The differences between isolation switches, load switches, and high-voltage circuit breakers are explained clearly in one article.
What is a load switch?
It is a control electrical device with a simple arc extinguishing device that can carry load distribution and closing circuits. It can interrupt a certain load current and overload current, but cannot interrupt short-circuit current. It must be used in series with a high-voltage fuse to cut off short-circuit current.
The function of load switch:
1) Disconnect and close cooperation.
Due to its arc extinguishing ability, it can be used to disconnect and close load currents and small dry loads with a certain multiple (usually 3-4 times) of overload current; It can also be used to open and close no-load transformers with larger capacity than isolation switches, longer no-load lines, and sometimes large capacity capacitor banks.
2) Alternative role.
The series combination of load switch and current limiting fuse can be used instead of Circuit Breaker. The load switch is responsible for breaking and closing overload currents that are less than a certain multiple, while the current limiting fuse is responsible for breaking larger overload currents and short-circuit currents.
3) The load switch combined with a current limiting fuse in series is referred to as a "load switch fuse combination" in national standards.
The fuse can be installed on the power side of the load switch or on the receiving side of the load switch. When it is not necessary to frequently replace the fuse, the former arrangement should be adopted in order to utilize the function of the load switch as an isolation switch to isolate the voltage applied to the current limiting fuse.
What is an isolation switch?
It is a control electrical device without an arc extinguishing device, whose main function is to isolate the power supply to ensure the safe maintenance of other electrical equipment. Therefore, it is not allowed to operate with load.
But under certain conditions, it is allowed to turn on or off low-power circuits.
It is the most commonly and frequently used electrical device in high-voltage switches.
The function of isolation switch:
1. After disconnection, establish a reliable insulation gap and separate the equipment or line that needs maintenance from the power supply with a clear disconnection point to ensure the safety of maintenance personnel and equipment.
2. Change the circuit according to operational needs.
3. It can be used to separate and combine small currents in power lines, such as the charging current of bushings, busbars, connectors, and short cables, the capacitance current of switch voltage equalization capacitors, the circulating current during double busbar switching, and the excitation current of Voltage Transformers.
4. According to the specific situation of different structural types, it can be used to separate and combine the no-load excitation current of a certain capacity transformer.
High Voltage Isolating Switches can be divided into outdoor high-voltage isolating switches and indoor high-voltage isolating switches according to their installation methods.
Outdoor high-voltage isolation switch refers to a high-voltage isolation switch that can withstand the effects of wind, rain, snow, dirt, condensation, ice, and thick frost, and is suitable for installation on terraces.
According to the different insulation pillar structures, it can be divided into single column isolation switches, double column isolation switches, and three column isolation switches. The single column isolation switch directly uses the vertical space under the overhead busbar as the electrical insulation for the break, therefore, it has obvious advantages such as saving floor space, reducing the number of connecting wires, and having a particularly clear opening and closing state. In the case of ultra-high voltage transmission, the use of single column isolation switches in substations has a more significant effect on saving floor space.
Isolation switches are mainly suitable for low-voltage terminal distribution systems in residential and building areas.
Main function: Load breaking and connecting lines.
What is a vacuum circuit breaker?
Named after its high vacuum insulation medium for both the arc extinguishing medium and the contact gap after arc extinguishing; It has the advantages of small size, light weight, and is suitable for frequent operation and arc extinguishing without maintenance, and is widely used in distribution networks.
Vacuum circuit breaker is an indoor distribution device in a 3-10kV, 50Hz three-phase AC system, which can be used for the protection and control of electrical equipment in industrial and mining enterprises, power plants, and substations. It is particularly suitable for places that require oil-free, low maintenance, and frequent operation. Circuit breakers can be configured in central cabinets, double-layer cabinets, and fixed cabinets for the control and protection of High-Voltage Electrical Equipment.
Principle and Function
1) The working principle is that when the moving and stationary contacts are opened under the action of the operating mechanism, an arc is generated between the contacts, and steam is emitted from the surface of the contacts at high temperature. Due to the special shape of the contacts, a magnetic field is generated when current passes through, and the arc moves rapidly along the tangent direction of the contact surface under the action of this magnetic field. Part of the metal steam condenses on the metal cylinder (shielding cover), and the arc is extinguished at natural zero crossing, and the dielectric strength between the contacts quickly recovers.
2) Function of vacuum circuit breaker
Circuit breakers have overload, short circuit, and undervoltage protection functions, and have the ability to protect circuits and power sources.
The difference between load switch and isolation switch
The first difference is that the two cut off different currents.
Because the isolation switch does not have an arc extinguishing device, it is only suitable for cutting off no-load current and cannot cut off load current or short-circuit current. Therefore, the isolation switch can only be operated safely when the circuit is safely disconnected, and it is strictly operated with load to avoid safety accidents. Due to the arc extinguishing device, the load switch can overload current and rated load current, but it cannot cut off short-circuit current.
The second point is that the load switch has an arc extinguishing device, while the isolation switch does not have such a device. So, what is the difference between having this arc extinguishing device and not having it?
The so-called arc extinguishing device is designed to better assist in the opening and closing of switchgear, as well as effectively limit the arc and help extinguish it. There is such an arc extinguishing device, which is safer for switchgear. So most switch devices are equipped with arc extinguishing devices. Especially household switch appliances.
The third point is that the two have different roles
Due to the lack of arc extinguishing devices, isolation switches can only be used to isolate the live and power-off parts of high-voltage circuit devices, in order to ensure the maintenance and inspection of high-voltage circuits by personnel and ensure their safety.
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. Therefore, their functions are different, but both are applied to high-voltage equipment.
What is the difference between high-voltage load switch and vacuum switch
1. High voltage load switches can be disconnected with load and have self extinguishing arc function, but their breaking capacity is very small and limited.
2. High voltage isolating switches are generally not capable of breaking loads. They do not have arc extinguishing enclosures in their structure, and there are also isolating switches that can break loads. However, their structure is relatively simpler compared to load switches.
3. High voltage load switches and high-voltage isolation switches can both form obvious disconnection points. Most circuit breakers do not have isolation functions, and there are also a few circuit breakers with isolation functions.
4. High voltage isolation switches do not have protective functions, and the protection of high-voltage load switches is generally achieved by adding fuses, with only quick break and overcurrent protection.
5. The breaking capacity of high-voltage circuit breakers can be made very high during the manufacturing process. Mainly relying on the use of current transformers in conjunction with secondary equipment for protection. It can have functions such as short circuit protection, overload protection, and leakage protection.
High voltage load switch is an electrical device that functions between high-voltage circuit breaker and high-voltage isolation switch. High voltage load switch is often used in series with high-voltage fuse; Used for controlling Power Transformers. High voltage load switches have simple arc extinguishing devices because they can switch on and off certain load currents and overload currents. But it cannot disconnect short-circuit current, so it is usually used in series with high-voltage fuses to provide short-circuit protection.