Transmission and Distribution MCQ [Free PDF] – Objective Question Answer for Transmission and Distribution Quiz

Explanation:

The diameter of the ACSR  conductor can be calculated by
D = (2x – 1)xd where
x = number of layer
d = diameter of each strand

Therefore, Total diameter of ACSR conductor
D = (2×2 -1)3
D = 9

Explanation:

• Usually, telecommunication lines and power lines travel close to each other, then the current flowing through power line produces magnetic flux linkage between telecommunication lines so that voltage is induced in the telecommunication line which causes the disturbance in communication.
• To reduce this effect t the conductors are transposed. Transposition can be made either to the power conductors or telephone (communication ) lines at regular intervals.
• When conductors are not transposed at regular intervals, the inductance and capacitance of the conductors will not be equal.
• When conductors such as power lines are run in parallel to transmission lines, there is a possibility of high voltages induced in the lines.  This can result in acoustic shock or noise.

Explanation:

• High voltage transmission lines and substations can cause radio interference.
• Since radio noise is associated with corona, it mainly depends on the potential gradients at the conductors.
• Radio interference due to corona is of the importance for lines above 200 kV.
• In electromagnetic effect, the current flowing in the power line produces magnetic flux linkage with the communication line conductor which induces an emf in the telecommunication line conductor.
• An electrostatic affect the electric field is produced by the charges of the earth induces a voltage in between the conductors of the telecommunication lines.

Answer.2. Decrease inductance

Explanation:

• Total inductance is given as L = 2*10-7 * ln(d/r’)
  A bundle conductor is a conductor made up of two or more sub-conductors and If we use bundled conductors, the effective radius will increase hence increase in radius will decrease the inductance.
• Bundled conductor Primarily used to reduce the potential gradient on the surface of the conductors so that occurrence of Corona can be reduced.
• It helps in obtaining better voltage regulation and efficiency by reducing the inductance and skin effect present in the power lines.

Explanation:

• The skin effect is inversely proportional to the skin depth.

The skin depth is given as
skin depth = 1/√(πfµσ) where
f = frequency
µ = permeability
σ = conductivity

• So by increasing the frequency, the skin depth decreases, and skin effect increases.

Explanation:

Proximity effect

• The alternating magnetic flux produced in the conductor due to the current flowing through the neighboring conductor gives rise to the circulating current which increases the resistance of the conductor. This phenomenon is called the proximity effect.
• The proximity is more in the case of power cable and underground line where the distance between the conductor is small.
• This effect is negligible in the case of overhead transmission lines because the distance between the conductors is large.
• The proximity effect is absent in the case of DC transmission because the frequency of DC transmission is zero.
• The proximity effect depends upon the size of the conductor, spacing between the conductor, frequency and permeability of the conductor material.

Explanation:

Transmission line constant

• Transmission lines are the circuit with the distributed constant such as Resistance, Inductance, Capacitance, Conductance which is distributed along the length of the transmission line.
• These constant are not concentrate at any point. There value expressed as per kilometer length of the line.

Explanation:

• Generally, the length of the short transmission line is less than 80 km, therefore, charging current and leakage current is very less.
• Hence the capacitance and conductance effects are negligible for short transmission lines only.

Explanation:

• In skin effect the eddy current causes the electron to be repelled towards the outermost surface of the conductor.
• Repelling the electron towards the outer surface of the conductor increase the conductor resistance.
• Due to skin effect, the area of the current flowing path is reduced.

Explanation:

The charging current drawn by the cable is capacitive in nature, therefore, it leads the voltage by 90°.