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Z-Bus Building Algorithm

The Zbus of a...

Question

The $Z_{b u s}$ of a system is

$Z_{B U S} = ⎡ ⎢ ⎣ \begin{matrix} 0.1 & 0.1 & 0.1 0.1 & 0.2 & 0.1 0.1 & 0.1 & 0.3 \end{matrix} ⎤ ⎥ ⎦ p . u$

If a 3 phase fault occurs at BUS-2, the p.u. fault current in each phase is -

A

5 \sqrt{3} p u

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B

5 pu

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C

10 pu

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D

10 \sqrt{3} p u

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Solution

The correct option is B 5 pu
5 pu

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Q. For the configuration shown in figure the breaker connecting a large system to bus 2 is initially open. The system 3-phase fault level at bus 3 under this condition is not known. After closing the system breaker, the 3-phase fault level at bus 1 was found to be 5.0 p.u. What will be the new 3-phase fault level at system bus 3 after the interconnection? All per unit values are on common base. Prefault load currents are neglected and prefault voltage are assumed to be 1.0 p.u. at all buses.

E_{g}

X_{T}

X_{L i n e}

X_{d}

The prefault voltage is 1.05 p.u. and prefault load current is neglected. For a bolted three-phase short circuit at bus 1 use

Z_{b u s}

to calculate the contribution to the fault current from the transmission line.

Z_{b u s}

matrix is given as,

Z_{b u s} = + j [\begin{matrix} 0.11565 & 0.04580 0.04580 & 0.13893 \end{matrix}] p . u .

Q. Statement:
For a power system the admittance and impedance matrices for the fault studies are follows.

Y_{b u s} = ⎡ ⎢ ⎣ \begin{matrix} - j 8.75 & j 1.25 & j 2.50 j 1.25 & - j 6.25 & j 2.50 j 2.50 & j 2.50 & - j 5.00 \end{matrix} ⎤ ⎥ ⎦

Z_{b u s} = ⎡ ⎢ ⎣ \begin{matrix} j 0.16 & j 0.08 & j 0.12 j 0.08 & j 0.24 & j 0.16 j 0.12 & j 0.16 & j 0.34 \end{matrix} ⎤ ⎥ ⎦

The pre-fault voltages are 1.0 p.u. at all the buses.
The system was unloaded prior to the fault. A solid 3 phase fault takes place at bus 2.

Q: The post fault voltages at buses 1 and 3 in per unit respectively are

s 1

s 2

= 1 + j0 p.u. +ve sequence impendance are Z

s 1

s 2

= 0.001 + j0.01 p.u and Z

_{L}

= 0.006 + j0.06 p.u, 3-

ϕ

. Base MVA = 100, voltage base = 400 kV(L-L).

Nominal system frequency = 50 Hz. The reference voltage for phase 'a' is deifned as V(t) = V

_{m}

ω

t). the symmetrical 3

ϕ

fault occurs at centre of the line i.e, and point 'F' at the time '

t_{o}

' the +ve sequence impendance from source S

_{1}

to point 'F' equals (0.004 + j0.04) p.u. The wave from corresponding to phase 'a' fault current from bus X reveals that decaying d.c. offset current is -ve and in magnitude at its maximum initial vale. Assuming that the negative sequence are equal to +ve sequence impendance and the zero sequence (Z) are 3 times +ve sequence (Z).

Instead of the three phase fault, if a single line ground fault occurs on phase 'a' at point 'F' with zero fault impendance, then the rms of the component of fault current (I

_{x}

) for phase 'a' will be

Q. The pre-fault voltage are 1.0 p.u. at all buses. The system was unloaded prior to the fault.
A solid 3 phase fault takes place at bus 2.
The post fault voltages at buses 1 and 3 in per unit respectively are

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