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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,

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Presentation on theme: "GROUNDING SYSTEM DESIGN FOR ISOLATED LOCATIONS AND PLANT SYSTEMS Marcus O. Durham THEWAY Corp / U of Tulsa Robert A. Durham Central & Southwest Srvcs,"— Presentation transcript:

1 GROUNDING SYSTEM DESIGN FOR ISOLATED LOCATIONS AND PLANT SYSTEMS Marcus O. Durham THEWAY Corp / U of Tulsa Robert A. Durham Central & Southwest Srvcs, WTU Marcus O. Durham THEWAY Corp / U of Tulsa Robert A. Durham Central & Southwest Srvcs, WTU

2 GROUNDING SYSTEM DESIGN FOR ISOLATED LOCATIONS AND PLANT SYSTEMS Marcus O. Durham THEWAY Corp / U of Tulsa Robert A. Durham Central & Southwest Srvcs, WTU

3 Combination Surge Management V Clamp voltage PROTECTION DEVICES F Filter frequencies I Shunt current E Block energy

4 GROUNDING Introduction u Common featurenot always effective u Technology well definedapplication is art

5 PRESENT TECHNOLOGY Introduction u NEC35 pp requirements -- not design u GreenRP industrial -- not electronics u EmeraldRP power quality sensitive equip u Lightningshield & shunt discharges - not devices u Previousrequirements & design procedures

6 PRESENT TECHNOLOGY Introduction u NEC35 pp requirements -- not design u GreenRP industrial -- not electronics u EmeraldRP power quality sensitive equip u Lightningshield & shunt discharges - not devices u Previousrequirements & design procedures

7 PROJECT 10 Case Studies of Ground Problems u Situationpresent problem u Environmentinfluences effectiveness of system u Analysisinvestigates alternatives & unique u Summarybrief response to situation little things mean a lot -- pay attention to detail

8 REMOTE SENSOR ERRATIC Case 1 Situationvery low readings prior to lightning Environment petrochemical plant, Alabama Gulf Coast pipeline station 1/2 mile soil = sand, > 50,000 ohm-cm isoceraunic 80 TSDY, intense combination = one of most difficult

9 REMOTE SENSOR ERRATIC Case 1 Situationvery low readings prior to lightning Environment petrochemical plant, Alabama Gulf Coast pipeline station 1/2 mile soil = sand, > 50,000 ohm-cm isoceraunic 80 TSDY, intense combination = one of most difficult

10 REMOTE SENSOR ERRATIC Cause u V diff common (-) to remote gnd signal current fluctuation u Cloud crossing creates potential varies w / location under storm u Strike = saturate ground system elevated potential to outside

11 u Inside = equipotential u Egress = difference u Trigger protectors short time u Dump excessive transient I on lines u Time - delay on response u Isolate remote ground, metallic bonding won’t REMOTE SENSOR ERRATIC Effect

12 AWG 2/0 bond Lo R = 0.0003 / ftHi Z to lighting L = 0.5 uH / ftf = 1 Mhz XL = 3 ohm / ft (4 order, 10000X) I surge > 3000 AV drop = 9000 v / ft REMOTE SENSOR ERRATIC No Such Thing As Common Ground EE

13 UNUSED POINTS INDUCE ERRORS Case 2 Situationunused analog damaged during storm Environment pipeline station S. Texas cap rock soil = rock 15, 000 to 100, 000 ohm-cm isoceraunic 38 TSDY

14 u Extra input cards u Multi - conductor cable u Surges induced on every wire u Analog in more susceptible to spurious u Digital less prone but surges coupled u Never let float UNUSED POINTS INDUCE ERRORS Cause

15 UNUSED POINTS INDUCE ERRORS Connections Load on unused Join intermediate terminals Open field ends Care to isolate shield from other ground

16 Digital Out Analog In Analog Out GND LOAD 250W In + _ + _ + _ + _ UNUSED POINTS INDUCE ERRORS Termination

17 FAILURE DURING STORM Case 3 Situationsensors 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

18 u Remote xmitters in yard u Existing unshielded cable - entry lightning energy u Effective grounds in plant & yard u No strike lose DCS input u Close strike to towers, tanks severe differential voltage lose transmitter also FAILURE DURING STORM What Is It?

19 u Isolate unshielded cable u Common modeDCS u Differential modexmitter u In - lineboth u MOV 36 V, 160 J u Woops, commercials ground protector FAILURE DURING STORM Fix MOV

20 DATA FAILURE BETWEEN BLDGS Case 4 Situationperimeter comm lines, terminals 5 X Environment petrochemical plant, Alabama Gulf Coast pipeline station 1/2 mile soil = sand, > 50,000 ohm-cm isoceraunic 80 TSDY, intense combination = one of most difficult

21 u Different ground potential u Isolate signal & protection u Prefer fiber u Twisted - pair, shield 1 end u 2 Com, 1 Dif MOV DATA FAILURE BETWEEN BLDGS Tap Protection

22 u Gas tube u MOV or Transzorb u Inductor comm type frequency / baud length V & I DATA FAILURE BETWEEN BLDGS AC & Remote Protection

23 + _ s + _ + _ s Isolated Signal Ground xmitter + _ PROTECTION Local, AC & Remote

24 PROTECTION BLOWS FUSES Case 5 Situationprotectors operate, fuses blow Environment petrochemical plant, Alabama Gulf Coast pipeline station 1/2 mile soil = sand, > 50,000 ohm-cm isoceraunic 80 TSDY, intense combination = one of most difficult

25 PROTECTION BLOWS FUSES Follow Through Current u Gas tubeslong u Zenershort u MOV15 sec u Shorts transmitter u 90 fuses per storm

26 u Smallminimize loop compliance u Largelimit I u Powercontinuous u 4 - 20 ma, 24 VDC ~ 600 ohm u In positive lead PROTECTION BLOWS FUSES Non - Incendive Resistor

27 +24V X -24V (gnd) fuse indicator limiting wire xmitter P protector Total= Sensor + Wire + Add = 250 + 17 /kft + 330 > 580 PROTECTION BLOWS FUSES Resistance

28 PROTECTION BLOWS FUSES Loop Compliance Resistor = 24V / 50 ma > 480 ohm I loop = ( 600 / Total R) * 20 ma < 20 P = (0.020) 2 * 330 = 0.13 W

29 u Generally shorts u Positive leadblow fuse u Negative leadground loop PROTECTION BLOWS FUSES Semiconductor Failure S S D I I

30 CURRENT IN ELECTRODES Case 6 SituationI = 14 A in both ground beds Environment petrochemical plant, Alabama Gulf Coast pipeline station 1/2 mile soil = sand, > 50,000 ohm-cm isoceraunic 80 TSDY, intense combination = one of most

31 u Marshalling panelpos, neg, gnd u Chassisshort to shield u Eachsmall circulating I u 1400 digital inputslarge I CURRENT IN ELECTRODES Non - Isolation

32 u Shorted together u Do not crop to jacket u Insulate individual ends u Do not touch metal u Terminate on shield strip u Single point ground CURRENT IN ELECTRODES Shields

33 CURRENT IN ELECTRODES Single Point

34 FAN MOTOR ON TOP OF BOILER Case 7 SituationFails when lightning hits surrounding Environment power generation, W Texas soil = shallow top soil on rock, ~ 100,000 ohm-cm isoceraunic 43TSDY

35 u 4160 V motor u 70 ft above earth u 5 kv unshielded triplex u In tray & conduit u Acts as antenna u 2 grounding conductors FAN MOTOR ON TOP OF BOILER Equipment

36 L = 0.279 uHy / ft L = 56 uHy / 100 ft L = 0.5 uHy / ft typical XL = 220 ohm @ 1 MHz XL >> R FAN MOTOR ON TOP OF BOILER Gnd Conductor Z ( AWG 4 )

37 u Lightning arrestors on terminals u MOV u Bond all metal u Shield cable FAN MOTOR ON TOP OF BOILER Fix

38 STRUCTURE ATTRACTS LIGHTNING Case 8 SituationDamages xmitters & boards Frequent hits Environment research facility NE Oklahoma soil = loam, 6500 ohm-cm isoceraunic 55 TSDY

39 u Not tallest structure u More conductive than others u Bond around base pins u Bond framework u 1 / 0 AWG u Non - corrosive terminals u Gound guy wires STRUCTURE ATTRACTS LIGHTNING Dissipate Energy

40 u Rat - race ring u If > 50 ft, criss - cross u Bond to existing grid u Radials 1 / 0 AWG u 5 ft rods, 20 ft spacing STRUCTURE ATTRACTS LIGHTNING Ground Network

41 HIGH RESISTIVITY SOIL Case 9 SituationSingle motor from distribution system Environment pump SE New Mexico soil = 6500 ohm-cm on rock at 4 ft isoceraunic 47 TSDY

42 u Dwight’s formula R = [ p / 191.5 b] [ ln ( 48 b / a ) - 1 ] R = 177 ohm, 1 rod R = 76 ohm, 3 rods > 25 ohm >> 5 ohm HIGH RESISTIVITY SOIL 5 / 8 “ x 8 ‘ Rod

43 u Retain moisture u Alkalinityfree ions u Resistivity3000 ohm - cm u 1 rod10.6 ohm u 3 rod4.6 ohm HIGH RESISTIVITY SOIL Concrete ACME CONCRETE

44 SHOCK ON GROUNDED PANEL Case 10 SituationGrounded panel permitted shock Environment pumping panel, NE Oklahoma soil = loam, 6500 ohm-cm isoceraunic 55 TSDY

45 u Power panel outdoors u Overhead distribution, 277 / 480 Y gnd u 5 / 8 “ x 8 ‘ rod u Occasional shocks u Inspected returned to service SHOCK ON GROUNDED PANEL System

46 u Secondary pinch ~ 50 ohm u Circulating I = 1 amp u Two ground paths u Gnd rod ~ 25 ohm u Body ~ 40,000 to 1,000 ohm SHOCK ON GROUNDED PANEL Problem

47 277/480 v120 v SHOCK ON GROUNDED PANEL

48 0.6 ma 40 K 24.4 ma 1 K 341 ma 14 A Install lo Z ground SHOCK ON GROUNDED PANEL Body Current

49 u Personnel6 ma u Equipment30 ma u Not required for this SHOCK ON GROUNDED PANEL GFCI

50 CURRENT IMPACT MAPhysiology 1 sensation 8painful shock 15can’t let go 20possible damage 50ventricular fibrillation 100probable death

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

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

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


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