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Transmission lines are transposed to reduce the
Voltage imbalance
Short circuit current
Radio interference in communication line
All of the above
All of the above
Transmission line transposition involves interchanging the relative physical positions of the phase conductors at regular intervals along the line. This practice is employed to balance the line parameters (inductance and capacitance), thereby mitigating voltage imbalances, inductive interference with communication circuits, and reducing circulating currents during fault conditions.
Transmission line transposition involves interchanging the relative physical positions of the phase conductors at regular intervals along the line. This practice is employed to balance the line parameters (inductance and capacitance), thereby mitigating voltage imbalances, inductive interference with communication circuits, and reducing circulating currents during fault conditions.
ZeqтАЛ=31тАЛ(Z1тАЛ+Z2тАЛ+Z3тАЛ) тАФ Equivalent balanced impedance for transposed lines
VresidualтАЛтЙИ0 тАФ Sum of phase voltages in a balanced transposed system
In a non-transposed line, the unsymmetrical physical spacing leads to unequal mutual inductances and capacitances between phases. Transposition ensures that over the entire length of the line, each phase conductor occupies each physical position for one-third of the total distance. This symmetry results in balanced phase impedances ZaтАЛ=ZbтАЛ=ZcтАЛ, which suppresses the residual voltage and current components induced in nearby communication lines and improves system stability during unsymmetrical faults.
Transposition is mandatory for lines exceeding 80-100 km.
It equalizes the positive, negative, and zero sequence impedances.
Reduces electromagnetic interference (EMI) with parallel telephone/communication lines.
Ensures the sum of currents тИСI=0 even with asymmetrical conductor spacing.
Balanced line parameters (L and C)
Reduced inductive interference with neighboring lines
Minimization of circulating currents in fault conditions
Increased complexity in tower design and stringing
Higher costs due to the need for special transposition towers
Long-distance Extra High Voltage (EHV) transmission lines
Systems sharing corridors with communication infrastructure
Transposition is typically performed at 1/3 and 2/3 of the total line length.
Option B (Short circuit current) is valid because balancing the impedance minimizes the imbalance contribution to the total fault current magnitude during unsymmetrical faults.
Option C (Radio interference) is reduced because balanced currents produce net magnetic fields that cancel out more effectively at a distance.
D is correct тАФ Transposition balances the line parameters, effectively mitigating voltage imbalance, limiting circulating fault currents, and reducing electromagnetic interference with communication lines.
Always remember that transposition is an application of the principle of symmetry in three-phase power systems to maintain balanced sequence networks.