opened, which are energized in the gas-oil mixture.

This mixture is formed as a result of the decomposition of oil under the influence of high temperatures (it can reach 6000 degrees).

How does the oil circuit breaker turn off

The MW is turned off by pressing the corresponding button.

At the same time, the latch is activated, which prevents it from turning off spontaneously in normal mode, the spring is released and the rods come out of the sockets – the switch is turned off.

When the contacts are disconnected and opened in the poles, an electric arc is formed in the oil (if the disconnection occurred under voltage), which burns for a fraction of a second.

During its extinguishing, the oil heats up very strongly at the place where the contacts are separated, gas is released. The arc is extinguished.

Oil circuit breaker marking

All basic information about the MW can be obtained by examining the markings on a special plate attached to the front of the equipment.

Consider marking based on MV VMG-133:

1. The first letter “B” is a switch.
2. The second letter “M” – the type of switch – low oil.
3. The third letter “G” – belonging to the species – potted.
4. 133 – series.

Operation and maintenance 

The oil switch in the working substation is in the on position most of the time. Shutdown is performed in case of accidents, scheduled and freelance repairs.

Maintenance of devices is carried out by specially trained electrical personnel of the organization responsible for the operation of the substation.

It includes the following works:

1. Checking the level of transformer oil in the pots, topping up if necessary.
2. Checking the tightening of bolted connections of tires. If necessary, loose connections are crimped to prevent overheating and breakage.
3. Cleaning with rags poles, pots, tires from dust, dirt, cobwebs.
4. Inspection, reassembly, cleaning of contacts.
5. Cleaning of contact connections in conductive parts.

Design diagrams and where oil circuit breakers are used (by series)

There are the following main MV series:

1. VMP. This is an oil switch. In it, the arcing contacts are located inside the tank, and the workers are located outside the switch. They are used for high breaking currents in closed switchgear 6-10 kV.
2. VK – oil column switch. It is used in switchgear of retractable design.
3. VGM. It is used to turn off large currents. Devices of this type have 2 pairs of working and arcing contacts. Double interruption of the current allows for more efficient arc quenching.
4. VMUE – core. It is applied in installations of 35 kV.
5. TDC. It is used in installations of 110 and 220 kV.

What is the difference between VMP and VPM switches 

Both types of circuit breakers are classified as low oil circuit breakers and are three-pole switching devices.

In general, they are very similar, but have several differences:

1. Design features.
2. Dimensions.
3. Installation features.

Control and drive system

The MV can be controlled through the buttons of the control circuit, or by manually acting on the solenoid coil.

The drive is designed to turn on the device in manual or automatic modes, as well as to keep it on.

There are the following types of drives:

1. Manual (automatic). This drive allows you to control the oil circuit breaker both manually and automatically using the built-in electromagnet.
2. Spring. This type of drive turns on the MW due to the energy of the wound spring. The spring is wound manually, using an electromagnet, or an electric motor.
3. Spring-cargo. The inclusion is carried out by the energy of the cocked springs and the load raised to the upper position.
4. Electromagnetic. The control of the oil circuit breaker is carried out by creating a traction force in an electromagnetic coil with a core. To turn on the core interacts with the lever mechanism.

Possible damage

Oil switches are not the most reliable electrical equipment, they break down periodically.

List of the most common breakdowns:

1. Overheating of contact connections in tires, pots, followed by emergency shutdown.
2. Bad turn on.
3. Frequent outages.
4. Deterioration of insulation, overlapping of poles during short circuit (short circuit).
5. Breakdowns of mechanisms and drives.
6. Malfunctions of the contact system (not full inclusion of moving contacts, their freezing in an intermediate position, breakage of socket contacts).

Advantages and disadvantages of oil circuit breakers

Let us first list the main advantages of this type of MW:

1. Unpretentiousness, the ability to operate at different temperatures.
2. Simple construction.

Disadvantages:

1. High explosion and fire hazard.
2. It is necessary to constantly monitor the level of oil in the pots, top up if necessary, have an oil economy.
3. The need for qualified personnel who would be engaged in maintenance and repair.

How oil circuit breakers are tested

After repairs and scheduled maintenance of oil circuit breakers, high-voltage tests are mandatory. They include the supply of high voltage to the poles of the devices.

For oil circuit breakers with a voltage of 6 kV, most often 30-36 kV test voltage is supplied from a step-up transformer from a special laboratory.

The test voltage is applied for 5 minutes to each phase in turn (or immediately to 3 phases, if the design of the testing laboratory allows). If during this time the insulation withstands this voltage and no breakdown occurs, then the test is considered successful.

Also, before and after the test, the insulation resistance of each pole is measured, which should be 1,3 times greater than what it was before the test.

If the test is successful, the oil circuit breaker is put into operation, but if a breakdown occurs at some phase, then an inspection and, if necessary, repair is carried out (search for the place of breakdown, strengthening or replacing the insulation in this place).

After that, high-voltage tests are again carried out until all three phases withstand the test voltage for a predetermined time.

The expediency of replacing with a vacuum

Oil circuit breakers became most popular and widespread in the XNUMXth century, in the XNUMXst century they are all actively replaced by vacuum circuit breakers.

The latter have the following advantages:

1. Significantly smaller dimensions and weight.
2. High reliability.
3. Easy to maintain.
4. Much easier and safer switching on and off.
5. Much more resource.

Based on the above points, it becomes obvious that vacuum circuit breakers are superior in all respects compared to oil circuit breakers.

Of course, replacing an entire section of a substation, or an entire substation, from oil circuit breakers to vacuum circuit breakers is difficult: it is time consuming and expensive.

However, over a long distance of several decades, such an investment fully justifies itself.

Features of overhaul

Overhaul of the oil circuit breaker may include the following work:

1. Breaker trip, disassembly, tire disconnection.
2. Draining oil from pots.
3. Disassembly, cleaning, lubrication, repair, adjustment of the drive.
4. Cleaning, repair, testing, replacement of insulators.
5. Cleaning of contact conductive surfaces.
6. Trial.
7. Pole insulation resistance measurement.
8. Testing of insulators.
9. Measurement of transient resistance of tires.
10. Turn-on adjustment.
11. Lubrication of the jaws for a softer connection of the circuit breaker to the busbars in the cubicle.
12. Assembling the circuit breaker after repair, topping up the oil.
13. Removing dust, dirt, oil from tires and pots.
14. Tightening loose tire bolts.
15. Cleaning of the workplace after the completion of all work.

Overhaul is carried out by strictly specially trained personnel who have all the necessary permits and permits to work in installations and substations with a voltage of 6 kV and above.

The work is carried out under the supervision of a responsible person with an electrical safety group of at least 5. Strangers should not have access to the place of work, and the workplace itself should be fenced, warning and prohibition posters should be posted.

Overhaul and testing of oil circuit breakers is carried out, as a rule, once every 6 years, with intensive use much more often.

After each emergency shutdown of the device, high-voltage tests are carried out before it is turned on again.