What is the minimum ampacity required for primary line conductors if a 300 KVA transformer with a 480-volt delta primary and 240-volt secondary delivers 150 amps to several 3Ø loads?

To determine the minimum ampacity required for the primary line conductors of a 300 KVA transformer with a 480-volt delta primary, we need to use the formula that relates power, voltage, and current. The power in kilovolt-amperes (KVA) can be converted to amps using the formula:

[

\text{Amps} = \frac{\text{KVA} \times 1000}{\text{Volts}}

]

In this scenario:

• The transformer rating is 300 KVA.

• The primary voltage is 480 volts.

Plugging in these figures:

[

\text{Amps} = \frac{300 \times 1000}{480} \approx 625 \text{ amps}

]

This calculated value represents the total primary current that the transformer can deliver under full load.

The next thing to consider is how we account for the different load conditions that exist on the primary side while the transformer is supplying 150 amps on the secondary side to three-phase loads. The 150 amps at the secondary (240 volts) must also be considered for its impact on the primary side.

To find the corresponding primary current when the transformer supplies 150 amps