CPR Lightning Damage Investigation CPR Lightning Damage Investigation and Mitigation Strategiesand Mitigation Strategies

Peter Brackett

Canadian Pacific RailwayPeter_Brackett@cpr.ca

AAR Surge Testing at LTI Lab

AAR Surge Testing at LTI Lab

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

WOOD71”

>5000v

WOOD53”

4000v

WOODAAR&STRAP

3400v

WOOD1.5” STRAP

19000v

WOODEN TERMINAL BD1.5” ALUMINUM STRAP

1900v

METAL PANELS - LIRP2250V

Lightning is Generated by Circulating Wind and Lightning is Generated by Circulating Wind and Water in Thunderstorm CloudWater in Thunderstorm Cloud

LightningLightning

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).

FARADAY CAGE PRINCIPAL

CPR’s Implementation of Faraday Cage and Low Impedance Reference Plane (LIRP) Wiring

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

CPR Lightning Damage Investigation CPR Lightning Damage Investigation and Mitigation Strategiesand Mitigation Strategies

Peter Brackett

Canadian Pacific RailwayPeter_Brackett@cpr.ca

403-319-7781