HOW TO SIZE A TRANSFORMER !

Electrical transformers are used in everyday life.
A transformer is a passive electrical device that is used to increase the voltage level at the power generating station (Step up) or to decrease the voltage level (Step down) for Electrical power distribution purpose.
Transformer sizing is a very important step and we must make informed decisions regarding proper transformer sizing and its impact on the electrical system under different operating and loading conditions
This video explains in detail the steps to be followed for the kVA calculation of a Transformer.

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Link for video on "Understanding Electrical Load Schedule"    • UNDERSTANDING ELECTRICAL LOAD SCHEDULE  

Why is it important to size a Transformer Correctly!!

1. Higher costs due to oversized transformer, conductors, and Circuit breakers in case an oversized transformer rating is selected.
2. Larger transformer KVA Rating will result in higher fault level (assuming the same transformer impedance), which will require increased CB rating as well as increase in the maximum interrupting current.
3. In case of an undersized transformer KVA rating, it may create issues within electrical distribution systems, including loss of loads and voltage drop during starting of large motors may exceed the acceptable limits.

The starting point of the Transformer Sizing is the load that will be supplied by Switchboard/Panel that will be fed by the Transformer.
Peak Load (PL) should be used for this purpose. PL is obtained from the Electrical Load Schedule.
We should not use Connected Load for transformer kVA calculation as it will be result in an oversized transformer.

Once the Peak Load is known, the Transformer kVA rating is calculated by adding this Peak Load and the expected Future Growth
Future Growth is normally considered between 10% - 30% depending on what additional loads are expected in the future.