【Electrical knowledge】Definition and difference of high voltage load switch, isolating switch, and vacuum circuit breaker
This article tells you the definitions and differences between high-voltage load switches, disconnectors, and vacuum circuit breakers, and what are the types of high-voltage load switches, so that you can distinguish them clearly.
Outdoor high voltage vacuum circuit breaker ZW8-12
1. High voltage load switch
With a simple arc extinguishing device, it can be a control electrical appliance that can divide and close the load. It can switch on and off a certain load current and overload current, but it cannot break the short-circuit current. It must be used in series with the high-voltage fuse, and the short-circuit current can be cut off with the help of the fuse.
The role of high voltage load switch:
1. Breaking and closing function. Because it has a certain arc extinguishing ability, it can be used to break and close the load current and the overload current smaller than a certain multiple (usually 3-4 times); it can also be used to break and close the allowable capacity of the isolating switch. Large no-load transformers, longer no-load lines, and sometimes used to break and close large-capacity capacitor banks.
2. Substitution. The series combination of load switch and current-limiting fuse can replace the circuit breaker. That is, the load switch is responsible for breaking and closing the overload current less than a certain multiple, while the current-limiting fuse is responsible for breaking the larger overload current and short-circuit current.
3. The load switch combined with the load switch and the current-limiting fuse in series is called the "load switch-fuse combination appliance" in the national standard. The fuse can be installed on the power supply side of the load switch or on the receiving side of the load switch. When the fuse does not need to be replaced frequently, the former arrangement should be adopted so that the load switch can also be used as an isolating switch to isolate the voltage applied to the current-limiting fuse.
Indoor high voltage isolation switch GN19-12
2. Isolation switch
A control electrical appliance without an arc extinguishing device. Its main function is to isolate the power supply to ensure the safe inspection and maintenance of other electrical equipment, so it is not allowed to operate under load. But under certain conditions, small power circuits are allowed to be switched on or off. It is the most frequently used electrical device among high-voltage switches.
The function of the isolating switch:
(1) Change the wiring according to the operation needs.
(2) According to the specific conditions of different structure types, it can be used to divide and combine the no-load excitation current of a transformer with a certain capacity.
(3) After opening, establish a reliable insulation gap, and separate the equipment or lines that need to be repaired from the power supply with an obvious disconnection point to ensure the safety of maintenance personnel and equipment.
(4) It can be used to divide and close small currents in the line, such as the charging current of bushings, busbars, connectors, and short cables, the capacitive current of switch equalizing capacitors, the circulating current when double busbars are switched, and the excitation of voltage transformers current, etc.
According to the different installation methods, high-voltage isolating switches can be divided into outdoor high-voltage isolating switches and indoor high-voltage isolating switches.
Outdoor high-voltage isolating switch refers to a high-voltage isolating switch that can withstand the effects of wind, rain, snow, pollution, condensation, ice, and thick frost, and is suitable for installation on the terrace.
According to the structure of the insulating pillar, it can be divided into the single-column isolating switch, double-column isolating switch, and three-column isolating switch. Among them, the single-column isolating switch directly uses the vertical space as the electrical insulation of the fracture under the overhead busbar. Therefore, it has the obvious advantages of saving floor space, reducing lead wires, and at the same time, the opening and closing status is particularly clear. In the case of ultra-high voltage transmission, the effect of saving floor space is more significant after the substation adopts a single-column disconnector.
Isolating switches are mainly used in low-voltage terminal power distribution systems such as residential houses and buildings in low-voltage equipment.
Outdoor high voltage vacuum circuit breaker ZW32-24
3. Vacuum circuit breaker
It is named because the arc extinguishing medium and the insulating medium of the contact gap after arc extinguishing are both high vacua; it has the advantages of small size, lightweight, suitable for frequent operation, and no maintenance for arc extinguishing. It is more suitable for use in distribution networks. Universal.
A vacuum circuit breaker is an indoor power distribution device in a 3-10kV, 50Hz three-phase AC system, which can be used for protection and control of electrical equipment in industrial and mining enterprises, power plants, and substations, especially suitable for oil-free, less In places where maintenance and frequent operations are used, circuit breakers can be configured in central cabinets, double-layer cabinets, and fixed cabinets to control and protect high-voltage electrical equipment.
(1) Working principle of vacuum circuit breaker
When the dynamic and static contacts are opened under the action of the operating mechanism, an arc is generated between the contacts, and the surface of the contacts volatilizes steam at high temperatures. Since the contacts are designed in a special shape, a magnetic field is generated when the current passes, and the arc is in the Under the action of this magnetic field, it moves quickly along the tangential direction of the contact surface, and part of the metal vapor condenses on the metal cylinder (shield), and the arc is extinguished when it naturally crosses zero, and the dielectric strength between the contacts quickly recovers.
(2) Function of vacuum circuit breaker
The circuit breaker has overload, short circuit, and Undervoltage protection functions, and has the ability to protect lines and power supplies.
4. The difference between the load switch and isolating switch
The first difference is that the current cut-off between the two is different.
Because the isolating switch has no arc extinguishing device, it is only suitable for cutting off the no-load current, but cannot cut off the load current and short-circuit current. Therefore, the isolating switch can only be operated safely when the circuit is safely disconnected, and it is strictly with Load operation, so as not to cause safety accidents. Because the load switch has an arc extinguishing device, it can overload the current and the rated load current, but it cannot cut off the short-circuit current.
The second point is that the load switch has an arc extinguishing device, but the disconnector does not have such a device.
So what's the difference if there is this arc extinguishing device? The so-called arc extinguishing device is to better help the opening and closing of switching appliances and to effectively limit the arc and help the arc to extinguish. Having such an arc extinguishing device is safer for switching electrical appliances. Therefore, most switching appliances are equipped with arc extinguishing devices. Especially household switching appliances.
The third point is that the functions of the two are different.
Because there is no arc extinguishing device, the isolating switch can only be used to isolate the part that needs to be charged and the part that needs to be powered off in the high-voltage circuit device, so as to ensure the maintenance and inspection of the high-voltage circuit by personnel and ensure the safety of personnel.
The load switch is applied to fixed high-voltage equipment, which can cut off the fault current and rated current in the high-voltage equipment, so the functions of the two are different, but both are used in high-voltage equipment.
5. The difference between high voltage load switch and a vacuum circuit breaker
(1) The high-voltage load switch can be broken with load and has the function of a self-extinguishing arc, but its breaking capacity is very small and limited.
(2) The high-voltage isolating switch does not have a protection function, and the protection of the high-voltage load switch is generally protected by a fuse, only quick-break and over-current.
(3) Both the high-voltage load switch and the high-voltage isolation switch can form an obvious disconnection point. Most circuit breakers do not have the isolation function, and a few circuit breakers have the isolation function.
(4) High-voltage isolating switches generally cannot be broken with the load. There is no arc extinguisher in the structure, and there are also isolating switches that can break loads, but the structure is different from that of load switches, which is relatively simple.
(5) The breaking capacity of the high-voltage circuit breaker can be made very high in the manufacturing process. It mainly relies on adding current transformers to cooperate with secondary equipment for protection. It can have short circuit protection, overload protection, leakage protection, and other functions.
A high-voltage load switch is an electrical appliance whose function is between a high-voltage circuit breaker and a high-voltage isolating switch. A high-voltage load switch is often used in series with high-voltage fuses; it is used to control power transformers. The high-voltage load switch has a simple arc extinguishing device because it can switch a certain load current and overload current. However, it cannot break 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.
Types of high voltage load switches
【1】Vacuum type high-voltage load switch: use a vacuum medium to extinguish the arc, the electric life is long, and the price is relatively high. It is suitable for products of 220 kV and below.
【2】Pneumatic high-voltage load switch: use the compressed gas of the piston during the breaking process to blow out the arc, and its structure is relatively simple, suitable for products of 35 kV and below.
 Compressed air type high-voltage load switch: use compressed air to blow out the arc, and can break a large current. Its structure is more complicated, and it is suitable for products of 60 kV and above.
 Sulfur hexafluoride type high-voltage load switch: use sulfur hexafluoride gas to extinguish the arc, its breaking current is large, and the function of breaking capacitive current is good, but the structure is more complicated, suitable for products of 35 kV and above.
 Solid gas-generating high-voltage load switch: use the energy of the breaking arc itself to make the gas-generating material in the arc chamber generate gas to blow out the arc. Its structure is relatively simple, and it is suitable for products of 35 kV and below.
 Oil-immersed high-voltage load switch: Use the energy of the arc itself to decompose and gasify the oil around the arc and cool it to stop the arc. Its structure is relatively simple, but heavy, and it is suitable for outdoor products of 35 kV and below.