GATE Electrical Engineering (EE) 2019 Solved Paper

Question : 52 of 65

Marks: +1, -0

30 {kV}, 50 {Hz}, 50 {MVA}

generator has the positive, negative, and zero sequence reactances of

0.25 {pu}, 0.15 {pu}

, and

0.05 {pu}

, respectively. the neutral of the generator is grounded with a reactance so that the fault current for a bolted LG fault and that of a bolted three-phase fault at the generator terminal are equal. The value of grounding reactance in ohms (round off to one decimal place) is_____________.

Your Answer:

Validate

Solution:

Given data:
A 3-

ϕ

alternator

30 {kV}, 50 {Hz}, 50

MVA has sequence reactance's

X_{1-}=0.25 {pu}, X_{2}=0.15 {pu}, X_{0}=0.05 {pu}

Neutral of alternator grounded with a reactance to make

|I_{f(L G)}|=|I_{f(L L L)}|

\;{3 . {E}_{ {a} 1}}/{ {X}_{1}+ {X}_{2}+ {X}_{0}+3 {X}_{ {n}}}=\;{ {E}_{ {a} 1}}/{ {X}_{1}}

{X}_{1}+ {X}_{2}+ {X}_{0}+3 {X}_{ {n}}=3 {X}_{1}

0.45+3 X_{ {n}}=0.75

X_{n}=0.1 {pu}

{Z}_{\;\text "base "\;}=\;{[ {kV} \;\text " base "\;_{( {LL})}]^{2}}/{ {MVA} \;\text " base "\;_{(3-φ)}}=\;{30^{2}}/{50}=18 Ω

∴ X_{n}(Ω) \;\; =0.1 × 18

\;\; =1.8 Ω

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