The applications of high-voltage load switches correspond directly to their structural characteristics. Structurally, load switches fall into two primary categories: the first is designed for independent mounting on walls or support structures, featuring a construction similar to that of a disconnector (isolating switch); the second is designed for installation within high-voltage switchgear cabinets-particularly those utilizing vacuum or SF6 gas technology-and bears a closer resemblance to a circuit breaker. The overall utility of the load switch encompasses the combined functions of both of these structural types.
When a load switch is in the "open" position, it-much like a disconnector-presents a clearly visible point of electrical separation; it therefore serves an electrical isolation function. This provides an essential prerequisite for ensuring reliable power disconnection for equipment or power lines undergoing maintenance or de-energization.
Load switches are equipped with a rudimentary arc-extinguishing mechanism, enabling them to interrupt and make (close) load currents falling within the device's own rated current capacity. Consequently, they can be utilized to switch transformers, capacitor banks, and distribution lines of specific capacities. In certain industrial settings, where a workshop transformer is situated at a considerable distance from the high-voltage distribution room's main circuit breaker, a clearly visible point of disconnection may not be observable within the transformer room itself during power-off procedures. In such instances, a high-voltage load switch is often installed directly on the wall of the transformer room; this arrangement allows for the local switching of the transformer's no-load current while simultaneously providing a visible point of disconnection, thereby ensuring the safety and reliability of the power-off operation.
When paired with high-voltage fuses, a load switch can effectively function as a circuit breaker with limited fault-current interrupting capacity. In this configuration, the load switch itself is responsible for making and breaking normal operational load currents, while the high-voltage fuses are tasked with interrupting short-circuit fault currents. Typically, the load switches employed in such applications are of the vacuum or SF6 gas type; the entire ring main unit assembly remains compact in size and is capable of supporting transformers with a maximum capacity of up to 1250 kVA.