Deck 2: Electrical Protection and Transmission Line Characteristics

Question 1

When a transmission line is energized, the wave that propagates on it is

A)current wave only
B)voltage wave only
C)both (A) and (B)
D)power factor wave only

Answer 1

both (A) and (B)

Question 2

Protective relays are devices that detect abnormal conditions in electrical circuits by measuring

A)current during abnormal condition
B)voltage during abnormal condition
C)constantly the electrical quantities which differ during normal and abnormal conditions
D)none of the above

Answer 2

constantly the electrical quantities which differ during normal and abnormal conditions

Question 3

The voltage appearing across the contacts after opening of the circuit breaker is called______voltage.

A)recovery
B)surge
C)operating
D)arc

Answer 3

recovery

Question 4

Ionization in circuit breaker is facilitated by

A)high temperature
B)increase of mean free path
C)increasing field strength
D)all of the above

Question 5

In a circuit breaker the basic problem is to

A)maintain the arc
B)extinguish the arc
C)transmit large power
D)emit the ionizing electrons

Question 6

Overheating of relay contacts or contact born out is due to

A)slow making and breaking of load circuit contacts
B)foreign matter on the contact surface
C)too low contact pressure
D)all of the above

Question 7

Interruption of large currents by relay requires

A)arc suppressing blow out coils
B)wide separation of the opened contacts
C)high speed opening of contacts
D)all of the above

Question 8

Shunt capacitance is neglected while considering

A)short transmission line
B)medium transmission line
C)long transmission line
D)medium and long transmission lines

Question 9

The arc voltage produced in A.C. circuit breaker is always

A)in phase with the arc current
B)lagging the arc current by 90?
C)leading the arc current by 90°
D)none of the above

Question 10

The time of closing the cycle, in modern circuit breakers is

A)0.003 sec
B)0.001 sec
C)0.01 sec
D)0.10 sec

Question 11

Insulation resistance of high voltage circuit breakers is more than

A)1 mega ohms
B)10 mega ohms
C)100 mega ohms
D)500 mega ohms

Question 12

H.R.C. fuses provide best protection against

A)overload
B)reverse current
C)open-circuits
D)short-circuits

Question 13

The ground wire should not be smaller than No ______ copper.

A)2
B)4
C)6
D)10

Question 14

The delay fuses are used for the protection of ________.

A)motors
B)power outlet circuits
C)fluorescent lamps
D)light circuits

Question 15

Which of the following is the least expensive protection for overcurrent is low voltage system ?

A)Rewireable fuse
B)Isolator
C)Oil circuit breaker
D)Air break circuit breaker

Question 16

Resistance grounding is used for voltage between

A)33kVto66kV
B)HkVto33kV
C)3.3kVandllkV
D)none of the above

Question 17

The contacts of high voltage switches used in power system are submerged in oil. The main purpose of the oil is to

A)lubricate the contacts
B)insulate the contacts from switch body
C)extinguish the arc
D)all of the above

Question 18

In Railway applications ______ circuit breaker is used.

A)SFe
B)bulk oil
C)minimum oil
D)air break

Question 19

To protect most of the electrical equipment handling low power, the types of relays used are

A)thermocouple
B)electronic and bimetallic
C)both (A) and (B)
D)none of the above

Question 20

Wave trap is used to trap waves of

A)power frequencies
B)higher frequencies entering generator or transformer units
C)either of the above
D)none of the above

Question 21

Ungrounded neutral transmission system is not recommended because of system

A)insulation being overstressed due to over voltages
B)insulation overstress may lead to failure and subsequent phase to phase faults
C)being inadequately protected against ground fault
D)all of the above

Question 22

The reflection co-efficient at the open circuited end of a transmission line.

A)zero
B)infinity
C)unity
D)none of the above

Question 23

For the protection of power station buildings against direct strokes the requirements are

A)interception
B)interception and conduction
C)interception, conduction and dissipation
D)interception, conduction, dissipation and reflection

Question 24

The interaction between a transmission line and communication line is minimized by

A)transposing transmission as well as communication lines
B)increasing the height of the trans-mission line tower
C)increasing the distance between the two lines
D)all of the above

Question 25

When a wave propagates on a transmission line, it suffers reflection several times at

A)tapping
B)load end
C)sending end
D)sending and other end