Atlantic Scientific Corp'

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Atlantic Scientific Corp.
Investment in Lightning Protection for Equipment
Survival - What Cost?
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Atlantic Scientific Corp.
Surge Lightning Protection
A seminar from the home of Lightning and
Severe Weather - FLORIDA -
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The lowest bidder wins the contract

• If your specification is basic you get
  exactly
• what you specify.
• Install a surge protector 1.26c worth of
  protection
• A ground bar will be installed 6 ground
  rod
• Significant effort goes into specifying the
  equipment to
• be procured and installed yet the protection
  often gets
• very little attention.

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The design of the lightning protection scheme
needs to take on as much detail as the
selection of the equipment to be installed. This
is an Investment in Failure Prevention . Done
correctly, it is economic and will significantly
reduce the installed lifetime cost and
ongoing maintenance costs.
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Misunderstandings and Myths

• There is nothing you can do about a direct
  strike
• Lightning will always cause damage no matter
  what you do.
• If you get lightning related damage, improve
  the earthing system
• The lower the earth impedance, the lower the
  risk of lightning related damage.
• The cone of protection using a lightning rod,
  will prevent the equipment from getting struck by
  lightning
• The equipment is actually struck by lightning.

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"WORKS"
Lightning Protection

• In FLORIDA all the FL DOT microwave sites are
  400 towers
• that get struck between 1 10 times a year.
• There are over 5,000 cellular sites in FLORIDA
  with
• 100 towers that are struck by lightning on a
  regular basis.
• If you could not prevent lightning related
  damage,
• Florida would have closed down many years ago.

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(No Transcript)
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Lightning Statistics for the USA
During 1988, 89, 90 91 EPRI funded the National
Lightning Detection Network (NLDN), across the
USA. The network detected 53,4 million lightning
events within 230 miles of one of the 130 sensors
in the network, and the peak current was
measured. This data was analyzed by SUNYA under
contract EPRI TR-103603s This is some of the
conclusions. The average/ median peak current
was Less than 1 had in excess of The
average / median peak current was Less than 1
had in excess of
First Stroke in a negative flash
35 kA
First Stroke in a positive flash
55 kA
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Energy in a Lightning related surge

• IEEE C62-41.2 tells us a C class is 10kA
  20kV
• UL 1449 3rd edition type 1 SPD 10 or 20kA
  rating
• EPRI tells us 35kA median with 1 exceeds 120kA
• IEC 61312-3 tells us the Maximum is 200kA
• A UPS does not protect your site

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SPD Design Criteria
55 kA
35 kA
- ve strokes
Quantity
ve strokes
lt20 chance of survival
lt100
Surge Current in kA
10kA
70kA
60kA
50kA
40kA
30kA
20kA
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Awesome Power
A Tree literally EXPLODING !!
Farm House
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Understaning the functions of a Surge Protection

• A Surge Protection component is a Voltage
  sensitive switch

• In the normal state it is a high impedance path

• In the switched state it is a low impedance path

• The transition time is nanoseconds -
  microseconds,
• depending on the technology

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Components of a Protection System

• A single point earthing system
• An acceptable impedance to ground
• Surge Protection on the AC Power
• Surge Protection on all connected lines, data
  or comms.
• All surge protectors with primary / Secondary
  functionality

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Impedance of the earthing system
5 ohm or 50 ohms ?

• Many specify 5 ohms in an effort to minimize
  lightning related damage (misunderstood cause
  effect)
• NEC Requires 25 ohms or two ground rods for a
  safety earth
• Cellular companies choose design over measurement

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Impedance of the earthing system is effected by
Temperature Moisture
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Relationship between earth and surge protectors

• Surge Protectors and earth work as a team

• Surge Protection without good earthing
  diminishes
• the ability to divert damaging currents

• Earthing without Surge Protection cannot
  equalize
  
  potentials when ground gets elevated

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Earthing System for Traffic Signals
Equipment Cabinet
Distance 2 x the rod length for optimum
performance
10 20 earth rod
10 20 earth rod
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Earthing and Grounding
High Performance Economic Earthing array at an
intersection
Traffic Cabinet
20 Ground Rods
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Elevated Earth Potential minimised due to
inter-connect
Cameras
Traffic Cabinet
100kV
75kV
Earth Impedance
50kV
25kV
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Economic Improved earth impedance
All poles have a ground rod, Inter-connect them
to get an Array can lower impedance by a
factor. 30? to 3?
ITS installation
At least 6 stranded
Traffic Intersection
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Elevated Ground Potential
AC Line
60
40
Utility
Utility
SPD
SPD
50? Earth
50?
40
60
60
40
Percentages are for illustration only
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Line
Line
SPD
SPD
Utility
Utility
Neutral
Neutral
40
60
50? Earth
5? Earth
5?
50?
60
40
Surge on a connected line
Percentages are illustration only
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IEC 479-1 and IEEE Std 80 on Grounding Safety
Criteria For Humans
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Resistive Coupling
Electrocuted animal
DISTANCE
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Lightning killed 504 sheep when a stroke hit the
ground in this rocky Pasture in Utah. A stroke
to high-resistance soil can produce exceptionally
high voltage in the ground and spread over an
unusually large area.
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The coupling mechanism
Direct Strike Coupling Mechanism as defined in
IEC 61312-3 for a typical building with a remote
transformer. This is also defined as scenario 2
in IEEE C62.41.2
LOAD
Surge Protector
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Lightning close to the Transformer
Each house gets surge of 30kA / 8 3.75kA
30kA
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Lightning close to a house
The house gets surge of 30kA /0 30kA
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AC Power Surges
Surge on connected lines to the site 10kA
IEEE C62-41
Surge on connected lines leaving the site 100kA
IEC 61312-3
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The functions of a surge protector
LOAD
L1
L2
L3
N
G
Shunt or Divert 50/50 split (IEC)
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The functions of a surge protector
LOAD
L1
L2
L3
N
G
Equalize potentials from elevated earth 50/50
split (IEC)
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Let-thru vs Surge Current
The Let-Thru-Voltage Increases with The Current
in the Surge
This phenomena Can be prevented with a
Multi-Stage Hybrid Or Cascade
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LTV increases with the current in the surge
2600v _at_ 20kA
2,000v
L T V
1,000v
NOT TO SCALE
330v
40,000A
20,000A
10,000A
500A
5,000A
Current in the surge
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AC Power Cascade Protection
Primary Secondary surge protection
Lightning Surge
Primary Surge Protector
20,000A 40,000v
2,500v
Secondary
250v
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AC Power Cascade Protection
L O A D
AC Line
Lightning Strike to the site or a nearby structure
Secondary
Primary
100,000A lt20Mv
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Multistage devices for Comms-Data
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Cascade or Hybrid
GDT
L T V
Values and components used are for
demonstration purposes only !!
5 Kv
MOV
MOV
1 Kv
SAD
100 V
16 V
TIME
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What causes the damage
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What causes the damage ??
Typically the percentage of damage caused by
each mechanism for stand-alone isolated
installations.

• 1 - 5 Induced surges
• 5 - 10 Surge on externally connected lines
• 80 - 95 Earth / ground coupling

These risk factors are influenced by many issues
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Induced Surges

• This mechanism is related to the
  Electro-magnetic
• Pulse (EMP) generated by a direct or nearby
  strike.
• Inductive loops are particularly venerable,
  however cables
• running up and down poles, when struck, will
  have induced
• surges.
• This mechanism generally requires a direct
  strike to the pole.
• Most cables, such as COAX are shielded to
  minimize the risk.

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Surges on externally connected lines

• It is well understood that a surge can be
  delivered on
• a Utility connected AC power line.
• An area where there are overhead power feeds
  are
• particularly susceptible to large surges on
  the AC.
• Utility switching surges are very common
• Surge on communications lines are not uncommon.
• Surges on Antennae lines are frequent.

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Earth / Ground coupling

• Equi-potential earth problems
• Resistive coupling Voltage Gradients
• Nearby lightning or elevated ground potential
• Described in IEEE C62.41.2 IEC 61312

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Cost of a typical protection system

• Ground rods 1 or more 10 to 20
• Earth Inter-connect single point Ground 2
  solid
• AC Power Primary surge protector - gt80kA MOV
• AC Power Secondary surge protector - gt20kA
• CCTV - RTMS - DMS surge protector - 10kA
• Communications Data surge protector 10kA
• Plus labor for the grounding system - /Hr

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Cost of Failure

• Equipment replacement cost 100 - 1500
• Truck roll labor 300 - 600
• System Outage - incalculable
• System down in thunderstorm needed most
• Cost of potential congestion - 1,160 per
  traveler/yr
• Potential chaos incalculable

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INvestment into a Protection System
The investment should be at least 10 of the
Electronic and Electrical Equipment at a
site 5,000 site gt500 protection
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Specifying the protection system

• Be specific identify the performance
• e.g. Let thru voltage and surge current
  capacity.
• Do not over-specify - Response time
• The problems are in the details
• Specify things that can be verified easily
• Add details but not manufactures or part
  numbers
• Specifying or equivalent does not work !
• Specify product performance that is known to
  work
• Specifying solutions from the traffic industry
  to ITS is a mistake

Some sample specifications
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Conclusions

• A Surge Protector of 20kA surge capacity is not
  enough
• The relationship of Earthing and Surge
  Protection is critical
• A Primary-Secondary surge protection scheme is
  important
• Single point grounding MUST be used.
• All wires connected to/from a site MUST have
  Surge Protection
• Adequately detail the protection system in the
  specification

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Thank you
Any Questions ??
For more information contact - Bill Cook
bill.cook_at_atlanticscientific.com or John Roth
- john.roth_at_atlanticscientific,com
800-544-4737 extn 133 or 134