Midterm Flashcards
(42 cards)
A system which is not solidly earthed but is connected to earth through a current limiting impedance.
IT System
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
A power system where neutral of a generator, power transformer or grounding transformer are directly connected to the ground through a conductor of negligible resistance and reactance
Solidly Grounded
Key design elements for static dissipators based on point discharge theory includes (3)
a. Number of dissipator electrodes
b. Radius of the dissipator electrode
c. Dissipator construction material
The most common source of lightning cloud form
Cumulonimbus
It is also called earthing well
Inspection point
The typical duration of a lightning flash is approximately
0.5 seconds
British design of lightning protection system is based on (3)
a. Rolling sphere method
b. Use of natural conductors
c. Protective angle or cone method
The National Electrical Code recommends additional electrode if a resistance to ground greater than
25 ohms
Factors affecting earth resistivity includes except
a. Type of soil
b. Method of measurement
c. moisture content
d. temperature
Method of Measurement
A lightning flash is a constant source of
Current
An installation where an earth terminal is not provided by the electric supply company
TT System
In the British standard, S1 refers to
Strike directly to the structure
Electric shock severity is determined by the following except
a. ambient temperature
b. length of time current flows
c. path of current through body
d. amount of current through body
Ambient Temperature
The minimum recommended thickness of stainless steel sheet considered as part of LPS is
0.50mm
Basic test methods for earth resistance measurements include (3)
a. clamp-on test method
b. Dead earth method
c. Fall-of-potential method
Improving earth resistance include (3)
a. treat the soil
b. use of multiple rods
c. lengthen the earth electrode in the earth
A neutral conductor is usually colored
white
The average peak current for the first impulse of lightning is
18kA
The lightning protection system is required to (3)
a. Intercept the lightning strike
b. Conduct the lightning strike safely to ground
c. Disperse the strike safely in the earth
The permanent joining of metallic parts to form an electrically conductive path that ensures electrical continuity and the capacity to conduct safely any current likely to be imposed
Bonded
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
The cone of protection is determined by
Both height of structure and storm cloud
Most common form of lightning that account for 90% or more of the cloud-to-ground flashes worldwide is
Category 1
