Starting methods on board: DOL, star–delta, soft starter, VFD

Why not start everything direct-on-line

Why not start everything direct-on-line? The generator decides. A 37 kW start on a 625 kVA generator is manageable. A 200 kW ballast pump, or a big motor on the emergency generator, is not.

Star–delta is cheap and simple, which is why it is still common on fire, ballast and cooling water pumps and on fans.

Soft starter and frequency converter

A soft starter ramps the voltage up with thyristors. There is no changeover surge, but the torque is still reduced. A frequency converter starts at low frequency with full torque and the lowest current, at a higher price, with harmonics to deal with on the switchboard.

After a blackout: LVP and LVR

After a blackout. This starter has low-voltage protection (LVP): when the supply fails, MC drops out and its holding contact opens, so when the voltage comes back the pump stays stopped until someone presses START. A starter with low-voltage release (LVR) drops out too, but closes again by itself as soon as the voltage returns.

Rules differ on which a fire pump should have. US rules ask for LVR on fire pump controllers where an automatic restart is not hazardous (46 CFR 111.70-3). With an unattended engine room and one generator on the board, SOLAS asks for the standby generator to start and connect by itself, with automatic restart of essential auxiliaries, in sequence where necessary (II-1/53.2.1). Many ships keep LVP on the starters and let the power management system restart them one after another.

A star–delta starter that restarts goes through star again, because its timer reset when the supply was lost. That is exactly what the generator needs when many motors come back at once.

Check yourself