Question

a single-phase 240-volt load is drawing 43 amps and connected to the secondary of a 25 kva 480-volt primary to 240-volt secondary transformer. how much current is flowing in the primary winding?

Answer 1

To determine the current in the primary winding, we utilize the power equivalence between the transformer's primary and secondary, with the power calculated as 10320W. Dividing this by the primary voltage of 480V gives us a primary current of 21.5A.

Step-by-step explanation:

To calculate the current flowing in the primary winding of the transformer, we can use the principle that the power on the primary side of the transformer is equal to the power on the secondary side, assuming 100% efficiency and ignoring losses. The formula to calculate the power of a single-phase load is:

Power (P) = Voltage (V) × Current (I)

For the secondary winding, we have:

Power on secondary = 240V × 43A
Power on secondary = 10320W

Since the transformer is rated at 25 kVA, we can also say:

Power on primary = 25 kVA × 1000 = 25000W

Now using the conservation of power for the transformer, the primary power should equal the secondary power:

Power on primary = Power on secondary

To find the primary current, rearrange the primary power formula:

Current on primary (Ip) = Power on primary / Voltage on primary

Current on primary = 10320W / 480V
Current on primary = 21.5A