MCQs on Power Systems


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01․ Proximity effect is more in case of
power cables
over head lines
same in both cases
none 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.

02․ Proximity effect depends on
frequency
distance between the conductors
relative permeability
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 depends on 1. Frequency 2. Conductivity 3. Relative permeability 4. Distance between the conductors

03․ Skin effective is more in case of
communication lines
power lines
same in both cases
none of the above

Skin effect ∝ 1/skin depth Skin effect is inversely proportional to the skin depth. skin depth = 1/√(πfµσ) Where, f = frequency µ = permeability σ = conductivity In case of communication line frequency is higher. So that skin depth is very small and hence skin effect is larger. In case of power lines frequency is small and hence skin depth is larger, so that skin effect can be neglected.

04․ Apart from the skin effect the non uniformity of the current distribution is also caused by
bundled conductors
ferranti effect
proximity effect
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.

05․ Transmission lines are transposed to reduce
ferranti effect
skin effect
proximity effect
interference with neighbouring communication lines

If power line and telecommunication lines are running close to each other, the current flowing in the power line produces magnetic flux linkage with the communication line conductor induces an emf in the telecommunication line conductor.This is called electro magnetic induction. Similarly due to earth effect electric field is produced by the charges of the earth induces a voltage in between the conductors of the telecommunication lines. This is called electro static induction. This both electro magnetic induction and electro static induction produces the voltage between the telecommunication line conductors which causes interference to the telecommunication signals which is called radio interference. To reduce this radio interference in the telecommunication line, either power line or both power and telecommunication lines are transposed at regular intervals of length the transmission line.

06․ In transmission lines distribution constants are
resistance
inductance and capacitance
inductance and resistance
both 1 and 2

Transmission line parameters are 1. Inductance 2. Capacitance 3. Resistance 4. Conductance

07․ Aluminium is now most commonly employed conductor material in transmission lines than copper because
it is more conductive
its tensile strength is more
costlier
it is cheaper and lighter

Aluminium is now most commonly employed conductor material in transmission lines than copper because it is cheaper and lighter. The conductivity of the copper material is more than aluminium. But due to its lighter weight and less cost aluminium is preferred over the copper material.

08․ The skin effect of conductor will increase when
diameter decrease
resistivity decrease
frequency decrease
all of the above

Skin effect ∝ 1/skin depth Skin effect is inversely proportional to the skin depth. But, skin depth = 1/√(πfµσ) Where, f = frequency µ = permeability σ = conductivity Therefore, Skin effect ∝ √(πfµσ) When resistivity decrease, its conductivity will increase. This will increase the skin effect.

09․ ACSR means
Aluminium conductor steel reinforced
Aluminium core steel reinforced
Aluminium copper steel reinforced
all conductor steel reinforced

ACSR means Aluminium Core Steel Reinforced. The inner layer is done by Steel. The outer layer is done by the aluminium. Steel provides the additional mechanical strength.

10․ The inductance of single phase two wire line is given by
4×10-7× ln(d/r') H/m
4×10-7× ln(r'/d) H/m
0.4×10-7× ln(d/r') H/m
0.4×10-7× ln(r'/d) H/m

The inductance of single phase two wire line is

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