Suggestion:
Advantages of the cast resin dry transformer in comparison to the oil transformer are:
1. Lower operation and maitenance cost, since the oil maintenance is more expensive
2. Lower volume within the relevant kVA range
3. etc.
Advantages of the oil transformer in comparison to the cast resin dry transformer are:
1. Can be built to bigger kVA rating
2. Can easily be rewound
3. Etc.
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The reason for selecting an oil immersed transformer over a dry type is so that it may be installed externally without any additional weatherproof enclosure wheras dry types require a housing of some description.
Liquid insulated transformers are smaller and lighter, more efficient and quieter. Mineral oil transformers are less expensive then cast coil. Info on 500kVA 15kV secondary unit substation transformers from ABB's web site:
Dimensions are inches, weight is pounds.
Liquid insulated transformers are considered by some engineers to be more resiliant to faults. Transient voltage induced faults can be self-healing to a degree. Also, it is easy to asses the condition of the transformer by oil analysis.
generally dry type transformer are more costier than the oil-filled counterparts of the the same MVA capacity and is usually the only choice when you have to installed at above or below ground level where the containment of the oil(or other liquid such as silicone) is critical in time of tank rupture and also because of fire-hazard consideration.
From operation experience, dry-type transformes are also more prone to failure esp in tropical climate as it is more suscepible to hot spot problem at the inner LT windings caused by restricted airflow at the ventilation ducts(hence less effective cooling.Oil type is relatively free from such problem
Whenever there is a choice between oil-filled and dry-type, I would prefer oil-type in view of its lower first cost, more robust and resilent reliability towards adversed operating conditions
In general, indoor locations favor the dry type, and outdoor for fluid-insulated versions, based on regional custom and facilty fire/contaiment requrements.
electicuwe has a good point. Mineral-oil transformers are not suitable for indoor use unless enclosed in a fire-rated vault. Non-flammable (e.g. silicone) liquid insulated transformers, dry type and cast-coil type do not require a vault. Silicone may be more expensive than dry type.
castresin dry type transformers:
They only make use of flame retardent inorganic material which free the transformers from all restriction that applied to oil filled electrical equipment such as oil collecting pit, firewalls, fire extinguishing equipment etc.
These transformers can be used for indoor installation close to their point of use.
Ramesh
Fluid insulating mediums, such as air gas and oil, are self healing. Solid materials don't have this property, one arc and they're gone. Once an arc is extinguished in fluid, however, the fluid flows and regains its insulating ability. Fluid flow also aids in cooling.
