GROUNDING SYSTEM DESIGN FOR ISOLATED LOCATIONS AND PLANT SYSTEMS

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GROUNDING SYSTEM DESIGN FOR ISOLATED
LOCATIONS AND PLANT SYSTEMS

• Marcus O. Durham THEWAY Corp / U of
  Tulsa
• Robert A. Durham Central Southwest
  Srvcs, WTU

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GROUNDING SYSTEM DESIGN FOR ISOLATED
LOCATIONS AND PLANT SYSTEMS

• Marcus O. Durham THEWAY Corp / U of
  Tulsa
• Robert A. Durham Central Southwest
  Srvcs, WTU

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(No Transcript)
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GROUNDINGIntroduction

• Common feature not always effective
• Technology well defined application is art

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PRESENT TECHNOLOGYIntroduction

• NEC 35 pp requirements -- not design
• Green RP industrial -- not electronics
• Emerald RP power quality sensitive equip
• Lightning shield shunt discharges - not
  devices
• Previous requirements design procedures

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PRESENT TECHNOLOGYIntroduction

• NEC 35 pp requirements -- not design
• Green RP industrial -- not electronics
• Emerald RP power quality sensitive equip
• Lightning shield shunt discharges - not
  devices
• Previous requirements design procedures

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PROJECT10 Case Studies of Ground Problems

• Situation present problem
• Environment influences effectiveness of system
• Analysis investigates alternatives unique
• Summary brief response to situation

little things mean a lot -- pay attention
to detail
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REMOTE SENSOR ERRATICCase 1

• Situation very low readings prior to
  lightning
• Environment
• petrochemical plant, Alabama Gulf Coast
• pipeline station 1/2 mile
• soil sand , gt 50,000 ohm-cm
• isoceraunic 80 TSDY , intense
• combination one of most difficult

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REMOTE SENSOR ERRATICCase 1

• Situation very low readings prior to
  lightning
• Environment
• petrochemical plant, Alabama Gulf Coast
• pipeline station 1/2 mile
• soil sand , gt 50,000 ohm-cm
• isoceraunic 80 TSDY , intense
• combination one of most difficult

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REMOTE SENSOR ERRATICCause

• V diff common (-) to remote gnd
• signal current fluctuation
• Cloud crossing creates potential
• varies w / location under storm
• Strike saturate ground system
• elevated potential to outside

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REMOTE SENSOR ERRATICEffect

• Inside equipotential
• Egress difference
• Trigger protectors short time
• Dump excessive transient I on lines
• Time - delay on response
• Isolate remote ground , metallic bonding
  wont

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REMOTE SENSOR ERRATICNo Such Thing As
Common Ground

• AWG 2/0 bond
• Lo R 0.0003 / ft Hi Z to lighting
• L 0.5 uH / ft f 1 Mhz
• XL 3 ohm / ft (4 order, 10000X)
• I surge gt 3000 A V drop 9000 v / ft

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UNUSED POINTS INDUCE ERRORSCase 2
Situation unused analog damaged during
storm Environment pipeline station S .
Texas cap rock soil rock 15 , 000 to
100 , 000 ohm-cm isoceraunic 38 TSDY
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UNUSED POINTS INDUCE ERRORSCause

• Extra input cards
• Multi - conductor cable
• Surges induced on every wire
• Analog in more susceptible to spurious
• Digital less prone but surges coupled
• Never let float

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UNUSED POINTS INDUCE ERRORSConnections

• Load on unused
• Join intermediate terminals
• Open field ends
• Care to isolate shield from other ground

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UNUSED POINTS INDUCE ERRORSTermination
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FAILURE DURING STORMCase 3
Situation sensors commonly failed w/o direct
hit Environment power generation, SW
Oklahoma pipeline gas yard 200 yds
soil river bottom, 3000 ohm-cm,
excellent isoceraunic 55 TSDY
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FAILURE DURING STORMWhat Is It?

• Remote xmitters in yard
• Existing unshielded cable - entry lightning
  energy
• Effective grounds in plant yard
• No strike
• lose DCS input
• Close strike to towers, tanks
• severe differential voltage
• lose transmitter also

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FAILURE DURING STORMFix

• Isolate unshielded cable
• Common mode DCS
• Differential mode xmitter
• In - line both
• MOV 36 V, 160 J
• Woops, commercials ground protector

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DATA FAILURE BETWEEN BLDGSCase 4

• Situation perimeter comm lines , terminals 5
  X
• Environment
• petrochemical plant, Alabama Gulf Coast
• pipeline station 1/2 mile
• soil sand , gt 50,000 ohm-cm
• isoceraunic 80 TSDY , intense
• combination one of most difficult

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DATA FAILURE BETWEEN BLDGSTap Protection

• Different ground potential
• Isolate signal protection
• Prefer fiber
• Twisted - pair, shield 1 end
• 2 Com, 1 Dif MOV

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DATA FAILURE BETWEEN BLDGSAC Remote
Protection

• Gas tube
• MOV or Transzorb
• Inductor
• comm type
• frequency / baud
• length
• V I

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PROTECTIONLocal , AC Remote
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PROTECTION BLOWS FUSESCase 5

• Situation protectors operate , fuses blow
• Environment
• petrochemical plant, Alabama Gulf Coast
• pipeline station 1/2 mile
• soil sand , gt 50,000 ohm-cm
• isoceraunic 80 TSDY , intense
• combination one of most difficult

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PROTECTION BLOWS FUSESFollow Through Current

• Gas tubes long
• Zener short
• MOV 15 sec
• Shorts transmitter
• 90 fuses per storm

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PROTECTION BLOWS FUSESNon - Incendive Resistor

• Small minimize loop compliance
• Large limit I
• Power continuous
• 4 - 20 ma, 24 VDC 600 ohm
• In positive lead

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PROTECTION BLOWS FUSESResistance

• Total Sensor Wire Add
• 250 17 /kft 330 gt 580

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PROTECTION BLOWS FUSES Loop Compliance

• Resistor 24V / 50 ma gt 480 ohm
• I loop ( 600 / Total R) 20 ma lt 20
• P (0.020) 2 330 0.13 W

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PROTECTION BLOWS FUSESSemiconductor Failure

• Generally shorts
• Positive lead blow fuse
• Negative lead ground loop

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CURRENT IN ELECTRODESCase 6

• Situation I 14 A in both ground beds
• Environment
• petrochemical plant, Alabama Gulf Coast
• pipeline station 1/2 mile
• soil sand , gt 50,000 ohm-cm
• isoceraunic 80 TSDY , intense
• combination one of most

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CURRENT IN ELECTRODESNon - Isolation

• Marshalling panel pos, neg, gnd
• Chassis short to shield
• Each small circulating I
• 1400 digital inputs large I

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CURRENT IN ELECTRODESShields

• Shorted together
• Do not crop to jacket
• Insulate individual ends
• Do not touch metal
• Terminate on shield strip
• Single point ground

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CURRENT IN ELECTRODESSingle Point
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FAN MOTOR ON TOP OF BOILER Case 7

• Situation Fails when lightning hits
  surrounding
• Environment
• power generation, W Texas
• soil shallow top soil on rock,
  100,000 ohm-cm
• isoceraunic 43TSDY

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FAN MOTOR ON TOP OF BOILER Equipment

• 4160 V motor
• 70 ft above earth
• 5 kv unshielded triplex
• In tray conduit
• Acts as antenna
• 2 grounding conductors

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FAN MOTOR ON TOP OF BOILER Gnd Conductor
Z ( AWG 4 )

• L 0.279 uHy / ft
• L 56 uHy / 100 ft
• L 0.5 uHy / ft typical
• XL 220 ohm _at_ 1 MHz
• XL gtgt R

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FAN MOTOR ON TOP OF BOILER Fix

• Lightning arrestors on terminals
• MOV
• Bond all metal
• Shield cable

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STRUCTURE ATTRACTS LIGHTNINGCase 8

• Situation Damages xmitters boards
• Frequent hits
• Environment
• research facility NE Oklahoma
• soil loam, 6500 ohm-cm
• isoceraunic 55 TSDY

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STRUCTURE ATTRACTS LIGHTNINGDissipate Energy

• Not tallest structure
• More conductive than others
• Bond around base pins
• Bond framework
• 1 / 0 AWG
• Non - corrosive terminals
• Gound guy wires

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STRUCTURE ATTRACTS LIGHTNINGGround Network

• Rat - race ring
• If gt 50 ft, criss - cross
• Bond to existing grid
• Radials 1 / 0 AWG
• 5 ft rods, 20 ft spacing

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HIGH RESISTIVITY SOILCase 9

• Situation Single motor from distribution
  system
• Environment
• pump SE New Mexico
• soil 6500 ohm-cm on rock at 4 ft
• isoceraunic 47 TSDY

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HIGH RESISTIVITY SOIL5 / 8 x 8 Rod

• Dwights formula
• R p / 191.5 b ln ( 48 b / a ) -
  1
• R 177 ohm , 1 rod
• R 76 ohm, 3 rods
• gt 25 ohm
• gtgt 5 ohm

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HIGH RESISTIVITY SOILConcrete

• Retain moisture
• Alkalinity free ions
• Resistivity 3000 ohm - cm
• 1 rod 10.6 ohm
• 3 rod 4.6 ohm

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SHOCK ON GROUNDED PANELCase 10

• Situation Grounded panel permitted shock
• Environment
• pumping panel, NE Oklahoma
• soil loam, 6500 ohm-cm
• isoceraunic 55 TSDY

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SHOCK ON GROUNDED PANELSystem

• Power panel outdoors
• Overhead distribution, 277 / 480 Y gnd
• 5 / 8 x 8 rod
• Occasional shocks
• Inspected returned to service

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SHOCK ON GROUNDED PANELProblem

• Secondary pinch 50 ohm
• Circulating I 1 amp
• Two ground paths
• Gnd rod 25 ohm
• Body 40,000 to 1,000 ohm

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SHOCK ON GROUNDED PANEL
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SHOCK ON GROUNDED PANELBody Current

• 0.6 ma 40 K
• 24.4 ma 1 K
• 341 ma 14 A
• Install lo Z ground

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SHOCK ON GROUNDED PANELGFCI

• Personnel 6 ma
• Equipment 30 ma
• Not required for this

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CURRENT IMPACT

• MA Physiology
• 1 sensation
• 8 painful shock
• 15 cant let go
• 20 possible damage
• 50 ventricular fibrillation
• 100 probable death

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REVIEW

• Grounding systems
• Various environments
• Diverse problems
• Common solutions
• Little things mean a lot

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SUMMARY

• 1. Environment - thunderstorms vs hits
• 2. Earth resistivity - multiple in concrete
• 3. Equipotential network
• 4. Single point connection
• power neutral
• signal common
• shield

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SUMMARY

• 5. Bond metal
• 6. Protection devices
• 7. Bond to chassis vs isolate remote
• 8. Terminate unused
• short in
• load out
• bond wires