Location of Main Power Transformers in Hydro Electric Plant

The choice of location of the main power transformers in hydropower plant is inter-related with the selection of the type and rating of the transformers. The selection of single-phase or 3-phase type of transformers, the method of cooling, and the kVA rating are also directly related to the basic switching provisions selected for the plant, the number and rating of generators associated with each transformer or transformer bank, and the location of the transformers.

In order to determine the most suitable and economical installation, including the type, rating, and location of the main power transformers, adequate studies, including comparative estimates of total installed first cost and total annual cost for each scheme studied, should be made during the preliminary design stage along with studies to determine the basic switching arrangement and general arrangement of the hydroelectric powerplant.

Locations at which the main power transformers may be placed are: between the powerhouse and dam, on the draft tube deck, in the switchyard, and near the powerhouse but not in the switchyard. From the viewpoint of electrical efficiency, the power connections between the generators and transformers should be as short as practicable. This consideration favors the location of the transformers at or near the powerhouse. In deciding between the upstream or downstream location at the powerhouse, consideration should be given to the location of the switchyard and the nature of the high-voltage connections between it and the transformers.

In some cases the location of the transformers on the draft tube deck may increase the cost of the powerhouse structure. However, if such a location makes possible a direct overhead connection to the switchyard, this feature may more than balance any increased cost of the structure. At small plants and, where the switchyard can be located close to the powerhouse, a transformer location in the switchyard may be economical.

Where transformers are located between the powerhouse and dam, special high-voltage cable connections to the switchyard may be required. In selecting the location for the transformers, as well as in planning the general plant arrangement, consideration should be given to the requirements for transporting and untanking the transformers.