In short. At a port, power does not stop at the generator terminals; it must survive the journey through salt, moisture, distance and heavy, dynamic loads. Cranes impose rapidly changing and regenerative demand, reefer yards are large steady loads with pull-down peaks, conveyors restart loaded, and shipyard welding is nonlinear. Size the plant on transients and restoration, specify enclosures and switchgear for a marine atmosphere, and check the cable runs for voltage drop at the far end.
The port power chain
A port or terminal on the Andhra Pradesh coast, a container freight station inland or a shipyard is electrically a chain: grid supply, substation and transformers, medium and low voltage distribution, normal and emergency switchgear, the generator plant, and then a long reach of cable to cranes, pumps, reefer points, terminal buildings, lighting masts, security, IT, workshops and sometimes vessels alongside. Each link is exposed to a marine atmosphere and to continuous operation. Port power engineering is therefore the sum of load, transients, distribution, environment, protection and continuity, and a generator chosen on kVA alone fails at one of the other five.
Start with operations rather than equipment. Which operations cannot stop, which can shut down safely, which loads are safety-related, which need UPS ride-through, which can be shed, and how long the facility must run without the grid. The answers differ between a container terminal, a bulk terminal, a shipyard, a fishing harbour with ice plants and a temporary marine construction site, and the critical-load register that results is the input to everything else. The method is on critical-load classification.
Load types that behave unlike ordinary industry
| Load | Electrical character | What it does to a generator | Engineering response |
|---|---|---|---|
| Quay and yard cranes | Rapid cycles of hoist, lower, travel; regenerative on lowering | Large swings in kW and kVAr; reverse power on lowering | Size on crane cycle data; confirm braking resistors or regenerative handling |
| Reefer container points | Many compressors, steady average with pull-down peaks | High base load, diversity needed | Measured diversity per terminal; staged energisation |
| Bulk conveyors | Large motors, often loaded at restart | Starting torque far above normal | Sequenced restart downstream to upstream; starter review |
| Pumps (ballast, dredge, fire, drainage) | Direct-on-line starts against existing head | High inrush | Soft start where possible; sequence |
| Shipyard welding | Intermittent, nonlinear, high peaks | Average kW misleads; harmonic heating | Size on peak coincidence; alternator for nonlinear duty |
| High-mast lighting | Discharge or LED drivers, switched in banks | Inrush on energisation | Stagger bank switching |
| Terminal operating systems | Servers, gate systems, radio | Cannot tolerate the transfer gap | UPS with generator behind |
Cranes
Crane rated power is not the generator requirement. A ship-to-shore crane may be rated at over a megawatt, but its demand over a cycle swings from a large positive peak during hoisting to a negative value during lowering as the drives regenerate. A diesel plant cannot absorb that energy and will trip on reverse power unless the crane’s braking resistors are active or the plant always carries enough other load to absorb the regeneration. Rubber-tyred gantry cranes, whether diesel-electric or electrified, have the same behaviour on a smaller scale. Actual crane electrical data and the operating cycle are required; a steady-state kVA figure is not adequate. Dynamic response is covered on generator transient response.
Reefers
A reefer yard is the most constant large load in a container terminal. Each refrigerated container draws a few kilowatts on average and considerably more during pull-down after plugging in or in high ambient, and a yard of several hundred slots adds up to a megawatt-class load that must be held through any outage to protect cargo. The design value is the measured coincident demand of the terminal, with staged re-energisation of reefer banks after transfer so that the pull-down peaks do not coincide.
Conveyors and post-outage recovery
A normal start and a post-outage recovery are different events. After an outage, bulk conveyors may be loaded with material, pumps face an existing hydraulic condition, and cranes are mid-cycle. Restoration of a conveyor network typically proceeds from the discharge end upstream, each belt proven running before the next is started, following the plant’s own control philosophy. The generator must be sized for the loaded restart of the largest belt, not its running load. Starting methods are compared on motor starting on generators.
Distance and voltage drop
Port sites are large, and generator output may travel hundreds of metres to a crane rail, a reefer block or a berth. Voltage drop then becomes a design variable in its own right, because a motor at the far end that sees a depressed voltage draws more current, starts more slowly and may stall.
ΔV = √3 × I × L × (R cos φ + X sin φ)
In this expression ΔV is the line-to-line voltage drop in volts, I is the load current in amperes, L is the one-way cable length in kilometres, R and X are the cable resistance and reactance in ohms per kilometre, and cos φ is the load power factor. For a 300 A load at 0.85 power factor over 250 metres of 240 square millimetre copper cable with R of about 0.1 and X of about 0.08 ohms per kilometre, ΔV is roughly 1.73 × 300 × 0.25 × (0.085 + 0.042), about 16 volts or 4 percent of 415 V at full load, and several times that during a direct-on-line start (illustrative). Cable values must be taken from the manufacturer’s data for the installation method and temperature. The screening method is on voltage drop and cable sizing.
Environment, enclosures and temporary distribution
Salt-laden air, humidity, spray and sun attack everything on a quay. Generator enclosures and switchgear should have a marine-grade coating system, corrosion-resistant fasteners and hinges, sealed cable entries, and an ingress protection rating suited to the exposure, with air intakes positioned and filtered to limit salt reaching the radiator and alternator. Radiators and windings need inspection at shorter intervals than inland. Where the power is temporary, the source is mobile but the physics are not: temporary cables experience transport, coiling, rain, sunlight, diesel and oil contamination, abrasion from vehicles and repeated connection, and should be inspected, insulation-tested, identified, protected by ramps or trays and re-inspected through the hire. Earthing and bonding of temporary distribution on a wet quay deserve a deliberate design rather than a single rod. Practical guidance is on rental cables and distribution and acoustic and weatherproof enclosures.
Common mistakes
- Sizing the plant on crane rated power or on average kW. The plant is either oversized by a factor of two or trips on the first regenerative lowering.
- Energising the whole reefer yard in one step after transfer. The coincident pull-down peak exceeds the plant rating and the yard goes dark again.
- Restarting a loaded conveyor network from the feed end. Upstream belts bury the stopped downstream belts and the restart becomes a clearing job.
- Using an inland-specification enclosure on the quay. Corrosion takes the radiator, the louvres and the controls within a few seasons.
- Ignoring the cable run to the far berth. The motor at the end sees 10 percent low voltage at start and the breaker trips on prolonged inrush.
What to send us
Send the critical-load register or operating model for the facility, the single-line diagram with cable lengths to the main load centres, crane electrical data and duty cycles where cranes are included, the number of reefer points and measured yard demand, conveyor and pump ratings with starter types, the required autonomy, and the exposure of the proposed generator location. For temporary marine work, include the site layout and the planned duration. Send your port or marine power requirement.
Questions engineers ask
Can a diesel generator run a container crane?
Yes, when it is sized on the crane’s cycle data rather than its rating, when the regenerative energy on lowering is absorbed by braking resistors or by other load on the bus, and when the governor and voltage regulator can follow the rapid swings. Crane electrical data and operating cycle are essential inputs.
How much generator capacity does a reefer yard need?
Measured coincident demand is the only reliable basis, since each reefer draws a few kilowatts on average and more during pull-down. Several hundred slots typically mean a megawatt-class load (illustrative), energised in banks after transfer.
What enclosure specification suits a port?
A marine-grade paint system, corrosion-resistant fasteners, sealed entries, a suitable ingress protection rating and filtered air intakes positioned away from spray. Radiators and alternators should be inspected more often than at inland sites.
Why do far-end motors fail to start on the generator?
Usually voltage drop over long cable runs, which is worse on a generator than on the grid because the generator’s own voltage dips during the start. Larger cable, a soft starter or placing the set nearer the load solves it.
Technical content reviewed by Srinivas Reddy, Managing Partner, Reddy Generators. Last updated 19 October 2026.