Classification of Overhead Transmission Lines
A transmission line has three constants namely Resistance
[R], Inductance [L] and capacitance [C] which are uniformly distributed along
the whole length of the line. The resistance and inductance parameters are
connected in series with the line where as the capacitance is connected between
lines conductors i.e., in case of single phase lines the capacitance is placed
between line conductor and neutral, in case of 3-phase line, it forms like a
shunt path throughout the length of the line. Hence, the capacitance effects
introduce more complications in transmission line calculations.
1. Short Transmission
Line: when the length of the transmission line less
than 80 Km and the voltage is less than 20 kV then this type of transmission
line is called short Transmission Line
Due to smaller length and lower voltage, the capacitance
effects are very small and hence it can be neglected. Therefore, the
performance of transmission line can be studied with resistance and inductance
parameters only
2. Medium Transmission
Lines: when the
length of the transmission lines is lies between 80 – 240 Km and the operating
voltage is lies between 20 – 100 kV then this type of transmission line is
called Medium Transmission Lines.
Due to the sufficient length of the line and voltage, the
capacitance effects are taken in to account. The capacitance may be distributed
along the length of the line [or] lumped at one [or] more points in the line.
3. Long Transmission Lines: When the length of the transmission
line is more than 240 Km and its voltage is greater than 100 kV then this type
of transmission line is called “Long Transmission Lines”.
In order to study the performance the long transmission lines, the transmission line constants [R], L and C are considered to be uniformly distributed over the whole length of line and rigorous methods are employed for solution.
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