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In which of the following transmission lines capacitance effect is negligible?
Long transmission lines
Short transmission line
Medium transmission line
Any of the above
Short transmission line
In a short transmission line (typically defined as having a length less than 80 km or an operating voltage below 20 kV), the shunt capacitance is extremely small and can be neglected for analysis purposes without significant loss of accuracy. The line is modeled solely by its series resistance and inductance.
In a short transmission line (typically defined as having a length less than 80 km or an operating voltage below 20 kV), the shunt capacitance is extremely small and can be neglected for analysis purposes without significant loss of accuracy. The line is modeled solely by its series resistance and inductance.
VsтАЛ=VrтАЛ+IrтАЛ(R+jX) тАФ Voltage drop equation for short transmission line
IsтАЛ=IrтАЛ тАФ Current relationship for short transmission line
The shunt capacitance in a transmission line is proportional to its length. In short lines, the capacitive reactance (XCтАЛ=2╧АfC1тАЛ) is so large compared to the load impedance that the shunt current is negligible. Consequently, the analysis simplifies to a series R-L circuit, whereas medium and long lines require distributed or lumped parameter models that account for shunt capacitive charging currents.
Short lines are defined as length < 80 km or voltage < 20 kV.
Neglecting capacitance simplifies the ABCD parameters where A=1,B=Z,C=0,D=1.
Ferranti effect is absent in short lines because the charging current is insignificant.
Simple mathematical calculations
No complex number iterations required
Not suitable for lines longer than 80 km
Less accurate for high-voltage systems
Distribution lines
Local sub-transmission networks
| Feature | Short Line | Medium Line |
|---|---|---|
Line Length | < 80 km |
|
In medium lines, capacitance is lumped at the middle (Nominal-T) or ends (Nominal-Pi).
In long lines, parameters are treated as uniformly distributed along the length.
B is correct тАФ Due to the short length of the line, the capacitive reactance is high, making the shunt charging current negligible for engineering calculations.
Always remember the classification thresholds (80 km/20 kV) as they define the complexity level of the ABCD parameter matrix required for the problem.