Among the switching equipment, a place of honor, as a veteran, is occupied by an oil switch, used in both closed and open switchgears of any voltage.
Its main function is to enable or disable individual lines of a normally operating electrical system or in unusual situations. Switching off depending on the circumstances occurs automatically or manually.
In this article we will look at the existing types of these devices, their classification and labeling. Also pay attention to the pros and cons of such switches, features and rules for their use. For a better understanding of the material, we picked up diagrams, tables, visual photos and thematic video reviews.
The content of the article:
- Pros and cons of oil switches
Oil switch classification
- View # 1 - tank type equipment
- View # 2 - Pot or Low Oil Switches
- Oil Switch Marking
- Rules of operation of MW
- Conclusions and useful video on the topic
Pros and cons of oil switches
These devices are relatively uncomplicated. They have a good breaking capacity, do not depend on weather conditions. In the event of faults, repairs can be carried out. MV tanks are suitable for outdoor installation. There are conditions for the installation of embedded current transformers.
An important role in the work of the MW is played by the rate of contact divergence. A situation may arise when the contacts diverge with great speed and the arc instantly reaches a length that is critical for it. In this case, the magnitude of the recovering voltage may not be enough for punching the contact gap.
Disadvantages more from tank switches. The first is the presence of a large amount of oil, therefore, considerable dimensions of these units and switchgear. The second is fire and explosion hazard, in case of emergency situations the consequences can be the most unpredictable.
The oil level in the tank and in the inlets, as well as its condition, must be kept periodically under control. In the presence in the serviced power supply networks of MW, it is necessary to have a special oil industry.
The photo shows the VMG oil switch. It can shut off any load and short-circuit currents, including the tripping current limit. This type is widely used in transformer substations
Oil switch classification
The use of oil switches began at the end of the last century. Almost until the mid-twentieth century, there were simply no other disconnecting devices in high-voltage networks.
There are two large groups of these devices:
- Tank, which is characterized by the presence of a large amount of oil. For this equipment, it is both the medium in which the arc is extinguished, and also insulation.
- Low oil or low volume. About the amount of filler in them says the name itself. These switches contain dielectric elements, and oil is only needed for arc suppression.
The former are mainly used in distribution installations from 35 to 220 kV. The second - up to 10 kV. VMT low-oil devices are also used in external switchgears designed for 110 and 220 kV.
The principle of arc extinction in both species is identical. The arc that appears when the high-voltage contacts of the circuit breaker are opened causes an rapid evaporation of the oil. This leads to the creation of a gas envelope around the arc. This formation consists of oil vapors (about 20%) and hydrogen (H2).
The arc gap is deionized as a result of the rapid cooling of the arc trunk by mixing high and low temperature gases in the shell.
At the time of occurrence of arcs in the contact zone, the temperature is very high - about 6000⁰. Depending on the installation, emit switches used for internal, external use, as well as for use in the PKK - complete switchgear.
View # 1 - tank type equipment
Switching equipment of this type can have one tank or more depending on the voltage. In the first case it is up to 10 kV, in some cases up to 35. Each phase of the switches operating in high voltage installations is placed in an individual tank.
All tank switches have approximately the same layout. A steel tank at the oil inlets places arcing chambers. External contacts bridged traverse
Drives to both tank and low-oil switches can be manual, automatically assembled on a solenoid turn-on coil, or spring-loaded. In the second case, the magnetic property of the solenoid is used, which makes it possible to tighten the metal core connected by means of a special system with the MV shaft.
When a direct current is applied to the solenoid winding, the unit is turned on by drawing in the magnetic core rod and then turning the switch shaft.
The shaft is held in this position by a special latch. Simultaneously with the inclusion of the solenoid sets a certain position of the tripping springs, which upon receipt of a special electric pulse will turn off the MV.
The shutdown process starts the second solenoid by knocking out a roller mechanism (latch). As a result, the shaft is instantly rotated by the spring and is turned off. The operation of a solenoid drive requires the presence of a battery to power it with direct current.
When the battery is missing, use a spring drive. The inclusion is performed using an electric motor or due to muscular efforts. Manual disconnection is possible for low-power units with a value of short-circuit currents in the range of up to 30 kA, for which shutdown a maximum of 25 kg must be applied.
Odnobakovy MV with an open arc
In some switchgears install tank switches that do not have arcing chambers. The electric arc is extinguished here in the simplest way - by double breaking the contacts in an oil-filled container. Such devices with an open arc are domestic models of the naval base and VME. They are rated for a rated current of 1.25 kA.
Scheme VME-6-200. The design consists of a tank (1), a cover (2), porcelain insulators (3), fixed contacts (4), moving contacts (5), cross member (6), arcing contacts (7), plates (8), springs (9), shaft (10)
The symbol “E” denotes the excavator, the digit 6 denotes a voltage of 6 kV, 200 denotes the rated current in amperes. The cut-off current for this MV is 1.25 kA. The tank of this MV is made of steel and is connected to the lid of iron casting by means of bolts. The walls of the tank are covered with insulation (13).
The six porcelain insulators passing through the lid end with copper brackets that perform the function of fixed working contacts. The VME series has a manual flywheel drive.
On the traverse or contact bridge are moving contacts. Here are also arcing mobile contacts in the form of brass angles. Copper plates with brass tips located at the bottom of the insulator ends are fixed arcing contacts. Insulating traction through the contact with the drive mechanism informs the movement of the moving contacts.
With the raised position, the crosshead, the fixed contacts are closed, the spring responsible for the disconnection is compressed, MV is turned on. The switch is connected to the latch drive shaft, which holds it in the working position. At any disconnection the latch is released, the spring is opened and the traverse rapidly follows down. In this case, there is a sequential opening of the working contacts: 4 and 5, then - 7.8.
This causes at each pole of the circuit breaker the opening of a circuit at two points, the appearance of an arc and the decomposition of oil. Inside the shells 12, the pressure reaches from 0.5 to 1 MPa, thereby activating the deionization process. Within a maximum of 0.1, the arcs are redeemed, and the shells, rising, are under the lid and increase the volume of the air cushion.
When all the phases of the MV are in the same container, the oil isolates the contacts between themselves and from the tank body, which must be grounded
The latter serves as a buffer, reducing the force of impact in the arc-extinguishing process. The normal height of the airbag is approximately 25% of the volume. Exceeding this threshold may cause an explosion.
Such switches are easy to operate, relatively inexpensive, they are convenient to use in open substations. But hot oil vapors, even when simply in contact with oxygen, are flammable.
The burning of the arc in the oil environment starts the process of polycondensation, which impairs the electrical strength of the oil. The tank clogs the sediment consisting of carbon particles. Therefore, revisions of the unit with oil change are necessary.
Oil circuit breakers with arc chamber
The breaking capacity and reliability of the tank type switches significantly increases the presence of the arc chute. It is placed in the oil in the tank. In three-tank circuit breakers, each phase is placed in a separate tank.
One pole of the tank switch in the cut. It is equipped with a C-35 - 630 - 10 arc-extinguishing camera. Marking indicates that the circuit breaker is designed for installation in switchgears of 35 kV and above, is rated for a rated current of 630.4 kA, the tripping rating is 10 kA
The design is more complicated than that of a VM without arcing chambers and consists of:
- poles (1);
- current transformer (2);
- drive enclosures (3);
- rods (4);
- contact fixed (5);
- arc chambers (6);
- isolation (7);
- heating element (8);
- oil release devices (9).
The upper part of the camera is equipped with a fixed contact. When turned on it penetrates a moving contact, having the form of a rod. In the event of a shutdown, the rod leaves the fixed contact, as a result of which an arc appears in the chamber. The magnitude of the pressure arising in this case exceeds by an order of magnitude the corresponding parameter of the switches that are not equipped with an arc chute.
A pressure of 8-7 MPa cuts the diameter of the arc, increases the breakdown strength of the gap after the current passes through the zero mark. As a result, a faster arc extinction process occurs. Following the exit of the movable contact from the chamber, exhaust gas with partial oil trapping follows through the free opening.
The arc barrel cools rapidly, intense deionization occurs. With increasing current, the efficiency of the arc-suppressing chamber increases. MW can work as an open arc equipment in case of disconnection of small currents.
In addition to increasing the pressure of the steam mixture in the gap of the arc to accelerate the extinction of the arc using a method such as enhanced blast of a steam cocktail in the arc zone. There is a longitudinal blowing, cross, counter
The type of automatic blast is determined by the design of the arc chamber. In the first case, the vapor mixture vector has a longitudinal direction with respect to the arc trunk (fragment a). With the transverse direction, the sullen flow moves in the direction perpendicular to the arc column or at a certain angle (fragment b).
In the case when the flow of the flow has a direction opposite to the vector of motion of the mobile contact with the arc, there is a counter-blowing. Often in arcing devices, combinations of these methods are used.
The arc in MW is extinguished in 3 stages. In the first (a), in the arc, the release of electricity occurs and a high pressure is generated in a closed shell. At the time of release of the mixture from the shell begins the second stage (b). The third (in) - removal from the chamber of the remnants of heated gases and decomposition products
At the last stage, the camera is being prepared for participation in the next shutdown cycle. For automatic re-shutdown, this step is crucial.
View # 2 - Pot or Low Oil Switches
In closed installations, pot switches are used as generator and distribution. In the open - as substation and distribution. Insulating functions in the switches of this type oil does not perform, it is necessary only as a medium for extinguishing the arc.
The fire and explosion hazard of low-volume VMs is much lower than that of tank ones. They are installed both in the open switchgear and in the closed switchgear of any voltage up to 110 kV. The role of isolation of the poles in relation to each other and the earth is performed by such dielectrics as porcelain, cast resin, and steatite.
The oil in these VMs takes up only 3 to 4% of the pole volume. The small volume of oil, the small weight and the convenient sizes are the indisputable advantage of this equipment. However, they are used in such nodes of the system where no high requirements are placed on the switches.
These limitations are explained by the strong coupling of the disconnecting ability with switchable current, the inability of the structure to work in conditions of frequent disconnections.
Another reason is the difficulty in implementing multiple high-speed automatic reclosing. In low-volume switches use the following types of oil blast: transverse, longitudinal, mixed. Experts consider the first to be the most effective.
For switches of this type intended for closed switchgear, contacts are placed in a steel tank. MV of 35 kV and above have a porcelain shell. More used equipment is suspended 6-10 kV. Its body is fixed on a common frame for all poles. All three poles have an arc-suppressing chamber, each is designed for one contact break, and for large voltages, 2 or more.
The design of low oil switches includes moving and fixed contacts (1 and 3), an arcing chamber (2), contacts (4) working
According to the above scheme, switches VMP, VMG, MG are produced, designed for voltages up to 20 kV. A feature of the design of switches for large currents is that the working contacts are placed outside, and the arcing inside the tank.
Switches of the VMP series are often used in closed devices, as well as 6-10 kV switchgears. In the complete switchgears install switches series VK. They are equipped with a built-in electromagnetic or spring drive, and are designed for indicators of tripping currents of 20 - 31.5 kA and for current ratings of 630 - 3150 A.
Kolonkovye switches, manufactured specifically for switchgear, different retractable design. In installations of 35 kV install VM column type of VMK and WMEP series. RU 110, 220 kV equipped with switches of the TDC series. The unit has a welded base on which its three poles are placed. Management - spring drive.
On the photo switch VMT-110. The image on the left shows the nodes of which it consists of: a spring drive (1), an insulator, a switch reference pole (2), an arcing device (3), a base (4), a control mechanism (5)
On the right side of the photo, a module is shown, where: 1 —throw, 2 - a movable contact connected to the down-conductor through current collectors. Arcing chamber, marked with number 3, fixed contact - 5. All of the above is placed in a hollow insulator (4) of porcelain. Inside it is transformer oil, and on top is a cap (6).
The latter is equipped with a pressure gauge to monitor the pressure in the module. In addition, on the lid there is a unit for filling with compressed gas mixture, automatic exhaust valve, oil indicator (8). Mobile contact and control device are connected by insulating rods.
The design of the pole is identical for the entire series of switches. In MV tanks for currents from 630 to 1600 A there is 5.5 kg of oil, above 1600 and up to 3150 A inclusive - 8 kg.
To increase reliability, the design of individual switches additionally includes controls and protections:
- tripping electromagnets;
- relays that act instantaneously and with exposure at a threshold current;
- undervoltage relay;
- additional contacts.
Depending on the layout method, there are low oil switches with a lower arrangement of the arc chamber and an opposite one - the upper one. In the first case, the movable contact realizes the movement from top to bottom, in the second - vice versa. The breaking capacity of the latter is higher.
Oil Switch Marking
Decoding the manufacturer’s markings on the oil switch will allow you to familiarize yourself with the basic information about it. Let us consider for example the labeling of the VMG-133 switch. The first character “B” indicates that there is a switch in front of you.
This diagram shows the composition of the symbol for high-voltage switches, including for oil-filled equipment.
Second - "M" indicates the type of switch, in a particular case - low oil. Letter "G" determines the belonging to a particular type - pot. 133 - MB series.
Rules of operation of MW
Repair, operational personnel, specialists associated with the maintenance and operation of oil circuit breakers are required to know the relevant instructions, device, equipment operation principle.
Employees serving CF during the operation must control:
- Effective voltage, load current. Indicators should not go beyond table values.
- The height of the oil column in the poles, no leakage.
- Presence of grease on rubbing parts. Contacts may lose their mobility and freeze if lubrication of rubbing elements becomes thick and dirty.
- The dustiness of the premises in which switchgears are located.
- Compliance of mechanical characteristics of operated switches with tabular norms.
After each trip, you need to inspect the equipment. Information about these outages are recorded in a special log. There must be a defect log in order to record information about faults detected during the operation of the unit. The switch on which the trip has occurred as a result of a short circuit is subject to inspection.
Check for oil release. If this happened, moreover, in large quantities, this indicates an abnormal trip of the short circuit. Equipment is taken out of service and inspected. When the oil is dark, need replacement. The rate of opening is adversely affected by the viscosity of the oil, which increases with a drop in temperature.
Sometimes it becomes necessary to replace the old lubricant during the repair with a new one: CIATIM-221, GOI-54 or TsIATIM-201.
Table with technical characteristics of oil switches. If the actual values do not correspond to the factory values, the adjustment is repeated.
After removing MV from work, insulators, traction, and insulation of tanks for cracks are subject to thorough inspection. Strongly polluted insulation is rubbed. The need for an extraordinary repair appears after a certain amount of faults.
Periodic inspection (software) is carried out monthly. At the same time pay attention to the degree of heating of the switch. TR (maintenance) is carried out annually. It includes such works as checking and eliminating defects in fasteners, drive kinematics, oil level, and seals. Insulating parts are also checked for their integrity.
After 3-4 years after the overhaul, perform the average (CP). It includes the whole set of works TP plus additionally carry out measurements of the transition resistance of the poles and check the mechanical and speed parameters.
In case of detection of inconsistency of controlled characteristics with tabular data, the switch is disassembled, the adjustment and the full range of high-voltage tests are performed.
During an extraordinary repair, they mostly try to leave the previous adjustment unchanged. For this reason, the switch is disassembled to a minimum. The frequency of major repairs - from 6 to 8 years. A general inspection is carried out in its scope, cylinders are removed from the frame, the tires are disconnected, the drive, arcing devices, and block contacts are repaired.
After all, make adjustment, painting, connect tires, conduct tests. For all the work out the documentation.
In addition to oil type switches in high-voltage networks, other disconnecting devices are used. For example, gas and vacuum. We have other articles on our website, which detail the characteristics and design of these types of switches, as well as the features of their use:
- Vacuum switch: device and principle of operation + nuances of choice and connection
- Gas-insulated circuit breakers: selection guidelines and connection rules
Conclusions and useful video on the topic
Device, types, purpose and operation of MW:
Detailed review of VMP-10:
All the basic requirements for switches operating in high voltage conditions are also met by oil switches. Most of them are safe and reliable in operation, provide quick disconnection, easy to install. Despite this, manufacturers are striving to ensure even greater compliance with the requirements for CF.
Do you have knowledge of oil circuit breakers and want to supplement the material with useful information? Maybe you noticed a discrepancy or error? Or do you have questions on the subject? Write to us, please, about this under the article - we will be grateful to you.