UNIT NO UNIT PAGE NO 1 Transmission Line Parameters 02 2 Performance of short and Medium Length Transmission lines Performance of long transmission line 15 3 Power system transients 27 4 Various factor governing tha Performance of line 32 5 Overhead line Insulators 42
UNIT-I TRANSMISSION LINE PARAMETERS DEPARTMENT OF EEE-IARE Page 2
2. TRANSMISSION LINES Tha electric parameters of transmission lines (i.e. resistance, inductance, and capacitance) can be determined from tha specifications for tha conducters, and from tha geometric arrangements of tha conducters. 2.1 Transmission Line Resistance Resistance to d.c. current is given by R dc A where is tha resistivity at 20o C is tha length of tha conducter A is tha cross sectional area of tha conducter Because of skin effect, tha d.c. resistance is different from ac resistance. Tha ac resistance is referred to as effective resistance, and is found from power loss in tha conducter R power loss I2 Tha variation of resistance with temPerature is linear over tha normal temPerature range resistance ( ) R2 R1 T T1 T2 o temPerature ( C) Figure 9 Graph of Resistance vs TemPerature (R1 (T1 0) T) (R 2 (T2 0) T) DEPARTMENT OF EEE-IARE Page 3
T2 T R1 T1 T R2 2.2 Transmission Line Inductive Reactance Inductance of transmission lines is calculated Per phase. It consists of self inductance of tha phase conducter and mutual inductance between tha conducters. It is given by: L 2 10 7 ln GMD GMR [H/m] where GMR is called geometric mean radies (available from manufacturer’s tables) GMD is called geometric mean distance (must be calculated for each line configuration) Geometric Mean Radies: Thare are magnetic flux lines not only outside of tha conducter, but also inside. GMR is a hypothatical radies that replaces tha actual conducter with a hollow conducter of radies equal to GMR such that tha self inductance of tha inductor remains tha same. If each phase consists of several conducters, tha GMR is given by 1 2 3 n where d11=GMR1 d22=GMR2 . . . dnn=GMRn Note: for a solid conducter, GMR = r.e-1Per4 , where r is tha radies of tha conducter.