# Electricity Transmission And Distribution: Electrical Questions

Electricity Transmission And Distribution. Questions and Answers on Electricity Transmission And Distribution. The correct answer is given in every question.

## Electricity Transmission And Distribution

A uniformly-loaded D.C. distributor is fed at both ends with equal voltages. As compared to a similar distributor fed at one end only, the drop at the middle point is ?

A. one-fourth
B. one-third
C. one-half
D. twice

A. one-fourth

Transmitted power remaining the same, if supply voltage of a D.C. 2-wire feeder is increased 100 percent, saving in copper is ?

A. 25 percent
B. 50 percent
C. 75 percent
D. 100 percent

B. 50 percent

There is a greater possibility of occurrence of corona during ?

A. dry weather
B. winter
C. summer heat
D. humid weather

D. humid weather

The spacing between phase conductors of a 220 kV line is approximately equal to ?

A. 2 m
B. 3.5 m
C. 6 m
D. 8.5 m

C. 6 m

The presence of ozone due to corona is harmful because it ?

A. reduces power factor
B. corrodes the material
C. gives odour
D. transfer energy to the ground

B. corrodes the material

As compared to a 2-wire D.C. distributor, a 3-wire distributor with same maximum voltage to earth uses only ?

A. 31.25 percent of copper
B. 33.3 percent of copper
C. 66.7 percent of copper
D. 125 percent of copper

A. 31.25 percent of copper

The operating voltage of supertension cables is up to ?

A. 3.3 kV
B. 6.6 kV
C. 11 kV
D. 33 kV

D. 33 kV

Which of the following is the demerit of a ‘constant voltage transmission system’ ?

A. Increase of short-circuit current of the system
B. Availability of steady voltage at all loads at the line terminals
C. Possibility of better protection for the line due to possible use of higher terminal reactants
D. Improvement of power factor at times of moderate and heavy loads

A. Increase of short-circuit current of the system

The square root of the ratio of line impedance and shunt admittance is called the ?

A. surge impedance of the line
B. conductance of the line
C. regulation of the line
D. none of the above

A. surge impedance of the line

Most of the high transmission lines in Pakistan are ?

A. underground
C. either of the above
D. none of the above

### Electric Transmission MCQs

The phenomenon qf rise in voltage at the receiving end of the open-circuited or lightly loaded line is called the ?

A. Seeback effect
B. Ferranti effect
C. Raman effect
D. none of the above

B. Ferranti effect

310 km line is considered as ?

A. a long line
B. a medium line
C. a short line
D. any of the above

A. a long line

Besides a method of trial and error, which of the following methods is employed for solution of network problems in interconnected system ?

A. Circulating current method
B. Thevenin’s theorem
C. Superposition of currents
D. Direct application of Kirehhoffs laws
E. All of the above

E. All of the above

A booster is a ?

A. series wound generator
B. shunt wound generator
C. synchronous generator
D. none of the above

A. series wound generator

The corona is considerably affected by which of the following ?

A. Size of the conductor
B. Shape of the conductor
C. Surface condition of the conductor
D. All of the above

D. All of the above

Which of the following D.C. distribution system is the simplest and lowest in first cost ?

B. Ring system
C. Inter-connected system
D. None of the above

The usual spans with R.C.C. poles are ?

A. 40—50 meters
B. 60—100 meters
C. 80—100 meters
D. 300—500 meters

C. 80—100 meters

When a conductor carries more current on the surface as compared to core, it is due to ?

A. permeability variation
B. corona
C. skin effect
D. unsymmetrical fault

C. skin effect

The wooden poles well impregnated with creosite oil or any preservative compound have life ?

A. from 2 to 5 years
B. 10 to 15 years
C. 25 to 30 years
D. 60 to 70 years

C. 25 to 30 years

Series capacitors on transmission lines are of little use when the load VAR requirement is ?

A. large
B. small
B. fluctuating
D. any of the above

B. small

Electricity Transmission And Distribution

If variable part of annual cost on account of interest and depreciation on the capital outlay is equal to the annual cost of electrical energy wasted in the conductors, the total annual cost will be minimum and the corresponding size of conductor will be most economical. This statement is known as ?

A. Kelvin’s law
B. Ohm’s law
C. Kirchhoffs law

A. Kelvin’s law

The angular displacement between two interconnected stations is mainly due to ?

A. armature reactance of both alternators
B. reactance of the interconnector
C. synchronous reactance of both the alternators
D. all of the above

A. armature reactance of both alternators

When an alternator connected to the bus-bar is shut down the bus-bar voltage will ?

A. fall
B. rise
C. remain unchanged
D. none of the above

C. remain unchanged

The underground system cannot be operated above ?

A. 440 V
B. 11 kV
C. 33 kV
D. 66 kV

D. 66 kV

When the interconnector between two stations has large reactance ?

A. the transfer of power will take place with voltage fluctuation and noise
B. the transfer of power will take place with least loss
C. the stations will fall out of step be¬cause of large angular displacement between the stations
D. none of the above

C. the stations will fall out of step be¬cause of large angular displacement between the stations

When a live conductor of public electric supply breaks down and touches the earth which of the following will happen ?

A. Current will flow to earth
B. Supply voltage will drop
C. Supply voltage will increase
D. No current will flow in the conductor

A. Current will flow to earth

The current drawn by the line due to corona losses is ?

A. non-sinusoidal
B. sinusoidal
C. triangular
D. square

A. non-sinusoidal

For transmission of power over a distance of 500 km, the transmission voltage should be in the range ?

A. 150 to 220 kV
B. 100 to 120 kV
C. 60 to 100 kV
D. 20 to 50 kV

A. 150 to 220 kV

The effect of corona can be detected by ?

A. presence of ozone detected by odour
B. hissing sound
C. faint luminous glow of bluish colour
D. all of the above

D. all of the above

On which of the following factors skin effect depends ?

A. Frequency of the current
B. Size of the conductor
C. Resistivity of the conductor material
D. All of the above

D. All of the above

Electricity Transmission And Distribution

Constant voltage transmission entails the following disadvantage ?

A. large conductor area is required for same power transmission
B. short-circuit current of the system is increased
C. either of the above
D. none of the above

B. short-circuit current of the system is increased

Corona usually occurs when the electrostatic stress in air around the conductor exceeds ?

A. 6.6 kV (r.m.s. value)/cm
B. 11 kV (r.m.s. value)/cm
C. 22 kV (maximum value)/cm
D. 30 kV (maximum value)/cm

D. 30 kV (maximum value)/cm

For aluminium, as compared to copper, all the following factors have higher values except ?

A. specific volume
B. electrical conductivity
C. co-efficient of linear expansion
D. resistance per unit length for same cross-section

B. electrical conductivity

For which of the following equipment current rating is not necessary ?

A. Circuit breakers
B. Isolators
C. Load break switch
D. Circuit breakers and load break switches

B. Isolators

For transmission of power over a distance of 200 km, the transmission voltage should be _________ kv ?

A. 132 kV
B. 66 kV
C. 33 kV
D. 11 kV

A. 132 kV

Owing to skin effect ?

A. current flows through the half cross-section of the conductor
B. portion of the conductor near the surface carries more current and core of the conductor carries less current
C. portion of the conductor near the surface carries less current and core of the conductor carries more cur¬rent
D. any of the above

B. portion of the conductor near the surface carries more current and core of the conductor carries less current

In AC.S.R. conductors, the insulation between aluminium and steel conductors is ?

A. insulin
B. bitumen
C. varnish
D. no insulation is required

D. no insulation is required

A conductor, due to sag between two supports, takes the form of ?

A. semi-circle
B. triangle
C. ellipse
D. catenary

D. catenary

Which of the following characteristics should the line supports for transmission lines possess ?

A. Low cost
B. High mechanical strength
C. Longer life
D. All of the above