On board, the choice between a dry type and an oil-immersed transformer is less about electrical performance than about what happens when something goes wrong in a space people have to escape from.
Why dry type dominates on board
An oil-immersed transformer carries a volume of flammable liquid inside the hull. That brings a fire load, a containment requirement, and often a fire-rated enclosure with it. A dry type unit removes all three. There is no liquid to leak into the bilge, no bund to install, and no spill to clean up.
The trade-off is thermal. Air is a poorer cooling medium than oil, so a dry type unit of the same rating tends to be physically larger unless the design is pushed. In a machinery space where volume is limited, that is a real constraint and it belongs in the enquiry.
VPI and cast resin construction
Marine dry type transformers come in two main constructions, and the difference matters in a salt-laden atmosphere.
- VPI (vacuum pressure impregnated). The wound assembly is impregnated under vacuum and pressure so that the varnish fills voids in the winding. It produces a solid, well-bonded winding at moderate cost.
- Cast resin. The windings are encapsulated in epoxy. The encapsulation is a physical barrier, not just an impregnation, so moisture and salt cannot reach the conductor in the first place.
For marine work, cast resin is the more common choice. The encapsulation does three things at once: it prevents moisture ingress, it braces the winding against short-circuit forces, and it gives the unit a clean, wipeable surface. See cast resin transformers.
What the environment asks of the design
- Windings braced so that conductor movement under short-circuit force is prevented.
- Core and coil assembly clamped against vibration over the life of the vessel.
- Insulation system rated for the ambient temperature of the space, not a shore standard.
- Corrosion-resistant fixings and a coating system specified for marine exposure.
- Sealed enclosure with gasket materials suited to the temperature and the atmosphere.
- Cable entries and drainage arranged so water cannot collect at the base.
Testing and records
Every unit receives routine testing before dispatch: winding resistance, ratio and vector group, impedance and load loss, no-load loss and current, applied and induced voltage withstand, and insulation resistance. The measured values are recorded on the test sheet that ships with the unit.
Keep that sheet, the nameplate details and the dimensional drawing with the vessel documentation. The same records are what a surveyor asks for at the next classification survey, and reconstructing them later is far harder than filing them on delivery.
If you are weighing dry type against an oil-immersed design for a particular space, send the rating and the room dimensions and we can come back on what fits. See the marine transformer range, or contact us.
Related Products
Related Applications
Request a Custom Quote
Need a custom transformer for your application? Send us your technical requirements and our engineering team will provide a custom solution within 24-48 hours.
Related equipment
If you are specifying this as part of a larger distribution scheme, the surrounding scope is covered on the oil and gas electrical distribution, MV switchgear and compact substations pages.
Frequently Asked Questions
How do I approach specifying a marine dry type transformer?
Start from the load and the environment, then let the equipment follow. Working from a catalogue rating backwards is how projects end up with either a marginal unit or one that costs money sitting under-loaded.
What makes a marine transformer different from an ordinary one?
The construction around the transformer, not the electrical function. Continuous vibration, salt-laden air, confined spaces and the classification society approval route all shape the design. Vibration-resistant core clamping, corrosion protection and the documentation package matter as much as the rating.
Which classification approvals are needed?
It depends on the flag state and the class society the vessel or platform is registered under. Approval requirements are confirmed against your project before production rather than assumed, and the documentation package is assembled to the route your project follows.
Which standard applies, and is it certified?
The applicable standard and clause set are agreed against your project specification before production starts. Where a project names IEC 60076 for the transformer, we work to those clauses and the routine test report ships with the unit.
What do you need from us to quote?
The single-line diagram or a description of the application, the voltages, the load with its duty, the site conditions, and any standard the project specifies. Send what you have – if something is missing, it can be worked out together rather than delaying the enquiry.