Electrical appliance vacuum circuit breaker is a device designed for operation as part of electrical high-voltage networks. It received its name from the design feature - the vacuum chamber, due to which momentary quenching of the electric arc is achieved.
The device is used as a switch designed to perform equipment shutdown in case of emergency situations or in the framework of current operation. Let's take a closer look at what a vacuum switch is and what it is for.
The content of the article:
- How does a high-voltage vacuum switch work?
Vacuum circuit breakers
- How does the switch drive work?
- Features roll-out designs
Installation and connection of the device
- Connect directly to the network
- How is grounding done?
- Putting the device into operation
- How to choose a vacuum switch?
- Conclusions and useful video on the topic
How does a high-voltage vacuum switch work?
The basis of the functionality of the vacuum chambers used in the construction of switches is the physical properties of the gas that is in a discharged state. Under such conditions, the property of a gas, characterized as electrical strength, changes significantly upwards.
This effect is highly discharged (range from 10-6 to 10-8 N / cm2) has been successfully used in the construction of switches, supplemented by gas vacuum chambers, through which electrical contact groups pass.
One of the models of the vacuum circuit breaker is the device used in the operation of power electrical networks. The device is considered more modern and reliable in comparison with similar devices, but of a different type of performance.
The current flowing through the contact groups (at the time of the contact connector) forms an electrical discharge - an arc. Arc burning takes place due to partial ionization of metal vapors, inevitably generated from high temperature. The passage of current between the contacts through the formed plasma is maintained until the current passes to the zero bus.
As soon as the moment of transition through “zero” comes, the electric arc goes out. The total process takes less than 7-10 microseconds.
Vacuum circuit breakers
A variety of vacuum circuit breakers, in view of their design, is quite large. Therefore, it is difficult to give a characteristic of these devices in general. Meanwhile, regardless of the design differences, the principle of action remains unchanged.
Block diagram of explosives: 1 - top output; 2 - vacuum chamber; 3 - polymer insulator; 4 - bottom output; 5 - tape contact; 6 - power spring; 7 - traction rod; 8 - spring off; 9 - gear lever; 10 - drive shaft; 11 - release; 12 - body
Consider for general reference. three pole vacuum circuit breakerequipped with a spring-motor drive. This device is designed for indoor installation or for installation outdoors. In any case, its installation is carried out inside special distribution metal boxes.
Devices can be operated in various areas of the national economy. However, there are some limitations.
Thus, vacuum circuit breakers are not designed for installation and subsequent operation in the following conditions:
- rooms, where there is a fire, explosive atmosphere;
- the installations constructively providing frequent switching;
- mobile (mobile) type installations;
- energy systems of sea and river vessels.
Vacuum-type circuit breakers usually have two types of construction design:
- Under the stationary installation.
- Under the installation with the hardware cart.
Regardless of the version, the instrument case contains three poles, equipped with arcing chambers.
Inside the vacuum chambers there are movable contactors operated by a spring-motor mechanism. The instrument case is complemented by a front panel, which contains display elements and control devices.
External main elements of the switch: 1 - poles of the device; 2 - inclusion lock mechanism; 3 - window for lifting; 4 - handle mechanics, blocking external chains
Three poles of the main circuit are made in the form of columns. The location of the poles is usually on the back of the spring-motor drive chassis. Each pole is supplemented with an arc quenching chamber, which is enclosed inside a polymer insulator. In order to enhance the electrical strength, the insulator case has a ribbed shape.
Inside each vacuum chamber mounted contact group of two elements - moving, stationary. The moving contact element through the traction insulator is connected to the switching mechanism. Further connection with the lower contact output. A fixed contact through a conical fit is connected to the upper contact output of the device.
How does the switch drive work?
The moving contacts of the vacuum chambers are mechanically connected to the shaft of the spring-motor drive. Due to the power spring, pre-cocked (installed in the stretching state), the drive can be easily activated by simply pressing the control button or another mechanism.
Block diagram of the vacuum chamber: 1 - stationary terminal block; 2 - fixed contact; 3 - mobile contact; 4 - metal screen; 5 - ceramic (polymer) insulator; 6 - bellows; 7 - movable terminal block contact
A spring (usually two springs) is driven by a chain drive. The normal mode of operation of the equipment involves charging the spring with an electric motor equipped with a gearbox. However, there is a manual cocking handle, which is used in case of accidents or loss of power.
The cocked spring is locked with a trigger. This mechanism is controlled through an electromagnetic actuator or through the power button. As soon as the activation mode is activated, the fixation is released, the spring force of the spring actuates the cam mechanism. That, in turn, acts on the shaft, which is mechanically connected to the switching mechanism of the moving contacts of the vacuum chambers.
The operation to turn off the vacuum switch is performed by activating the "Disconnected" mode - with an electromagnet or a button. The sequence of actions is almost the same as the first mode. It also involved power shut-off springs, the state of which sets the shut-off trigger mechanism.
Control panel and display elements: 1 - “on” mode; 2 - “disabled” mode; 3 - cocked spring condition; 4 - condition of the released spring
Convenience of operation and control of operation of the device are provided by the control panel. The following elements are located along the front of the panel: a counter for the number of cycles, a status indicator of a cocking spring, a status indicator for a vacuum switch.
Features roll-out designs
The equipment of vykatny execution is collected on the basis of the special hardware cart. With this accessory, the switch is inserted inside or out of the cabinet.
The hardware trolley acts not only as a transport device, but also performs the function of a device switching controller into test mode or into operation mode as soon as the switch is pushed into the cabinet.
Hardware trolley: 1 - roller (4 pcs.); 2 - base; 3, A - the base is mobile; 4 - handle (2 pcs.); 5 - driver's nest; 6 - blocking bar; 7 - locking element; 8 - connector for the secondary circuit; 9 - mechanics of blocking the device; 10 - blocking contacts; 11 - screw fixation plate; B - motionless part
The vacuum switch is attached directly to the moving part of the cart. The fastener is bolted. Meanwhile, the hardware trolley also has a fixed part, where the drive of the movable part is fixed. The movement of the movable module relative to the stationary is performed by the screw of the trolley control handle.
The mobile part is a metal base on four wheels, treated with electroplated coating. Here there is an external mechanical lock (pressure plate) of the earthing, lock screw drive, the block contacts, the mechanism for blocking the switch and other elements that ensure movement or fixation.
Installation and connection of the device
Before starting to install a vacuum switch, it is necessary to inspect all externally accessible elements in order to ensure that there are no damages and defects. Then, the insulation surfaces of the poles are cleaned with a dry, lint-free cloth.
It is not allowed to introduce equipment into the system if there are chipped, cracked, or deformed areas on the insulating surfaces. Be sure to check the scheme of the secondary circuits, as well as the connection of the body bus.
Check the installed device. It is important to carefully check every detail, every element of fasteners. High-voltage devices do not forgive even the slightest mistake
Before installation, the operability of the switch should be checked using a manual switch (idle without power) and make sure that the control panel lights are in the correct position. Then you need to check the presence of pole covers. If equipment is used for nominal 1600A and above, protection covers must be removed before installation.
Connect directly to the network
The terminals of the contact tips of the conductors of power cables must be cleaned before connecting to the breaker terminals.
The stripping procedure differs according to the terminal material used:
- For copper and aluminum terminals without additional coating, stripping is carried out with emery paper of M20 grit or lower, followed by degreasing of the metal surface.
- If the copper or aluminum terminals are covered with a layer of silver, it is enough to clean them with a lint-free cloth.
It is unacceptable to use cables whose silver coating of the terminals is damaged over an area of more than 5%. In this case, the damaged item must be replaced. More information about the terminals for connecting wires can be found in this stuff.
The outer conductors are led to the terminals of the vacuum circuit breaker so that mechanical forces are not created on the outlets of the device from the outer conductors. Connections are made by means of a bolt coupling with the use of flat elastic metal washers.
How is grounding done?
Stationary devices are connected to the “earthen” site by means of a bolted connection (M12) directly at the point indicated by the label “Grounding”.
Elements of the hardware cart and switch chassis through which the device is grounded. As a rule, these points are marked with an appropriate sign printed next to the element
The area of the contact point “Grounding” must be degreased before connecting. Grounding conductor should choose a bus of sufficient cross-section (Rules for electrical installations), a flexible wire or a conductor woven by a harness. Before lining the conductor on the contact surface of the contact surface, lubricate with a special lubricant (CIATIM-203).
The withdrawable type design is grounded using hardware cart components. The grounding of the vacuum circuit breaker is carried out through the hardware trolley design, for which there are also fasteners.
Putting the device into operation
The device is commissioned after additional verification of the installed and prepared equipment. In particular, the reliability of the grounding, the state of the fastener of the assembly components, the access of the cooling medium to the potentially heating elements are checked.
The surfaces of current-carrying rods in contact with the lamellas of rosette contact groups must be treated with a small amount of CIATIM lubricant. In general, it is necessary to perform all the procedures foreseen by the PES in case of acceptance tests, and make sure that the value of the operating voltage is within acceptable limits.
Install a vacuum circuit breaker. Installation work is carried out only by qualified personnel. The same requirements apply to personnel who are selected to service high-voltage equipment.
A vacuum circuit breaker may be operated by personnel authorized to service electrical installations operating at voltages higher than 1000 volts. The approved access group for servicing persons should not be lower than the third. Before working with the equipment, the staff passes the minimum to study the subtleties of a particular equipment model.
How to choose a vacuum switch?
The device is selected taking into account its nominal parameters, which are considered relative to the parameters of the existing network at the place of installation. The choice is made according to the criterion of the most loaded modes of operation assumed for the operating conditions.
The rated voltage of the vacuum circuit breaker is allowed to be equal (or increased) with respect to the rated voltage of the system fed through the circuit breaker.
The parameter of the nominal long-term current is chosen above the nominal value of the current of the fed system. The parameter of the rated cut-off current is chosen above the maximum value. rated current KZ (taken into account the moment of contact divergence).
A rating plate is the first thing to notice when choosing a switch. Based on the values of the parameters, it is already possible to determine whether the device is suitable for a particular installation or not
From the point of view of possible short-circuit conditions, the choice is made taking into account the most severe modes.
The aperiodic component is calculated with consideration for the zero voltage conditions in any of the phase lines. In this case, the aperiodic current parameter set by the equipment manufacturer should be taken into account.
Conclusions and useful video on the topic
You can learn more about the device, how it works and how to install a vacuum switch in the following video:
Vacuum switches from other types of devices have a relatively simple and reliable structure. Therefore, this type of equipment serves for a long time without any complaints. Resource normal wear is determined by the number of operations equal to not less than 20,000. Under the condition of timely maintenance, this resource increases by 5-10%. Meanwhile, maintenance of explosives is limited to a small number of easy operations.
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