Bangladesh Major Problem

1. A presentation to ITS&S about
Lightning and Grounding

2. Lightning Protection

3. Generation of Lightning
• Thunderstorms
• Cold front - air aloft sinks
• Warm air at ground rises
• Vertical air flow, up and down
• Friction between water droplets
• Droplets become charged
• Charges separate within cloud
• High voltages develop
• Within, cloud to cloud
• Cloud to Earth
• Air breakdown occurs
• LIGHTING DISCHARGE

4. Some Facts
• Average duration 50 microseconds
• Average speed of Lightning stroke 20,000 mph
• Average Temperature 30,000 degrees C
• Average Length 3 km
• Average Energy 300,000,000 joules
• Average Power 10,000,000,000,000 watts (10 terawatts)
• Average number of strokes per flash, 4
• 200 thunderstorms in progress world wide any time
• 100 flashes per second worldwide any time
• Astraphobia – fear of thunder and lightning

5. Forms of Lightning
• Cloud to Ground – our major concern !
– Cloud discharge to ground
• Within a cloud
– Discharge in a cloud
• Cloud to cloud
– Discharge between clouds
• Heat lightning
– Intracloud, far away
– Thunder not audible
• Sheet Lightning
– Intracloud, diffuse
• Cloud to air
– Bolt-from-the-blue

6. Strikes vs Tower Height
• Lower Mainland @ 5 thunderstorm days per year = low risk
• Until you get hit of course

7. Thunder
• Sound of the explosion along the superheated lightning channel
– 30,0000 degrees
• Superheated air, gas pressures 10 to 100 atmospheres
• Shockwave is what we hear
• Rumblings are primarily due to the various distances between
observer and tortuous path of the lightning discharge
• Speed of sound is ~ 1000 ft per second
– count the seconds between the flash and the onset of thunder to determine your
distance to strike; seconds = thousands of feet

8. Strike Current Waveform
• Example for a Typical Strike
– Rise Time ~ 5 seconds
– Crest ~ 25 kA
– Fall time ~ 50 seconds to half of crest value

9. Lightning Parameters
Parameter
Percentage of Strokes EXCEEDING Value indicated
90% 50% 10% Max Observed
Crest (peak) Current 2 to 8 kA 10 to 25 kA 40 to 60kA 230 kA
Rate of Rise to Crest 2 kA/us 8 kA/us 25 kA/us 50 kA/us
Time to Crest 0.3 to 2 us 1 to 4 us 5 to 7 us 10 us
Duration of Single Stroke 0.1 to 0.6 ms 0.5 to 3 ms 20 to 100 ms 400 ms
Time between Strokes 5 to 10 ms 30 to 40 ms 80 to 130 ms 500 ms
Total Stroke Duration 0.01 to 0.1 s 0.1 to 0.3 s 0.5 to 0.7 s 1.5 s

10. Current Distribution
• Percentage exceeding a given current
• 50 % will exceed 10,000 amps

11. Strike Current Spectrum
• Most Energy concentrated DC to 1 kHz.
• Destructive energy
range < 1 kHz
• Not energy > 1MHz
that destroys radio
installations
• It will sound loud
on radio though!

12. Primary Protection
• Cloud to Ground discharges of concern to us
• Need to direct the lightning current to earth as directly as
possible
• Protection of Life and Property
– Fire Protection
– Shock Protection
– Equipment Protection

13. Ground
• Cloud to Ground Strike current seeks earth ground
– the strike point
– directly to surface or via tree, tower, antenna etc.
• Current flows outwards from strike point through earth
• Earth ground is not a good conductor
• Thousands of amperes flow through ohms of resistance
• Thousands of volts per foot exist outwards from strike point

14. A Simple Calculation
• Strike current = 20,000 A
– for 10 usec
• Voltage along feedline = 2000 V
– bye bye coax
• Voltage across ground rod = 200 V
– 4 MW for 10 usec
• Voltage at top of ground rod = 200,000 V
– Side flashing may occur
• This is called GROUND RISE
• This 200 kV will diminish exponentially with
distance from the ground point
• Voltage gradient immediate vicinity is dangerous
– See cow >
0.1 ohms
0.01 ohms
10 -100 ohms Earth
Rod
Feed line
& Tower
ANTENNA

15. Station Grounds
• Multiple grounds exist out of necessity
• Electrical - AC Power “green wire” power
safety
• Lightning - Towers, feed lines
• Signal – chassis, shields, coax,
• Antenna RF – ground planes, counterpoises

16. Unsafe Ground System
• Multiple unconnected Grounds > Problem
• Lightning currents flowing in each
ground system not equal
• Dangerous voltages will develop
between equipments due to different
ground system impedances
• Extreme shock hazard.

17. Safer Ground System
• Multiple, Connected Grounds much Safer
• Connecting all grounds together creates
an EQUIPOTENTIAL environment
• Voltage drop between ground systems
ideally ZERO if wire has zero resistance
• Ground rise will be same everywhere
and differential voltages will be minimal
• Multiple ground points leads to lowering resistance to ground thus
lowering of Ground Rise overall

18. Wire Sizing
• What Gauge wire is needed to carry a strike current
• Wire Melt, called FUSING as in blowing a fuse, is the issue
• #6 is typical code
• For 50 sec, fusing
current ~ 800 kA

19. Bonding
• Objective is to create an EQUIPOTENTIAL AREA
• Bonding means an electrical connection between equipments
– mechanically connected hardware is not bonding.
• Independent, random unconnected ground systems where conductivity is not
assured is unacceptable
• All grounds and equipments must be electrically connected
– voltage differences are small and shock hazard is suppressed
– lower impedances are achieved
– large currents are distributed over many paths lowering voltages
• “All grounds … . must be bonded together in order to protect life and property
(ARRL 2010 Handbook pg 28.7)

20. Grounding Impedance
• Grounding is not just a simple Resistance problem
• The rate of rise of current, kA / microsecond, is same as a High Frequency
Signal and must be treated the same way.
• LOW IMPEDANCE to Ground is the requirement
• DC resistance can be achieved with large diameter copper
• INDUCTANCE of the ground system is the limiting factor
• (how could the inductance of straight wires be of any consequence?)

21. Inductance
• Conductors carrying the rapidly increasing strike current generate a
rapidly changing magnetic field.
• A changing magnetic field produces a back EMF that opposes the
applied voltage thus constraining the rate at which the current can rise.
• This is Inductance
• Current cannot rise instantly in the presence of inductance

22. Inductive Voltage
• Relationship between Voltage and Current for an inductance
• V is the voltage developed across and inductor
• L is the inductance value
• i is the current
• t is time
• di/dt is the rate of change of current with time,
i.e amps per sec

23. Wire Inductance
• 1 foot of #6 AWG copper
– Inductance = 0.26 H per foot
– Resistance = 0.0004 ohm per foot
– 2 S rise time
• Resistive Voltage drop / foot at 20 kA = 8 volts / foot
• Inductive voltage drop / foot at 10 kA/s = 2600 volts / foot
• The impedance to ground is clearly limited by L

24. Arrestors
• Coax’s, Rotor Cables, any wires, to outdoor antennas are prime
conduits for destructive energy to enter house / shack.
• Arrestors are placed across cables to ground
• Zero current flow to ground under normal conditions
– Does not shunt your signal to ground
• Elevated voltages to ground will cause conduction to ground to divert
harmful current and limit excessive voltages

25. Arrestor Requirements
• Designed for TRANSIENT performance, the strike.
• NOT for continuous application of high voltage or current
• Excessive power dissipation will cause failure
• Industry Standard test waveform is 8 x 20 s
– Rises to peak in 8 s and falls to 50% in 20 s
• Arrestors pass currents / clamp voltages for the 8 x 20 s test without
self destructing

26. Facts about Lightning
• A strike can average 100 million volts of
electricity
• Current of up to 100,000 amperes
• Can generate 54,000 o
F
• Lightning strikes somewhere on the Earth
every second
• Kills 100 BD residents per year

27. Lightning Doesn’t Go Straight
Down

28. What Does This Mean?
• Lightning can strike ground up to ten miles
from a storm (Lightning out of the blue)
• There is an average of 2-3 miles between
strikes
• So how can we tell how far away lightning
has struck?

29. Use The Five Second Rule
• Light travels at about 186,291 milesmiles/second
• Sound travels at only 1,088 feetfeet/second
• You will see the flash of lightning almost
immediately
• 5280/1088= 4.9
• About 5 seconds for sound to travel 1 mile

30. Stepped Leader

31. Streamers

32. Four Main Features of Lightning
Protection
• 1) Air terminal
• 2) Conductors
• 3) Ground termination
• 4) Surge protection

33. Air Terminal and Conductors

34. Grounding Rod

35. Surge Protection Is A Must

36. Effects Of Lightning

37. Myths about lightning
LIGHTNING NEVER STRIKES TWICE
(Truth: it hits the Empire State Building about 25 times a year)
RUBBER (TYRES) WILL INSULATE ME FROM LIGHTNING
(Truth: it has travelled miles through space…a few inches of rubber mean
nothing at all)
YOU SHOULD NEVER TOUCH SOMEONE AFTER HE/SHE HAS BEEN HIT BY
LIGHTNING (Truth: It is perfectly safe.)
LIGHTNING CAN BE PREVENTED
(unconfirmed/sheer advertising)
FIRST STRIKES FROM LIGHTNING CAN BE PREDICTED
(unconfirmed/sheer advertising)
NEW HIGH-TECH TYPES OF LIGHTNING RODS CAN CONTROL LIGHTNING
(unconfirmed/sheer advertising)
BOLT FROM THE BLUE

38. Introduction
Design Requirements:
– Reliable operation of protection systems
– Personnel, public and plant safety
Other Considerations:
– Practical
– Constructible
– Maintainable
– Cost effective

39. Theory and Practice
• Soil resistivity is the key factor determining the
resistance of the electrode
• Wide variation and seasonal change
• Resistivity largely determined by electrolytes
(moisture/minerals/dissolved salts)
• Resistivity of soil changes rapidly with 20% or
more moisture content

40. Ground electrode size and depth
• Resistance of electrode = Resistance of metal electrode + Contact resistance +
Resistance of soil
• Increasing diameter of rod doesn’t reduce resistance
• Doubling the rod length reduces resistance by up to
40%
• Multiple parallel electrodes reduce resistance but not
dramatically less
• Rg (Rod) Ohms = ρ (ohm-cm)/298 cms for 3m rod by
16mm diameter

41. Current Loading capacity
• Earth can dissipate high currents for short
durations
• Serious heating and vaporisation of moisture
can occur with smoking
• I = 1140 x d/ √ ρ x t
– Where I = max current in A/m
– d = rod diameter in mm
– ρ = earth resistivity in ohm-cm
– t = seconds

42. Soil Resistivity Test Methods
Wenner Method

43. Soil Resistivity Test Plan
Main constraints:
• Physical site constraints (barriers, rivers etc)
• Buried metal services and structures
• Limited site access
• Private/public land access restrictions
Electrified rail corridors have significant
constraints:
• Hazards (trains)
• Shared services corridors

44. Soil Resistivity Test Plan
Input Data
• DBYD (Dial-before-you-dig) and site surveys
• Construction data for buried services
• Geotechnical data
• Meteorological data
Three Case Studies Presented
• Using geotechnical input data
• Accommodating probe spacing restrictions
• Influence of buried services

45. Many of the following slides courtesy
of
Todd Sirola C.O.O.
SAE Inc.
Todd provided a presentation to the CCBE last fall
on the following topics
Threats To Equipment
Grounding Fundamentals
Electrical Protection Systems
Case Studies

46. How do we get lightning?
• We need convection, cumulo-nimbus clouds,
the ones with the anvil shape, the result of a
collision of warm and cold air masses
• Ice pellets and grauple
• Super cooled water droplets above the
freezing level
• Earth has a positive charge, the bottom of the
cloud negative charge
• Air is a great insulator so the charges build up

47. Capacitor Analogy

48. And then, BOOM!

49. • At some point the charge is large enough to
overcome the insulator
• The leaders build out slowly at relatively low
current in both directions
• Once they join the current flows. Upwards of
400,000 amps peak
• Power levels in excess of 1 Gigawatt may be
encountered
• Systems need to be engineered with this in
mind

50. • lightning can, and often does, strike the same
spot more than once--even the same person.
U.S. park ranger Roy Sullivan reportedly was
struck seven times between 1942 and 1977.
• Take especially swift action if your hair stands
on end, as that means charged particles are
starting to use your body as a pathway.

51. Just remember
Lightning energy and power system ground
faults will find a path to earth.
The key is to design an electrical protection
system to ensure it doesn’t damage
equipment.

52. Evidence in Nature

53. Electrical representation of a tree
Roots
Branches
Trunk

55. Types of Lightning
• Cloud to Cloud (CC)
• Cloud to Air (CA)
• In Cloud
• Cloud to Ground (CG)
• Peak or Positive Giant
• Blue Streak
• Red Sprite

57. A plug for Todd, he can provide
Design, Supply and Install
Professional Engineering Support
Grounding System Audits
System Resistance (R-Value) Testing
Soil Resistivity Testing
Forensic Analysis
Educational and Training Seminars

58. What are the threats
Lightning
• Direct
• Induced
• AC mains
• Telecom twisted pair
Electric power systems
• Switching operations
• Power system ground faults

65. A typical Ham installation

66. Definition of Grounding
An engineered , low impedance path to
earth.
Definition of Soil Resistivity
A measurement of the electrical resistance of
a unit volume of soil. The commonly used unit
of measure is the ohm-m.

67. Factors Influencing Soil Resistivity
Soil Type (chemical makeup)
• natural elements (clays, quartz)
• foreign elements (salts, fertilizer)
Moisture Content
Temperature

68. Soil Type
Soil Type Resistivity (ohm-m)
Clays 10-150
Sandy Clays 150-600
Pure Sand 600-5000
Gravel 5000-30,000
Shale/Slate 400-1,000
Limestone 1,000-5,000
Sandstone 5,000-50,000
Granite 1,000-80,000

69. Moisture Content

70. Temperature
Temperature Resistivity (ohm-m)
20 0
C 72
10 0
C 99
0 0
C 130
0 0
C (ice) 300
-5 0
C 790
-15 0
C 3,300

71. Ground Resistance Formula
R = ρ X f
R = ground resistance
ρ = soil resistivity
f = a function determined by the
shape and size of the
electrode

72. Electrical Protection Systems
Outside Ground Electrodes
• Low R value, Low Impedance, High
capacitance,
• High energy dissipation
Inside/Equipment Grounding
• Single point
Surge Protection Devices (SPD’s)
• AC system, Incoming telecom, Transmission
lines
Structural Lightning Protection
• Lightning rods, Down conductors
Proactive Lightning Detection

73. What makes a good outside
grounding system?
Low Impedance
• Low Resistance
• Low Inductance
• High Capacitance
High Energy Dissipation
Proper Orientation
Corrosion Resistance
Theft Resistant

74. Low Impedance Grounds
Z = V / I
or
Z = [ R2
+ (2πƒL - 2πƒC-1
)2
]1/2
Lower Resistance
Lower Inductance
Increase Capacitance

75. Low Impedance Grounds
• Increase electrode surface area
• Use a capacitive enhancement
product
• Increase conductor size
• Minimize bends
• Maximize bending radius
• Eliminate 90º bends
• Decrease # of connections

76. The Trouble with “T”
Connections
Lightning travels in straight lines.
90 degree connections offer much higher
impedance than a straight horizontal conductor.

77. Weaknesses of
Conventional Grounding Systems
• Poor lightning protection
• Higher surge impedance
• Seasonal fluctuation of R value
• Subject to corrosion
• Multiple connections

78. How can I lower Ground Resistance?
Add more rods?

79. How can I lower Ground Resistance?
Rods must be spaced appropriately or
their benefit is diminished.
#Rods *Multiply By
2 1.16
4 1.36
8 1.68
16 1.92
24 2.16
*Multiplier if rods are spaced one length apart.

80. How can I lower Ground Resistance?
Conductive Concrete

81. Horizontal Electrode Construction

89. Vertical Electrode Construction

90. What about inside the shack
Or how to keep Greg on the air

91. Single Point Grounding
Buildings should be converted to single point grounding.
This method eliminates current loops and creates an
environment in which it is easier to protect equipment
against power surges from whatever source.

92. Single Point Grounding
Typical Radio Site Layout

93. Single Point Grounding
Typical Radio Site Layout

94. Single Point Grounding

95. Single Point Grounding

96. Single Point Grounding
Materials used for inside grounding
• Green insulated grounding conductor
• Rated double holed compression lugs with
stainless steel hardware
• Copper ground bars with insulated
mounting brackets
• NON-Metallic mounting clips
• Parallel Compression Connectors
Label all conductors at both ends with
permanent identification labels

97. Surge Protection
Surge Protection is required for all metallic
conductors that enter the building:
• Telephone lines
• Intranet Line
• AC Power Systems
• Transmission lines

98. Surge Protection

99. Types of Surge Protection
Voltage Limiting Devices
• Gap devices e.g. air gap carbon arrestors and gas tubes
• silicon avalanche diodes, metal oxide varistors.
Current Limiting Devices
• Fuse links
• Circuit breakers
• Heat coils
Other
• Quarter Wave Stubs
• Neutralizing transformers
• Isolation transformers
• Dielectric fiber optics

100. Case Studies
CKVR Television, Barrie Ontario
Tower located at the studio
Complex on top of the hill overlooking Barrie

101. Case Study:
CKVR - Barrie Broadcast Tower
The protection system included a comprehensive approach to eliminating
damage due to lightning and electrical surges.
• Outside grounding electrodes
• Inside single point grounding
• LSC2000 Lightning Strike Counter
• ESID storm monitor linked directly
to a stand-by Generator

102. CKVR - Barrie Broadcast Tower
Outside Grounding
A total of 378 m of horizontal
electrode was installed at the
tower center and each of the guy
anchors. The overall ground
resistance of the system is 0.9
ohms.

103. CKVR - Barrie Broadcast Tower
Outside Grounding
Guy Anchor GroundingCompound Grounding

104. CKVR - Barrie Broadcast Tower
Inside Grounding
SAE Inc. installed a
Master Ground Bar
(MGB) in the equipment
building.
MGB

105. CKVR - Barrie Broadcast Tower
Lightning Strike Counter
Sensor Unit
Counter Unit

106. CKVR - Barrie Broadcast Tower
ESID - Generator Installation
The ESID detects storms in the area and automatically
switches the site to generator power.
ESID
Generator

107. Is there any science to this?
• It’s a lot of money to spend on the off hand
chance it might take a lightning hit.

108. Case Study:
CKVR - Barrie Broadcast Tower
On June 11, 2000 a severe storm rolled through
Barrie. Lightning knocked out a substation at 6:21
am cutting off power to the surrounding area.
Fortunately at 5:08 am the ESID had identified the
storm activity and switched the site to generator
power. The site remained on generator until 9:40
am when the storm had passed.
CKVR was never off the air.

109. Case Study:
CKVR - Barrie Broadcast Tower
During the same storm the LSC2000 registered 3
direct strikes to the tower. Global Atmospherics
data confirmed the times and provided peak
currents:
4:55 am 20 kA
5:10 am 35 kA
5:59 am 59 kA
The grounding system absorbed the energy of the
strikes and no damage occurred to any of the
sensitive broadcasting equipment.