s Objective Questions on Electrical Transmission | 3 | Electrical Study App by SARU TECH

# Objective Questions on Electrical Transmission | 3

1. Peterson coil is used in

Peterson coils is arc suspension coil, is a grounding reactor and used in between neutral pt. and earth in ac power transmission line.

2. Calculate the reactance of Peterson coil suitable for a 33 kV, 3 phase transmission line having capacitance to earth of each conductor as 4.5µF. Assume supply frequency to be 50 Hz?

Supply frequency=50Hz,line to earth capacitance (C)=4.5ÂµF *10-6 F.For Peterson coil grounding ,reactance XL of the Peterson coil should be equal to Xc is line to earth capacitive reactance.Reactance of Peterson coil XL=Xc⁄3=1⁄3ωc=`1⁄3*2Ï€fc=1⁄(3*2Ï€*50*4.5*10-6)=235.8Ω

3. When power cables are laid in proximity of communication cables, what minimum horizontal and vertical clearance there should be for the separation between these 2 cables?

separation between power and communication cables should be 0.6mt. It should not be less than 0.4mt for 1 core cable and 0.3mt for multicore cables.

4. Where bird guard is used ?

BIRD GUARD is used for protection of conductor.It is a stick of ebonite with a rounded top/saw tooth type fixed on crossarm to prevent flashover due to bird’s pecking on the conductor.

5. Where is annealed copper conductor used?

Suggestion: Because of its superior conductivity, annealed copper became the international standard to which all other electrical conductors are compared. In 1913, the International Electrotechnical Commission set the conductivity of copper in its International Annealed Copper Standard (IACS) to 100%. Today, copper conductors used in building wire often exceed the 100% IACS standard

6. Litz wires are used for intermediate frequencies to overcome-

Litz wire reduces the impact of the skin effect and the proximity effect. Litz wire is a type of cable used in electronics to carry alternating current. The wire is designed to reduce the skin effect and proximity effect losses in conductors used at frequencies up to about 1 MHz.

7. For effective use of a counterpoise wire

If the surge impedance will be smaller than the leakage resistance then positive reflection will occur and the potential of the tower will be raised which will result in flash over of the insulator discs and finally a line to ground fault will occur.

8. When bundle conductor are used in place of single conductor the effective inductor and capacitance will respectively

Building increases self GMD-D and hence effective inductor reduces and capacitance increases.

9. A 100 km long transmission line is loaded at 110 kV. If the loss of line is 5 MW and the load is 150 VA the resistance of the line is

Line loss PL = IL2 X R
Line electric current IL = 150 X 10 6 / 110 X 103 = (150/ 110)X 103
PL = IL2 X R
15 X 106 = (150 / 110)2 X 106 X R
R = 8.06 ohm/phase

10. The conductor of a 10 km long single phase, two wire line are separated by a distance of 1.5 m the diameter of each conductor the inductor of the circuit is

inductor of the circuit/Km L = 4 X 10-7ln D / r mH/km
=4 X 10-7ln D / 0.7788 X 5 X 10-3mH/km
= 2.381 mH/Km
Inductance = 2.381 mH/Km X 10 = 23.81 mH

11. ACSR conductor means

ACSR – aluminum conductor steel reinforced.
Generally these conductors are using at overhead transmission lines because of high-capacity, high-strength.

12. The function of steel wire in a ACSR conductor is

The center strands are of steel for the strength required to support the weight without stretching the aluminum due to its ductility. This gives, the conductor an overall high tensile strength.

13. Why ACSR is used in case of transmission lines?

ACSR is aluminum conductor steel reinforced. ACSR has more mechanical strength. Galvanized steel is used in core of the conductor.

14. Which of conductor is used in case of 33 kV transmission line?

for 33 kv transmission line conductors used is Dog. Deer, zebra used for 220KV and moose used for 400 kv transmission line.

15. If length of capacitor is doubled its capacitor is

capacitance /cable is proportional to the length of the cable. So if length is doubled then will also be doubled.

16. A 100km long transmission line is loaded at 110 kV. If the loss of line is 15 MW and the load is 150 MVA, the resistance of the line is

PL=IL2R
Here, IL=(150 X 106)/(110 X 103)=(150/110)X103
∴ 15X106=(150/110)2 X 106 X R
Or, R = 8.06 ohms/phase

17. A 2 wire feeder line runs for 1km it has a total resistance of 1 ohm and 600 v between line at the sending end if it is supplying a load of 100 A at a midway of its length the voltage at the far end of feeder is

Drop in the 0.5ω of midway resistance = 0.5 X 100 = 50
Far end voltage = 600 – 50 = 550 V

18. Conductor configuration determines

Conductor size depends on electric current rating, but not on voltage rating.

19. In high voltage transmission lines the top most conductor is

The top most conductor of overhead transmission is earth conductor. Earth conductors provide a low impedance path for current. In overhead lines, the earth wire is often hung at the top of poles to help provide lightning protection for the phase wires.

20. What materials are used for overhead trolley wire?

Copper Alloys (Cadmium Copper /Silicon Bronze) are used for making trolley wire.Its standard cross section is circular grooved &the standard size has a cross sectional area of 80 mm2.