After opening the circuit breaker, a reliable insulation gap is established, separating the equipment or line requiring maintenance from the power supply with a clearly visible disconnect point to ensure the safety of maintenance personnel and equipment.
Line switching is performed according to operational needs.
It can be used to switch small currents in lines, such as the charging current of bushings, busbars, connectors, and short cables; the capacitive current of the equalizing capacitor in the switch; the circulating current during double busbar switching; and the excitation current of voltage transformers.
Depending on the specific structural type, it can be used to switch the no-load excitation current of a transformer of a certain capacity.
Disconnecting switches are mainly used in low-voltage equipment, particularly in residential buildings and other low-voltage terminal power distribution systems. Main functions: disconnecting and connecting lines without load.
Used to isolate the power supply, disconnecting high-voltage maintenance equipment from energized equipment, creating a clearly visible disconnect point.
Disconnecting switches work in conjunction with circuit breakers to perform switching operations as needed for system operation, changing the system's wiring configuration.
Used to connect or disconnect small current circuits.
Generally, a set of disconnecting switches is installed on both sides of a circuit breaker to isolate the circuit breaker from the power supply, creating a clear disconnection point. Because the original circuit breakers were oil circuit breakers, which require frequent maintenance, clear disconnection points on both sides are necessary for easy maintenance. Typically, the outgoing line cabinet supplies power downwards from the upper busbar through the switch cabinet. A set of disconnecting switches is needed before the circuit breaker to isolate it from the power supply. However, sometimes there is a possibility of power coming through the circuit breaker, such as reverse power from other loops or capacitors. Therefore, a set of disconnecting switches is also needed after the circuit breaker.
Disconnecting switches are mainly used to reliably isolate the parts of a high-voltage power distribution system that need to be de-energized from the energized parts, ensuring the safety of maintenance work. Disconnecting switches have all their contacts exposed to the air, providing a clear break point. They lack arc-extinguishing devices and therefore cannot be used to interrupt load current or short-circuit current. Otherwise, under high voltage, a strong electric arc will be generated at the break point, which is difficult to extinguish on its own and may even cause a flying arc (phase-to-ground or phase-to-phase short circuit), damaging equipment and endangering personal safety. This is the serious accident known as "operating a disconnecting switch under load." Disconnecting switches can also be used to switch certain circuits to change the system's operating mode. For example, in a double-busbar circuit, a disconnecting switch can be used to switch a running circuit from one busbar to another. They can also be used to operate circuits with low current.