| Hong Kong Island high-voltage fuses overview |
It is mainly used for overload and short circuit protection of high voltage transmission lines, voltage transformers, voltage transformers and other electrical equipment.
Its structure generally includes a fuse tube, a contact conductive part, a support insulator and a base, and the fuse tube is filled with quartz sand fine particles for arc extinguishing. Fuse is a metal wire or metal sheet made of a metal material with a lower melting point, connected in series in the protected circuit. When the circuit or the equipment in the circuit is overloaded or malfunctions, the fuse heats up and melts, thereby cutting off the circuit and The purpose of protecting a circuit or device.
Selection of high-voltage fuse type There are two types of high-voltage fuses commonly used in 3 ～ 66kV power stations and substations: It is an indoor high-voltage current-limiting fuse with rated voltage levels of 3, 6, 10, 20, 35, and 66kV. Common models are RN 1, RN 3, RN 5, XRNM 1, XRN T 1, XRN T 2, XRN T3 type is mainly used to protect the overload and short circuit of power lines, power transformers and power capacitors; RN2 and RN 4 types have a rated current of 0.5 ~ 10A, which is a special fuse for protecting voltage transformers. The other type is outdoor high-pressure jet fuses. When the fuse melts to generate an arc, the arc burns against the white paper to produce gas and stretches the arc. The arc inductance reacts to change phase, and a zero break occurs when the current crosses zero In order to open the circuit, the current limiting effect is not obvious. Commonly used are drop-out fuses . The types are RW 3, RW 4, RW 7, RW 9, RW 10, RW 11, RW 12, RW 13, and PRW series. Their functions are the same as those of RN 1. Under certain conditions, unloaded overhead lines, no-load transformers, and small load currents can also be disconnected and closed. Outdoor porcelain sleeve type current limiting fuse RW 10- 35 / 0.5 ~ 50-2000MVA type RW10-35 / 0.5 ~ 1-2000MVA is an outdoor product dedicated to protect 35kV voltage transformers. So choose according to the type of fuse and different protection objects.
1. Select by working voltage (1) General conditions U e≥Uwe In the formula: U e——rated voltage of fuse Uwe-rated voltage of the grid at the installation That is, the rated voltage (kV) of the fuse should not be less than the rated voltage (kV) of the power grid where the fuse is installed. (2) For current-limiting fuses The current-limiting fuses with quartz sand as the fuse filling material can only be selected according to the condition of Ue = Uwe. In this case, the maximum overvoltage multiple generated by such fuses is limited to the specified 2.5 times the phase voltage. This value does not exceed the insulation level of appliances of the same voltage level. If the fuse is used in a power grid whose operating voltage is lower than its rated voltage, the threat caused by multiples of overvoltage may increase by 3.5 to 4.
2.Select according to working current and protection characteristics (1) General conditions I e≥Ije≥Ig · zd In the formula: I e——rated current of fuse, A I je——rated current of fuse, A I g · zd——Maximum continuous working current of circuit, A This condition is the overall requirement for selecting the rated current of the fuse, of which the selection of the rated current of the fuse is the most important. Its selection is related to its fusing characteristics and should be able to meet the requirements of protection reliability, selectivity and sensitivity. (2) Specific situation ①Protect power distribution equipment (ie, 35kV and below power transformers): Ije = K Ie Where Ie——rated working current of transformer loop, A K——Reliability coefficient, 1.5 ~ 2.4 is not taken into consideration when the motor is self-starting, 2.4 ~ 4.0 is taken into consideration when the motor is self-starting
Selecting according to this condition can ensure that the transformer does not fuse when the transformer passes the maximum continuous working current, through the transformer inrush current, and the impulse current generated by the motor from starting or short circuit outside the protection range, and it can ensure the selectivity of the front and rear protection actions and this paragraph. Short circuit in the range can clear the fault in the shortest time. ② Protection of power capacitors: Ije = K Ic · e In the formula: I c · e——rated current of capacitor circuit, A K —— Reliability coefficient, for jet fuses, 1.35 ～ 1.5; For current-limiting fuses, when a capacitor, the coefficient is 2 ～ 2.8; when a group of capacitors, the coefficient is 5 ～ 10 ③ Protection of power lines: Select by general conditions: Ie≥Ije≥I g · zd
3. Select by breaking current (1) General conditions I ke≥I dt (Ske≥Sdt) In the formula: I ke (or Ske) —— rated breaking current of the fuse, kA (or rated breaking capacity MVA) I dt——short-circuit full current, kA (installation place) For current-limiting fuses, take I dt≥I ″ (sub-transient current amplitude); for non-current-limiting fuses, take I dt≥I ch (maximum effective value of steady-state short-circuit current). (2) For drop-out fuse The breaking capacity of the drop-out fuse should be checked according to the upper and lower limit values. The maximum operating mode of the system should be applied when checking the upper limit value. The minimum operating mode should be used when checking the lower limit value.
High-pressure wall-through bushings are also called high-pressure wall-through pipes, waterproof bushings, wall-embedded pipes, and waterproof bushings are divided into rigid waterproof bushings and flexible waterproof bushings. The two are mainly used in different places. Flexible waterproof sleeves are mainly used in places such as civil defense walls and pools. Rigid waterproof sleeves are generally used in locations such as basements where pipes need to pass through. Flexible waterproof casing is suitable for the hardware fittings of the structure where the pipeline passes through the wall subject to vibration or strict waterproof requirements. General manufacturers are manufactured according to the S312, 02S404 standard atlas developed by the Institute of Building Science. Flexible waterproof casings pass through walls. If non-concrete is used, concrete walls should be used instead, and the casings must be solidified in the walls at one time. Flexible waterproof casings are widely used in construction, chemical, steel, tap water, and sewage treatment. And other units. Rigid waterproof casing is a steel pipe plus a wing ring (annular sleeve made of steel plate is placed on the steel pipe), which is installed in the wall (mostly concrete wall). It is used for general pipeline penetration, which is beneficial to the waterproofing of the wall. The outer wing ring, the inner ring and the like are also available. The flange inner wire is sold in sets or can be processed on its own. It is used for pipes that require shock absorption, such as pipes connected to water pumps passing through walls. Both flexible waterproof sleeves and rigid waterproof sleeves are hardware fittings for pipes passing through the walls of buildings subject to vibration or strict waterproof requirements, and are often used in construction, chemical, steel, tap water, sewage treatment and other units.
Under the specified conditions of use, a certain capacity of no-load transformers (315KVA indoor, 500KVA outdoor) can be connected and disconnected; no-load overhead lines (5KM indoor, 10KM outdoor) can be connected and disconnected; can be connected Connect and disconnect a certain length of no-load cable line. 1. The load switch can be disconnected with a load and has a self-extinguishing function, but its breaking capacity is very small and limited. 2. Generally, the disconnecting switch can not be disconnected with load. There is no arc extinguishing cover on the structure, and there is also an isolating switch that can disconnect the load. The structure is different from the load switch, which is relatively simple. 3. Load switches and disconnectors can form obvious disconnect points. Most circuit breakers do not have isolation function, and a few circuit breakers have isolation function. 4. Isolation switch does not have protection function. The protection of load switch is generally added with fuse protection. 5. The breaking capacity of the circuit breaker can be made very high in the manufacturing process. It mainly depends on the current transformer and the secondary equipment to protect it. Can have short circuit protection, overload protection, leakage protection and other functions. (FN3-10R) --- The main shaft drives the piston to compress the air when the brake is opened, so that the compressed air is ejected from the nozzle at high speed to blow out the arc; FN5-10D --- the arc extinguishing tube with a complete arc extinguishing device Make up. (Vacuum tube)
Characteristics of high voltage load switch A. It can isolate the power supply and has obvious disconnection points. It is mostly used for fixed high-voltage equipment. B. There is no arc extinguishing device, and the normal working current and short circuit can be passed in the closed state. C. It is strictly forbidden to connect and disconnect the circuit with load, and it is often used in series with the high-voltage circuit breaker .
Precautions for high voltage load switch A. For vertical installation, the switch frame, closing mechanism, cable sheath, and protective steel pipe should be reliably grounded (cannot be grounded in series). B. No-load opening and closing operations should be performed several times before operation. There is no jamming in each rotating part, and the closing is in place. There is a sufficient safety distance after opening. C. The fuse of the fuse used in series with the load switch should be selected properly, that is, the fuse should be blown first when the fault current is greater than the breaking capacity of the load switch, and then the load switch can be opened. D. The contact is good when the switch is closed, and there is no overheating at the connection part. During the inspection, pay attention to check the porcelain bottle for dirt, cracks, porcelain dropout and flashing discharge. Do not flush the switch with water. (When a high voltage cabinet controls a transformer, it is best to stop the circuit high voltage cabinet when replacing the fuse.) A high-voltage load switch is an electrical appliance that functions between a high-voltage circuit breaker and a high-voltage isolation switch . High-voltage load switches are often used in series with high-voltage fuses; they are used to control power transformers. The high voltage load switch has a simple arc extinguishing device, because it can switch on and off a certain load current and overload current. However, it cannot disconnect the short-circuit current, so it is generally used in series with a high-voltage fuse, and the fuse is used for short-circuit protection.