Closed bus tie

Closed bus-tie operation runs the main switchboard with the bus-tie breaker shut, so all online generators feed one common busbar and share load through the power management system. It improves fuel economy because fewer sets run nearer their optimum load, and it simplifies load transfer. The penalty is fault propagation: a short circuit or a faulty set can collapse the whole bus, so closed-bus operation needs fast, selective protection and generator decoupling. DP-class notations restrict closed-bus running unless the protection and PMS demonstrate that a single fault will not black out the ship.