Effects of high voltage on transmission efficiency

An electric transmission line has four parameters, namely resistance (R), inductance (L), shunt capacitance (C) and shunt conductance (G). The parameters can be modeled as shown in Figure 1.6 below.

Fig. 1.6: Parameters in Transmission Line

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 chargingcurrent to flow in the line and assumes importance of for medium and long transmission lines. These parameters are uniformly distributed throughout but can be lumped for the purpose of analysis on approximate basis. These parameters together with the load current and power factor determine the electrical performance of the line. The term performance includes the calculation of sending end voltage, sending end current, sending end power factor, power loss in line, efficiency of transmission, regulation and limits of power flow during steady state and transient condition.

 The R in this element represents the “conductor loss”, mainly due to temperature, spiraling, frequency and skin effect.  The G in this element represents the “dielectric loss”, (due to loss in the insulator: dirt, salt, moisture, and other contaminants) and due to corona loss (meteorological conditions: particularly rain and conductor surface irregularities).

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