MCQs on Power Systems


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01․ If the diameter of the conductor is increased
the inductance is increased
the inductance is decreased
the resistance is increased
no change in inductance and resistance

Resistance R = ρl/a Where, ρ = Resistivity l = Length of the conductor a = area of the conductor If the diameter of the conductor is increased, area will increase and resistance is decreased. If the diameter of the conductor is increased, radius will increase and inductance is decreased.

02․ Due to proximity effect, the increase in conductor resistance is not negligible in
underground cable
overhead transmission lines
communication lines
all of the above

Proximity effect occurs due to current in mutual conductors. The effective area of current flowing path is reduced because of non uniform flux linkage between the two adjacent conductors. Proximity effect is more in case of power cables, because the distance between the conductors is small. This effect is negligible in case of over head transmission lines, because the distance between the conductors is larger.

03․ The fact that current density is higher at the surface when compared to centre is known as
carona
proximity effect
skin effect
all of the above

Accumulation of current on the surface of the conductor is called skin effect. Due to skin effect the area of current flowing path is reduced.

04․ The presence of earth in case of overhead lines
increase inductance
increase capacitance
decrease inducatance
decrease capacitance

Effect of earth on transmission line capacitance: Where, ε = Permittivity d = Distance between the conductor h = Height of the tower Therefore, Capacitance C ∝ 1/h Capacitance is inversely proportional to height of the tower. The effect of earth will increases the value of capacitance.

05․ The term self GMD is used to calculate
capacitance
inductance
resistance
both 1 and 2

The inductance of single phase two wire line is Where, GMD = Mutual Geometric Mean Distance GMR = Self GMD or Geometric Mean radius Therefore, the term self GMD is used to calculate inductance of the transmission line.

06․ Inductance of transmission line will decrease when
both GMD and GMR increase
both GMD and GMR decrease
GMD increase and GMR decrease
GMD decrease and GMR increase

Inductance of two wire transmission line Where, GMD = Mutual Geometric Mean Distance GMR = Self GMD or Geometric Mean radius Therefore, by increasing of GMR and decreasing of GMD, inductance of transmission line will decrease.

07․ If we increase the spacing between the phase conductors, the line capacitance
increases
decreases
remains unaffected
none of the above

Capacitance of a two wire transmission line is Where, d = Space between the conductors r = radius of the conductors Therefore, if we increase the spacing between the phase conductors, the line capacitance will decrease.

08․ If we increase the length of the transmission line, the charging current
increases
decreases
remains unaffected
none of the above

Where, c = capacitance f = frequency l = length of the transmission line Therefore, by increasing the length of transmission line, capacitive reactance will decrease and charging current increases.

09․ In triangular configuration, inductance and capacitance values are ------ and ------ respectively
less, less
higher, higher
less, higher
higher, less

Inductance of a transmission line In triangular configuration distance between the conductors is smaller than horizontal configuration. Therefore, Inductance is less. Capacitance of a transmission line: In triangular configuration distance between the conductors is smaller than horizontal configuration. Therefore, capacitance is higher.

10․ If we increase the spacing between the phase conductors, the value of line inductance
decrease
increase
remains unaffected
none of the above

Inductance of a transmission line Therefore, if we increase the spacing between the phase conductors, the value of line inductance will increase.

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