# Recent questions and answers in Electric Power Transmission

The main consideration for operating transmission line at high voltage is (a) to increase efficiency only. (b) to reduce power loss only. (c) to increase power transmission capability only. (d) All of the above

Do you think is DC better than AC to transmit energy?

A long transmission line has considerable ……………….. effect. A) series capacitance B) shunt capacitance C) series inductance D) shunt inductance

A single-line-to-ground fault on a overhead transmission line creates (A) voltage sag (B) voltage swell (C) over voltage (D) voltage flicker

For a transmission line open circuit and short circuit impedances are 20 Ω and 5 Ω. Then characteristic impedance is: (1) 100 Ω (2) 50 Ω (3) 25 Ω (4) 10 Ω

A 10 km long line has a characteristic impedance of 400 ohms. If line length is 100 km, the characteristic impedance is: (1) 4000 Ω (2) 400 Ω (3) 40 Ω (4) 4 Ω

A cable has inductance of 0.22 mH per kilometer and capacitance of 0.202 µF per kilometer. The surge impedance of the cable is (a) 50 Ω (b) 42 Ω (c) 33 Ω (d) 28 Ω

In an AC transmission line difference in phase of voltage at two ends of the line is due to (a) System voltage (b) Insulators (c) Resistance of line (d) Reactance of line

If 5000 kW power is transmitted at 220 kV in place of 11 kV, reduction in the value of electric current will be (a) 90% (b) 95% (c) 5% (d) 10%

In long AC transmission lines, the receiving end voltage becomes greater than sending end voltage at light load or no load operation. This is due to (a) Ferranti effect (b) Skin effect (c) Proximity effect (d) Corona effect

For extra high voltage ac transmission lines, conductors used are (a) All aluminium (b) All steel (c) AAAC (d) ACSR

Which of the following relations is true for long transmission line ? (a) VS = AVR – BIR (b) VS = BVR + AIR (c) VS = AVR + BIR (d) VS = BVR – AIR

Which of the following is used for power factor improvement in transmission line ? (a) Three phase induction (b) An overexcited three phase synchronous motor running on no load (c) Three phase AC series motor (d) Choke

The connected load of a consumer is 2 kW and his maximum demand is 1.5 kW. The load factor of the consumer is (a) 0.375 (b) 0.75 (c) 1.33 (d) None of these

If diameter of each conductor of a transmission line is ‘d’, then the diameter of n-layer stranded conductor will be (a) (2n – 1) d (b) (2n + 1) d (c) (3n – 1) d (d) (3n + 1) d

The bundled conductor in EHV transmission line system provides (a) increased inductance (b) reduced capacitance (c) increased capacitance (d) increased voltage gradient

The power loss in a transmission line depends on (a) current in the line. (b) resistance of the line. (c) length of the line. (d) All of the above

The presence of earth in case of overhead transmission line (a) increases capacitance (b) increases inductance (c) decreases capacitance (d) decreases inductance

Effect of increase in temperature in an overhead transmission line is (a) to increase stress and length both (b) to decrease stress and length both (c) to decrease stress and increase length (d) None of the above

A transmission line to be reciprocal, the condition is (a) A = D (b) AC – BD = 1 (c) AD – BC = 1 (d) AB – CD = 1

Shielding angle of an EHV line is about (a) 20° (b) 50° (c) 70° (d) 90°

An overhead transmission line has a span of 260 m. The weight of the conductor is 0.68 kg/m. The maximum allowable tension in the line is 1550 kg. Maximum sag of the line should be (a) 5.8 m (b) 4.6 m (c) 2.7 m (d) 3.7 m

The input impedance of a short circuited loss less transmission line of characteristic impedance 50 Ohm is

Corona loss is less when the shape of conductor is:

What type of insulator will be used if the direction of the transmission line is to be changed?

Why are shunt reactors connected at the receiving end of long transmission line system: (1) To increase the terminal voltage (2) To compensate voltage rise caused by capacitive charging at light load (3) To improve power factor (4) None of these

In case of a ‘High Voltage DC’ transmission, how many minimum conductors are required?

Earth wire on EHV overhead transmission line is provided to protect the line against:

Consider the following statements: Over head transmission lines are provided with earth wires: 1 . To protect the transmission line from direct lightning strike 2. To protect the transmission line insulation from the indirect lightning strike 3. To balance the line currents 4. To provide path for neutral current Which of these statement/s is/are correct? (1) 1 and 3 (2) 1 and 4 (3) 1 only (4) 2 on|y

To increase power transfer capability of a long transmission line, we should:  (1) Increase line resistance (2) Increase transmission voltage (3) Decrease line reactance (4) Both (2) & (3)

Transmission of power by a.c. cables is impossible beyond   (a) 500 km (b) 300 km (c) 250 km (d) 45 km

The inductance of single phase two wire power transmission line per km gets doubled when the  (a) Distance between wires is doubled  (b) Distance between the wires is increased four fold  (c) Distance between the wires is increased as square of the original distance  (d) Radius of the wire is doubled

Galloping in transmission line conductors arises generally due to - (A) asymmetrical layer of ice formation (B) vortex phenomenon in light winds (C) heavy weight of line conductors (D) adoption of horizontal conductor

The inductance of a power transmission line increases with (A) decrease in line length. (B) increase in conductor diameter. (C) increase in spacing between phase conductors. (D) increase in load current carried by conductors.

In which of the following transmission lines, the value of the Shunt admittance should be approximated to zero ? (A) A 66 kV 35 km long line (B) A 132 kV 200 km long line (C) A 220 kV 300 km long line (D) A 400 kV 500 km long line

The electric breakdown strength of insulating materials depends on  (A) Nature of applied voltage (B) lmperfection of dielectric material (C) Pressure, temperature and humidity (D) All or these

A 40 kVA transformer has a core loss of 400 W and a full load copper loss of 800 W. The proportion of full load at maximum efficiency is

The number of insulator discs (each rated 11 kV) required in a suspension type insulator string of 220 kV line is

A 3 layer, total diameter of an ACSR conductor is 5 cm. Find the diameter of each strand?

If the insulation resistance of a cable of length 10 km is 1 mega ohm, its insulation resistance for 50 km length will be

Stability of a transmission line can be increased by

The function of steel wire in ACSR conductors is (A) To take care of surges. (B) To reduce corona. (C) To reduce inductance. (D) To provide additional mechanical strength

In a transmission line if booster transformers are to be used, preferred location will be  (A) At the receiving end (B) At the sending end (C) At the intermediate point (D) Anywhere in the line

For 11kV line the inductance per km per phase will be of the order of:  (A) 1 H (B) 0.1 H (C) 1 mH (D) 0.1 mH

For 11 kV line the capacitance per km per phase will be of the order of:  (A) 1 Farad (B) 0.1 Farad (C) 0.01 Farad (D) 0.01 microF

In case the height of transmission tower is increased, which of the following parameter is likely to change?  (A) Resistance (B) Inductance (C) Capacitance (D) None of the above