Answer MET Question 10

Question: A. Explain the potential hazards of liquid-cooled transformers are used onboard ships. 

Solution: The transforms used on board ships are generally air cooled while oil cooled transformers are very common on land. The oil can present a serious hazard in the event of leakage. If the oil due to any reason leaks into the winding it will cause short circuit and oil fire shall take place. The properties of transformer oil are:
Electrical properties: Dielectric strength, specific resistance, dielectric dissipation factor.
Chemical properties: Water content, acidity, sludge content.
Physical properties: Inter-facial tension, viscosity, flash point, pour point.
The environment at sea is harsh and cause the loss of oil properties result in deterioration. The oil doesn't ignite so easily, but upon ignition it will result in uncontrolled fire. This will cause injury to person in vicinity, loss of power and blackout.
Additionally the oil cooled transformer require more maintenance and more care while handling. Mishandling and carelessness during maintenance and handling will result in oil loss and spillage.

1.    Thermal stability.

2.    Excellent insulating properties.

3.    High flash point > 140 degree Celsius.

4.    Low pour point < - 6 degree Celsius.

5.    Viscosity should remain low at temperature.

The cooling oil used in transformer is flammable at high temperatures and present a considerable fire hazard due to large quantity used.

A defective or aged insulation of winding or a high electrical surge may cause overheating in the transformer and leads to ignition of oil. The situation is compounded by damage to the transformer tank or oil carrying lines resulting in spray fire