MCQs on Power Systems

01․ Bundled conductors are used for EHV transmission lines primarily for reducing the

Corona loss ∝ (V_ph - V_c)² Where, V_ph = Operating voltage of the transmission line V_c = Critical disruptive voltage Therefore, if V_c is more, corona loss will be less. V_c ∝ r Where, r = radius of the conductor Bundled conductors increases effective radius of the conductor and due to this, critical disruptive voltage will increase. Therefore, corona loss decreases by using of bundled conductors.

02․ Which of the following statements is true? Corona loss increases with

Where, f = Supply frequency δ = Air density factor r = Radius of the conductor d = Distance between the conductors V_ph = Operating voltage of the transmission line V_c = Critical disruptive voltage Therefore, Corona loss ∝ supply frequency and Corona loss ∝ (V_ph - V_c)² V_c ∝ r Therefore, corona loss increases with the decrease in conductor size and increase in supply frequency.

03․ The corona loss on a particular system at 50 Hz is 1 kW/km per phase. What is the corona loss at 60 Hz in kW/km per phase?

Where, f = Supply frequency δ = Air density factor r = Radius of the conductor d = Distance between the conductors V_ph = Operating voltage of the transmission line V_c = Critical disruptive voltage Therefore,

04․ A 1- phase transmission line operating at 30 kV has radius of 1 cm and distance between conductors is 0.5 m. Assume m = δ =1, g = 21 kV/cm and frequency f = 50 Hz. Find the critical disruptive voltage?

Where, m = Surface factor δ = Air density factor r = Radius of the conductor d = Distance between the conductors g = Dielectric strength of air

05․ Which of the following statements is/are true? Due to corona,

Corona is the electrical discharge of atmospheric air. If the operating voltage is more than dielectric strength of atmospheric air, air molecules are ionized and start accumulating on the conductor surfaces producing corona. The effects of corona are 1. Interference increases 2. Power loss increases 3. Charging current increases

06․ Critical disruptive voltage is a voltage at which

The voltage at which corona is just initiated is called critical disruptive voltage(Vc). At this critical disruptive voltage, corona is not visible but noise can be heard. Where, m = Surface factor δ = Air density factor r = Radius of the conductor d = Distance between the conductors g = Dielectric strength of air

07․ Which of the following statements is/are true? Corona is reduced by

Where, f = Supply frequency δ = Air density factor r = Radius of the conductor d = Distance between the conductors Vph = Operating voltage of the transmission line Vc = Critical disruptive voltage Therefore, Corona loss ∝ supply frequency and Corona loss ∝ (Vph - Vc)² Vc ∝ r Vc ∝ ln(d) Therefore, corona loss will decrease by 1. Increasing the radius of the conductor 2. Increasing the distance between the conductor 3. Decreasing the supply frequency 4. Increasing the height of the tower 5. Using transposition

08․ Critical visual voltage is the voltage at which

The voltage at which corona is visible with blue or violet colour is called critical visual voltage(Vv). Critical visual voltage Where, m = Surface factor δ = Air density factor r = Radius of the conductor d = Distance between the conductors g = Dielectric strength of air

09․ Which of the following statements is/are true?

Where, f = Supply frequency δ = Air density factor r = Radius of the conductor d = Distance between the conductors Vph = Operating voltage of the transmission line Vc = Critical disruptive voltage Corona loss ∝ (f + 25) Therefore, corona loss is more in HVAC system compared to HVDC system.

10․ If the conductor diameter decreases, inductance of the line,

The inductance of single phase two wire line is Where, d = distance between the conductors r' = 0.7788 r r = radius of the conductor Therefore, If the conductor diameter decreases, inductance of the line increases.