AC Fault Location

Two single-phase AC voltage sources supply a faulted transmission line. The fault resistance R F R_F divides the line into two impedances: m Z L m Z_L on the left, and ( 1 m ) Z L (1-m) Z_L on the right, where 0 < m < 1 0 < m < 1 . Source voltages V S V_S and V R V_R are known, as well as source currents I S I_S and I R I_R . Real-valued quantities m m and R F R_F are unknown.

Determine the value of m m .

Details and Assumptions:
1) V S = 9 + j 5 V_S = 9 + j 5
2) V R = 10 + j 0 V_R = 10 + j 0
3) Z L = 0 + j 10 Z_L = 0 + j 10
4) I S = 1.46647424295 + j 0.0552747566158 I_S = 1.46647424295 + j 0.0552747566158
5) I R = 0.0676118569678 j 0.126267206432 I_R = 0.0676118569678 - j 0.126267206432
6) j = 1 j = \sqrt{-1}


The answer is 0.37.

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2 solutions

Karan Chatrath
Jan 26, 2021

Applying Kirchhoff's laws for this circuit leads to the equations cast into a matrix form as such:

[ Z L I S I S + I R Z L I R I S + I R ] [ m R F ] = [ V S V R I R Z L ] \left[\begin{matrix} Z_LI_S&I_S+I_R\\-Z_LI_R&I_S+I_R\end{matrix}\right] \left[\begin{matrix} m\\R_F\end{matrix}\right] =\left[\begin{matrix} V_S\\V_R-I_RZ_L\end{matrix}\right] m = [ 1 0 ] [ Z L I S I S + I R Z L I R I S + I R ] 1 [ V S V R I R Z L ] = 0.37 \implies m = \left[\begin{matrix} 1&0\end{matrix}\right]\left[\begin{matrix} Z_LI_S&I_S+I_R\\-Z_LI_R&I_S+I_R\end{matrix}\right] ^{-1}\left[\begin{matrix} V_S\\V_R-I_RZ_L\end{matrix}\right] =\boxed{0.37} R F = [ 0 1 ] [ Z L I S I S + I R Z L I R I S + I R ] 1 [ V S V R I R Z L ] = 6 \implies R_F = \left[\begin{matrix} 0&1\end{matrix}\right]\left[\begin{matrix} Z_LI_S&I_S+I_R\\-Z_LI_R&I_S+I_R\end{matrix}\right] ^{-1}\left[\begin{matrix} V_S\\V_R-I_RZ_L\end{matrix}\right] =6

From a mathematical point of view, this circuit is easy to solve, but I do not quite grasp the intuition behind a 'fault'. Some explanation of that would be helpful.

A fault is an unintended short circuit

Steven Chase - 4 months, 2 weeks ago
Steven Chase
Jan 27, 2021

To make this one easy to understand, I will write out the equations, which can then be put into matrix form. The first equates two expression for the voltage at the fault point. The second makes a loop from the left side through the fault resistance.

V S m Z L I S = V R ( 1 m ) Z L I R V S m Z L I S R F ( I S + I R ) = 0 V_S - m Z_L I_S = V_R - (1-m) Z_L I_R \\ V_S - m Z_L I_S - R_F (I_S + I_R) = 0

Solve these two equations for m m and R F R_F

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If yes ,how to do it?
If no,how police and military officers can do that ,I have seen in films.
Thanks in advance.


Talulah Riley - 4 months, 1 week ago

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