A ship is a small isolated grid. Power is generated at one voltage, distributed at another, and consumed by equipment that expects a third. Transformers sit at every one of those boundaries, and a vessel typically carries several of them rather than one.
Where shipboard transformers sit in the system
Main switchboards commonly run at 440 V or 690 V. Most onboard loads do not. Machinery and lighting on the low-voltage side draw 230 V or 400 V, while some propulsion and thruster drives are fed at higher voltage to keep cable sizes and fault levels manageable. A transformer between the switchboard and the distribution board is what makes those different systems coexist.
The same principle applies to shore power. When a vessel connects to a terminal supply, the incoming voltage and frequency rarely match the ship’s own system, and an isolation transformer is normally placed at that boundary to match voltage and to break the earth connection between ship and shore.
Core types and where each is used
Shipboard transformers divide into a few practical groups, and the choice between them is driven by fire risk, weight and the environment the unit sits in.
- Dry-type distribution transformers are the default on most modern vessels. They contain no liquid, so a failure does not create a flammable spill or a fire spread path inside the machinery space.
- Cast resin transformers are dry-type units with the windings encapsulated in epoxy. The encapsulation seals the windings against moisture and salt-laden air, which matters in a machinery space. See cast resin transformers.
- Isolation transformers provide galvanic separation between two systems. They are used at shore connections and wherever an earth fault on one side must not transfer to the other.
- Autotransformers are smaller and lighter for the same rating because part of the winding is shared, but they provide no isolation between primary and secondary.
- Instrument transformers, current and voltage types, scale high currents and voltages down to levels that protection relays and meters can accept.
Wye and delta on a shipboard system
Three-phase shipboard transformers are wound wye or delta, and the choice determines how voltage and current relate on each side.
- Wye (star). Line voltage is √3 times phase voltage; line current equals phase current. A neutral point is available, which suits four-wire systems where single-phase loads are supplied alongside three-phase ones.
- Delta. Line voltage equals phase voltage; line current is √3 times phase current. No neutral is available, and the configuration can continue to deliver a reduced three-phase supply if one phase is lost.
A common mismatch is a transformer whose winding is rated for one voltage while the supply runs at another. If the supply matches the winding rating, delta applies. If the supply is about 1.73 times the winding rating, the winding is connected in wye.
Rated capacity and why it is quoted in kVA
Shipboard transformers are rated in kVA rather than kW because the winding has to tolerate the full current regardless of the phase relationship between voltage and current. The rating covers heating, not useful output, and a load with a poor power factor can draw rated current while converting considerably less of it into work.
Two losses determine how much heat the unit rejects into the space around it. Copper loss varies with the square of the current and therefore tracks load. Core loss is present whenever the transformer is energised, even at no load, and depends on core material, flux density and supply frequency. Both end up as heat inside the switchboard room.
Installation requirements that come from the rules, not from preference
Shipboard installation is governed by classification society rules and by SOLAS, so several of the constraints are not optional.
- Mounting must resist vibration and shock, and hold the unit against the motion the vessel is surveyed for.
- The space around the unit has to allow ventilation and heat rejection, and the arrangement must preserve fire integrity in the boundary it sits behind.
- Grounding is specified rather than discretionary, and its purpose is to make protective devices operate quickly under fault conditions.
- Enclosure and any hazardous-area certification must match the space the unit is installed in.
- Cable entries and drainage are arranged so that water does not collect at the base of the unit.
Ventilation is often underestimated. Airflow has to be sized against the heat the transformer actually produces, which scales with the kVA rating and the losses at expected load rather than with the physical size of the enclosure.
How to specify a shipboard transformer
A quotation request can be turned around much faster when the following are stated, and most of them come from the vessel’s electrical documentation rather than from the purchaser.
- Rated capacity in kVA, together with the load profile and expected duty.
- Primary and secondary voltage, phase arrangement, and whether a neutral is required.
- Supply frequency and the cooling method implied by the installation space.
- Classification society and any type-approval requirement the vessel is held to.
- Ambient temperature in the machinery space and the temperature rise permitted at rated load.
- Enclosure type, ingress protection, and any hazardous-area classification.
- Footprint and weight limits, which are often the binding constraints on a refit.
Testing and documentation worth asking for
Routine tests on a completed unit normally include winding resistance, ratio and polarity checks, insulation resistance, and a separate-source withstand test on the primary and secondary circuits. Temperature-rise verification by test or by calculation is a separate item and is worth naming explicitly in the specification, because it is the test that confirms the rating holds in the actual installation space.
On delivery, keep the routine test report, the nameplate details, and the dimensional drawing with the vessel’s documentation. The same records are what a surveyor will ask for at the next classification survey.
If you are working from a vessel drawing or a refit scope, send the ratings and the space available and we can come back on the configuration. See the ship transformer range, or contact us with the requirements.
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