NEIEP Mechanics Practice Exam

A transformer with a primary voltage of 440 volts, 100 turns, and a 15:1 voltage ratio of transformation will have what secondary current if the primary current is 25 amps?

1. 125 amps

2. 375 amps

3. 500 amps

4. 600 amps

The correct answer is: 375 amps

To determine the secondary current in a transformer, you can use the principle of conservation of energy, which states that the power input to the primary side is equal to the power output of the secondary side (ideally without losses). The formula relating primary and secondary voltages and currents is given by: \[ V_p \times I_p = V_s \times I_s \] where \( V_p \) and \( I_p \) are the primary voltage and current, and \( V_s \) and \( I_s \) are the secondary voltage and current. Given a primary voltage (\( V_p \)) of 440 volts and a primary current (\( I_p \)) of 25 amps, the input power can be calculated as: \[ P_p = V_p \times I_p = 440 \, \text{V} \times 25 \, \text{A} = 11,000 \, \text{watts} \] With a transformation ratio of 15:1, we can find the secondary voltage (\( V_s \)) by dividing the primary voltage by the voltage ratio: \[ V_s = \frac{V_p}{15} = \frac{440}{15} \approx