A new service line is being setup to feed a group of apartments in a neighborhoo

Question

A new service line is being setup to feed a group of apartments in a neighborhood. 3-phase distribution transformers are built from 3-single-phase units each rated at 20 kVA. Answer the following questions (a) What factors have to be considered while sizing the distribution transformers? (b) The neighborhood requires 120 V and 240 V single-phase, 240 V three-phase and 208 V single-phase voltage connections. What type of transformer connection should be adopted? Justify your answer. (c) After careful examination of the demand curve, the distribution engineer concludes that the maximum kVA of the neighborhood is 30 kVA. Is it possible to make any changes in the transformer connections to reduce the cost of power distribution? Justify your answer with relevant equations or numerical calculations.

Explanation / Answer

Answer a.) Factors considered while sizing distridution transformers are

1.)Kilovoltampere (kVA) rating

2.)Voltage ratings, ratio, and method of Connection (Delta or star connection)

3.)Voltage tappings

4.)Temperature ratings

5.)Impedance Values of transformer

6.)Sound levels

7.)Effects of transformer failures

8.)Harmonic content of load

9.)Paralleling transformers

10.)Insulation classes

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