Oil circuit breaker. Types of oil circuit breakers

To automate the operation of equipment that is powered by electricity, use special oil switches.

Oil circuit breaker is a device that performs the switching on or off of individual circuits in an electrical system, in its normal operating mode or in an emergency situation, in manual mode or from an automatic system command. Such a device is used in the organization of many power supply networks.

Classification of equipment

To ensure the stable operation of electrical equipment, the following types of oil circuit breakers can be used:

• The system with a large capacity and oil in it - tank.
• Using dielectric elements and a small amount of oil - low-oil.

The circuit of the oil circuit breaker has a special device for damping the formed arc during the breaking of the circuit. According to the principle of the action of arcing devices such equipment is divided into the following groups:

• Using forced blasting of the working environment. Such a device has a special hydraulic mechanism for creating pressure and supplying oil at the point where the chain is broken.
• Magnetic quenching in oil is carried out using special electromagnets of elements that create a field that moves the arc into narrow channels to break the created chain.
• Oil circuit breaker with an auto-drain. The scheme of the oil circuit breaker of this type provides for the presence of a special element in the system that discharges energy from the formed arc to move the oil or gas in the tank.

The tank type of the system

Tank switches are very popular due to the simplicity of the design. It consists of an oil circuit breaker from the input, arc extinguishing system and the contact system, which are placed in a tank with oil. When using equipment in a system with a voltage of 3-20 kW, all three contacts (phases) can be located in the same tank, with an increase in the voltage index up to 35 kV the phase should be located in a separate tank. In two cases, an automatic or remote control system may be used, however, for the first version, manual operation may be used, and for the second version, a re-engaging device is required.

In the one-tank type, when all three phases are in the same container with oil, the medium used isolates the contact from each other and from the tank body, which must be grounded. The oil, in addition, serves to extinguish the formed arc and to isolate the phases of electricity supply from each other at the time of the network failure.

Principle of operation of single-tank switches

When the system is triggered, the contact of the arc chute is first broken. If the mains contact is broken with a high voltage, an arc arises which decomposes the oil due to the action of high temperature. When the arc is applied to the oil, a gas bubble forms, in which the arc itself will be located. The created bubble is 70% hydrogen, and this gas will be supplied under pressure in this state. The effect of hydrogen and created artificial pressure will lead to de-ionization of the formed arc during the contact rupture. In this way, the oil circuit breaker conducts the circuit.

How the three-way switch works

The three-tank switch has a slightly different operating principle, which is associated with its use in a high-voltage network. The oil circuit breaker, which is used in a network with voltages above 35 kV, has a special blowing mechanism in the arc extinguishing chamber. The arcing system used can consist of several operating modes. They allow to increase the rate of arc extinction during the breeding of the contact.

In order to secure this process, the electricity transmitting elements are placed in a special oil tank, with a separate tank for each phase. Also, various actuators of oil circuit breakers are used to allow the working fluid to flow in the chosen direction. The system has a special element for controlling the arc size, which is represented by a shunt. After the loss of the formed arc, the current supply stops finally.

Advantages of the system

The arc extinguishing system of this type has a number of features, because of which it is used in many power supply circuits. The merits of the system include the following:

• High interruption efficiency, which allows the use of similar equipment in high voltage networks.
• The simplicity of the design makes it reliable and maintainable. Repair of oil circuit breakers should be carried out exclusively by professionals, since such equipment is responsible for executing an important command from an automatic control system or operator. Also this quality causes a relatively small cost of this type of equipment.

Disadvantages of the system

Despite the great popularity of this system of damping the electric arc, which is formed when the contacts are broken, it has some drawbacks:

• Using a large amount of oil to ensure reliable performance of the tasks.
• Large dimensions of the arc chute, associated with the need to use oil in large quantities.
• Fire hazard. It is connected with the fact that during the formation of the arc the temperature of the oil rises. If the amount of working fluid is less than the recommended level, it may be boiling and burning.

Low-oil type of equipment

The oil circuit breaker VMP, or in other words low-oil, in addition to the working fluid to insulate the elements of the system from each other, has special elements made of dielectric materials. In this case, the oil is used only for the formation of gas. Each element of the system in which the circuit is broken has a separate chamber with an arcing device. This uses a special drive in the system, which provides a transverse blast.

Due to the small amount of oil during the off state, the contacts are above the level of the oil used in the chamber, which increases the reliability of the power failure. Due to contamination of the working environment, it may eventually lose its basic dielectric properties. Also, when creating such a system, designers took into account the fact that decomposition products are formed over time. For them, specially created oil separators.

Advantages and disadvantages of the system

An oil circuit breaker of this type is often used to ensure a reliable network break in the power supply circuits of small length and power. Its merits include the following:

• Use a small amount of oil.
• Relatively small size and weight of the construction, increasing the scope of its application.

Such positive qualities allowed using the network breakaway system in the arrangement of power supply for enterprises, offices or other industrial buildings where there is a network with high voltage.

The disadvantages are the following:

• To ensure reliable operation, you must constantly check the oil level and top up it if necessary.
• The high cost of equipment is associated with the use of expensive dielectric materials in its manufacture.

The type of oil circuit breakers is selected according to the characteristics of the power supply circuit in which they will be used.