CameraIcon

SearchIcon

MyQuestionIcon

2

You visited us 2 times! Enjoying our articles? Unlock Full Access!

Direct Current vs. Alternating Current

A 10 MVA, 13....

Question

A 10 MVA, 13.8 kV alternator has positive, negative and zero sequence reactances of 30%, 40% and 5% respectively. The value of resistance that must be placed in the generator neutral so that the fault current for a LG fault of zero fault impedance will not exceed the rated line current is ________ $Ω$ .
18.43

Open in App

Solution

The correct option is A 18.43
Let base MVA be 10 MVA,

base kV = 13.8 kV

$E_{a} = (1 + j 0) p . u$

$Z_{B} = \frac{(13.8)^{2}}{10} = 19.044 Ω$

$I_{f} = \frac{3 E_{a}}{Z_{1} + Z_{2} + Z_{0} + 3 (Z_{n} + Z_{f})} = \frac{3 \times 1}{j (0.3 + 0.4 + 0.05) + 3 R_{n}} = 1$

$\Rightarrow \frac{3}{\sqrt{(0.75)^{2} + (3 R_{n}})^{2}} = 1$

$R_{n} = 0.9682 p . u$

$R_{n} = 18.439 Ω$

Suggest Corrections

thumbs-up

5

Similar questions

Q. A 10 MVA, 13.8 kV alternator has positive, negative and zero sequence reactances of 30%, 30% and 10% respectively. The value of reactance (in per unit) that should be placed in generator's neutral so that the fault current for a line to ground fault (with zero fault impedance) will not exceed the rated line current is ____ (Asuming system to unloaded prior to fault).

Q. A 30 MVA, 3-phase, 50 Hz, 13.8 kV, star-connected synchronous generator has positive, negative and zero sequence reactances, 15%, 15% and 5% respectively. A reactance (X

_{n}

) is connected between the neutral of the generator and ground. A double line to ground fault takes place involving phase 'b' and 'c' with a fault impendance of j0.1 p.u.. The value of x

_{n}

(in p.u.) that will limit the positive sequence generator current to 4270 A is

Q. The positive, negative and zero sequence impedance of 3-

ϕ

generator are 0.4 pu, 0.3 and 0.2 pu respectively. For a line to line fault with fault impedance

Z_{f}

and fault current is

I_{f 1} = 0.2 I_{f}

I_{f}

is the fault current with zero fault impedance, then value of

Z_{f}

will be ______pu.

Q. A synchronous generator is rated 25 MVA, 11 kV. It is star connected with neutral point solidly grounded. The generator is operating at no-load rated voltage. Positive, negative and zero sequence reactance are 0.2 p.u., 0.2 p.u. and 0.08 p.u. respectively. A line to line fault occurs on b and c phase of generator. Then the magnitude of fault current will be

Q. Three 6.6 kV, 3-

ϕ

, 10 MVA alternators are connected to a common bus. Each alternator has a positive negative and zero sequence reactances as 0.15 p.u., 0.1 p.u.,0.05 p.u. respectively. A single line to ground fault occurs at point F, as shown in figure below.

I_{f}

is the fault current when all the alternator neutrals solidy grouned

I_{f}^{'}

is the fault current when only one neutral is solidly grounded and other two neutrals are isolated. Then the value of

| I_{f} - I_{f}^{'} | =

View More

Join BYJU'S Learning Program

similar_icon

Related Videos

lock

Direct Current Vs Alternating Current

PHYSICS

Watch in App

explore_more_icon

Explore more

Direct Current vs. Alternating Current

Standard IX Physics

Join BYJU'S Learning Program

CrossIcon