Substation Transformers

Substation Transformer Picture The transformer is the heart of the substation. The transformer changes the relationship between the incoming voltage and current and the outgoing voltage and current. Substation transformers are rated by their primary and secondary voltage relationship and their power carrying capability. For example, a typical substation transformer would be rated 69-13 kV and 20 MVA; meaning the primary or high voltage is 69 kV, the secondary or low voltage is 13 kV and the transformer has a power rating of 20 MVA or 20,000 KVA. Substation transformers, like most utility transformers, consist of a core and coils immersed in oil in a steel tank. The oil serves both as an insulator and as a coolant to keep the core at reliable operating temperatures.

Substation Transformer With Fans Picture Some large transformers have fins for the oil to circulate through and thus dissipate heat. Some add fans to force air across the fins. Others add pumps to forcibly circulate oil. And in some situations, a utility may even add water spray systems which sprays the transformer case with cooling water on hot days and high load conditions.