(a) Construction of a Lighting Transformer Used Onboard

A lighting transformer used onboard is generally a step-down transformer designed to reduce the ship’s main switchboard voltage (typically 440 V) to safer lighting voltages such as 220 V or 110 V. It consists of:

• Laminated iron core made from thin insulated sheets to reduce eddy current losses.
• Primary and secondary windings, wound cylindrically and insulated using materials such as varnished paper, cloth, or other dielectric materials.
• Cooling arrangement:
  • For higher-capacity transformers, the windings may be immersed in transformer oil for insulation and cooling.
  • Smaller lighting transformers use air cooling with simple encapsulation.
• Terminals or bushings provided externally for connecting to the ship's electrical system.

(b) All-Day Efficiency of a Transformer

All-day efficiency (also known as operational efficiency) is the ratio of useful energy output (kWh) to total energy input (kWh) over a 24-hour period.

It is especially important for transformers supplying variable loads continuously, such as lighting transformers on ships.

$$All\:day\:efficiency=\frac{kWh\:output\:in\:24\:houts}{kWh\:input\:in\:24\:hours}$$

This efficiency accounts for:

• Core (iron) losses, which occur continuously.
• Copper losses, which vary depending on the load throughout the day.

(c) How Iron Losses Are Made Negligible in a Transformer

Iron losses consist of hysteresis and eddy current losses. They are minimized by:

• Using high-grade CRGO (Cold Rolled Grain Oriented) silicon steel with high magnetic permeability and electrical resistivity.
• Laminating the core into thin insulated sheets to restrict eddy currents.
• Operating the core at an optimal magnetic flux density to reduce hysteresis losses.
• Using effective core geometry and minimizing excess core material to limit unnecessary flux paths.

(d) Why Iron Losses Are Negligible During a Short-Circuit Test

In a short-circuit test, only a very small voltage (typically 5–10% of rated voltage) is applied to circulate rated current in the windings. Because of the low applied voltage:

• The magnetic flux in the core is extremely small.
• Iron losses, which depend on flux density (approximately proportional to (B^2) or higher), become negligible.
• The test mainly measures copper losses (I²R), since current is high but flux is low.