Medium transmission line:- When the length of an overhead transmission line is between 100 km and 250 kin with an operating voltage ranging from 20 kV to 100 kV, it is considered as a medium transmission line.
In medium lines, the series impedance and shunt admittance (pure capacitance) lumped at a few pre-determined locations are considered for calculation. These lines can be analyzed by using load end capacitance, nominal-T, and nominal-π methods.
Short transmission line:- When the length of an overhead transmission line is less than 80 km with an operating voltage upto 20 kV, it is considered a short transmission line. Due to the smaller length and low operating voltage, the charging current is low. So, the effect of capacitance on the performance of short transmission lines is extremely small and therefore, can be neglected.
Long transmission line:- Lengths of more than 250 km are classified as long transmission lines; with an operating voltage of above 100 kV.
Total inductance when inductor are connected in series
L = L1 + L2
L = 4 + 6 =10H
During the no-load condition, the current flowing is only charging current due to line capacitance. It increases the capacitive var in the system. Since the line is under no load the line inductance will be less. Therefore, the capacitive var becomes greater than inductive var during no load or light load condition. Due to this phenomenon, the receiving end voltage becomes greater than the sending end voltage. This effect is also called the Ferranti effect.
In the case of short lines, the effect is negligible, but it increases rapidly with the increase in the length of the line. Therefore, this phenomenon is observable only in medium and long lines. For long high voltage and EHV transmission lines, shunt reactors are provided to absorb a part of the charging current or shunt capacitive VAr of the transmission line under no load or light load conditions, in order to prevent the overvoltage on the line.
By the term, torque is meant the turning or twisting moment of a force about an axis. It is measured by the product of the force and the radius at which this force acts. Consider a pulley of radius r meter acted upon by a circumferential force of F Newton which causes it to rotate at N r.p.m.
The angular speed of the pulley is
ω = 2πN/60 rad/sec
Work is done by this force in one revolution
= Force × distance = F × 2πR Joule
The power developed = Work Done/Time
= (F × 2πR)/60/N
= (F × R) × (2πN)/60
The power developed = T × ω watt or P = T ω Watt
pmech = (ωT)