Post on 14-Dec-2015
CPR Lightning Damage Investigation CPR Lightning Damage Investigation and Mitigation Strategiesand Mitigation Strategies
Peter Brackett
Canadian Pacific RailwayPeter_Brackett@cpr.ca
WOODEN BOARD 4000V++Track/Rail (Simulated with Inductors)
Vb
Va
Vb Va
Test #65/171" #6 Wire & AAR Surge Path to Gnd
Length of Surge Path to Gnd Va= >5000VVb= >5000V(Scope=4000V Max I/P)
Test 66/1AAR Ground Strap 53 Inch Surge Path
#6 Bond Wire Remove 18" of #6 Wire
Va= 4000VVb= 4000V
Ground Reference (Floor/Skin of Bungalow)
Safetran GCP Crossing Equipment
Surge Generator 8by20 MicroSecWaveform 18,000 Amps
Digital Scope
Wooden Terminal Board
AAR GND STRIP, #6 WIRE & 1.5” ALUM STRAP
3400VVb Va
Test 89/3
27" x 1.5" Alum Strap+12" x 1.5"Jumper
Length of Surge Path to Gnd + 20" of AAR StrappingSurge Path to Gnd
Va= 3400VVb= 3388V
AAR Ground Strap
#6 Bond Wire 27"L by 1.5W x 1/4D Aluminum Strap
Wooden Terminal Board
1.5” ALUMINUM STRAP1900V
USE TO RETROFIT EXISTINGVb Va
Test 88/237"L by 1.5W x 1/4D Aluminum Strap
Surge Path to Gnd Surge Path to Gnd
Va= 1900VVb= 2400V
AAR Ground Strap
METAL PANELS - LIRP2250V
LOW ENERGY - REMOVE PAINTED EDGES
Vb Va Test 5/1Metal Panels withArrestors Gnd'd DirectlyPovides distributed
Distributed Surge Paths groundpath and completesto Gnd Via Metal Panels Faraday Cage outside
Enclosure
Also provides aLow Impedance Ref Plane and Separation of "Dirty" Outside Wiring from"Clean" Inside Wiring
Va= 2250V
Metal Frame inside Bungalow Vb= 2450V
Metal Surge Panels
Lightning is Generated by Circulating Wind and Lightning is Generated by Circulating Wind and Water in Thunderstorm CloudWater in Thunderstorm Cloud
Mystery of Lightning Lightning is mysterious because it occurs in a time
frame that is so different from our normal experiences.
We are familiar with 60Hz AC distribution and DC battery systems. This is our normal frame of reference. AC is like driving a car down a highway and DC is like walking along the same highway but lightning is like a supersonic jet flying at car level shooting off super-supersonic rockets.
So Lightning doesn’t seem to react the same way, it doesn’t need a conductor to move, it makes its own paths usually invisible paths through the air.
Mystery of Lightning
Lightning’s time horizons are microseconds, millionths of a second.
Lightning can be understood if we think in the timeframe of the lightning event and analyze the paths based on high-speed charge movement not the time frame of familiar electrical activity.
Surge Damage Investigation:
Radio/Fiber Bungalow
150’ Tower
150’ Rolling Sphere of Lightning Protection Zone
Maple Creek Saskatchewan Communication Tower Site View from the East
CPR 10 by12 Communication Site CPR 10 by12 Communication Site
2by6 wood/drywall construction with metal skin
Antenna Coax & Lighting Cables
Ground Wire
Site Physical Geometry: Remote Connections
Tracks Dispatch Office Street
150 ft Underground 25 Pair Telephone cable
Grain Elevators feed from Dispatch Office
3rd Party
Fibre Bldg
Fibre 150 ft Underground
Power Service
CPR Radio Tower with Fibre Connection
East
North
Electrical Electrical ConnectionsConnections
Telephone
Grounds
Fiber with Shield Ground
AC Power
Radio Racks
Fibre Racks
Coax
AC SPD
Skid Frame
Telephone
Grounds
Fiber with Shield Ground
AC Power
Radio Racks
Fibre Racks
Coax
AC SPD
Skid Frame
Coax Arrestors- No Damage
DamageDamage Locations
Damage Summary:Damage Summary:1) All three telephone line connections (at both end of wires)
2) Radio Equipment In-Line AC protector and internal power supplies
3) Fibre AC connections to Power Supply
4) No Damage on Coax Antenna connections
5) No Damage to upstream AC power
6) No significant damage to Telephone equipment in Dispatcher Office where 25 pair cable originated from
7) No Damage to the Fibre Equipment- still functioned from Battery
How Did the Damage Occur? How Did the Damage Occur? What was the Damage Mechanism?What was the Damage Mechanism?
Challenge:
What current flow path can explain:
- the observed damage
- the undamaged equipment
- the undamaged remote connections.
Radio2Radio1 RTI
Fibre 2nd Row
Charger
Charger
Radio Telephone Interface
LightningLeader
Strike
Equipment Ground Plate
Strike Raises Potential of
Ground Plate Forcing Current
into SiteTelco Remote Cable Current Flow Through Equipment Vaporizes Conductors
Fibre Charger
Internal wiring Inductance
Voltage moves faster than
external Grid Inductance
Voltage driving Current through
AC Chargers
No Coax Damage
In Line 120V SPD
Multiple Equipment Multiple Equipment DamageDamage
Caused by:Ground Plate Potential Rise driving current into site
Current Flow through equipment out to remote telco connections vaporizing small wires
Potential Difference between Ground Plate and far side Power Ground driving current through Power Supplies vaporizing conductors
Surge Mitigation Strategies:Surge Mitigation Strategies:
1. Reference all external connections to a Low Impedance Reference Plane (LIRP) with Surge Protection Devices (SPD’s).
2. Incorporate this Low Impedance Reference Plane (LIRP) into a conductive enclosure following the Faraday Cage shielding principles. (Charge applied to a conductive enclosure is forced to the outside of the enclosure).
LIRPLIRPLow Impedance Reference Plane Low Impedance Reference Plane
(LIRP) with Surge Protection (LIRP) with Surge Protection
Devices (SPD’s).Devices (SPD’s).
4. Reduce Z*di/dt voltage rise across equipment by avoiding surge current paths through equipment. Designating one location ie top or bottom as the common path for external connections and routing all external connections via this path best accomplishes this. Avoid hidden paths such as connection of rack mounting bolts into frame of building beneath floor.
5. Use current division to control the dissipation of lightning strike energy on an antenna tower grounding system through multiple paths
6. Treat Surge Energy Conduction as high frequency current (~100Khz). The more surface area the surge path has the less Voltage Rise. For the same amount of metal a flat bar or hollow tube has less IZ (Impedance) voltage rise.
7. Maximize bend radius in surge current wire paths.Surge currents are a high force event like water surging into a fire hose.Bends greater than 12” do not increase IZ voltage rise.
8. Minimize coupling between surge current carrying wires and signal wires. Insulated wires run close to each other couple 70% of surge energy between wiresInsulated wires run with a 3” separation couple less than 40%, 6” less than 25%Wire run against a conductive plane to radiate energy into plane and less into free space.Wires separated by a conductive plane have minimal coupling. Wires crossing at right angles have minimal coupling