3.17. Calculate the phase-neutral capacitance per meter of the 345-kV line descr

Question

3.17. Calculate the phase-neutral capacitance per meter of the 345-kV line described in Section 3.10 TABLE 3.1 LINE DATA m?irt,e,t ; Line voltage (kV) 138 345 765 Conductors per phase (18-in. spacing) Number of strands aluminum/steel Diameter (in.) Conductor GMR (ft) Current-carrying capacity per conductor (A)770 Bundle GMR-R, (ft) Flat phase spacing (ft) GMD phase spacing (ft) Inductance (H/m × 10-7) XL (/mi) Capacitance (F/m x 10-12) ix-I (MQ-mi to neutral) Resistance (/mi), dc, 50°C Resistance (/m), 60 Hz, 50 Surge impedance loading (MVA) 547 0.977 1.165 0.0329 0.0386 0.0479 54/19 1.424 45 10101250 26.0 9.83 0.03290.2406 0.6916 17.5 22.05 32.76 56.70 13.02 0.789 8.84115912.78 0.186 0.16180.0539 0.0190 0.16880.0564 0.0201 45.0 8.81 0.596 0.535 0.142 0.129 50 415 2268

Explanation / Answer

3.17.solution

The general form (Fig-D) of capacitance between one phase and neutral for a three phase line is

Cn = 2pk / ln (GMD/GMR)

Cn=2pk/in(32.76/0.2406)

Cn=2pk/in(136.15)

Cn=2pk/4.91

GMD is Geometric Mean Distance and GMR is Geometric Mean Radius of the particular

configuration. GMR used for calculation of capacitance is slightly different from GMR used for
  inductance It is also assumed that the phase lines are transposed

So the line to neutral capacitance Cn is two times C.

Cn = 2pk / ln (D/r)

   Cn = 2pk /in(1.165/r)

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