Functions and constructions of Inter connecting transformer in thermal power plant switch yard?

Generators are typically designed to operate at voltages in the 11-22kV range. It is theoretically possible to have higher voltage generators (one European manufacturer offers generators with voltages up to around 70kV), the optimum economic voltage is much lower.



But the economics of bulk power transmission favor higher voltages - 110 kV and above. In most cases, the maximum voltage is around 500kV, but there are examples of higher voltage transmission in a few cases.



So the function of a transformer in a power plant switch yard is to increase the voltage from the level produced by a generator to the level associated with transmission.Functions and constructions of Inter connecting transformer in thermal power plant switch yard?The function of the inter-connecting transformer is - as the name suggests - to inter-connect two systems at different voltages. Normally, they will be either 400kV/132kV or 220kV/110kV, of say about 100 MVA rating. They are bi-directional. During the plant start-up, they "import" power from the grid either at 400kV or 220kV and step down to 132kV or 110kV to supply the station auxiliaries. Once the plant is started and synchronized to the grid, the same transformer can now be used to "export" power to the grid.



They are normally auto-transformers and they will have a delta connected tertiary winding of about 33kV voltage rating, for providing a circulating path for the zero-sequence currents. The spec would read: 400/132/33kV, 100MVA.Functions and constructions of Inter connecting transformer in thermal power plant switch yard?Major function is to share the load among the available transformers.



Then to switch load to backup transformers for maintenance activities.



To last is to handle dynamic load conditions during peak hours.

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