Electrical Power Systems

18 Electrical Power Systems
Resistance and Inductance of
Transmission Lines
2.1 INTRODUCTION
2
Power system engineering is that branch of Electrical Engineering which concerns itself with
the technology of generation, transmission and distribution of electrical energy. The power
system growing into a vast and complex system represents one of the most vital systems in
every modern nation. The basic purpose of a transmission network is to transfer electric energy
from generating units at various locations to the distribution system which ultimately supplies
the load. Transmission line also interconnect neighbouring power utilities which allows not
only economic dispatch of electrical power within regions during normal conditions, but also
transfer of power between regions during emergencies.
An overhead transmission line consists of a group of conductors running parallel to each
other and carried on supports which provide insulation between the different conductors and
between each conductor and earth. A transmission line has four parameters—resistance,
inductance, capacitance and shunt conductance. The shunt conductance accounts for leakage
currents flowing across insulators and ionized pathways in the air. The leakage currents are
negligible as compared to the current flowing in the transmission lines. The series resistance
causes a real power loss in the conductor. The resistance of the conductor is very important in
transmission efficiency evaluation and economic studies. The power transmission capacity of
the transmission line is mainly governed by the series inductance. The shunt capacitance
causes a charging current to flow in the line and assumes importance for medium and long
transmission lines. These parameters are uniformly distributed throughout but can be lumped
for the purpose of analysis on approximate basis.
2.2 LINE RESISTANCE
The dc resistance of a solid round conductor is given by
R dc = r×l
A
where r = resistivity of conductor
l = length of conductor
A = cross sectional area of conductor
...(2.1)