Three new types of Digital Static Transfer Switches (DSTS) are said to meet any site-maintenance and fault-coordination requirements. The switches are classified based on how they react to downstream faults. The Type 1 DSTS features smaller, undersized SCRs protected by a fuse. In the event of a downstream fault, the fuse will clear to protect the SCRs from rupturing. As a result, the load will be dropped until the fuse is replaced. The Type II DSTS features SCRs that are designed to short-circuit in the event of a fault, but not rupture. In this instance, no fuses are required as the SCRs will continue to conduct current during the fault, thereby coordinating with the facility electrical distribution system. The SCR may need to be replaced if it shorts. The SCRs in a Type III DSTS are sized such that they can withstand a fault, so they will neither short nor rupture. No maintenance is needed because the SCRs will continue to meet their performance specs after the fault.
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