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Participant

Join Date: Feb 2017
Posts: 1

# Three-Phase PI Section Line in Matlab

02/07/2017 5:37 AM

Hello, i am having problems determinating corect parameters to Three-Phase PI Section Line in Matlab/Simulink which we can see below. Frequency is 50 Hz and line length is 8 km.

I also know the impedance matrix equation of the line, which is seen below.

So my question is if the calculation procedure below is correct?

Z=R + jX

positive sequence resistance=0,446 Ω/km

zero sequence resistance=1,35 Ω/km

positive sequence inductance=X/(2pi*f)=0,087/(2pi*50)=0,000277 H/km

zero sequence induktance=X/(2pi*f)=1,32/(2pi*50)=0,0042 H/km

positive sequence capacitance=1/(2pi*f*X)=1/(2pi*50*0,087)=0,0366 μF/km

zero sequence capacitance=1/(2pi*f*X)=1/(2pi*50*1,32)=0,00241 μF/km

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Guru

Join Date: Dec 2010
Posts: 1263
#1

### Re: Three-Phase PI Section Line in Matlab

02/07/2017 6:08 PM

Three things :-

The numbers in the picture of Matlab Simulink Line parameters seem to bear little relation to your parameters.

You are using the convention of "," for decimal point - English practice is to use "." & this is what I think Matlab requires.

Strangely, you use numbers .087 and 1.32 for both inductance and capacitance. I do not think your matrix has any capacitance in it.

Your formula and arithmetic are correct, however, I thought Xc = 1/(2*pi*f*C) and Xl = 2*pi*f*L require parameters in Henries and FARADS while you describe capacitance unit as microfarad. The computed values in Farads appear to me to suggest very unrealistic values for shunt capacitance of a line.

I suggest you "double check" the values of capacitance/km for the line. Line capacitance shunt impedances will be [very roughly, depends on line spacing] 100 kohm/km.

Guru

Join Date: May 2007
Location: NYC metropolitan area.
Posts: 3069
#2

### Re: Three-Phase PI Section Line in Matlab

02/08/2017 1:16 PM

No it is not. Since all the reactances are shown are positive then they are defined as inductive, only those that are negative are defined as capacitive. That means that 0.087 is the inductive reactance, if it were capacitive it would be shown as -0.087.

If you have shown us all the information that is available to you then the instructor is forcing you to estimate the capacitive reactance that you then plug into your formula to back calculate the capacitance. Such information is readily available on the web.

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