The so-called SF6 load switch refers to installing the circuit breaker on the movable arm of the isolating switch, forming a combination of isolating switch and circuit breaker, called a load switch. Due to the installation of the circuit breaker, the load switch has the ability to break short circuits. Since the short-circuit breaking capacity here is provided by the circuit breaker, it is also called current breaking.
Let's assume that the load switch controls a motor, and now one phase of the motor has a short circuit for some reason, and the corresponding circuit breaker trips, while the current of the other two phases surges. If this load switch is able to automatically break, the contacts of the load switch (note that it is not the circuit breaker) will have a large current, which may burn the contacts of the load switch. This current is called transfer current. Therefore, low-voltage load switches are not allowed to switch off automatically.
SF6 load break switch has a simple arc extinguishing device, which can cut off rated load current and a certain overload current, but cannot cut off short-circuit current. Load switches can be divided into high-voltage load switches and low-voltage load switches according to the voltage used. High-voltage load switches are electrical appliances that function between high-voltage circuit breakers and high-voltage isolating switches. They are often used in series with high-voltage fuses to control power transformers. High-voltage load switches have a simple arc extinguishing device because they can break and connect a certain load current and overload current. However, it cannot interrupt short-circuit current, so it is generally used in series with high-voltage fuses to provide short-circuit protection.
It should be installed vertically, and the switch frame, closing mechanism, cable sheath, and protective steel pipe should be reliably grounded (cannot be connected in series).
Before operation, several no-load on-off operations should be performed. There should be no jamming in each rotating part, and after closing, there should be sufficient safety distance after opening.
The fuse element used in conjunction with the SF6 load break switch should be appropriately selected, that is, the fault current should be greater than the breaking capacity of the load switch, so that the fuse element can melt first before the load switch can switch off.
When closing, the contact should be good, and there should be no overheating at the connection. During inspection, attention should be paid to checking whether the porcelain bottle is dirty, cracked, chipped, or has a flashing discharge phenomenon. Water should not be used to wash the switch. (When replacing a fuse in a high-voltage cabinet that controls a transformer, the high-voltage cabinet of that circuit should be shut down as much as possible)
SF6 load break switch is mainly used to break and switch load current, and can also be used in conjunction with high-voltage fuses to replace circuit breakers.