Lightning Protection and Grounding Solutions for Wireless Networks

Bogdan (Bogey) Klobassa

Solutions for Wireless Networks

Director-Protection Technologies

Times Microwave SystemsAn Amphenol Company

Aircraft Triggered Return Stroke

Few Facts About the Lightning Event

• Typically, more than 2,000 thunderstorms are active throughout the world at any given moment producing on the order of 100 flashes per second. As our society b d d dbecomes more dependent upon computers and information/communications networks, protection from system disruptions becomes essentials.

• During fair weather, a potential difference of 200,000 to 500,000 Volts exists between the earth surface and ionosphere In a lightning event this potential will beionosphere. In a lightning event this potential will be responsible for lightning discharge currents of up to 100,000 Ampere.

• The average length and duration of each lightning stroke vary, but typically average about 30 microseconds producing average peak power per stroke of about 1 (one) T illi WTrillion Watts.

• The temperature along the lightning channel (flash) during the electrical discharge is in the order of 20,000 degrees Celsius (three time the temperature of the surface of the Sun)

• Wireless networks rely on communication towers for its• Wireless networks rely on communication towers for its transmission of Radio Frequency putting them statistically in a very high exposure zone. Average communication site in Florida, during thunderstorm season, will be exposed to 18 to 20 lightning strikes a year.

Annual Lightning Flash Rate - Global

Annual Lightning Flash Density - USA

The Lightning Event

The lower part of a thundercloud is usually negatively charged. The upward area is usually positively charged. Lightning from the negatively charged area of the cloud generally carries a negative charge to Earth and is called a negative flash. A discharge from a positively-charged area to Earth produces a positive flash

Definition of Pulse Wave-Shape

Measured Peak Lightning Currents

Ref: W.C. Hart, E. W. Malone, Lightning and Lightning Protection, EEC Press, 1979

Times to Peak Lightning Currents

Ref: W. C. Hart, E. W. Malone, Lightning and Lightning Protection, EEC Press, 1979

Communication Mast as Voltage Divider

360kV Peak

Strike Voltage Distribution andcable shield potential at entry port

Distributed Voltage across mast 360kV would arise at the top of a 40µH mast

with a relatively small 18 kA w/ a 2µS risetimestrike . The voltage would be distributed downthe mast to ground. If the cable shields werebonded to the mast at the 8 foot level, about28kV would be riding on shields going to theentrance panel

Peak Voltage on Cable Shields ~ 28kV going to entrance panel

Inductance Considerations

Lightning Current Distribution on Coaxial Cable

Typical Ground Resistance Values

– NFPA 70 NEC < 25 OHMS or two rods– IEEE Standard 142 Equipment Dependent– IEEE Standard 1100 < 5 OHMS– Motorola Standard R-56 < 5 OHMS

Verizon Wireless 8501 < 5 OHMS– Verizon Wireless 8501 < 5 OHMS– Bell Mobility Cellular < 5 OHMS– Essilor < 3 OHMS– GE Medical Systems < 2 OHMS

Rolling Ball Theory - Structural Protection

150’ RadiusStriking DistanceStriking Distance(100’ for flammableliquids)

Per ANSI/NFPA 780

Zone of Protection

Placement of Air Terminals

The Zone of Protection from lightning strikes can be defined using the rolling sphere model.g g p

Equipment Grounding with Coax Entering from a High Mounted Entry Panelfrom a High Mounted Entry Panel

Grounding at bottom of the rack creates a path for surge current to traverse the rack, upsetting orto traverse the rack, upsetting or destroying equipment.

Proper grounding of the equipment rack If coax jumperequipment rack. If coax jumper cables enter at the top, ground high. If they enter low, ground low. There will be minimal current flow through the rack.through the rack.

High Rise Building Grounding Considerations

Rooftop Installations

GPS AntennaCellular Antenna

Coaxial Cables from antennaLightning Rods (6)

Perimeter rooftop ground conductors for structural protection system with additional conductors bonding cellular

Coaxial Cable Entry panel

Lightning Rod structural protection system down-conductors (4)

antenna support

Separate ground down–conductor for antenna structure and entry port bond

Antenna support - entry panel ground bond to building steel

antenna structure and entry port bond

Equipment ground preferences:Marginal Bond to structural protection orseparate down conductor Good Bond to structural protection and

additional separate down conductor Better Single bond to structural steel

Rooftop GroundConsiderations

Water /Sewer GroundElectrical GroundGround Loop / Rods around building Ground Loop/Rods

gBest Combine all three methods

What are we going to do to protect this????

Application concerns and risk assessment:

•Equipment susceptibility due to the lightning exposureEquipment susceptibility due to the lightning exposure•High cost of repair•What is the level of protection included in the TTE against IEC, Telcordia, IEEE standards?•Are all ports for RF/Power/Data and Telemetry hardened to withstand this environment?•Dense design package of TTE vs. Dielectric withstand to EMP

Roof top Mast and Antennas

Service Entry Bulkheads

After the fixAfter the fix

External View of Traditional Method and Proposed Solutionp

Traditional method consisting of:• High material and labor cost• Lack of provisions for other service entries

Proposed method:• Addresses theft issue• Does not require external shield grounding kits• Makes provisions for Coax/EWG/Data/DC and fiber• Minimal labor cost• All prep work performed at the shelter manufacturer• Lack of provisions for other service entries

• Theft exposure• Very high impedance return path to ground• High preventative maintenance

• All prep work performed at the shelter manufacturer

Interior View of Traditional Method and Proposed Solutionp

RF ProtectorsRF ProtectorsBulkhead mounted

2/0 Conductors

Propose method:

2/0 Conductorsto ground

Traditional method:• Requires separate Inside MGB (IMGB)• Trapeze or other method to ground SPDs• Performance affected by long ground wires

Propose method:• All RF protectors bulkhead mounted for best surge performance• Assembly accommodates different wall thickness• Provisions for grounding of all protectors to the same SPG• Low impedance ground path for lightning current • Control of MGB potential rise due to low “L” of assembly• Performance affected by long ground wires

• High impedance IMGB ground conductor• Single point ground by installation• High ground loop probability

p y• Accommodates for additional equipment mounting

Ground Lead Considerations for Installation of RF ProtectorsApplied Surge Wave-Shape 6KV/3KA (8X20us)

Bulkhead mounted SPD without added ground “L”Surge return directly connected to protector ground

Effects of 1.5 ft ground lead inductance of #1 AWG Cu wireVoltage and energy throughput drastically increases

+25.6V, -9.2V +544V, -176V

+

-

Su rge

Gen er ator

DUTCe nter Pin

Chass isGround

Voltage Measuredat O-scope

+

-

Surge

Generator

DUTCenter Pin

Voltag e Measured at O-

GroundInductance

Vo g e e su ed Osco pe

Note: The length of the grounding conductor connected to any lightning protection device has a major effect on the protector performance as illustrated by the above test. Leadless/Bulkhead installation technique for RF lightning protection devices will eliminate this additive voltage and energy throughput to the protected equipment

True Single Point Grounding (SPG) by Design

Lightning Protector

Feed-throughLP-FT-DFDF

Blank hole plugLP-NP/DP

Installed Views

Typical Performance Parameters for DC Blocked (20-1000MHz) RF Lightning Protector

•DC blocked design•DC blocked design •Multi-strike capability•Broad band performance up to 1GHz•Exceptional RF characteristics•Universal bulkhead and flange mounting•Elongated Female connectorsW th i ti k t i l d d•Weatherization gasket included

•Solid Brass design / White Bronze plating•Phosphor Bronze center pin construction•Silver plated center pin•Insertion Loss: < 0.1dB•Return Loss: <-26dB•VSWR: <1.1:1 •Energy throughput: <200uJ• IP67 Weatherized

RF Lightning Protector Surge Performance ExamplesExamples

User voltage: 5VdcVoltage throughput: <12VpkEnergy throughput: <110uJ

Voltage throughput: <2VpkEnergy throughput: <150nJ

Energy throughput: <110uJ

Lightning Protector Energy Throughput Calculations into 50 Ohm LoadCalculations into 50 Ohm Load

800.0E-12500.0E-3

LP-STRDFF 6kV/3kAEnergy & Voltage Plotted into 50 Ohms with 0.08VDC Offset when applicable

50 Oh V lt

600.0E-12

700.0E-12

350.0E-3

400.0E-3

450.0E-3

50 Ohm VoltageVoltage over DC (ABS)Energy Over DC Offset

300 0E-12

400.0E-12

500.0E-12

200.0E-3

250.0E-3

300.0E-3

y Le

t-thr

u (jo

ules

)

hrou

gh (V

olta

ge)

100.0E-12

200.0E-12

300.0E 12

50.0E-3

100.0E-3

150.0E-3

Ener

gy

Let-t

h

000.0E+0000.0E+0

-400

.E-6

-360

.E-6

-320

.E-6

-280

.E-6

-240

.E-6

-200

.E-6

-160

.E-6

-120

.E-6

-80.

E-6

-40.

E-6

200.

E-9

40.E

-6

80.E

-6

120.

E-6

160.

E-6

200.

E-6

240.

E-6

280.

E-6

320.

E-6

360.

E-6

Time

Passive Intermodulation (PIM) Considerations

Antenna & ODUBroadband Protection - Antenna

Incorporated into the ODURF protector

RF Protector

RF protector

LMR400 LMR200

Shelter

RF protector

Tower

IDULMRJumper

Antenna

Broadband Protection - Antenna Separated from ODU

Lightning Protector

ODU

LMR Jumper

Lightning Protector

ODU

LMR400 LMR200

ShelterLightning Protector

Tower

IDULMRJumper

Lightning Damage to the RF Protector

Thank you and Questions ???