High-voltage load switches are often used in series with high-voltage fuses to control power transformers. The selection principles are as follows: 1. Distinguish indoor and outdoor types. Outdoor types can be used indoors, but indoor types cannot be used outdoors. 2. The actual breaking current on site should be less than the rated breaking current of the high voltage load switch. 3. Calculate the short-circuit current at the end as the basis for selecting the maximum transfer current. 4. Correctly select the fuse. First, it can be selected according to the capacity of the protected device. Second, it must cooperate with the upper level protection, that is, the time corresponding to the action current on the second curve should be less than the time of the upper level protection action. Make the protection of the power grid selective. 5. Pay attention to the application of high voltage load switch. In the place where the operation is infrequent, in order to save resources, the gas generating type can be selected, and the vacuum type should be used in operation to achieve the purpose of maintenance-free. 6. When remote operation is needed, it should be equipped with electric mechanism and manual mechanism.