EE Elective Q2 Flashcards
In the British standard, S1 refers to
Strike directly to the structure
A lightning flash is a constant source of
current
The most common source of lightning cloud form is
cumulonimbus
The National Electrical Code recommends additional electrode if a resistance to ground greater than
25 ohms
The typical duration of a lightning flash approximately
0.5 sec
Improving earth resistance includes
Treat the soil,
Use multiple rods, and
Lengthen the earth electrode in the earth
This method of measuring earth resistance is best applied when a simple ground system with existing return path through multiple grounds is present
clamp-on
Methods of designing the air termination network includes
The rolling sphere,
The protective angle design, and
The mesh design
Types of LPS earthing systems includes except
a) Type A
b) Type B
c) Type C
d) Foundation earth electrode
c) Type C
Key design elements for static dissipators based on point discharge theory includes
Radius dissipator electrode,
Number of dissipator electrode, and
Dissipator construction material
The positive leader ground-to-cloud discharge
Category 2
Refers to location where at risk of full lightning strike and the full lightning electromagnetic field
LPZ 0a
The minimum recommended thickness of stainless steel sheet considered as part of LPS is
0.50 mm
The cone of protection is determined by
Both height of structure and storm cloud
The lightning protection system is required to
Conduct the lightning strike safely to ground,
Disperse the strike safely in the earth, and
Intercept the lightning strike
Basic test methods for earth resistance measurements
Clamp-on test method,
Dead earth method, and
Fall-of-Potential method
Factors affecting earth resistivity includes except
a) Type of soil
b) Method of measurement
c) Moisture content
d) Temperature
b) Method of measurement
The average peak current for the first impulse lightning is
18kA
The average peak current for the first impulse lightning is
18kA
British design of lightning protection system is based on
Rolling sphere method
Protective angele or cone method
Use of natural conductors
Most common form of lightning that account for 90% or more of the cloud-to-ground flashes worldwide is
Category 1
Lightning effect can be compared to
capacitor
Are typically three or four high current pulses in a single flash made up of various discharge components
Strokes
A device used on power systems above 1000V to protect other equipment from lightning and switching surges
Lightning Arrester
Devices that divert lightning surges to ground
Lightning Rods
Other devices similar to Lightning Arresters also surge diverter, but generally for voltages well below 1000 volts
Surge Suppressor
TVSS (Transient Voltage Surge Suppressor)
The heart of all arresters
MOV (Metal Oxide Varistor)
A semiconductor that is sensitive to voltage. It is very fast acting electronic switch.
MOV Disk
Meaning of CSST
Corrugated Stainless Steel Tubing
Design of LPS refers to the location where the protected zone inside the building
LPZ 1
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
LPZ 0b
Design of LPS that refers to the location where protected zone with further dampened magnetic field
LPZ 2
This method simply rolls a sphere around the building to be protected.
The rolling sphere
Only used in simple structures or for small sections of larger structures.
The protective angle design
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
The mesh design
A neutral conductor is usually colored
white
A system which is not solidly earthed but is connected to earth through a current limiting impedance
IT System
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
Bonded
An installation where an earth terminal is not provided by the electric supply company
TT system
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
d) ambient temperature
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.
Peterson coil
The path followed by the fault current as the result of low impedance occuring between the phase conductor and earthed metal
earth fault loop
It is called earthing well
inspection point
Color of neutral conductor
Gray
The vast majority of of surge suppressors today use
Metal Oxide Varistor
A device that establishes an electrical connection to the earth
Grounding electrode
Insulation breakdown occurs because of the following except
a) Mechanical
b) Electrical
c) Chemical
d) Thermal
b) Electrical
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
b) Medium front
Color of equipment grounding conductor
Green
The selection of the insulation strength of equipment in relation to the voltages which can appear on the system
Insulation coordination
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
TN-S System
The following are gapped surge arresters type except
a) Valve Arrester
b) Expulsion Arrester
c) ZnO Surge Arrester
d) Spark Gap Arrester
c) ZnO Arrester
Useful life of Metal Oxide Varistors is largely dependent on magnitue of
Current
Level of current through a body that would cause possible suffocation
30 mA
Use to reduce the steepness of wave fronts to protect turn to turn insulation from surges applied to or reflected within machine windings
High Voltage Surge Capacitors
The recommended minimum protective margin for lighting and switching surges in insulation coordination is
1.15 and 1.20
The insulation is unusual, because combined neutral and earth wiring is used in both the supply and within the installation itself
TN-C System
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
d) Temperature of body
Voltage variations can be designated as follows except
a) instantaneous
b) momentary
c) steady
d) temporary
c) steady
Transients can be classified as impulsive and ________
oscillatory
A protection device which reduces the steepness of wave frof a surge
surge absorber
Consist of two 1.5cm rods which are bent at 90 degree angle with a gap in between
Rod gap arresters
A protective device which conducts the high voltage surges on the power system to ground
Surge diverter
Color of neutral conductor in 120/240 V single phase circuit
White
Current to which sensation can be felt
1mA
Maximum length to which grounding is tap to water pipe insude building
10ft
Maximum length of grounding conductor for cable and primary protection
6m
