A 10 MVA, 11 kV alternator 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 ohms is

To determine the resistance that must be placed in the neutral for a single-phase to ground fault such that the zero sequence fault current does not exceed the rated line current of the alternator, we can follow these steps:

1. Calculate the rated line current (I_line) of the alternator using the formula:

[

I_{line} = frac{S}{sqrt{3} times V_{line}}

]

where ( S ) is the apparent power in MVA and ( V_{line} ) is the line voltage in kV.

Given:

– ( S = 10 , text{MVA} )

– ( V_{line} = 11 , text{kV} )

[

I_{line} = frac{10 times 10^6}{sqrt{3} times 11 times 10^3} approx 523.6 , text{A}

]

2. The zero sequence reactance (X0) is given as 10%. We calculate the zero sequence reactance in ohms:

[

X_0 = frac{10}{100} times frac{V_{line}^2}{S}

]

[

X_0 = 0.1 times frac{(11 times 10^3)^2}{10