Transformer

What Sets This Type Apart

A marine transformer converts electrical energy from one AC voltage level to another with no moving parts, transferring power through mutual induction between primary and secondary windings wound on a common iron core. Aboard ship it typically steps the 440 V or 690 V generator bus down to 220 V or 110 V for lighting, navigation electronics and galley equipment, or steps up for high-voltage propulsion plant on larger tonnage. Unlike a generator or converter, it does not change frequency and cannot regulate voltage under load beyond its fixed turns ratio and any tap settings selected at commissioning.

Dry-type transformer, cutaway — Cutaway of a dry-type distribution transformer inside its ventilated enclosure, showing the laminated core with a wound limb carrying the HV and LV windings, the unwound return limb, and the HV and LV terminals.

Main Components

Core

Laminated silicon-steel sheets, insulated from each other to limit eddy-current losses. Core geometry (shell-type or core-type) affects size and leakage reactance.

Windings

Copper or aluminium conductors, insulated with class B, F or H materials depending on expected hot-spot temperature. Winding arrangement (delta, star, zig-zag) determines fault behaviour and harmonic performance.

Cooling and enclosure

Dry-type units rely on air (natural or forced cooling); oil-filled units use mineral oil or synthetic ester as both dielectric and coolant, circulated by natural convection or fans and pumps on larger ratings. Oil-filled transformers need a conservator tank, breather and often a Buchholz relay; dry-type units need only a temperature sensor set in the windings.

Tap changer

Off-load tap links, moved with the unit de-energised, let yard staff correct for a supply that sits consistently a few percent off nominal; on-load tap changers are rare in shipboard power distribution and mostly confined to shore-connection or cold-ironing transformers.

Selection and Sizing

Sizing starts from the connected and diversified load on the downstream board, expressed in kVA, plus margin for future additions. Key figures to check against the load list and site conditions:

Rated power (kVA) and duty, continuous or intermittent, since some units feed only bow-thruster or mooring-winch boards.
Primary and secondary voltage and vector group, matched to the switchboard it will parallel or feed.
Impedance percentage, which sets the fault current the downstream protection has to clear.
Insulation class and ambient temperature rating for the compartment it sits in, since engine room ambient is far hotter than a switchgear room.
Ingress protection rating if mounted in an exposed or damp space.

Dry-type is generally preferred inside accommodation and control spaces because it carries no fire load of oil; oil-filled units are common in engine rooms where their better overload tolerance and lower through-life losses offset the added fire-fighting and containment requirement.

Regulations and Class

Class rules require transformers in essential and emergency circuits to be sized and protected so that a single fault does not remove both a service and its standby supply from the same transformer. Oil-filled transformers above a certain oil quantity typically fall under the society's rules for fire protection of oil-filled electrical equipment, including bunding or a drip tray and, on larger ratings, fixed fire detection. Periodic survey checks insulation resistance, winding temperature alarms, and physical condition of bushings, tap links and any oil, including dielectric strength and moisture content by sample.

Typical Faults

Fault	Cause	Consequence
Insulation breakdown	Moisture ingress or long-term thermal ageing beyond the winding's insulation class	Inter-turn short, tripping upstream protection, possible winding burn-out
Overheating alarm	Sustained overload or blocked ventilation on a dry-type unit	Accelerated insulation ageing, eventual failure if ignored
Buchholz trip	Gas evolution from arcing or overheating inside an oil-filled unit	Automatic disconnection; unit must be inspected before re-energising
Low oil level	Seal or gasket leak at the conservator or radiator	Loss of cooling and dielectric margin, risk of moisture entry
Tap link loosening	Vibration over time on an off-load tap changer	Increased contact resistance, localised heating at the tap board

What to Look for in a Supplier

Type test certificates for temperature rise, short-circuit withstand and dielectric strength from a recognised test house.
Class society product certification or type approval for the intended flag and society.
Documented vector group and impedance so the unit can be paralleled or coordinated with existing switchgear without recalculating protection settings from scratch.
Availability of spare bushings, gaskets and tap links matched to the specific model, not generic equivalents.
Willingness to supply factory acceptance test data, not only a certificate of conformity.

A transformer that trips on Buchholz gas or hits a high winding-temperature alarm should never simply be reset and reloaded; de-energise it and sample the oil or check insulation resistance first, because the fault that caused the trip is still there.