低压隔离开关

低压隔离开关 This article is contributed by zhangzhaojing7 DOC documents may experience poor browsing on the WAP side. It is recommended that you first select TXT, or download the source file to the local view. Low voltage isolating appliance Use 1. knife switch and classification of electrical equipment maintenance, to cut off the power supply, the maintenance and the live part of detachment, and keep the isolation distance effectively, need to be subjected to over voltage level voltage in the fracture. A knife switch is a switching device that serves as an isolating power source. The knife switch of isolating power supply is also called isolating switch. Isolated knife switches are generally no-load on-off devices. They can only be switched on or off "negligible current" (refer to the capacitive current or voltage transformer current of the bus, short cable, or voltage transformer). Some knife switches have the ability of breaking and closing. When their breaking capacity meets the required current, they can be switched on or broken off under the condition of no fault. The knife switch used as the isolating power supply must satisfy the isolating function, that is, the switch fracture is obvious and the fracture distance is qualified. Knife switch and fuse combination into a unit called the knife switch with fuse knife switch; movable part (moving contact) by the fuse holder fuse with body composition, called fuse knife switch. A knife switch fuse assembly is provided with auxiliary elements, such as an operation lever, a spring, an arc cutter, etc., and can be assembled into a load switch. The load switch has the capability of switching on or breaking off the load current and certain short-circuit protection function under non fault conditions. 2. the main parameters of low voltage knife switch, the main parameters of low voltage knife switch are: rated insulation voltage, that is, the maximum rated voltage. Rated working current. Rated work system: divided into 8h work system, uninterrupted work system, two kinds. Usage categories: Classification Based on the nature of the operation load and the degree of operation. According to the frequency of operation is divided into class A and class B, a class of normal use, B is the number of operations is not much, if only the isolation switch; according to the operating load properties of many classification, such as the operation of no-load circuit, on-off resistive circuit and operation motor load etc.. Rated off and breaking capacity: the maximum allowable current of switching equipment with on-off capacity. The rated short-time withstand current. The short circuit short circuit making capacity electrical switch capability. The rated short-circuit current (limited). 9 operation performance: according to different categories, the number of operating cycles in the condition of rated current. 3., how to choose the knife switch correctly and choose the knife switch principle is as follows: (1) the rated voltage of the knife switch should be equal to or greater than the rated voltage of the power supply, and the rated current should be equal to or greater than the working current of the circuit. If a small electric motor is controlled by a knife switch, the starting current of the motor shall be taken into consideration, and a switch with a higher rated current shall be selected. The on-off capability and other performances of the knife switch shall be in accordance with the requirements of the appliance. When the knife switch is disconnected from the load current, it should not exceed the allowable current value. The switch of the general structure is not allowed to operate with load, but the knife switch with arc extinguishing chamber can be used frequently without load operation. The three-phase short circuit current of the switch on the knife switch shall not exceed the required dynamic and thermal stability values. 4. commonly used knife switch what type of knife switch from the isolated power supply, there are obvious disconnection point, in order to ensure the safety of personnel in the maintenance of electrical equipment. The ordinary knife switch can not be operated with load. It is equipped with arc extinguishing cover or switch with auxiliary contact knife which can be broken off quickly on the movable contact knife. It can cut off the load which is not more than the rated current. The commonly used isolation knife switch types are as follows: 1. HD11, HS11 series, front handle, only to do with the isolation switch; HD12, HS12 series, switch cabinet for operation maintenance in front of the front on both sides; the HD13, HS13 series, positive for the operation, maintenance of the switch cabinet behind; the HD14 series, for power distribution box. Difference between 5. knife brake (knife switch) and isolating switch The knife switch and the isolating switch belong to the knife type switch. They are similar in shape, structure, principle, and method of operation. But they are very different and must be strictly distinguished. The knife switch is one of the simplest switching devices designed to turn off the circuit below 500V. It can only be operated manually. As the circuit is broken, there is often arc, so the knife switch is equipped with arc extinguishing device or fast breaking contact. In order to increase arc extinguishing ability, its knives are usually shorter. The isolation switch has high and low voltage, unipolar, triode, indoor and outdoor, it has no special arc extinguishing device, can not be used to connect and cut off the load current and short-circuit current, only in the electrical line cut off, in order to operate. Its main function is to isolate the power supply, so that there is an obvious disconnection point between the power supply and the power cut electrical equipment, so there is no need to consider arc extinguishing. In order to ensure reliable isolation of the power supply, to avoid over-voltage breakdown or interphase flashover, the knife is usually done longer, and the distance between the two is also greater. In a word, the isolating switch can not be used as a knife switch, and the knife switch is only allowed to isolate the circuit when the voltage is not high, and it must be connected in series with the fuse. 6. isolation switches and buses which must be a serious defect isolation switch and the bus stop following serious defects must be disabled: Porcelain damage or serious dirt, porcelain discharge phenomenon; the test pressure does not meet the standard; the operating mechanism is not flexible; the serious overload, the temperature is too high; the switch rated the voltage and the form of site does not meet the requirements; the contact switch, a serious discharge phenomenon; the bus for safety distance is not enough or touch the branches; the soft bus breaking phenomenon; 9 bus support insulators or voltage level does not meet the practical requirements. 7. what about the function of the disconnector? How to operate the isolating switch is mainly used to isolate the power supply. There should be an obvious disconnection point so that the equipment can be safely checked and repaired. The utility model can also be used in conjunction with circuit breakers to perform switching operation and change the operation mode of the system. The utility model can also be used for connecting or disconnecting the voltage transformer and a certain capacity no-load transformer and a certain length no-load circuit and a bus bar. The isolation switch has no arc extinguishing device. Only the inductive current of 2A and the capacitive current of 5A are cut off, otherwise the arc light is short circuited. Operating isolation switches must be strictly in accordance with the principle of equal potential. In conjunction with the circuit breaker should be closed after the circuit breaker, isolating switch and circuit breaker isolating switch off again. When switching the bus, it is possible to break and close the switch under the condition of equal equipotential at both ends. To prevent misoperation of the disconnector, a locking device must be provided between the disconnector and the breaker. 8. knife switch occurs arc fault prevention measures to prevent the occurrence of arc fault switch, security equipment and personal safety, applicability should first consider the knife switch; secondly should be used in the process of inspection and maintenance work, and in strict accordance with the procedures. Specifically, should pay attention to the following: 1 will not switch circuit for it cannot be broken; it should check whether its action is flexible in operation, there is no blocking phenomenon; check the arc shield is complete and strong, we should check the cover or cover of the knife switch the arc shield; only to switch power supply isolation, the sequence of operations should be in accordance with the provisions, is not allowed to break the no load current; switch arc shield, generally do not allow for breaking load; the multipole switch, should ensure synchronization and contact the pole action good; and found that the arc shield burn and carbonization, should be replaced immediately; whether the knife switch is mounted in the box, should keep the knife switch parts clean, to avoid the accumulation of dust and oil pollution caused by phase Arcing or short circuit causes arcing fault. 9. switch operation notes, operator switch should pay attention to the following: first, before disconnecting the switch, check whether the breaker is in the disconnection state; The operation of a single pole knife switch, open should be opened, then pull on both sides, closing in reverse order; the power operation, circuit breakers, at load side isolation switch, pull the power switch, power supply in reverse order; the event with a load of open or closed the isolation switch, should be in accordance with the following provisions: wrong to pull the switch on the edge arc, emergency speed closed; as has been opened, is not to close, and timely reporting. When the switch is wrongly connected, no matter whether it causes an accident or not, it is not allowed to be opened again and corresponding measures are taken. 10. knife switch operation should be checked before the knife switch which projects should check the following items before operation: check whether the load current exceeds the rated value of the knife switch; check knife switch conductive part of the dynamic and static contacts have no bad contact, dynamic and static contact without burning (body) and wire connections, in case not normal circumstances, should be promptly repaired; the connecting rod and the base check insulation insulation parts without burn and discharge phenomenon; each component check switch operating mechanism is in good condition, the action is flexible, opening and closing over the same period, whether the three-phase accurate. 11., in the operation of the knife, with load, wrong, wrong pull, what measures should be taken with the load wrong, when the knife switch, although the wrong, or even in the arc when the switch is closed, nor shall the knife open again. Because of the load switching, the three-phase arc short circuit accident will occur. With load wrong broach, when the blade has just left the fixed contact moment, will produce arc, at this time should be closed immediately, in order to eliminate the arc, prevent accidents. If the knife switch has been completely removed, then no further switching on. If it is a single-phase knife brake, if it is pulled out after operation, it is found that the other two phases should not continue to operate, and corresponding measures should be taken to restore it. 12. why blackout at the first pull line side switches, power supply first bus side switches power first pull line side switches, power supply first bus side gate, all in the misoperation, reduce accidents. The detailed analysis is as follows: when the power failure occurs, the possible misoperation is: the breaker has not broken the power supply, and the broach is pulled out first, resulting in a load broach. Another case is that the circuit breaker has been disconnected, but the electrician is operating the knife gate, and the equipment should not be cut off due to the wrong interval. When the breaker is not disconnect the power supply, there are two types of error broach gate: a case of the first pull bus side switches, short circuiting arc in the breaker, will cause short-circuit; another is the first pull line side switches, arc short-circuit point in the circuit breaker, circuit breaker protection device tripping, can remove the fault, narrowing the range of accident. So the first pull power line side switches. The power supply, if the circuit breaker in the closing position, then go to knife switch in the following two conditions: if the first line side gate, then bus side switches, bus side switches with a load equal to line transmission, the event will cause short circuiting arc, bus fault, artificially expanded accident if the first bus side switches; then, line side switches, equal to the line side switches with load to power transmission line, in case of arc short circuit breaker, protection device tripping, can remove the fault, narrowing the scope of the accident. So when charging the first bus side gate. 13. the use of isolation switch (switch) should pay attention to the use of isolation switch should pay attention to the following items: when used in conjunction with the circuit breaker, isolating switch and grounding switch, with grounding switch, must be installed in electrical or mechanical interlocking device, in order to ensure the proper sequence of operation, which is only after cutting the current circuit breaker, isolating switch can switch; only after the isolation switch is closed, the circuit breaker can be closed. Equipped with isolation switch grounding switch, the main switch without breaking the grounding switch not closing; similarly, before the grounding switch does not switch, the main switch is not closing. The grounding wire shall be connected with copper wire or earthing bolt of not less than 50mm2, so as to ensure reliable grounding. On the friction parts of the switch, power grease should be applied to strengthen lubrication. Check the synchronization and contact condition of the switch before running. Opening the isolation switch indication signal, should make the breaking opening distance of 80% after the main switch; and the switching indication signal should be in the main switch has reliable contact to send. Abnormal phenomena in 14. isolation switch isolating switch in the operation and treatment in operation will appear the following abnormal phenomenon: loose fasteners; the insulator due to external trauma, aging and loosening the adhesive; insulator serious fouling; the closing tightly or closing is not in place; and because of poor contact, the temperature is too high. If such phenomena occur, they should be dealt with promptly so as to avoid failure. First of all, surveillance should be strengthened and necessary and possible to reduce the load immediately, until measures are taken to eliminate the hidden danger. If the isolation switch is installed on the bus, the bus shall stop as much as possible. For example, the load is transferred to the other bus so that the bus exits. If the bus stop running, may cause greater economic losses, then consider the use of live working methods for repair, such as tightening loose fasteners and so on. Usually, only in the case that cannot but take the temporary isolation switch, short circuited emergency measures. If the overvoltage occurs, such as flashover, discharge and breakdown to the ground, the power shall be cut off immediately or operated by live working method. Load switch application uses 15. load switch and low voltage classification system is the foundation of the knife switch, increase the number of auxiliary components, such as shell, rapid operating mechanism, interrupter and current protection device (fuse). Therefore, the working current in the rated current can be disconnected and closed. Fuses can protect against excessive loads and short circuits. The load switch can be separated from the open type load switch and the closed type load switch. The open type load switch (commonly known as plastic cover, rubber cover knife switch) is mainly used for rated voltage below 380V, the current in the circuit below 60A, general lighting, electric heater such as loop control switch, not frequent operation and short-circuit protection for the load zone. The enclosed load switch (also known as HH10, iron switch, HH11 series, other models have been eliminated by now) for rated voltage 500V, rated current do not frequent operation and short-circuit protection in electrical equipment and power distribution equipment in the 200A below. Asynchronous motors can also be used for direct starting and breaking. The closed type load switch also has the mechanical locking function of the outer shell door. When the switch is in the closing state, the door of the outer shell can not be opened. 16. load switch before operation should check the following items which project to examine load switch before the operation of the content and the knife load switch conductive parts inspection switch of the corresponding part of the same operation mechanism; check switch components are in good condition, the locking device is intact; the metal dust check shell and the base have no fuse caused that should be cleaned, so as not to reduce the insulation performance; protective grounding of the metal shell should be reliable, to prevent electric shock accidents; inspect whether the fuse rated current is matched with the rated current of the switch. 17. items hulled switch installation and use should be paid attention to while the iron casing switch have closed shell and interlocking device, but its security problems still can not be ignored. In order to ensure the safety of the installation and use of iron switch should note the following points: 1, not free to switch on the ground hulled operation, or in the face of switching operation, to prevent faults and switch cannot break shell explosion. Normally, the switches should be installed vertically at a location of a certain height. Switch shell should be reliably grounded. The contact shall be regularly repaired and the contacts must be bright and clean so as not to burn out due to poor contact. Check whether the fuse base is broken and whether the spring is rusty. Replace the defect once it is found. Check whether the wiring is loose, if found loose, should be re connected; Should always keep the interior wall does not accumulate dust. It is strictly prohibited to place all kinds of metal parts in the switch, so as not to fall into the switch caused by short circuit. 18. simple analysis of the existing problems in the application of low voltage electrical isolation low-voltage electrical isolation and fuse in practical application there are some unreasonable or even wrong usage, cause the increase of fault and accident, difficult operation and maintenance, or leave a long-term security risks. Our design specifications specify when maintenance is required, When testing and repairing equipment needs to break off the power supply, the isolating appliance should be set up. The isolation device shall be able to effectively isolate the circuit from the live part. The national standard also stipulates that the isolated electrical appliance must have enough safety isolation distance when the contact is in open position, and the separation of its main contact relative to the static contact must be clear and obvious. Obviously, the total power of any user line should set the electrical isolation, to meet user needs of grid maintenance; the user distribution network in a local circuit maintenance needs or single electric circuit should also set the electrical isolation. Fuse box for low voltage electrical isolation is the main product of separation switch, knife switch, and has the protective function (such as fuse knife switch, switch fuse and fuse isolator group). Their main purpose is isolation function, itself does not require frequent maintenance, so where the need to set up isolated electrical equipment, it should be preferred for this special insulation products. Some protection appliances may also have a certain isolation function (such as drawer type circuit breaker has a fixed type circuit breaker, obvious and reliable disconnect position indicating some fuse withdrawable fuse), so it is often used as electrical isolation. The unreasonable use of protective appliances and the lack of insulation products are the common problems in practical engineering. (1) the disadvantages of fuse as well as isolated electrical equipment. The Design Code stipulates that the fuse is allowed to be used as an isolating appliance. This provision can be derived from our early electrical maintenance procedures (mostly from the Soviet Union's electrical regulations). The provisions of the maintenance of electrical factory should be inspected the head end of the fuse circuit (mainly refers to the imitation of the Soviet RM10 and RT0 fuses for use by authorized persons) of the fuse pull out from the base, to form a clear disconnect point. Limited to our country at that time low-voltage electrical equipment level and variety of the actual conditions, fuse instead of isolating electrical appliances may be reasonable. At present, our country already has the protection and the separation function fuse combination electric appliance series product, this kind of practice's advantages and disadvantages is worth discussing. In urban civil buildings, fuses (RC1A, RL1, etc.) are commonly used as the total power supply for the house (or shop), feeder and feeder. Fuse for isolating the electric appliance mainly has the following problems: the fuse as overload relay protection and special product standard, it "in the normal installation and use conditions", "smooth" to ensure the long-term contact characteristics do not change to. In other words, in addition to melt, the fuse needs to be removed and replaced, and it is connected with its support piece for a long time without separation. The utility model can be used as an isolating appliance, so that the fuse and the support part are separated and connected more frequently, and the good conductive contact of the contact is difficult to be ensured. The fuse used by non skilled personnel in civil buildings, whose replacement cycle (or electric life) is shorter. As the most commonly used RC1A porcelain plug fuse, fuse the number of products allow only 2 ~ 3 times, that is 2 to 3 times the fuse melts, because the fusing process of insulation performance and strength of porcelain and the damage effect on the contact conductive contact performance, the need for timely inspection and replacement of porcelain plug-in or base. This type of application is usually replaced by a live isolating power supply without any isolated electrical isolation. This is also one of the causes of electric shock accidents. It can be seen that although the fuse may have isolation function when the fuse and the support are in separate position, the use of the fuse as a isolating appliance is more harmful than that of the fuse. (2) the unconventional use of isolating electric appliances causes the unconventional use of insulating appliances because of the poor specifications of our low voltage isolated electrical apparatus. Since 1960s, China's main isolator (such as HD11) and knife switch (such as HD13) series products, the maximum specification is only about 1500A of rated current. Due to the early domestic protection appliances breaking capacity level, our country has long been limited in design specification / low-voltage distribution transformer capacity of 1000kVA (rated 1440A) within the electrical isolation level can meet the needs of. In recent years, with the rapid progress and stop the ability to protect the electrical products of industrial and civil power are widely used in the single machine capacity of 1250 ~ 2500kVA (0.4kV rated current of 1800 ~ 3600A) of the transformer, the existing low voltage electrical isolation can not meet the requirements, so the low voltage side of total power line screen the knife switch generally each phase adopts a 3 pole or 2 pole switch (such as HD13) instead of. The main problem of this usage is brought: the three-phase knife switch operation phase, increased due to misoperation probability such as fault phase operation, so the design specification should be used in electrical isolation switch and disconnect the power of all pole. Make the switch switch screen bulky and bulky, such as the use of PGL screen frame manufacturing line screen, single screen width of up to 1200 ~ 1600mm. In recent years, some manufacturers have introduced the imported Q series (QA, QP) isolating switch with rolling contact, rated current up to 3150A, but for the industry supported AC22 and AC23 is the most common use of categories, its rated current will be reduced by about 1/2. In addition to the product size reduction, mechanical life has improved, the rated current than the country The production of HD series knife switches has not been improved significantly, but these problems have not been solved yet. Therefore, China's large capacity specifications of isolated electrical switch products need to be developed.