GROUNDING SYSTEM DESIGN FOR ISOLATED LOCATIONS AND PLANT

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

GROUNDING Introduction u Common feature u Technology well defined not always effective application is art

PRESENT TECHNOLOGY Introduction u NEC u Green u Emerald u Lightning u Previous 35 pp requirements -- not design RP industrial -- not electronics RP power quality sensitive equip shield & shunt discharges - not devices requirements & design procedures

PRESENT TECHNOLOGY Introduction u NEC u Green u Emerald u Lightning u Previous 35 pp requirements -- not design RP industrial -- not electronics RP power quality sensitive equip shield & shunt discharges - not devices requirements & design procedures

PROJECT 10 Case Studies of Ground Problems u Situation present problem u Environment influences effectiveness of system u Analysis investigates alternatives & unique u Summary brief response to situation little things mean a lot -- pay attention to detail

REMOTE SENSOR ERRATIC Case 1 Situation very 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

REMOTE SENSOR ERRATIC Case 1 Situation very 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

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

REMOTE SENSOR ERRATIC Effect 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 No Such Thing As Common Ground AWG 2/0 bond Lo R = 0. 0003 / ft L = 0. 5 u. H / ft XL = 3 ohm / ft Hi Z to lighting f = 1 Mhz (4 order, 10000 X) I surge > 3000 A V drop = 9000 v / ft EE

UNUSED POINTS INDUCE ERRORS Case 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

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

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

FAILURE DURING STORM Case 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

FAILURE DURING STORM What Is It? 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 Fix u Isolate unshielded cable u Common mode DCS u Differential mode xmitter u In - line both u MOV 36 V, 160 J u Woops, commercials ground protector MOV

DATA FAILURE BETWEEN BLDGS Case 4 Situation perimeter 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

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

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

PROTECTION BLOWS FUSES Case 5 Situation protectors 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

PROTECTION BLOWS FUSES Follow Through Current u Gas tubes u Zener u MOV u Shorts long short 15 sec transmitter u 90 fuses per storm

PROTECTION BLOWS FUSES Non - Incendive Resistor u Small u Large u Power u 4 minimize loop compliance limit I continuous - 20 ma, 24 VDC ~ 600 ohm u In positive lead

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

PROTECTION BLOWS FUSES Loop Compliance Resistor = 24 V / 50 ma > 480 ohm I loop = ( 600 / Total R) * 20 ma < 20 P = (0. 020) 2 * 330 = 0. 13 W

PROTECTION BLOWS FUSES Semiconductor Failure u Generally shorts u Positive lead u Negative lead blow fuse ground loop I S D I S

CURRENT IN ELECTRODES Case 6 Situation I = 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

CURRENT IN ELECTRODES Non - Isolation u Marshalling panel u Chassis u Each u 1400 digital inputs pos, neg, gnd short to shield small circulating I large I

CURRENT IN ELECTRODES Shields 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 Single Point Supply PLC 24+ 24 - 24+ 24 s + _ 120 V Load Source H N G Xducer H N G

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 43 TSDY

FAN MOTOR ON TOP OF BOILER Equipment 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 Gnd Conductor Z ( AWG 4 ) L = 0. 279 u. Hy / ft L = 56 u. Hy / 100 ft L = 0. 5 u. Hy / ft typical XL = 220 ohm @ 1 MHz XL >> R

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

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

STRUCTURE ATTRACTS LIGHTNING Dissipate Energy 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 Ground Network 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

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

HIGH RESISTIVITY SOIL 5 / 8 “ x 8 ‘ Rod 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 Concrete u Retain moisture u Alkalinity free ions u Resistivity 3000 ohm - cm u 1 rod 10. 6 ohm u 3 rod 4. 6 ohm ACME CONCRETE

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

SHOCK ON GROUNDED PANEL System 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 Problem 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 277/480 v 120 v

SHOCK ON GROUNDED PANEL Body Current 0. 6 ma 24. 4 ma 341 ma 40 K 1 K 14 A Install lo Z ground

SHOCK ON GROUNDED PANEL GFCI u Personnel 6 ma u Equipment 30 ma u Not required for this

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

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

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

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