Title Power Systems K-Notes.pdf ✅

3 Transmission Lines Skin Effect It is tendency of AC current to be concentrated on the surface of conductor. Cause: Non-uniform distribution of magnitude flux linkages Due to skin effect, the effective area of cross section of conductor decrease and hence resistances increases. In case of DC, There is no skin effect so R R DC AC   With increase in frequency, skin effect increases.  With increase in r , skin effect increases. Inductance of a Transmission line  Single Conductor Internal inductance 0 r 8    External inductance from distance ‘ d1 ’ to ‘ d2 ’ 0 r 2 ex 1 d L ln 2 d             Total inductance 0 r 0 r d2 ln 8 2 r               0 r 0 r 1 4 d d ln ln 2 2 r re                         r 0.7788r   = Geometric mean radius (GMR)  Single phase 2 – wire line Inductance of single wire 0 r d ln 2 r            Total inductance = 1 2 L L  0 sys d L ln r             If radius of both wire is not same, assume radius of 1st wire a r & that of second wire is b r b 0 sys a d L ln r r              a a r 0.7788r   & b b r 0.7788r   If instead of a single conductor per phase we use multiple conductor, then GMR is replaced by self GND (Geometric Mean Distance) and ‘d’ by mutual GMD.