High-voltage circuit breakers (referred to as high-voltage switches) are one of the main electrical equipment in substations. It can not only cut off and connect high-voltage lines and various no-load and load currents during the normal operation of the system, but also can automatically, quickly and reliably cut off various overload currents and various overload currents through the action of the relay protection device when the system fails. Short-circuit current prevents the occurrence and expansion of the scope of accidents.
1. High-voltage circuit breaker structure and classification
High-voltage circuit breakers can be divided into oil circuit breakers (more oil circuit breakers, less oil circuit breakers), sulfur hexafluoride circuit breakers (SF circuit breakers), compressed air circuit breakers, vacuum circuit breakers, etc.
With the rapid development of the national economy, the demand for electricity in all walks of life has also increased sharply, the load of the power system is increasing, and the requirements for power supply reliability are gradually increasing; the switches in the substation are gradually replaced by oil switches to new types of sulfur hexafluoride circuit breakers. Device.
①Sulfur hexafluoride circuit breaker
Sulfur hexafluoride circuit breaker is a circuit breaker that uses sulfur hexafluoride (usually represented by SF6) gas as the arc extinguishing medium and insulating medium, referred to as SF6 circuit breaker.
Sulfur hexafluoride circuit breaker is a new type of circuit breaker that uses sulfur hexafluoride gas as insulating medium and arc extinguishing medium. Sulfur hexafluoride gas is a colorless, odorless, non-toxic, and non-flammable inert gas. It has high electrical strength and good arc extinguishing performance, and its dielectric strength far exceeds that of traditional insulating gases. Therefore, its use in electrical equipment can reduce the size of the equipment, eliminate fires, and improve the reliability and safety of the power system.
Sulfur hexafluoride switch is composed of three parts: body structure (using three-phase common box structure), operating mechanism, and arc extinguishing device. It has the advantages of simple structure, small size, light weight, large current-breaking capacity, rapid arc extinguishing, multiple allowable breaking times, and long maintenance period. It is the direction for the promotion and application of power systems in the future.
Sulfur hexafluoride circuit breakers are often filled with 3 to 5 atmospheres of sulfur hexafluoride gas as the internal insulation of the circuit breaker. During the opening of the circuit breaker, the movable contact drives the piston to pressurize air to form a blower. Extinguishing the air flow. The basic structure of the arc extinguishing chamber of a sulfur hexafluoride circuit breaker is connected by a movable contact, an insulating nozzle and a compressed air piston, and is driven by an operating mechanism through an insulating connecting rod. The fixed contact is made into a tube shape, the moving contact is a socket type, and the ends of the moving and fixed contacts are inlaid with copper-tungsten alloy. The insulated nozzle is made of high temperature and corrosion resistant polytetrafluoroethylene.
When the circuit breaker opens, the moving contact and the piston move to the right together. After the moving and fixed contacts are separated, an electric arc is generated. When the piston moves quickly to the right, the gas on the right side is compressed, and an air flow is generated through the whistling, which blows the electric arc in stages and extinguishes the electric arc. Thereafter, the gas in the quarantine chamber is discharged into the switch body through the inner hole of the fixed contact and the cooler.
When the circuit breaker is closing, the operating mechanism drives the moving contact, nozzle and piston to move to the left, so that the fixed contact is inserted into the moving contact seat, so that the moving and fixed contacts have good electrical contact to achieve the purpose of closing.
The following points should be paid attention to during the wiring and debugging of the secondary wiring of sulfur hexafluoride circuit breaker:
(1) The opening and closing electrical interlock is realized by the conversion reactor, and there is a reliable opening and closing mechanical interlock in the mechanism. When opening the brake manually, if you cannot pull the opening ring (opening and locking), do not pull it forcefully; when you want to close but cannot pull the closing ring, do not pull it forcefully. At this time, you should observe the position of the pointer before opening and closing operations.
(2) The lead of the electric contact vacuum pressure gauge is in the lower part of the cover, and it is led out from the normally open contact of the pressure gauge. When leaving the factory, the lower limit pointer has been adjusted to 0.2MPa (considered by 0.25MPa, -10°C). When the sulfur hexafluoride gas pressure is reduced by at least 0.2MPa, the contacts will be closed and the relay protection circuit will be connected. The user can appropriately increase the lower limit according to the operating requirements, but it shall not be lower than 0.2MPa.
(3) The closing pull ring is on the outside of the box, and the opening pull ring is on the inside of the box. Do not pull it wrongly during manual operation.
(4) The energy storage motor must use AC power.
Sulfur hexafluoride circuit breakers use sulfur hexafluoride density relays to monitor changes in gas pressure. When the pressure of sulfur hexafluoride gas drops to the first alarm value, the density relay will act and report the signal of supplementary gas pressure. When the sulfur hexafluoride gas pressure drops to the second alarm value, the density relay will act and report the signal of the blocking pressure, and at the same time, the tripping and closing circuit of the switch will be disconnected to realize the opening and closing and locking.
②Vacuum circuit breaker
The vacuum circuit breaker gets its name because its arc extinguishing medium and the insulating medium in the contact gap after arc extinguishing are both high vacuum. It has the advantages of small size, light weight, suitable for frequent operation, arc extinguishing without overhaul, and it is more popular in the distribution network. Vacuum circuit breakers mainly include three parts: vacuum isolation chamber, electromagnetic or spring operating mechanism, bracket and other components.
(1) Vacuum solitary room.
According to different switch types, the vacuum quarantine chamber has an outer shielded ceramic vacuum interrupter, a centrally sealed cup-shaped longitudinal magnetic field miniaturized vacuum quarantine chamber, and an internally sealed glass bubble quarantine chamber. The basic structure is as follows:
1) Airtight insulation system (housing).
The airtight insulation system consists of an airtight insulation cylinder made of ceramic, glass or glass-ceramics, a movable end cover plate, and a fixed end cover plate stainless steel bellows. It is a vacuum airtight container. In order to ensure air tightness, in addition to strict operation techniques in the sealing type, the material itself is also required to have a small air permeability and internal outgassing.
2) Conductive system.
The conductive system is composed of a fixed conductive rod, a fixed arc surface, a fixed contact, a movable contact, a movable arc surface, and a movable conductive rod.
There are roughly three types of contact structures: cylindrical contact, transverse magnetic field contact with spiral groove arc surface, and longitudinal magnetic field contact. At present, the longitudinal magnetic field technology is usually used, and this kind of isolation chamber has a strong and stable arc breaking ability.
3) Screen hiding system.
The shield is an indispensable element in the vacuum interrupter, and there are many kinds of main shields surrounding the contacts, bellows shields, and pressure equalization shields. The function of the main shield is: ① Prevent the arc product from splashing on the inner wall of the insulating shell during the arcing process, thereby reducing the insulation strength of the shell. ②Improve the uniformity of the electric field distribution inside the arc extinguishing chamber, which is beneficial to reduce the local field strength and promote the miniaturization of the vacuum interrupter. ③It condenses the arc product and absorbs part of the arc energy, which helps to restore the strength of the gap medium after the arc.
(2) Operating mechanism.
According to different types of circuit breakers, different operating mechanisms are adopted. Commonly used operating mechanisms are spring operating mechanism, CD10 electromagnetic operating mechanism, CD17 electromagnetic operating mechanism, CT19 spring energy storage operating mechanism, CT8 spring energy storage operating mechanism.
(3) Other components.
Other components include bases, insulating supports, insulators and other components.
③Oil circuit breaker
An oil circuit breaker is a high-voltage switchgear that uses sealed insulating oil as the arc extinguishing medium for breaking faults. This type of circuit breaker has been used in power systems earlier, with mature technology and low price, and is widely used in power grids of various voltage levels. The oil circuit breaker is used to cut off and switch on the power supply, and can cut off the current quickly and reliably in the event of a short circuit.
Oil circuit breakers can be divided into two types, grounded case oil circuit breakers (referred to as oil circuit breakers) and live case oil circuit breakers (referred to as oil circuit breakers). No matter what kind of oil circuit breaker, the structure body needs to be filled with oil, and its main function is arc extinguishing, heat dissipation and insulation. Oil circuit breakers have a certain degree of danger, mainly because they may cause an explosion when a fault occurs. After the explosion, the high temperature oil in the oil circuit breaker will splash, forming a large area of combustion, causing a short circuit between phases or a short circuit to the ground, destroying electricity The normal operation of the system expands the accident and even causes serious personal injury or death.
(1) Multi-oil circuit breaker.
The fox-killing chamber of the multi-oil circuit breaker is installed in a grounded metal box, so more oil is used. Oil is used as both anti-solitary medium and ground insulation. The multi-oil circuit breaker has a simple structure and reliable performance, can be made into an ultra-high voltage level, and can be conveniently equipped with current transformers. It has strong compatibility and requires little influence from atmospheric conditions when used outdoors. Multi-oil circuit breakers have a long history of use, mature use and manufacturing technology, and have played an important role in the power system. In recent years, multi-oil circuit breakers are relatively bulky, consume a lot of steel and transformer oil, are difficult to transport and install, and have poor safety, and they are currently becoming obsolete.
(2) Less oil circuit breaker.
The arc extinguishing chamber of the oil-less circuit breaker is installed in an oil tank insulated from the earth. The fuel tank can be made of metal or insulating material. The oil filling in the box is only used for insulation between the arc extinguishing medium and the fracture, not for insulation to the ground, so the amount of oil used is small.
The oil-less circuit breaker is mainly composed of underframe, insulator, transmission system, conductive system, contact, arc extinguishing chamber, oil-gas separator, buffer and oil level indicator. When closing, the operating mechanism transmits the force to the main shaft through the driving arm link (see switch mechanism), and the main shaft drives 3 insulated pull rods to make the three-pole movable contact rod move upward in a straight line, and finally insert it into the static contact. The moving mechanism buckles the contact rod to keep the circuit breaker in the closed position. In this process, the breaking spring stretches and stores energy to prepare for opening. Opening is when the operating mechanism is tripped, due to the action of the breaking spring force, the main shaft rotates to drive the pull rod, so that the movable contact rod moves downwards. Finally, the pretension of the breaking spring should be applied, and the main shaft turning arm is close to the opening. Brake positioning piece, so that the circuit breaker is kept in the off position.
Outdoor oil-less circuit breakers with voltage levels of 110kV and above mostly adopt a floor-standing overall structure of unit breaks (or breaking units) connected in series and modular combination for breaking the arc. The voltage of the standard breaking unit is 55 ~ 110kV. For example, the SW6 type oil-less circuit breaker, the breaking unit is 55kV. The 220kV and 330kV oil-less circuit breakers belonging to this series will adopt the structure of double-column four-break and three-column six-break. , Each pole is composed of four and six breaking units in series, and capacitors are connected in parallel on each fracture to uniformly break the voltage distribution of the fracture; each pole is operated by a separate hydraulic operating mechanism. SW7-220 220kV oil-less circuit breaker, because the breaking unit is 110kV, each pole adopts a single-pole double-break structure.
The outstanding features of the oil-less circuit breaker are simple structure, easy manufacture and maintenance, low price and convenient use. Compared with oil-rich circuit breakers, oil-less circuit breakers are small in size, light in weight, and use less oil. They can be assembled into ultra-high voltage and oil-less circuit breakers using building blocks, and are widely used in power systems. The disadvantages are long arcing time, slower action, short overhaul period, large maintenance workload, and limited by the voltage of the unit break, it is difficult to develop UHV levels.
2. Operation and maintenance specifications for high-voltage circuit breakers
In order to ensure the long-term safe and reliable operation of high-voltage circuit breakers, and timely discover equipment defects and abnormal phenomena in the operation of the circuit breaker, the operation and maintenance personnel should carefully check the operating parameters and changes of the circuit breaker, and also according to the performance characteristics of different types of circuit breakers Carry out related inspections and maintenance.
①SF6 circuit breaker
(1) Before installation of SF6 pipelines, the pipes must be thoroughly blown with dry nitrogen, and all pipe flanges should be well sealed.
(2) Before installing the air pipe, the pipe must be thoroughly blown with dry air. During the installation, dust and debris must be prevented from falling into the pipe.
(3) When filling SF6 gas, measures should be taken to prevent SF6 gas from being damp.
(4) After filling the SF6 gas, check the pipe joints and flanges with a leak detector, and there should be no gas leakage.
(5) In the compressed air system (nitrogen), all joints and flanges should be checked under the specified pressure, and no air leakage is allowed.
②Vacuum circuit breaker
The vacuum circuit breaker should be checked and maintained once a year to ensure normal operation. The inspection should do the following work:
(1) Perform a fracture power frequency withstand voltage test on the pipe, test the vacuum degree and record it in the book.
(2) Conduct power frequency withstand voltage test on insulating parts.
(3) Test the opening distance, contact stroke and mechanical characteristics of the circuit breaker, and record them in the book.
(4) Check whether the connecting bolts, nuts, etc. of the adjustable parts of each connecting piece are loose, especially the connecting small screws at the knee of the auxiliary switch, and the lock nut connecting the vacuum tube moving conductive rod.
(5) Check whether all kinds of circlips, pins, etc. are loose at each rotating joint; add lubricating paste to each rotating and sliding part.
(6) For vacuum circuit breakers with a current greater than 1600A, the DC resistance of each pole should be tested and recorded.
(7) If you need to replace the temporary, it should be carried out according to the requirements of the product manual. After the replacement, the mechanical characteristic test and the withstand voltage test should be carried out.
(8) After the annual inspection and before putting it into operation, it should be operated continuously without load for 8-10 times, and it can be put into operation when everything is normal.
③Oil circuit breaker
The operation and maintenance of the oil circuit breaker refers to the patrol inspection (including spot inspection) and daily maintenance of the oil switch equipment in the live operation. It is a necessary means to ensure the safe operation of the oil switch.
(1) Check the casing of the oil switch and the supporting porcelain bottle for abnormal phenomena, and check whether there is noise during the operation of the oil switch.
(2) Whether the oil color is normal, and observe whether there is oil leakage or oil leakage on the oil switch shell; observe the oil level of the oil switch, if the oil level is not visible due to serious oil leakage, immediately remove the DC fuse of the trip circuit and hang it. Put up the warning sign of “No Switching” and notify the dispatcher to deal with the accident.
(3) Check whether the working joints of the oil switch are heated or not, the casing rubber gasket and the throttle, and the oil gauge are leaking oil, and the relative positions of the oil switches are normal.
(4) Whether the operating mechanism of the oil switch is complete and clean, and whether the “on-off” position indication and signal light are consistent with the actual position of the circuit breaker.
(5) In windy weather, check whether the wiring of the outdoor oil switch casing terminal is violently swinging or loose, and whether there is any sundries hanging on the upper part.
(6) In snowy and dense fog, check the outdoor oil switch bushing and insulator for discharge, ice hanging, and debris hanging on the upper part.
(7) Check whether the indication or display of the signal device is correct.