A 10 MVA, 11 kV alternators has positive, negative and zero sequence reactance of 25%, 40%, 10% respectively. The resistance that must be placed in the neutral such that zero sequence of fault current for a single phase to ground fault will not exceed the rated line current in pu is ______

To find the resistance that must be placed in the neutral to ensure that the zero sequence fault current does not exceed the rated line current in per unit (pu), we can follow these steps:

1. Calculate the Rated Line Current:

[ I_{rated} = frac{S_{base}}{sqrt{3} times V_{line}} ]

Where:

– ( S_{base} = 10 , text{MVA} = 10,000 , text{kVA} )

– ( V_{line} = 11 , text{kV} = 11,000 , text{V} )

Computing:

[ I_{rated} = frac{10,000 , text{kVA}}{sqrt{3} times 11 , text{kV}} = frac{10,000}{19.052} approx 524.92 , text{A} ]

Convert this to per unit (pu):

[ I_{rated(pu)} = 1.0 , pu ]

2. Zero Sequence Reactance:

Given ( X_0 = 10% ) of the base, or in per unit:

[ X_0 = 0.1 , pu ]

3. Desired Zero Sequence Fault Current:

The maximum desired zero sequence