Summary

• Distribution transformers are used both in electrical power distribution and transmission systems. Their power ratings as well as continuous voltage rating are the highest. The criteria for selection of a transformer and its technological details depend on its intended use or reasons, working conditions and operating requirements.
• Transformers are categorized on the basis of type of core used and kind of cooling used.
• The criteria used for selection of proper rating/size of DTRs are based on voltage rating, size/capacity/kva rating, number of transformers and etc.
• Transformers might be mounted on a pole placed in open space or fixed on the ground along with proper foundation depending upon their sizes and uses.
• Some significant purpose for distribution transformer failure are poor performance because of low oil level, draining of oil because of leakage/theft of oil, improper earthing, frequent faults on LT lines due to loose spans leading to short circuit, improper protection, mechanical failure of winding, manufacturing defects, etc. This purpose for transformer failure could be classified under the heads of ageing, improper structure/erection of distribution transformer, manufacturing defects, improper operation and maintenance and natural calamities.
• Transformer failure could also stem from poor O&M practices such as continuous over-heating and higher no-load losses.
• Transformer testing requires to be carried out to ensure that the distribution transformers are built along with adequate electrical and mechanical strength.
• Tests such as testing of windings - insulation and mechanical strength, testing of insulating transformer oil, must ideally be conducted here before their acceptance.
• Transformer life could be enhanced through following proper O&M practices.