Working Principle and Classification of Load Switch

Basic concept

The load switch is a kind of switching device between the circuit breaker and the isolating switch . It has a simple arc extinguishing device, which can cut off the rated load current and a certain overload current, but cannot cut off the short-circuit current.

Load switch classification

According to the voltage used, it can be divided into high-voltage load switches and low-voltage load switches.

High voltage load switch

There are six main types of high-voltage load switches.

There are six main types of high-voltage load switches.

①Solid gas-generating high-voltage load switch: Use the energy of breaking the arc itself to generate gas from the gas-generating material in the arc chamber to blow off the arc. Its structure is relatively simple, and it is suitable for products of 35 kV and below.

②Pneumatic high-pressure load switch: Use the compressed air of the piston to blow off the arc during the breaking process, and its structure is relatively simple, and it is suitable for products of 35 kV and below.

③Compressed air-type high-voltage load switch: Use compressed air to blow off the arc, which can break larger currents, and its structure is more complicated, which is suitable for products of 60 kV and above.

④SF6 type high voltage load switch: using SF6 gas to extinguish the arc, its breaking current is large, the breaking capacitor current performance is good, but the structure is more complicated, and it is suitable for products of 35 kV and above.

⑤Oil-immersed high-voltage load switch: Use the energy of the arc itself to decompose and vaporize the oil around the arc and cool the arc to extinguish the arc. The structure is relatively simple, but the weight is large, and it is suitable for outdoor products of 35 kV and below.

⑥Vacuum-type high-voltage load switch: using vacuum medium to extinguish arc, long electrical life, relatively high price, suitable for products of 220 kV and below.

Working principle

The working principle of the high-voltage load switch is similar to that of a circuit breaker. Generally equipped with a simple arc extinguishing device, but its structure is relatively simple. The picture shows a compressed air high-pressure load switch. Its working process is: when opening, under the action of the opening spring, the main shaft rotates clockwise, on the one hand, the piston is moved upward through the crank slider mechanism to compress the gas; the other is On the one hand, through the transmission system composed of two sets of four-bar linkage mechanism, the main switch knife is opened first, and then the arc extinguishing switch knife is pushed to open the arc contact, and the compressed air in the cylinder blows out the arc through the nozzle. When closing, through the main shaft and the transmission system, the main switch and the arc extinguishing switch are rotated clockwise at the same time, the arc contact is closed first; the main shaft continues to rotate, so that the main contact is closed subsequently. During the closing process, the opening spring stores energy at the same time. Since the load switch cannot break the short-circuit current, it is often used in combination with the current-limiting high - voltage fuse . The current-limiting function of the current-limiting fuse can not only complete the task of breaking the circuit but also significantly reduce the heat caused by the short-circuit current. And the role of electric power.

Low voltage load switch

Low-voltage load switch is also called switch fuse group. It is suitable for the AC power frequency circuit to manually turn on and off the load circuit infrequently; it can also be used for line overload and short circuit protection. The on-off circuit is completed by the contact knife, and the overload and short-circuit protection is completed by the fuse. The plastic cover knife switches and iron case switches used before the 1970s are all low-voltage load switches. The opening and closing speed of the small-capacity low-voltage load switch contacts is related to the operating speed of the handle. The operating mechanism of the large-capacity low-voltage load switch adopts the principle of spring energy storage. The opening and closing speed has nothing to do with the speed of the handle operation. The structure is simple and it is equipped with a reliable mechanical interlocking device. The switch cannot be closed and opened after the cover is opened. The cover cannot be opened after closing, which can ensure the safety of work.