Every drive lesson gets harder at sea, because a ship is a small island grid: a few generators, short cable runs, and no utility to hide behind. Land plants on weak grids inherit all these lessons.
The generator interaction set
Harmonics dominate: a generator’s source impedance runs several times a utility connection’s, so the same drive kW distorts voltage far more — and class societies write THD limits into rules. Practically, drive fleets aboard get input filtering by design: reactors as a floor, low-harmonic front ends or active filters as installed kW grows relative to generator size. Measure, don’t estimate — a THD survey during sea trials beats a finding at survey.
Regeneration needs somewhere to go: on a small grid, a regenerating winch or crane drive can push the busbar around. Options are the familiar ladder — resistors (dissipative, but grid-independent), shared DC systems between coordinated drives, or grid-tie regen sized against the minimum generator configuration that might be online. The load-management PLC deserves to know what drives may inject.
EMC on a steel hull: the hull is the ground plane, so motor-cable screening practice and gland-plate discipline decide whether the navigation and communication gear stays happy — EMC compliance categories for the bridge zone are strict for good reasons.
Generator sizing interaction: drive soft-start capability actually helps (no DOL inrush), but total drive kW vs generator kVA with harmonic derating applied is a calculation the electrical balance must show explicitly.
FAQ
Active front end on every big drive? Where its clean input and regen close two problems at once, it earns the premium; small auxiliary drives ride reactors happily.
Bow thruster drives — special case? The definitive one: huge intermittent load on the weakest bus condition (maneuvering) — its power-management interlocks are a design document of their own.
Zone Otomasyon engineers drive systems for vessels and island grids with the measurements to prove compliance. Marine drive systems.