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 ???