A+ Answers

1. Determine the voltage drop at the motor frame for an earth fault at the motor in the circuit shown in FIGURE 1. The phase voltage is 240 V.

2. An 11 kV motor is fed by cables from a transformer via switchgear, having a phase impedance of 0.3 + j0.3 ohm. The earth return path to the transformer neutral has a resistance of 0.42 ohm. Determine a suitable value of neutral resistance if the voltage rise at the motor in the event of an earth fault at the motor is not to exceed 430 V. Neglect transformer winding resistance.