What is the kW rating of a transformer that supplies 480 V and 40 A?

• A. 10 kW
• B. 19.2 kW
• C. 25 kW
• D. 40 kW

Answer: (B)

To determine the kW rating of a transformer supplying 480 V and 40 A, the calculation involves using the formula for power in kilowatts (kW).

First, calculate the apparent power (measured in volt-amperes, or VA) using the formula:

Power (VA) = Voltage (V) × Current (A)

In this case, substituting the given values:

Power (VA) = 480 V × 40 A = 19,200 VA

To convert this into kilowatts (kW), you divide the result by 1,000:

Power (kW) = 19,200 VA / 1,000 = 19.2 kW

Thus, the kW rating of the transformer is accurately calculated as 19.2 kW. This means option B is the correct answer as it directly reflects the calculated value based on the transformer specifications provided in the question.