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Midterms > EE Elective Q2 > Flashcards

EE Elective Q2 Flashcards

1
Q

In the British standard, S1 refers to

A

Strike directly to the structure

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2
Q

A lightning flash is a constant source of

A

current

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3
Q

The most common source of lightning cloud form is

A

cumulonimbus

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4
Q

The National Electrical Code recommends additional electrode if a resistance to ground greater than

A

25 ohms

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5
Q

The typical duration of a lightning flash approximately

A

0.5 sec

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6
Q

Improving earth resistance includes

A

Treat the soil,
Use multiple rods, and
Lengthen the earth electrode in the earth

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7
Q

This method of measuring earth resistance is best applied when a simple ground system with existing return path through multiple grounds is present

A

clamp-on

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8
Q

Methods of designing the air termination network includes

A

The rolling sphere,
The protective angle design, and
The mesh design

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9
Q

Types of LPS earthing systems includes except
a) Type A
b) Type B
c) Type C
d) Foundation earth electrode

A

c) Type C

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10
Q

Key design elements for static dissipators based on point discharge theory includes

A

Radius dissipator electrode,
Number of dissipator electrode, and
Dissipator construction material

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11
Q

The positive leader ground-to-cloud discharge

A

Category 2

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12
Q

Refers to location where at risk of full lightning strike and the full lightning electromagnetic field

A

LPZ 0a

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13
Q

The minimum recommended thickness of stainless steel sheet considered as part of LPS is

A

0.50 mm

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14
Q

The cone of protection is determined by

A

Both height of structure and storm cloud

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15
Q

The lightning protection system is required to

A

Conduct the lightning strike safely to ground,
Disperse the strike safely in the earth, and
Intercept the lightning strike

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16
Q

Basic test methods for earth resistance measurements

A

Clamp-on test method,
Dead earth method, and
Fall-of-Potential method

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17
Q

Factors affecting earth resistivity includes except
a) Type of soil
b) Method of measurement
c) Moisture content
d) Temperature

A

b) Method of measurement

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18
Q

The average peak current for the first impulse lightning is

A

18kA

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18
Q

The average peak current for the first impulse lightning is

A

18kA

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19
Q

British design of lightning protection system is based on

A

Rolling sphere method
Protective angele or cone method
Use of natural conductors

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20
Q

Most common form of lightning that account for 90% or more of the cloud-to-ground flashes worldwide is

A

Category 1

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21
Q

Lightning effect can be compared to

A

capacitor

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22
Q

Are typically three or four high current pulses in a single flash made up of various discharge components

A

Strokes

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23
Q

A device used on power systems above 1000V to protect other equipment from lightning and switching surges

A

Lightning Arrester

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24
Q

Devices that divert lightning surges to ground

A

Lightning Rods

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25
Q

Other devices similar to Lightning Arresters also surge diverter, but generally for voltages well below 1000 volts

A

Surge Suppressor
TVSS (Transient Voltage Surge Suppressor)

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26
Q

The heart of all arresters

A

MOV (Metal Oxide Varistor)

27
Q

A semiconductor that is sensitive to voltage. It is very fast acting electronic switch.

A

MOV Disk

28
Q

Meaning of CSST

A

Corrugated Stainless Steel Tubing

29
Q

Design of LPS refers to the location where the protected zone inside the building

A

LPZ 1

30
Q

Design of the LPS refers to the location where not at risk from a direct lightning strike considering the protected area through the rolling sphere but at risk from the full lightning electromagnetic impulse

A

LPZ 0b

31
Q

Design of LPS that refers to the location where protected zone with further dampened magnetic field

A

LPZ 2

32
Q

This method simply rolls a sphere around the building to be protected.

A

The rolling sphere

33
Q

Only used in simple structures or for small sections of larger structures.

A

The protective angle design

34
Q

Most commonly used method in designing the air termination network, is usually employed where the structure is simple, a square or rectangular building or typical house

A

The mesh design

35
Q

A neutral conductor is usually colored

A

white

36
Q

A system which is not solidly earthed but is connected to earth through a current limiting impedance

A

IT System

37
Q

The permanent joining of metallic parts to form an electrically conductive path that ensures electric continuity and the capability to conduct safely any current likely to be imposed

A

Bonded

38
Q

An installation where an earth terminal is not provided by the electric supply company

A

TT system

39
Q

Electric shock severity is determined by the following except
a) amount of current through body
b) path of current through body
c) length of time current flows
d) ambient temperature

A

d) ambient temperature

40
Q

Is an iron core reactor connected between transformer neutral and ground. It is used for limiting the capacitance earth fault current which is flowing when the line ground fault occurs in the line.

A

Peterson coil

41
Q

The path followed by the fault current as the result of low impedance occuring between the phase conductor and earthed metal

A

earth fault loop

42
Q

It is called earthing well

A

inspection point

43
Q

Color of neutral conductor

A

Gray

44
Q

The vast majority of of surge suppressors today use

A

Metal Oxide Varistor

45
Q

A device that establishes an electrical connection to the earth

A

Grounding electrode

46
Q

Insulation breakdown occurs because of the following except

a) Mechanical
b) Electrical
c) Chemical
d) Thermal

A

b) Electrical

47
Q

Transient over voltage is normally classified as one of the following types except
a) Slow front
b) Medium front
c) Fast front
d) Very fast

A

b) Medium front

48
Q

Color of equipment grounding conductor

A

Green

49
Q

The selection of the insulation strength of equipment in relation to the voltages which can appear on the system

A

Insulation coordination

50
Q

This is probably the most usual earthing system in the world, with the Electricity Supply Company providing an earth terminal at the incoming mains position

A

TN-S System

51
Q

The following are gapped surge arresters type except
a) Valve Arrester
b) Expulsion Arrester
c) ZnO Surge Arrester
d) Spark Gap Arrester

A

c) ZnO Arrester

52
Q

Useful life of Metal Oxide Varistors is largely dependent on magnitue of

A

Current

53
Q

Level of current through a body that would cause possible suffocation

A

30 mA

54
Q

Use to reduce the steepness of wave fronts to protect turn to turn insulation from surges applied to or reflected within machine windings

A

High Voltage Surge Capacitors

55
Q

The recommended minimum protective margin for lighting and switching surges in insulation coordination is

A

1.15 and 1.20

56
Q

The insulation is unusual, because combined neutral and earth wiring is used in both the supply and within the installation itself

A

TN-C System

57
Q

Electric shock severity is dependent on except

a) Length of time current flows
b) Path of current through the body
c) Amount of current through body
d) Temperature of body

A

d) Temperature of body

57
Q

Voltage variations can be designated as follows except

a) instantaneous
b) momentary
c) steady
d) temporary

A

c) steady

58
Q

Transients can be classified as impulsive and ________

A

oscillatory

59
Q

A protection device which reduces the steepness of wave frof a surge

A

surge absorber

60
Q

Consist of two 1.5cm rods which are bent at 90 degree angle with a gap in between

A

Rod gap arresters

61
Q

A protective device which conducts the high voltage surges on the power system to ground

A

Surge diverter

62
Q

Color of neutral conductor in 120/240 V single phase circuit

A

White

63
Q

Current to which sensation can be felt

A

1mA

64
Q

Maximum length to which grounding is tap to water pipe insude building

A

10ft

65
Q

Maximum length of grounding conductor for cable and primary protection

A

6m

Midterms (3 decks)

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