Diesel Generator Starting Procedure & Alternator On-Load | Marine Guide

1. Local Start That Respects the Iron

1. Local control set — proved in three checks:

   • Fuel, jacket-water and cooling systems lined up.
   • Sump, governor and alternator bearing levels checked.
   • Starting-air receiver pressure proved.

2. Pre-lube pump to auto with pressure proved for at least 2 minutes — bearings wet before they turn; check pressure drops across lube-oil filters.

3. Bar at least one full turn (two with ratchet spanner through the starter pinion, cocks open) — water, oil or fuel in a cylinder would hydraulic-lock it. Remove the turning gear before going further.

4. Blow through from local, shut cocks, LOCAL selected, START to rated speed — then leaks, firing on all units, lube-oil and fuel pressures and temperatures proved before changeover to remote.

2. Taking Load — Auto and Manual

Auto — panel decides

Mode selector to AUTO, ACB control to close — breaker shuts and load shares itself across governors.

Manual — operator earns it

Selector to MANU, synchroscope to the incoming set, governor trimmed to slow clockwise drift, breaker ordered just before 12, load balanced by hand.

Trim for incoming slightly fast (~4 s/rev drift) so the set takes load on closing — a slow incoming set would motorise and add load to the bus instead. Then synchroscope off and load balanced by hand across governors. Lamp backup (top-dark, two-bright) and the full four-condition ritual live in the alternators lesson.

3. Slip, Sync and Skewed Bars

Slip is synchronous speed minus rotor speed over synchronous speed — the 1–5% sag between no-load and full-load that lets rotor bars cut flux harder as torque demand rises. Near-constant speed is why induction motors rule auxiliaries. Synchronous machines lock rotors to field speed (constant speed all loads, needs DC excitation, can correct power factor); asynchronous (induction) ones always trail it — no trail, no induction, no torque.

Rotor bars short through end rings so induced current has a circulating path; skewing staggers each bar's field-cutting so torque flows continuously instead of jerking bar-by-bar — while defeating magnetic cogging lock between stator and rotor slots and silencing running hum.

4. Breakers and Clock Faces

ACB (air circuit breaker) rules generator duty at 400 V-plus currents. Stab CLOSE on an idle, unsynchronised set and nothing happens — the undervoltage interlock bars closure without control volts (reclose only past ~85%), guarding the bus against blind paralleling and riding through voltage loss.

5. Emergency Changeover — Tie Breaker, Link Interlock, ESB Loads

Normally the auto-bus-transfer (tie) breaker feeds the emergency switchboard from the live main bus. On falling mains voltage or frequency a start-up relay fires the emergency set from its own independent source (battery or air/hydraulic), the tie breaker opens, and the emergency breaker closes onto the emergency board alone. On restoration the relay drops out, the set goes off-load, and the operator returns the selector to manual and stops it. The interlock forbids paralleling main with emergency or shore with emergency — never both breakers at once.

Test rhythm (full drill in the emergency-generator lesson): carry out the routine start check, each independent starting mode, automatic transfer and controlled load test at the intervals in the vessel’s approved procedure. Keep fuel, coolant and stored-energy sources ready. On power return, essential kit like steering restarts in sequence rather than all at once.

6. Fail-to-Start Drill — the Overhauled Motor That Sits Dead

1. Terminal box: connection bars sound, star/delta links match the design — never run a delta motor in star on load (√3 overcurrent per phase, burnout unless the overload relay saves it).

2. Supply volts proved at the terminals; no power, blown fuse, tripped overload, burnt contactor coil, bad contacts, faulty control relay, open stop circuit — each gets a meter, not a guess.

3. Phase-to-phase continuity (U–V, V–W, W–U) with matched ohms — open bars show here; direction of rotation confirmed before coupling to load.

4. Megger phase-to-phase and phase-to-earth at 500 V: 1 MΩ minimum on motors — run it or rewind it on the evidence, and log the reading.

Do not confuse the victims: open circuit refuses to start (or burns the two healthy phases if one leg opens running); short circuit gulps fault current; earth fault leaks to hull. Each has its own meter proof — continuity, volts, insulation.