COMPUTATION OF TRANSMISSION LINES PARAMETERS
AIM
To determine the positive sequence line parameters L and C per phase per kilometre of a
Three phase single and double circuit transmission lines for different conductor
arrangements.
SOFTWARE REQUIRED: MATLAB 7.6
THEORY
Transmission line has four parameters namely resistance, inductance, capacitance and
conductance. The inductance and capacitance are due to the effect of magnetic and electric
fields around the conductor. The resistance of the conductor is best determined from the
manufactures data, the inductances and capacitances can be evaluated using the formula.
FORMULAS:
Inductance:
The general formula:
L = 0.2 ln (Dm / Ds) mH / KM
Where,
Dm = geometric mean distance (GMD)
Ds = geometric mean radius (GMR)
Single phase 2 wire system
GMD = D
GMR = re-1/4 = r' = 0.7788 r
Where, r = radius of conductor
Three phase – symmetrical spacing
GMD = D GMR = re-1/4 = r'
Where, r = radius of conductor &
GMR = re-1/4 = r' = 0.7788 r
Capacitance:
A general formula for evaluating capacitance per phase in micro farad per km of a
transmission line is given by
C = 0.0556/ ln (Deq / r) μF/km
Where,
GMD is the “Geometric mean distance” which is same as that defined for inductance under
various cases.
ALGORITHM:
Step 1: Start the Program
Step 2: Get the input values for distance between the conductors and bundle spacing of
D12, D23 and D13
Step 3: From the formula given calculate GMD
GMD= (D12, D23, D13)1/3
Step 4: Calculate the Value of Impedance and Capacitance of the line
Step 5: End the Program
PROCEDURE:
1. Enter the command window of the
MATLAB.
2. Create a new M – file by selecting File New – M – File
3. Type and save the program in the editor
window.
4. Execute the program by either pressing Tools – Run.
5. View the results
Experiment Statement:
A three phase transposed line has its conductors placed at a distance of 11M, 11 M & 22 M.
The conductors have a diameter of 3.625cm Calculate the inductance and capacitance of the
transposed conductors.
(a) Determine the inductance and capacitance per phase per kilometre of the above three
lines.
(b) Verify the results using the MATLAB program.
PROGRAM:
Output of the program
The inductance per phase per km is 1.377882 mH/ph/km
The capacitance per phase per km is 0.008374 mf/ph/km