A synchronous machine has the three line terminals connected together so that all three phases are in parallel. A single-phase alternating voltage is applied between the line terminals and the neutral terminals with ammeter, A, as shown below.

If the test voltage “V” is set equal to 0.55 per unit and the ammeter is reading 0.35 per unit, what is the zero sequence impedance in per unit?
A) 0.52
B) 0.9
C) 1.57
D) 4.71