The high-voltage circuit breaker (or high-voltage switch) can not only cut off or close the no-load current and load current in the voltage-separating circuit, but also cut off the overload current and the short-circuit current through the action of the relay protection device when the system fails. A fairly perfect arc extinguishing structure and sufficient current interrupting capability, can be divided into oil circuit breaker (multi-oil circuit breaker, oil-less circuit breaker), sulfur hexafluoride circuit breaker (SF6 circuit breaker), vacuum circuit breaker, compressed air circuit breaker And so on.
First, high voltage vacuum circuit breaker
1. Basic requirements for vacuum circuit breaker structure
1 The mechanical performance is stable, such as closing bounce time, it is hoped to protect the same state throughout the life. At the end of 1989, the Ministry of Energy's power department proposed that the vacuum circuit breaker closing bounce time must be less than 2ms;
2 sufficient mechanical strength to make the circuit breaker itself have sufficient dynamic stability.
3 The separation of the high pressure zone and the low pressure zone is preferably arranged in front and rear to help ensure the personal safety of the personnel in operation.
4 There must be sufficient space for inspection, adjustment and maintenance of the operating mechanism.
5 Optional mechanism, some models can be equipped with spring operating mechanism and electromagnetic operating mechanism, and some can only be used with one.
6 Simple structure, reliable work and low price.
7 easy to achieve anti-missing chain.
All vacuum circuit breakers, regardless of the structure, are equipped with a trip tension spring in the main body of the circuit breaker. During the closing process, the operating mechanism must provide the work of driving the switch movement, and simultaneously store the energy of the opening spring. When the opening is required, the operating mechanism value needs to complete the trip unlocking task, and the opening spring is released by the opening spring.
2, features
The vacuum circuit breaker can be divided into six parts according to its structure:
1 bracket. Install the frame of each functional component.
2 vacuum interrupter. An arc-extinguishing element that implements the closing and breaking functions of the circuit.
3 conductive loop. The connection with the dynamic end and the static end of the arc extinguishing chamber constitutes a current channel.
4 transmission mechanism. The movement of the operating mechanism is transmitted to the arc extinguishing chamber to realize the opening and closing operation of the arc extinguishing chamber.
5 insulation support. The insulating support bridges the functional components to meet the insulation requirements of the circuit breaker.
6 operating mechanism. Power drive unit for circuit breaker closing and opening.
3, the structure type
The types of vacuum circuit breakers can be divided from different angles. In general, they are mainly divided into the following two aspects:
The division of 1 amp use can be divided into indoor and outdoor styles, which are represented by ZN and ZW respectively.
The position division of the 2A breaker main body and the operating mechanism can be divided into an integral type and a split type. The integral vacuum circuit breaker operating mechanism and the switch body are mounted on the same skeleton, which is small in size, light in weight, convenient in installation and debugging, and stable in mechanical performance. The split type vacuum circuit breaker operating mechanism and the switch body are respectively installed at different positions of the switch cabinet. This type of installation is mainly affected by the installation method of the oil-less circuit breaker in China, and is more suitable for the oil-free transformation of the less oil switch cabinet. The advantage is that the inspection and maintenance are convenient, it is determined that the installation adjustment is a little troublesome, and the stability and reliability of the mechanical characteristics are less.
4. The operating mechanism of the vacuum circuit breaker operating mechanism is the driving device of the vacuum circuit breaker, and mainly has an electromagnetic operating mechanism and a spring operating mechanism.
1 vacuum circuit breaker requirements for the operating mechanism. Mainly as follows:
1) The output characteristics of the mechanism are matched as much as possible with the reaction characteristics of the vacuum circuit breaker;
2) It is necessary to have enough closing output work to ensure that the vacuum circuit breaker has the ability to close the short-circuit fault current;
3) After closing, the switch can be stably closed even in the accident state (that is, the switch has dynamic stability);
4) It must be ensured that it can be normally closed under the operating voltage of 85%~110%, and can be normally opened under the voltage of 65%~120%, but not at the rated operating voltage of 30%;
5) can be operated electrically or manually;
6) The electromagnetic mechanism should have the function of free tripping;
2 The reaction force characteristics of the vacuum circuit breaker closing. Conversely, the characteristic refers to the relationship between the various resistances (including the reaction force of the spring, the friction force, the electric power and the inertial force) and the stroke of the customer service. The reaction force characteristic tells us that the operating mechanism provides the closing work for the circuit breaker, which must be greater than the work done for the various resistances of the customer service, and the circuit breaker can complete the closing action.
3 electromagnetic operating mechanism of vacuum circuit breaker. Since the output characteristics of the solenoid electromagnet of the electromagnetic operating mechanism easily meet the requirements of the closing force characteristics of the vacuum circuit breaker, in the initial stage of the development of the vacuum circuit breaker, the electromagnetic operating mechanism for power distribution is mainly used. In addition, the electromagnetic mechanism has the advantages of simple structure, simple use, low cost, etc. It is the main matching mechanism of various circuit breakers in the current distribution system. The operation department is not only very familiar but also has accumulated a lot of valuable experience in use and maintenance. Commonly used electromagnetic operating mechanisms are CD10, CD17, and CD19. The CD10 electromagnetic operating mechanism was originally equipped with the operating mechanism of the SN10-10 type oil-less circuit breaker, which is a family-type output. At the beginning of the development of vacuum circuit breakers, there was no special operating mechanism, and there is still a vacuum circuit breaker equipped with a CD10 type operating mechanism. At present, the oil-less transformation of the oil-less switchgear cabinet can also adopt the CD10 type operating mechanism. The CD17 electromagnetic mechanism is an operating mechanism specially designed for vacuum circuit breakers. It is a direct push output. It has CD-17-I, CD-17-II, CD-17-III type, and is equipped with a breaking capacity of 20, respectively. 31.5, 40kA vacuum circuit breaker. Its volume and weight are much smaller than those of the CD-10 type mechanism. The combined and open operating current is only 2/3 of the CD10 type mechanism, and the installation takes up little space.
4 spring operating mechanism of the vacuum circuit breaker. The spring operating mechanism can be operated by AC and DC, and the operating current is very small, generally only 1.5-3A. Even if the DC power storage device required for DC operation is small, the manual energy storage can be opened and closed. Stream trip function. In the general terminal distribution room, the DC power storage device can be eliminated and the investment can be saved. Most of the circuit breakers of the foreign medium voltage class are mostly equipped with a spring operating mechanism.
The spring operating mechanism of the domestic vacuum circuit breaker is commonly used in the CT7 and CT8 types. Since these products have been put into operation, the faults are numerous, the maintenance department is large, and the volume is large, which is not ideal. For vacuum circuit breakers that need to be operated frequently, not only the spring operating mechanism is required to have a long service life, but also the work is very reliable.
At present, two new types of spring mechanisms are used in China, one is CT17 and the other is CT19. The former is a direct push output and the latter is a rotary output. Both products are small and compact, and the volume and weight are much smaller than those of the electromagnetic mechanism. For example, the CT17 mechanism weighs only 2/3 of the CD17 type. It seems that the product type test from many factories shows that the product is exaggerated during installation without any adjustment, reliable operation and long mechanical life, especially CT19, which has reached 20,000-30,000 times in many research tests. It is considered to have The advanced level of products in the 1990s is the ideal operating mechanism for vacuum circuit breakers.
The structure of the spring mechanism is relatively complicated, and the processing precision and assembly requirements of the parts are high, so the price is relatively expensive, and the cost and the price of the vacuum circuit breaker are increased. However, for the entire substation, the investment in the DC battery device can be saved, and the voltage stability requirement is not high, the operation safety is improved, and the maintenance workload is reduced.
5. Transmission and closing and opening operation of vacuum circuit breaker
The transmission chain of the vacuum circuit breaker is generally composed of a mechanism transmission link, a crank arm, a main shaft, an insulating push rod, a triangular arm and a contact spring device, and the transmission link should be simplified as much as possible to improve the efficiency of the transmission.
Taking the electromagnetic mechanism ZN39 vacuum circuit breaker as an example, the closing and opening operation of the vacuum circuit breaker is as follows:
When closing, the closing mechanism of the operating mechanism is energized - the closing core action - the mechanism and the transmission link action - the switch spindle rotation - the insulation push rod push - the triangular arm rotation - the lower pressure contact spring device - the arc extinguishing chamber The moving rod moves downward to contact the contact-contact spring cable to the end of the contact stroke. At the same time, the auxiliary switch of the mechanism cuts off the power supply of the closing contact coil, and the opening spring expands the energy storage. The gusset plate of the electromagnetic mechanism is held in the closing position by the semi-axle buckle, and the closing is completed.
When opening, the opening and closing coils in the mechanism are energized - the opening of the iron core - the gusset and the half shaft is tripped - the circuit breaker is quickly disconnected by the contact spring and the opening spring - the auxiliary switch of the mechanism is cut off The coil power supply - the mechanism is restored and held in the open position by the trip spring.
Second, high pressure oil circuit breaker
The high-pressure oil circuit breaker uses a sealed insulating oil as a switching device for breaking the arc extinguishing medium, and has two forms of a multi-oil circuit breaker and a low-oil circuit breaker. It is used in power systems earlier. The technology is very mature and cheap. It is widely used in voltage-grade power grids. Oil circuit breakers are used to cut off and turn on the power, and can cut off the current quickly and reliably in the event of a short circuit.
This oil circuit breaker was first made in 1895. Before 1930, the use of oil as an arc extinguishing medium to improve the breaking capacity of circuit breakers was the most effective method. Mineral oils (such as transformer oil) are commonly used in oil circuit breakers, which have high dielectric strength and strong arc extinguishing capability.
When the oil circuit breaker breaks the circuit, as long as the current in the circuit exceeds 0.1A and the voltage exceeds several tens of volts, an arc occurs between the moving contact and the static contact of the circuit breaker, and the current can continue to flow through the arc. Only when the contacts are separated by a sufficient distance, the circuit is disconnected after the arc is extinguished. When the 10kV oil-less circuit breaker opens a single 20kA current, the arc power can reach more than 10,000 kW, and the temperature of the arc arc column generated between the contacts of the circuit breaker can reach six or seven thousand degrees, or even more than 10,000 degrees.
Multi-oil circuit breakers and oil-less circuit breakers must be filled with oil, which is used for arc extinguishing, heat dissipation and insulation. The danger is not only the explosion in the event of a fault, but also the large-temperature combustion caused by the high-temperature oil in the oil circuit breaker after the explosion, causing phase-to-phase short circuit or short circuit to the ground, destroying the normal operation of the power system, so that The accident has expanded and even caused serious personal injury or death.
Arc extinguishing process: When the moving contact and the static contact of the circuit breaker are separated from each other, an arc is generated. The high temperature of the arc causes the insulating oil in the vicinity to evaporate and thermally decompose, forming a gas with strong arc extinguishing ability (mainly hydrogen). And the higher pressure bubbles, so that the arc is quickly extinguished.
There are six reasons for the explosion of an oil circuit breaker:
1 If the oil level is too low, the oil layer of the oil circuit breaker that is electrically shocked to the oil surface is too thin, and the combustible gas that is decomposed by the oil is cooled poorly. This part of the combustible gas enters the space under the top cover and mixes with the air to form an explosive gas. It is possible to explode and burn at its own high temperature.
2 The oil level in the oil tank is too high, and the gas decomposed by the oil can not be buffered in the tank, forming excessive pressure, which may also cause the fuel tank to explode and ignite.
3 The insulation strength of the oil is deteriorated, impurities or moisture are excessive, causing flashover inside the oil circuit breaker.
4 improper adjustment of the operating mechanism, component failure, will make the operation slow or unsuccessful after closing. When the arc can not be cut off and extinguished in time, excessive combustible gas is generated in the fuel tank, which may cause explosion and combustion.
5 The interrupting capacity is small, and the breaking capacity of the oil switch is an important parameter for the transmission and distribution system. When the breaking capacity is less than the short-circuit capacity of the system, the circuit breaker has no ability to cut off the strong short-circuit current of the system, causing the circuit breaker to burn and explode, causing a major accident in the transmission and distribution system.
6 The inlet and outlet lines of other oil circuit breakers pass through the insulating sleeve. When the insulation sleeve and the fuel tank cap, the fuel tank cap and the fuel tank body are not tightly sealed, the fuel tank is damp, or the fuel tank is unclean, and the insulating sleeve is mechanically damaged. Can cause a short circuit to the ground causing an explosion or fire accident.
Therefore, the circuit breaker should be strictly checked for compliance with the manufacturer's technical requirements before installation. The breaking capacity of the circuit breaker must be greater than the short circuit capacity of the circuit breaker circuit. During the inspection, the operation test shall be carried out to ensure the flexibility and reliability of the parts and adjust the synchronism of the three-phase operation. The connection between the circuit breaker and the electrical circuit should be tight, and the temperature can be observed with the test temperature wax sheet, and the contact damage should be replaced. The insulation test shall be carried out after the overhaul, and a special person shall be responsible for the inventory tool to prevent the tool from falling into the fuel tank and causing an accident. Before putting into operation, the sealing performance of the fuel tank cap of the insulating sleeve should also be checked to prevent the oil tank from entering the water and getting wet, causing the circuit breaker to explode and burn. After the circuit breaker cuts off the severe short circuit fault, the contact damage and oil quality should be checked.
The oil level should always be checked during operation and the oil level must be strictly controlled within the oil level indicator. If abnormalities are found, such as oil leakage, oil leakage, abnormal sounds, etc., measures should be taken. If necessary, the load should be reduced immediately or the power failure should be checked. When the fault tripping heavy compound brake is bad, and the current varies greatly, the circuit breaker fuel injection has a gas smell, it must stop running, and it is strictly forbidden to force the power to avoid explosion.
The oil circuit breaker arc extinguishing chamber is made of an insulating material and is disposed around the contact to limit the arc and generate a strong air blow to the arc to tell the air to extinguish. According to the energy generated by the air blowing, the arc chamber can be divided into three categories:
1 Self-energy air blow type arc extinguishing chamber, using the energy of the arc itself to decompose the oil out of the gas, and increase the pressure in the arc extinguishing chamber. When the arcing opening is opened, the arcing port is generated due to the pressure difference between the arc extinguishing chamber and the outside. High-speed oil flow, blowing the arc to extinguish it.
2 External energy blowing type arc extinguishing chamber is also called forced oil blowing type arc extinguishing chamber, which uses external energy (usually provided by spring stored in the oil circuit breaker closing process) to push the piston during the breaking process and improve the extinguishing The pressure in the arc chamber drives the oil and gas to blow the arc and extinguish the arc.
3The integrated chamber arc extinguishing chamber combines the advantages of self-energy blowing and external energy blowing, using the energy of the arc itself to extinguish the large current arc, using external energy to extinguish the small current arc, and improving the segmentation characteristics. The structure of the arc extinguishing chamber is slightly complicated, but the segmentation performance is good. Most of the ultra-high pressure and low oil circuit breakers use this arc extinguishing chamber.
There are four main types of arcing in the arc breaker chamber of the oil circuit breaker:
1 longitudinal blowing, oil and gas blowing through the arc surface in the direction of the arc axis;
2 transverse blowing, oil and gas blowing perpendicular to the direction of the arc axis;
3 vertical and horizontal blowing, using both horizontal blowing and longitudinal blowing to blow the arc;
4 ring blowing, oil and gas blowing from the surrounding direction perpendicular to the arc axis. According to the main blowing mode, the arc extinguishing chamber of the oil circuit breaker can be referred to as a vertical blow interrupter, a horizontal blow interrupter, a vertical and horizontal blow blow chamber, and a ring blow interrupter.
Third, high voltage SF6 circuit breaker
The SF6 circuit breaker is a circuit breaker that uses SF6 gas as the arc extinguishing and insulating medium. It belongs to the air blow breaker as well as the air circuit breaker, the difference is:
1 working pressure is lower;
2 During the arcing process, the gas is not discharged to the atmosphere and is recycled in a closed system.
The molecules of SF6 and the free electrons have very good mixing. When almost 100% of the electrons and SF6 molecules are mixed to form heavy negative ions, this property has great value for the deionization and arc extinguishing of the remaining arc columns, that is, SF6 has good electronegativity, its molecules It can quickly capture free electrons and form negative ions. The conduction of these negative ions is very slow, which accelerates the recovery rate of the dielectric strength of the arc gap, so it has good arc extinguishing performance. At 1.01*105Pa air pressure, the arc-extinguishing performance of SF6 is 100 times that of air, and it does not deteriorate after arc extinguishing and can be reused.
The excellent insulation and arc extinguishing performance of SF6 gas makes SF6 circuit breaker have the following advantages: strong breaking capacity, high fracture voltage, high number of continuous breaking, suitable for frequent operation, low noise, no fire hazard , electromechanical wear and so on, is a "no maintenance" circuit breaker with excellent performance. More and more SF6 circuit breakers are used in high voltage circuits. Common SF6 circuit breakers are available in LN1-35 and HB36.
Under normal conditions, SF6 is a non-combustible, odorless, non-toxic inert gas with a density approximately twice that of air. However, under the action of arc, SF6 gas will be decomposed in a small part, producing certain toxic low-fluoride substances, such as SOF4, SF4, SOF4 and SO2F2, which have an impact on human health and also have corrosion and deterioration effects on metal parts. Therefore, in the SF6 circuit breaker, an adsorption device is generally installed, and the adsorbent is activated alumina, activated carbon, molecular sieve and the like. The adsorption device can completely absorb the toxic substances generated by the gas such as SF6 decomposed at the high temperature of the arc. If used for frequent arcing, the metal vapor reacts with the SF6 gas decomposition product to form a fine powder (hydrofluoric acid salt, sulfur acid salt, etc.) which is well insulated and deposited on the contact surface. Corrosion of the contact material, so that the contact resistance increases sharply, so that the sealed contacts of the oil-filled SF6 gas cannot work reliably. Therefore, it is not suitable for the low-voltage electrical equipment that is frequently operated to use SF6 as the arc extinguishing medium.
Because SF6 gas decomposes out corrosive gas at high temperature during discharge, it has a very strong corrosive effect on aluminum alloy, and also damages phenolic resin laminate and porcelain insulation. If SF6 and N2 are used in combination, when the SF6 content exceeds 20%~30%, the dielectric strength is the same as that of the full SF6, and the corrosion is greatly reduced. Therefore, SF6 is often used in N2. In SF6 circuit breakers, the water content of SF6 gas must be strictly specified not to exceed the standard. The water and the SF4 in the arc decomposition product produce hydrofluoric acid (H2O+SF4→SOF2+2HF) to corrode the material. When the moisture content reaches saturation, it will also condense on the surface of the insulating member, so that the dielectric strength is significantly reduced, and even the creeping discharge is caused. The operation experience and the above analysis are all on the surface. Due to the small volume of the insulation structure of SF6 circuit breaker, if the water content of SF6 gas is high, the insulation level will be greatly reduced, the contact resistance will increase sharply, and damage or explosion accident will occur during operation. .
Therefore, each manufacturer and operation department requires a strict sealing process, and the water content of SF6 gas should not exceed the standard.
First, high voltage vacuum circuit breaker
1. Basic requirements for vacuum circuit breaker structure
1 The mechanical performance is stable, such as closing bounce time, it is hoped to protect the same state throughout the life. At the end of 1989, the Ministry of Energy's power department proposed that the vacuum circuit breaker closing bounce time must be less than 2ms;
2 sufficient mechanical strength to make the circuit breaker itself have sufficient dynamic stability.
3 The separation of the high pressure zone and the low pressure zone is preferably arranged in front and rear to help ensure the personal safety of the personnel in operation.
4 There must be sufficient space for inspection, adjustment and maintenance of the operating mechanism.
5 Optional mechanism, some models can be equipped with spring operating mechanism and electromagnetic operating mechanism, and some can only be used with one.
6 Simple structure, reliable work and low price.
7 easy to achieve anti-missing chain.
All vacuum circuit breakers, regardless of the structure, are equipped with a trip tension spring in the main body of the circuit breaker. During the closing process, the operating mechanism must provide the work of driving the switch movement, and simultaneously store the energy of the opening spring. When the opening is required, the operating mechanism value needs to complete the trip unlocking task, and the opening spring is released by the opening spring.
2, features
The vacuum circuit breaker can be divided into six parts according to its structure:
1 bracket. Install the frame of each functional component.
2 vacuum interrupter. An arc-extinguishing element that implements the closing and breaking functions of the circuit.
3 conductive loop. The connection with the dynamic end and the static end of the arc extinguishing chamber constitutes a current channel.
4 transmission mechanism. The movement of the operating mechanism is transmitted to the arc extinguishing chamber to realize the opening and closing operation of the arc extinguishing chamber.
5 insulation support. The insulating support bridges the functional components to meet the insulation requirements of the circuit breaker.
6 operating mechanism. Power drive unit for circuit breaker closing and opening.
3, the structure type
The types of vacuum circuit breakers can be divided from different angles. In general, they are mainly divided into the following two aspects:
The division of 1 amp use can be divided into indoor and outdoor styles, which are represented by ZN and ZW respectively.
The position division of the 2A breaker main body and the operating mechanism can be divided into an integral type and a split type. The integral vacuum circuit breaker operating mechanism and the switch body are mounted on the same skeleton, which is small in size, light in weight, convenient in installation and debugging, and stable in mechanical performance. The split type vacuum circuit breaker operating mechanism and the switch body are respectively installed at different positions of the switch cabinet. This type of installation is mainly affected by the installation method of the oil-less circuit breaker in China, and is more suitable for the oil-free transformation of the less oil switch cabinet. The advantage is that the inspection and maintenance are convenient, it is determined that the installation adjustment is a little troublesome, and the stability and reliability of the mechanical characteristics are less.
4. The operating mechanism of the vacuum circuit breaker operating mechanism is the driving device of the vacuum circuit breaker, and mainly has an electromagnetic operating mechanism and a spring operating mechanism.
1 vacuum circuit breaker requirements for the operating mechanism. Mainly as follows:
1) The output characteristics of the mechanism are matched as much as possible with the reaction characteristics of the vacuum circuit breaker;
2) It is necessary to have enough closing output work to ensure that the vacuum circuit breaker has the ability to close the short-circuit fault current;
3) After closing, the switch can be stably closed even in the accident state (that is, the switch has dynamic stability);
4) It must be ensured that it can be normally closed under the operating voltage of 85%~110%, and can be normally opened under the voltage of 65%~120%, but not at the rated operating voltage of 30%;
5) can be operated electrically or manually;
6) The electromagnetic mechanism should have the function of free tripping;
2 The reaction force characteristics of the vacuum circuit breaker closing. Conversely, the characteristic refers to the relationship between the various resistances (including the reaction force of the spring, the friction force, the electric power and the inertial force) and the stroke of the customer service. The reaction force characteristic tells us that the operating mechanism provides the closing work for the circuit breaker, which must be greater than the work done for the various resistances of the customer service, and the circuit breaker can complete the closing action.
3 electromagnetic operating mechanism of vacuum circuit breaker. Since the output characteristics of the solenoid electromagnet of the electromagnetic operating mechanism easily meet the requirements of the closing force characteristics of the vacuum circuit breaker, in the initial stage of the development of the vacuum circuit breaker, the electromagnetic operating mechanism for power distribution is mainly used. In addition, the electromagnetic mechanism has the advantages of simple structure, simple use, low cost, etc. It is the main matching mechanism of various circuit breakers in the current distribution system. The operation department is not only very familiar but also has accumulated a lot of valuable experience in use and maintenance. Commonly used electromagnetic operating mechanisms are CD10, CD17, and CD19. The CD10 electromagnetic operating mechanism was originally equipped with the operating mechanism of the SN10-10 type oil-less circuit breaker, which is a family-type output. At the beginning of the development of vacuum circuit breakers, there was no special operating mechanism, and there is still a vacuum circuit breaker equipped with a CD10 type operating mechanism. At present, the oil-less transformation of the oil-less switchgear cabinet can also adopt the CD10 type operating mechanism. The CD17 electromagnetic mechanism is an operating mechanism specially designed for vacuum circuit breakers. It is a direct push output. It has CD-17-I, CD-17-II, CD-17-III type, and is equipped with a breaking capacity of 20, respectively. 31.5, 40kA vacuum circuit breaker. Its volume and weight are much smaller than those of the CD-10 type mechanism. The combined and open operating current is only 2/3 of the CD10 type mechanism, and the installation takes up little space.
4 spring operating mechanism of the vacuum circuit breaker. The spring operating mechanism can be operated by AC and DC, and the operating current is very small, generally only 1.5-3A. Even if the DC power storage device required for DC operation is small, the manual energy storage can be opened and closed. Stream trip function. In the general terminal distribution room, the DC power storage device can be eliminated and the investment can be saved. Most of the circuit breakers of the foreign medium voltage class are mostly equipped with a spring operating mechanism.
The spring operating mechanism of the domestic vacuum circuit breaker is commonly used in the CT7 and CT8 types. Since these products have been put into operation, the faults are numerous, the maintenance department is large, and the volume is large, which is not ideal. For vacuum circuit breakers that need to be operated frequently, not only the spring operating mechanism is required to have a long service life, but also the work is very reliable.
At present, two new types of spring mechanisms are used in China, one is CT17 and the other is CT19. The former is a direct push output and the latter is a rotary output. Both products are small and compact, and the volume and weight are much smaller than those of the electromagnetic mechanism. For example, the CT17 mechanism weighs only 2/3 of the CD17 type. It seems that the product type test from many factories shows that the product is exaggerated during installation without any adjustment, reliable operation and long mechanical life, especially CT19, which has reached 20,000-30,000 times in many research tests. It is considered to have The advanced level of products in the 1990s is the ideal operating mechanism for vacuum circuit breakers.
The structure of the spring mechanism is relatively complicated, and the processing precision and assembly requirements of the parts are high, so the price is relatively expensive, and the cost and the price of the vacuum circuit breaker are increased. However, for the entire substation, the investment in the DC battery device can be saved, and the voltage stability requirement is not high, the operation safety is improved, and the maintenance workload is reduced.
5. Transmission and closing and opening operation of vacuum circuit breaker
The transmission chain of the vacuum circuit breaker is generally composed of a mechanism transmission link, a crank arm, a main shaft, an insulating push rod, a triangular arm and a contact spring device, and the transmission link should be simplified as much as possible to improve the efficiency of the transmission.
Taking the electromagnetic mechanism ZN39 vacuum circuit breaker as an example, the closing and opening operation of the vacuum circuit breaker is as follows:
When closing, the closing mechanism of the operating mechanism is energized - the closing core action - the mechanism and the transmission link action - the switch spindle rotation - the insulation push rod push - the triangular arm rotation - the lower pressure contact spring device - the arc extinguishing chamber The moving rod moves downward to contact the contact-contact spring cable to the end of the contact stroke. At the same time, the auxiliary switch of the mechanism cuts off the power supply of the closing contact coil, and the opening spring expands the energy storage. The gusset plate of the electromagnetic mechanism is held in the closing position by the semi-axle buckle, and the closing is completed.
When opening, the opening and closing coils in the mechanism are energized - the opening of the iron core - the gusset and the half shaft is tripped - the circuit breaker is quickly disconnected by the contact spring and the opening spring - the auxiliary switch of the mechanism is cut off The coil power supply - the mechanism is restored and held in the open position by the trip spring.
Second, high pressure oil circuit breaker
The high-pressure oil circuit breaker uses a sealed insulating oil as a switching device for breaking the arc extinguishing medium, and has two forms of a multi-oil circuit breaker and a low-oil circuit breaker. It is used in power systems earlier. The technology is very mature and cheap. It is widely used in voltage-grade power grids. Oil circuit breakers are used to cut off and turn on the power, and can cut off the current quickly and reliably in the event of a short circuit.
This oil circuit breaker was first made in 1895. Before 1930, the use of oil as an arc extinguishing medium to improve the breaking capacity of circuit breakers was the most effective method. Mineral oils (such as transformer oil) are commonly used in oil circuit breakers, which have high dielectric strength and strong arc extinguishing capability.
When the oil circuit breaker breaks the circuit, as long as the current in the circuit exceeds 0.1A and the voltage exceeds several tens of volts, an arc occurs between the moving contact and the static contact of the circuit breaker, and the current can continue to flow through the arc. Only when the contacts are separated by a sufficient distance, the circuit is disconnected after the arc is extinguished. When the 10kV oil-less circuit breaker opens a single 20kA current, the arc power can reach more than 10,000 kW, and the temperature of the arc arc column generated between the contacts of the circuit breaker can reach six or seven thousand degrees, or even more than 10,000 degrees.
Multi-oil circuit breakers and oil-less circuit breakers must be filled with oil, which is used for arc extinguishing, heat dissipation and insulation. The danger is not only the explosion in the event of a fault, but also the large-temperature combustion caused by the high-temperature oil in the oil circuit breaker after the explosion, causing phase-to-phase short circuit or short circuit to the ground, destroying the normal operation of the power system, so that The accident has expanded and even caused serious personal injury or death.
Arc extinguishing process: When the moving contact and the static contact of the circuit breaker are separated from each other, an arc is generated. The high temperature of the arc causes the insulating oil in the vicinity to evaporate and thermally decompose, forming a gas with strong arc extinguishing ability (mainly hydrogen). And the higher pressure bubbles, so that the arc is quickly extinguished.
There are six reasons for the explosion of an oil circuit breaker:
1 If the oil level is too low, the oil layer of the oil circuit breaker that is electrically shocked to the oil surface is too thin, and the combustible gas that is decomposed by the oil is cooled poorly. This part of the combustible gas enters the space under the top cover and mixes with the air to form an explosive gas. It is possible to explode and burn at its own high temperature.
2 The oil level in the oil tank is too high, and the gas decomposed by the oil can not be buffered in the tank, forming excessive pressure, which may also cause the fuel tank to explode and ignite.
3 The insulation strength of the oil is deteriorated, impurities or moisture are excessive, causing flashover inside the oil circuit breaker.
4 improper adjustment of the operating mechanism, component failure, will make the operation slow or unsuccessful after closing. When the arc can not be cut off and extinguished in time, excessive combustible gas is generated in the fuel tank, which may cause explosion and combustion.
5 The interrupting capacity is small, and the breaking capacity of the oil switch is an important parameter for the transmission and distribution system. When the breaking capacity is less than the short-circuit capacity of the system, the circuit breaker has no ability to cut off the strong short-circuit current of the system, causing the circuit breaker to burn and explode, causing a major accident in the transmission and distribution system.
6 The inlet and outlet lines of other oil circuit breakers pass through the insulating sleeve. When the insulation sleeve and the fuel tank cap, the fuel tank cap and the fuel tank body are not tightly sealed, the fuel tank is damp, or the fuel tank is unclean, and the insulating sleeve is mechanically damaged. Can cause a short circuit to the ground causing an explosion or fire accident.
Therefore, the circuit breaker should be strictly checked for compliance with the manufacturer's technical requirements before installation. The breaking capacity of the circuit breaker must be greater than the short circuit capacity of the circuit breaker circuit. During the inspection, the operation test shall be carried out to ensure the flexibility and reliability of the parts and adjust the synchronism of the three-phase operation. The connection between the circuit breaker and the electrical circuit should be tight, and the temperature can be observed with the test temperature wax sheet, and the contact damage should be replaced. The insulation test shall be carried out after the overhaul, and a special person shall be responsible for the inventory tool to prevent the tool from falling into the fuel tank and causing an accident. Before putting into operation, the sealing performance of the fuel tank cap of the insulating sleeve should also be checked to prevent the oil tank from entering the water and getting wet, causing the circuit breaker to explode and burn. After the circuit breaker cuts off the severe short circuit fault, the contact damage and oil quality should be checked.
The oil level should always be checked during operation and the oil level must be strictly controlled within the oil level indicator. If abnormalities are found, such as oil leakage, oil leakage, abnormal sounds, etc., measures should be taken. If necessary, the load should be reduced immediately or the power failure should be checked. When the fault tripping heavy compound brake is bad, and the current varies greatly, the circuit breaker fuel injection has a gas smell, it must stop running, and it is strictly forbidden to force the power to avoid explosion.
The oil circuit breaker arc extinguishing chamber is made of an insulating material and is disposed around the contact to limit the arc and generate a strong air blow to the arc to tell the air to extinguish. According to the energy generated by the air blowing, the arc chamber can be divided into three categories:
1 Self-energy air blow type arc extinguishing chamber, using the energy of the arc itself to decompose the oil out of the gas, and increase the pressure in the arc extinguishing chamber. When the arcing opening is opened, the arcing port is generated due to the pressure difference between the arc extinguishing chamber and the outside. High-speed oil flow, blowing the arc to extinguish it.
2 External energy blowing type arc extinguishing chamber is also called forced oil blowing type arc extinguishing chamber, which uses external energy (usually provided by spring stored in the oil circuit breaker closing process) to push the piston during the breaking process and improve the extinguishing The pressure in the arc chamber drives the oil and gas to blow the arc and extinguish the arc.
3The integrated chamber arc extinguishing chamber combines the advantages of self-energy blowing and external energy blowing, using the energy of the arc itself to extinguish the large current arc, using external energy to extinguish the small current arc, and improving the segmentation characteristics. The structure of the arc extinguishing chamber is slightly complicated, but the segmentation performance is good. Most of the ultra-high pressure and low oil circuit breakers use this arc extinguishing chamber.
There are four main types of arcing in the arc breaker chamber of the oil circuit breaker:
1 longitudinal blowing, oil and gas blowing through the arc surface in the direction of the arc axis;
2 transverse blowing, oil and gas blowing perpendicular to the direction of the arc axis;
3 vertical and horizontal blowing, using both horizontal blowing and longitudinal blowing to blow the arc;
4 ring blowing, oil and gas blowing from the surrounding direction perpendicular to the arc axis. According to the main blowing mode, the arc extinguishing chamber of the oil circuit breaker can be referred to as a vertical blow interrupter, a horizontal blow interrupter, a vertical and horizontal blow blow chamber, and a ring blow interrupter.
Third, high voltage SF6 circuit breaker
The SF6 circuit breaker is a circuit breaker that uses SF6 gas as the arc extinguishing and insulating medium. It belongs to the air blow breaker as well as the air circuit breaker, the difference is:
1 working pressure is lower;
2 During the arcing process, the gas is not discharged to the atmosphere and is recycled in a closed system.
The molecules of SF6 and the free electrons have very good mixing. When almost 100% of the electrons and SF6 molecules are mixed to form heavy negative ions, this property has great value for the deionization and arc extinguishing of the remaining arc columns, that is, SF6 has good electronegativity, its molecules It can quickly capture free electrons and form negative ions. The conduction of these negative ions is very slow, which accelerates the recovery rate of the dielectric strength of the arc gap, so it has good arc extinguishing performance. At 1.01*105Pa air pressure, the arc-extinguishing performance of SF6 is 100 times that of air, and it does not deteriorate after arc extinguishing and can be reused.
The excellent insulation and arc extinguishing performance of SF6 gas makes SF6 circuit breaker have the following advantages: strong breaking capacity, high fracture voltage, high number of continuous breaking, suitable for frequent operation, low noise, no fire hazard , electromechanical wear and so on, is a "no maintenance" circuit breaker with excellent performance. More and more SF6 circuit breakers are used in high voltage circuits. Common SF6 circuit breakers are available in LN1-35 and HB36.
Under normal conditions, SF6 is a non-combustible, odorless, non-toxic inert gas with a density approximately twice that of air. However, under the action of arc, SF6 gas will be decomposed in a small part, producing certain toxic low-fluoride substances, such as SOF4, SF4, SOF4 and SO2F2, which have an impact on human health and also have corrosion and deterioration effects on metal parts. Therefore, in the SF6 circuit breaker, an adsorption device is generally installed, and the adsorbent is activated alumina, activated carbon, molecular sieve and the like. The adsorption device can completely absorb the toxic substances generated by the gas such as SF6 decomposed at the high temperature of the arc. If used for frequent arcing, the metal vapor reacts with the SF6 gas decomposition product to form a fine powder (hydrofluoric acid salt, sulfur acid salt, etc.) which is well insulated and deposited on the contact surface. Corrosion of the contact material, so that the contact resistance increases sharply, so that the sealed contacts of the oil-filled SF6 gas cannot work reliably. Therefore, it is not suitable for the low-voltage electrical equipment that is frequently operated to use SF6 as the arc extinguishing medium.
Because SF6 gas decomposes out corrosive gas at high temperature during discharge, it has a very strong corrosive effect on aluminum alloy, and also damages phenolic resin laminate and porcelain insulation. If SF6 and N2 are used in combination, when the SF6 content exceeds 20%~30%, the dielectric strength is the same as that of the full SF6, and the corrosion is greatly reduced. Therefore, SF6 is often used in N2. In SF6 circuit breakers, the water content of SF6 gas must be strictly specified not to exceed the standard. The water and the SF4 in the arc decomposition product produce hydrofluoric acid (H2O+SF4→SOF2+2HF) to corrode the material. When the moisture content reaches saturation, it will also condense on the surface of the insulating member, so that the dielectric strength is significantly reduced, and even the creeping discharge is caused. The operation experience and the above analysis are all on the surface. Due to the small volume of the insulation structure of SF6 circuit breaker, if the water content of SF6 gas is high, the insulation level will be greatly reduced, the contact resistance will increase sharply, and damage or explosion accident will occur during operation. .
Therefore, each manufacturer and operation department requires a strict sealing process, and the water content of SF6 gas should not exceed the standard.
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