Power System Flashcards by Evelyn Yap

Which of the following type of fault that used only the equivalent positive impedance of the
circuit in the short-circuit calculation?

A. Line-to-line fault
C. Three-phase fault
B. Double-line-to-ground fault
D. Single-line-to-ground fault

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Causes of faults in power system

A. lightning and tree falling on line
B. storm, wind and jumping conductors
C. switching
D. all of these

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The top most conductor in a high transmission line is

A. earth conductor
B. R-phase conductor
C. Y-phase conductor
D. B-phase conductor

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The hazards exists only during the period of the time the _____ is there

A.short-circuit
B. lighting
C. switching
D. fault

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By which of the following methods the protection against direct lightning strokes and high voltage steep waves is provided?

A. Lightning arresters
B. Ground wire
C. Lightning arresters and ground wires
D. Earthing of neutral

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By which of the following methods voltage of transmission can be regulated?

A. Use of series capacitors to neutralize the effect of series reactance
B.Switching in shunt capacitors at the receiving end during heavy loads
C. Use of tap changing transformers
D. Any of the above methods

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The strain type insulators used when

A. the transmission line is dead ended
B. the direction of transmission line changes
C. the transimission line is short
D. A or B

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Which of the following insulator will be selected for high voltage application?

A. strain type
B. disc type
C. pin type
D. suspension type

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The effect of wind pressure is more predominant on
A. neutral wires
B. supporting towers
C. insulators
D. transmission lines

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Guy wire is used in the construction of distribution lines for what purpose?

A. Providing emergency Grounding
B. Support the conductor
C. Protection against surges
D. Support the pole

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Three phase short circuit of an alterator will be

A. very small
B. infinity
C. zero
D. maximum

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What can usually be assumed as the driving or source voltage for fault and voltage calculations in per unit method?

A. 1 pu
B. 10 p.u.
C. 3 p.u
D 5pu.

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ACSR means

A. Aluminum Conductor Steel Reinforced
B. Aluminum Cable Steel Reinforced
C. Aluminum Conductor Steel Ring
D. None of the above

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In ACSR conductor, the function of steel is to

A. provide additional mechanical strength
B. prevent corona
C. take care of surges
D.reduce inductance and subsequently improve power factor

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The skin effect in conductors is due to non-uniform distribution of current in it and major
portion of the current is near the ____ of the conductor.

A surface
B. center
C. axis
D. radial lines

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The effective resistance of conductor is increased by

A. skin effect
B. corona effect
C. proximity effect
D. both A and B

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

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

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If the specific resistance of the conductor is increased, what effect does it result on the skin effect?

A. remain same
B. increasing
C. decreasing
D. none of the above

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If the transmission voltage is increased, the percentage resistance drop will

A. remain unchanged
B. increase
C. none of the above
D. decrease

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The power transmission capacity of the transmission line is

A. proportional to the square of the voltage
B. directly proportional to the voltage
C. inversely proportional to the voltage
D. proportional to the cube of the voltage

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For constant transmission efficiency, voltage is increased n times, the size of the conductor
would be.

A. reduced to (1/n?) times of the original
B. increased to n? times of the original
C. reduced to (1/n) times of the original
D. increased to n times of the original

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To increase transmitted power over the line,

A. increase its capacitance
B. increase its line voltage
C. decrease its line inductance
D. any of these

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The transmission line inductance contributed by

the current in other conductor

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In practice, the three phase conductor of a thrèe phase line are seldom equilaterally. The
usual unsymmetrical spacing produces unequal inductance in the three phases, leading to unequal voltage drop and unbalance in the line. To effect this imbalance the positions of the conductor are interchanged at regular intervals in the line. This practice is known as
I transposition
II. Interchange

A. Either I or Il
B. Il
C. Both I or Il
D. I

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When the conductor of a three-phase circuit are not spaced equilaterally, the transposition is done to. A decrease the line inductance per phase B. minimize the effect of adjoining communication circuit C. balance the three phases of the circuit D. both A and B

The conductor are bundled primarily to

reduce reactance

To increase the capacity of a transmission line for transmitting power, which of the following must be decreased? A. Capacitance B Line inductance C. Voltage D. All of the above

The presence of earth alters the

electric field of the line capacitance of the line

If the height of transmission tower is increased A. the line capacitance will decrease but line inductance will remain unchanged B. the line capacitance and inductance will not change C. the line capacitance will increase but line inductance will decrease D. the line capacitance will decrease but line inductance will increase

If the height of transmission tower is increased, which of the following parameters is likely to change? A Capacitance C Resistance B. Inductance D. all of the above

In the analysis of which the following lines shunt capacitance is neglected? A. short transmission lines C. long transmission lines B. medium transmission lines D. medium as well as long TL

When the load at the receiving end of a long transmission line is removed, the sending end voltage is less than the receiving end voltage. This effect is known as A. Ferranti effect B. Proximity effect C. Kelvin effect D. Faraday effect

Shunt conductance in power transmission lines is due to leakage over the

insulators

The surge impedance of a transmission line differs from its characteristics impedance, as surge impedance consider line A. resistance of finite value B. capacitance to be zero C. inductance to be zero D. both C and B

In the design of a distributor, which of the following is the major consideration? A. Frequency B. Voltage drop C. kVA of system D. Current carrying capacity

The effect of corona can be detected by A. presence otozone detected by odour B. faint luminous glow of bluish colour C. hissing sound D. all of the above

The square root of the ratio of line impedance and shunt admittance is called A. surge impedance of the line B. regulation of the line C. conductance of the line D none of the above

The rise of temperature in transmission line A. increase the stress and the length B. decrease the stress and increase the length C. decrease the stress and the length D. increase the stress and decrease the length

most dangerous short circuits

dead-short circuits

Equipment used to limit short-circuit current level in substation

Series reactor

The interrupting current capacity of a circuit breaker depends on

symmetrical short ckt current

The protection against over-voltage due to lightning is provided by A. use of surge diverter C. low tower footing resistance B. use of overhead ground wires D. any of the above

An automatic device that operates at preset values is known as A. mercury switch C. relay B. fuse D. contactor

Which of the following protective device operates on the principle of Kirchoff's Current Law? A Instantaneous Overcurrent Relay C. Differential Protective Relay B. Undercurrent Relay D AC Time Overcurrent Relay

What is the IEEE standard device number for Distance Relay? A. 67 B. 59 C. 86 D. 21

D. 21 67 —- Ac directional 59 — - Over voltage 86 — - lockout

Overhead transmission lines generally use A. ACSR conductors B. all aluminum conductors C. copper conductor D. Steel conductor

On which of the following factors skin effect depends? A. frequency of the current B. resistivity of the conductor C. size of the conductor D all of the above

Which of the following materials is not used for transmission and distribution of electrical power? A. Copper B. Aluminum C. Steel D. Tungsten

Name the effect which resulted because of the size of conductor, frequency and the specific resistance of the conducting material. A. Corona effect B. Proximity effect C. Skin effect D. Thomson effect

In both skin effect and proximity effect A. the effective internal reactance of the conductor gets decreased B. their effect depends upon conductor size d, frequency f, resistivity p, and permeability Up C. the effect is negligible at power frequency and small conductors, but the effect is large for higher frequency and big conductors D. all of these

Basic function of a circuit breaker is to

extinguish the arc

A relay that can detect overload in the line

overcurrent relay

For which of the following equipment current rating is not necessary? A. circuit breakers C. isolators B. load break switch D. circuit breakers and load switches

A circuit is disconnected by isolators when A. line is energized B. line is on full load C. there is no current in the ine D. circuit breaker is not open

Earthing is necessary to give protection against A. danger of electric shock B. overloading C. voltage fuctuation D. none of the above

A device which monitor and operates when certain level has been reached. A. monitor C. relay B. Oscilloscope D. transformer

It is a protective relay which compares the sum of incoming currents against the sum of the outgoing currents. It operates when there is unbalance A. Relay balance C. Differential relay B. Current relay D. Over current relay

IEEE standard device number for ckt breaker

Computerized data gathering, monitoring and switching equipment

SCADA

Material generally used for armour of high voltage cables

steel

lowest cost bus bar schemes

single-bus bar scheme double bus—— most expensive

In Transmission lines the cross arms are made of

steel

Transmission line insulators are made of

porcelain

In transmission lines, the most effective protection against lightning strikes is one of the following. Which one is this? A. Lightning rods B. Petersen coils C. Lightning arresters D. Overhead wires