# Questions & Answers of Models and Performance of Transmission Lines and Cables

## Weightage of Models and Performance of Transmission Lines and Cables

Total 16 Questions have been asked from Models and Performance of Transmission Lines and Cables topic of Power Systems subject in previous GATE papers. Average marks 1.62.

The nominal$-\mathrm\pi$ circuit of a transmission line is shown in the figure.

Impedance $Z=100\angle\;80^\circ\;\Omega$ and reactance $X=3300\;\Omega$. The magnitude of the characteristic impedance of the transmission line, in $\Omega$, is_______________. (Give the answer up to one decimal place.)

Consider an overhead transmission line with 3-phase, 50 Hz balanced system with conductors located at the vertices of an equilateral triangle of length Dab = Dbc = Dca = 1m as shown in figure below. The resistances of the conductors are neglected. The geometric mean radius (GMR) of each conductor is 0.01 m. Neglecting the effect of ground, the magnitude of positive sequence reactance $\Omega/km$ (rounded off three decimal places) is________

A 3-phase, 50 Hz generator supplies power of 3MW at 17.32 kV to a balanced 3-phase inductive load through an overhead line. The per phase line resistance and reactance are 0.25$\Omega$ and 3.925$\Omega$ respectively. If the voltage at the generator terminal is 17.87 kV, the power factor of the load is___________.

A single-phase transmission line has two conductors each of 10 mm radius. These are fixed at a center-to-center distance of 1 m in a horizontal plane. This is now converted to a three-phase transmission line by introducing a third conductor of the same radius. This conductor is fixed at an equal distance D from the two single-phase conductors. The three-phase line is fully transposed. The positive sequence inductance per phase of the three-phase system is to be 5% more than that of the inductance per conductor of the single-phase system. The distance D, in meters, is _______.

At no load condition, a 3-phase, 50 Hz, lossless power transmission line has sending-end and receiving-end voltages of 400 kV and 420 kV respectively. Assuming the velocity of traveling wave to be the velocity of light, the length of the line, in km, is ____________.

A composite conductor consists of three conductors of radius R each. The conductors are arranged as shown below. The geometric mean radius (GMR) (in cm) of the composite conductor is kR. The value of k is ___________.

The horizontally placed conductors of a single phase line operating at 50 Hz are having outside diameter of 1.6 cm, and the spacing between centers of the conductors is 6 m. The permittivity of free space is 8.854×10-12 F/m. The capacitance to ground per kilometer of each line is

In a long transmission line with r,l,g and c are the resistance, inductance, shunt conductance and capacitance per unit length, respectively, the condition for distortionless transmission is

For a fully transposed transmission line

For a 400 km long transmission line, the series impedance is (0.0 + j0.5) Ω/km and the shunt admittance is (0.0 + j5.0) μmho/km. The magnitude of the series impedance (in Ω) of the equivalent π circuit of the transmission line is ________.

A 50 Hz synchronous generator is initially connected to a long lossless transmission line which is open circuited at the receiving end. With the field voltage held constant, the generator is disconnected from the transmission line. Which of the following may be said about the steady state terminal voltage and field current of the generator?

For a fixed value of complex power flow in a transmission line having a sending end voltage V, the real power loss will be proportional to

An extra high voltage transmission line of length 300 km can be approximateD by a lossless line having propagation constant β = 0.00127  radians per km. Then the
percentage ratio of line length to wavelength will be given by

A lossless transmission line having Surge Impedance Loading (SIL) of 2280 MW is provided with a uniformly distributed series capacitive compensation of 30%. Then, SIL of the compensated transmission line will be