eei occupational safety & h lth c itt c fhealth committee conference s/eei fall... ·...

EEI Occupational Safety & EEI Occupational Safety & H lth C itt C fH lth C itt C fHealth Committee ConferenceHealth Committee Conference

Brian ErgaBrian ErgaESCI, Inc.ESCI, Inc.SC , c.SC , c.

October 2, 2007October 2, 2007

Protective Grounding MethodsProtective Grounding Methods Tests

-Keith Wallace, P.E.

O P j t fOur Project focus:

Comparing Methods ofComparing Methods of Grounding

• worksite grounding with pole bands (cluster bars)pole bands (cluster bars)

• worksite grounding without pole bands (cluster bar)

OSHA RequirementsqOSHA 29 CFR1910 269( )(3)1910.269(n)(3)

"E i t ti l " T t ti"Equipotential zone." Temporary protective grounds shall be placed at such locations

d d i h t tand arranged in such a manner as to prevent each employee from being exposed to h d diff i l t i l t ti lhazardous differences in electrical potential.

Fault TestingFault TestingTransformers

3 x 333 kVA, 4.3% Z7200 / 480V

Vacuum BreakerLine Regulators(set at 10% raise)Generator

Breaker

2.5 MVAMotor-Generator

5kV output

MG PhaseConnection

NeutralConnection

Fault TestingNEETRAC Project No. 05-035

Not to scale

Seven (7) Spans - 1084.5 feet (330.6 meters)

Pole 6

127'

327 Ohms

Pole 5 Pole 3

196' 178'

106 Ohms53 Ohms282 Ohms

Pole 4 - Midspan

Pole 2

180'

238 Ohms

Pole 2

148.5'

176 Ohms

Pole 1

Fault TestinggThree grounding configurations

Fault Testing ResultsgThree pole categories

•No pole ground wireNo pole ground wire

•Insulated pole ground wire

•Bare pole ground wire

Worker in contact with Neutral

MMan

Fault TestingFault TestingNo pole ground wire

Case N b

Worker l i

Type worksite di h d

V Ф N

If (mA)Number location grounding method Ф-N

NB1 On neutral No pole band 20.3 20.3

NB2 On neutral Pole band 1 25.2 25.2

NB3 On neutral Pole band 2 20.5 20.5

Fault TestingFault Testingbare ground wire

Case N b

Worker l i


V Ф N


B1 On neutral No pole band 17.4 17.4

B2 On neutral Pole band 1 21.4 21.4

B3 On neutral Pole band 2 17.6 17.6

Fault TestingFault TestingInsulated ground wire

Case N b

Worker l i


V Ф N


IB1 On neutral No pole band 19.3 19.3

IB2 On neutral Pole band 1 24.7 24.7

Pole band 2 -- --

Worker Circuit – worker onWorker Circuit worker on pole

Man

Fault TestingFault TestingNo pole ground wire

Case Number

Worker location

Type worksite grounding method

V Ф-N*

If (mA)dry

If (mA)wet

N1 On A2 No pole band 448 .047 --

N2 On A2 Pole band 1 at A1 448 056 495N2 On A2 Pole band 1 at A1 448 .056 .495

* - removed Ф-N jumpers to increase current through worker - removed Ф-N jumpers to increase current through worker to measurable value

Fault TestingFault TestingInsulated ground wire

Case Number

Worker location


V Ф-N*

If (mA)dry

If (mA)wet

I1 On A2 No pole band 450 .037 .19

I5 On A2 Pole band 1 at A1 450 080 2 3I5 On A2 Pole band 1 at A1 450 .080 2.3

* - removed Ф-N jumpers to increase current through worker to measurable value

Fault TestingFault TestingBare ground wire

Case Number

Worker location


V Ф-N*

If (mA)dry

If (mA)wet

B1 On A2 No pole band 443 .039 .78

B5 On A2 Pole band 1 at A1 443 045 57B5 On A2 Pole band 1 at A1 443 .045 .57

* - removed Ф-N jumpers to increase current through worker to measurable value

Element TestinggPole resistivity

R=ρ*LVoltage sourceTest Resistor

R=ρ*LA

Wooden poleContact resistance

Contact resistanceWooden poleresistance

significantresistance significant

Element TestinggPole band contact resistance

R=ρ*L +R(band)ρ ( )A

Element TestinggStaple contact resistance

R=ρ*L +R(staple)ρ ( p )A

Element Testing Resultsg

Wooden pole resistances - from 500Ω -700kΩ /ft.Pole bands - from 4kΩ to 800kΩStaples/nails - from 10kΩ to 100kΩ

Pole band and staple resistance are a function of pole resistivity and surface moisture.

Fault TestingFault TestingResults

Pole band contact resistances are large and greatly reduce the theoretical effectivenessgreatly reduce the theoretical effectiveness of the pole band.

Worksite grounding provides as much or more protection than pole bands

Critical Factors The current through the worker is a function of:

•Fault current at jumper location

•Impedance of grounding jumpers

•Resistance of worker circuit (worker, pole, contact resistances)

•Pole resistivities

•Location of grounds relative to workers

NEETRAC Project 05-161Evaluation of Direct Neutral vs.

Pole Band Grounding


Types of Tests

1 - High current tests with temporary grounds Φ-G (2000 3500 A t 480 lt )(2000-3500 A at 480 volts)

2 - High voltage tests on dry pole without temporary grounds Φ-G (6650 Volts)

3 - High voltage tests on wet pole without g g ptemporary grounds Φ-G (6650 Volts)

4 – High voltage tests on wet pole with temporary4 – High voltage tests on wet pole with temporary grounds (6650 Volts)

Conclusions

1 – If pole band is used, bond phases to neutral, th t l t l b d ( id dditi l jthen neutral to pole band (avoid additional jumper impedance).

Conclusions

2 – In the case of a metal pole, the pole must be b d d t th t l C t t i t dbonded to the neutral. Contact resistances, and pole resistances are minimal.

Conclusions 3 – A worker located between the source and the temporary grounds will be exposed to a higher

lt d t ki th l d id fvoltage compared to working on the load side of the temporary grounds. (The extra conductor is in series with jumper impedance)in series with jumper impedance)

Larger exposure voltage

source

Ifault

Ifault source

Ifault

Ifault

Ifault Ifault

Conclusions 4 – The exposure voltage will reduce in direct proportion to the length of the temporary ground. I i th di t i f th tIncreasing the diameter size of the temporary ground also reduces the exposure voltage, but to a lesser extenta lesser extent.

Example: 10 ft Copper temporary groundExample: 10 ft Copper temporary ground

1/0 2/0 4/01/0 2/0 4/01.59Ω 1.57Ω 1.11Ω

Conclusions5 – Bracket grounding on adjacent poles will develop less Φ-N exposure voltage compared to p p g pgrounding at the worksite.

source 15 1mAsource 15.1mA

source 6.7mA

Developed following “man on the pole” models:

ΦA (3P3, 3P3G)

R =1 kΩ

ZTPG=0.9+j1.27 mΩ(10’, 2/0 TPG, Table 3)

R ff R= 260.5 kΩ

Rworker =1 kΩ

Gaff (3P3F)

ZN-R by WinIGS0 542+j0 366 Ω

(3P3 N)

Rgaff-R 260.5 kΩ

Downlead and Ground Rod (150 Ω)0.542+j0.366 Ω

T t lt did ’t h

Figure 12: Workpole Model for

Test results didn’t show much difference between bare pole ground and insulated pole groundDirect Grounding Method on

Wet CCA Wood Poleinsulated pole ground

Developed following “man on the pole” models:

ΦA (3P3, 3P3G)

ZTPG=0.9+j1.27 mΩ(10’, 2/0 TPG, Table 3)

Gaff (3P3F)

Rworker =1 kΩ

R =71 3

(3P3 N)

Rgafft-PB/N =71.3 kΩ

ZN R by WinIGSZN-R by WinIGS0.0344+j0.024 Ω Downlead & Ground

Rod (150Ω)

Figure 13: Workpole Model for Pole Band Grounding Method on gWet CCA Wood Pole

Computer Modeling

1Ph1Ph

1Ph

Modeled distribution line with four 150Ω grounds per mile to maximize neutral system

G

1Ph 1Ph 1Ph

1Ph

1Ph1Ph

3-Ph, 2.2 mi, 4 grounds/mi @ 150 Ohms

Ph-A line, customer loads & grounds

SUB 3P2 3P33P3G3P45 3P67 3P8 3P10 3P11 ST1 ST2 ST3

ST3A

ST4

ST4A

ST3BST3CST3Dy

impedance.

G

1Ph

1Ph1Ph1Ph 1Ph 1Ph 1Ph

Ph-A line, customer loads & groundsConductor Sizes Ph (N): 1/0 (#2) ACSR

SUB 3P2 3P33P3G3P45 3P67 3P8 3P10 3P11 ST1 ST2 ST3 ST4

ST5ST6ST7ST8ST9ST10ST11ST12Moved the1Ph 1Ph 1Ph 1Ph

1Ph

1Ph

1Ph

Ph-A line, customer loads & grounds

ST8AST8BST8CST8DST5A

ST5B

Moved the “man on the pole” model everywhere on

1Ph

1Ph

Ph-A line, customer loads & grounds ST5TST5B

ST5C

ST5D

everywhere on the distribution line to look for the worst case

1Ph

1Ph ST5D

ST5E

the worst case.

Conclusions

For these models, the worst case location for the pole band case on a wet pole is a function of the maximum fault current – i.e. near the substation.

For these models, the worst case location for the no pole band case on a wet pole is a function of p pthe maximum phase-to-remote earth – i.e. one half mile from the substation.

Conclusions

10kA

e kV

8kA 4kV

ent k

A

h vo

ltage

6kA

4kA

3kV

2kVult C

urre

ote

earth

2kA 1kV

Fau

e to

rem

421 3 Pha

se

Distance from the substation - milesDistance from the substation miles

Table 7Computed Exposure Currents for Wet CCA Wood Pole, Phase to Pole Contact (Figures 10, 12 and 13)

L-L SystemV lt

ΦA-NFault Current

I

Temporary Protective Ground (TPG) Connection

* ΦA -PB-N or ΦA-N-PB (Cases with Pole Band) $ ΦA-N (Cases with No Pole Band)VoltagekV

InSubstation

A

( ) $ ( )

TPG CurrentA

ΦA-Remote Earth

Voltage@ Work pole

V

Exposure Current

mA

TPG Current

A

ΦA-Remote Earth

Voltage@ Work pole

V

Exposure Current

mA

V V

12 5322 5092 230 0.24 2726 1785 6.8

11161 10180 461 0.48 3566 2335 8.9

24728 20250 916 0.96 4153 2720 10.4

25 5152 5049 228 0.24 3662 2398 9.17

10685 10250 463 0.48 5601 3668 14.0

21854 20060 908 0.95 7318 4793 18.3

35 5112 5038 228 0.24 3990 2613 10.0

10354 10060 455 0.48 6445 4221 16.1

21252 20020 906 0.95 9092 5954 22.8

* Representing a worse case, the work pole is located 150’ from the substation.$ Representing a worse case the work pole is located 0 565 miles from the substation$ Representing a worse case, the work pole is located 0.565 miles from the substation.General Note for All Cases: Presence or absence of a downlead with a ground rod has insignificant influence on computed exposure current.

Table 8Computed Exposure Currents on Steel Pole Connected to Neutral (Phase to Pole Contact), on Wood or Concrete Pole (Contact

between Phase and Hardware Connected to Neutral)

L-L SystemVoltage

kV

ΦA-NFault Current

in SubA

Temporary Protective Ground (TPG) Connection

* ΦA–PB-N or ΦA–N-PB or ΦA-N (Neutral Connected t St l P l N t l C t d t H d W dto Steel Pole or Neutral Connected to Hardware on Wood

or Concrete Pole )

TPG CurrentA

ΦA-Remote Earth

Voltage

Exposure CurrentmA

@ Work poleV

12 5322 5092 230 17

11161 10180 461 35

24728 20250 916 69

25 5152 5049 228 17

10685 10250 463 35

21854 20060 908 69

35 5112 5038 228 17

10354 10060 455 34

21252 20020 906 69

* Work pole is located 150’ from the substation.General Notes for All Cases: 1) Presence or absence of a downlead with ground rod has insignificant influence on computed exposure current. 2) Resistance of the (steel) pole base to remote earth is assumed to be 200 Ω.

Where do we go from here?•Need more accurate model of wooden poles (3 dimensional) surface potentials) p

•Need more accurate model of contact resistance

N d th d f d li f t ti l•Need method for modeling surface potentials on poles

•Perform parametric analysis varying types of wooden poles, grounding methods, voltage l l d f lt t l l

Keith Wallace P E

levels, and fault current levels


Incorrect Simple Model –wooden pole with no pole ground and pole bandwooden pole with no pole ground and pole band

voltage 1000 Ω.002 Ωjumper manSource

Rneutral

It is a common misconception that the pole band holds the voltage on the pole above the g ppole band at the same potential as the neutral.

Common MisconceptionIf the pole band held the voltage on the pole above

Equipotential Zone

voltage on the pole above the pole band at the same potential as the neutral, pthe current through the man would not change

h th h i th l man

whether he is on the pole or touching the pole band.

m

No published test data support this idea.support this idea.

Better Simple Model

1000 Ωman

Source impedance

voltage

1000 Ω+footing resistanceR+jXΩ

Source

SmallNeutral system network

Small section of pole

Pole Band Contact ResistanceSource Resistance

Pole Resistance/

pole groundGround

Better Models – insulated pole ground wire

contact resistance(conductor to hand)

source impedance

body resistance

contact resistance(f t t l )

jumper impedancesource voltage

(foot to pole)

pole resistance(one foot)

neutral impedance(multi-grounded) contact resistance

(pole to poleband)

nds

pole resistance(~35 feet)

pole groundwire

pole

gro

un

contact resistance(pole to earth)

contact resistance(pole to electrode)

electroderesistance

Better Models – bare pole ground wiresource impedance

contact resistance(conductor to hand)

body resistancejumper impedancesource voltage

contact resistance(foot to pole)

pole resistance(one foot)

neutral impedance(multi-grounded)

contact resistance(pole to pole band)

pole groundwire pole resistance

(one-three feet)contact resistance

(pole to staple)

pole groundwire

pole resistance(one-three foot)contact resistance

(pole to staple)

pole g

roun

ds

contact resistance(pole to staple)

(p p )

pole resistance(~2 feet)

l t th

contact resistance(pole to electrode)

electrode

pole groundwire

pole to earthresistance

electrodeto earth

resistance

Wooden Pole ResistivityPole Length Avg Treatment R(total) R ρPole Length.

(m.)Avgdia

(cm.)

Treatment ( )(kΩ)

R(Ω/m)

ρ(Ω-m)

1 11.6 12.7 Creosote 52 4475 227

2 9 2 14 0 CCA 161 17579 10812 9.2 14.0 CCA –dry

161 17579 1081

3 9.2 8.3 CCA –dry

193 20984 449

4 12.3 11.6 CCA –dry

139 9968 478

5 12.3 13.0 CCA –dry

178 14472 764

6 9.2 11.3 No treatment

40 4432 178


56 6129 275


52 5663 249

9 12.28 12.7 CCA –damp

36.5 2972 151da p

10 12.28 12.7 CCA –damp

36.9 2972 153

Pole Band Contact ResistanceSample Length of Pole

(m.)Avg. dia.

(cm.)Pole Description Pole ρ

(Ω-m)Pole Band (kΩ)


178 886.3

2 9.20 15.4 No 275 610.79. 0 5. Notreatment

75 6 0.7


275 558.6


275 34.5

5 12.31 15.3 No treatment – damp

249 4.3treatment damp

6 9.20 15.3 No treatment – damp

249 15.4

7 9 20 16 4 CCA damp 151 602 37 9.20 16.4 CCA – damp 151 602.3

8 9.24 16.4 CCA – damp 151 631.1

Jumper Impedance Table 4TPG Impedance Test Data (Tests Performed on Pole 3, NEETRAC/SOCO Project 05035)

NEETRA ∗TPG Description Polar $Current Phase Angle TPG ImpedancesC

Test IDmΩ in TPGs

AmpsBetween

Voltage and Current∠°

φC -φB

φB -φA

φA - N Total TPG

LengthFt

Total TPG Imp

PolarmΩ

PU TPG Impedance

RectangularmΩ

1b One One One 6.2 (φA – N) 3463 ∠34.6° 10 1.79 ∠34.6° 0.179 ∠34.6° 0.147+j0.1010’

1/0 CU10’

1/0 CU10’

1/0 CU2a 18.8 (φC – N) 3791 ∠23.8° 30 4.96 ∠23.8° 0.165 ∠23.8° 0.151+j0.07

3a 6.1 (φC –φB) 3530 ∠30.2° 10 1.73 ∠30.2° 0.173 ∠30.2° 0.149+j0.09

4a One 6’2/0 CU

One 10’

2/0 CU

One 6’

2/0 CU

3.46 (φC –φB) 3587 ∠34.6° 6 0.97 ∠34.6° 0.162 ∠34.6° 0.133+j0.09

5a 12.3 (φC – N) 3564 ∠23.3° 22 3.45 ∠23.3° 0.157 ∠23.3° 0.144+j0.06/0 CU /0 CU6a 3.32 (φA – N) 3564 ∠38.7° 6 0.93 ∠38.7° 0.155 ∠38.7° 0.122+j0.09

7a One 25’

4/0 CU

One 25’

4/0 CU

One 25’

4/0 CU

10.2 (φA – N) 3564 ∠45.4° 25 2.86 ∠45.4° 0.114 ∠45.4° 0.080+j0.08

8a 30.0 (φC – N) 3610 ∠47.5° 75 8.30 ∠47.5° 0.110 ∠47.5° 0.074+j0.08

9a 11.0 (φC –φB) 3587 ∠51.8° 25 3.10 ∠51.8° 0.123 ∠51.8° 0.076+j0.10

∗ TPGs are connected from φC- φB - φA – N on Pole 3 and voltage applied between φC and N.$ Current duration = 0.217 seconds (13 cycles).

Staple Contact Resistance

Sample Length of Avg Pole Description Pole ρ (Ω- StaplesSample Length of Pole (m.)

Avg. dia.

(cm.)

Pole Description Pole ρ (Ω-m)

Staples(kΩ)

1 9 78 12 7 Creosote 227 11 01 9.78 12.7 Creosote 227 11.0

2 8.60 12.7 Creosote 227 24.0

3 3.44 13.7 CCA 3097 36.5

4 2.56 13.7 CCA 3097 42.8

Jumper Impedance Testing

Includes resistance of conductors,of conductors, ferrules and clamps, and inductance of conductors.

Jumper Impedance –E l 1/0 CUExample 1/0 CU

a b c

Z V /I Z=18 08V/3791A at 23 8 degrees

n

Z=Van/I Z=18.08V/3791A, at 23.8 degrees

Z= 4.77 mΩ, at 23.8 degrees (.159 mΩ/ft.)

Z= 4.36 + j1.93 mΩ (X=.064 mΩ/ft.)Ground jumpers are Z= R + jX mΩj p1/0 CU, each ten ft. in length for a

R= Rcable +Rconnections

Rconnections= R – Rcable = 4.36 – 3.15 mΩlength for a 30 ft. total

Rconnections R Rcable 4.36 3.15 mΩ

Rconnections= 1.21 m Ω


a b cZ=V /I Z=12 3V/3564A at 34 6 degrees

n

Z=Van/I Z=12.3V/3564A, at 34.6 degrees

Z= 3.45 mΩ, at 34.6 degrees (.157mΩ/ft.)

Z= 2.84 + j1.96 mΩ (X=.089 mΩ/ft)

Z= R + jX mΩGround jumpers are


Rconnections= R – Rcable = 2.84 – 1.83 mΩ

j p2/0 CU, 22 ft. total

connections



a b c

Z V /I Z=30V/3610A at 47 5degrees

n

Z=Van/I Z=30V/3610A, at 47.5degrees

Z= 5 61 + j6 13 mΩ (X= 082 mΩ/ft)

Z= 8.31 mΩ, at 47.5 degrees (.111m Ω/ft.)

Z= 5.61 + j6.13 mΩ (X=.082 mΩ/ft)

Z= R + jX mΩGround jumpers are


Rconnections= R – Rcable = 5.61 – 3.95 mΩ

j p4/0 CU, each 25 ft. in length for a


length for a 75 ft. total

Test 1Ifault ~2000-3000kA

TestNo

NEETRA

CTest ID

*Grounding Method/Configuration

Worker Between

WorkerExposure Voltage

(V) or Current (ma)

ΦA to Remote Earth Voltage

(V)

Neutral to Remote Earth

Voltage(V)

Current in TPGsAmps

ZTPGs Across the Worker

Tests with Pole Band

1 1 Worksite grounds on Pole 2ΦA- ΦB- ΦC-N-PB

ΦA & PBΦA & N (Pole 2)

9.28.9

153 147 2105 Z3TPGs=4.4 mΩZ3TPGs=4.2 mΩ

2 2 Worksite grounds on Pole 2ΦA- ΦB- ΦC-PB-N

ΦA & PBΦA & N

8.911 95

157 145 2172 Z3TPGs=4.1 mΩZ =5 5 mΩΦA ΦB ΦC PB N ΦA & N

(Pole 2)11.95 Z4TPGs 5.5 mΩ

3 5 Worksite grounds on Pole 2 ΦA- ΦB- ΦC-PB-N

ΦA & N (10’ on source side of Pole 2)

21.22 154 139 2104 Z4TPGs=10 mΩ (Includes imp. of 10’ of phase and

neutral conductors)

4 6 Worksite grounds on Pole 2ΦA ΦB ΦC PB N

ΦA & N (10’ on load side of

12 154 142 2138 Z4TPGs=5.6 mΩΦA- ΦB- ΦC-PB-N on load side of

Pole 2)

Tests without Pole Band

5 3 Worksite grounds on Pole 2ΦA- ΦB- ΦC-N

ΦA & N(Pole 2)

9.3 156 146 2206 Z3TPGs=4.2 mΩ

6 4 Worksite grounds on Pole 2 ΦA & N 5 9 154 143 2150 Z =2 74 mΩ6 4 Worksite grounds on Pole 2ΦA- ΦB- ΦC & ΦB-N

ΦA & N(Pole 2)

5.9 154 143 2150 Z2TPGs=2.74 mΩ



18.9 157 141 2195 Z3TPGs=8.6 mΩ (Includes imp. of 10’ of phase and neutral conductors)

8 8 Worksite grounds on Pole 2ΦA ΦB ΦC N

ΦA & N (10’ L d Sid

9.4 153 143 2105 Z3TPGs=4.5 mΩΦA- ΦB- ΦC-N on Load Side

of Pole 2)

9 9 Grounds on Pole 3ΦA- ΦB- ΦC-N

ΦA & N( Pole 2)

15.1 129 112 3417 Z3TPGs=4.4 mΩ


ΦA & N ( Pole 1)

15.1 - - 3417 Z3TPGs=4.4 mΩ

11 11 Bracket Grounds on Poles 1 & 3 (ΦA- ΦB- ΦC-N on each pole)

ΦA & N on Pole 2

6.72 123 115 3259 (Pole 3)104 (Pole 1)

-

*Voltage applied between φA and N

Test 2 (dry) & Test 3 (wet)Test 3 (wet)

Pole Band with bare pole groundbare pole ground conductor

Tests 2 & 3

bare pole ground conductor with no pole groundpole ground

Tests 2 & 3

Pole band with no pole ground

Tests 2 & 3

no pole ground with no pole band

Test No

NEETRACTestID

VΦA-NkV

Downlead Connected to Neutral

Pole Band

Grounding Connection Reference

I1013ΩmA

$I5.67ΩmA

*RΦA-neutral or RΦA-remote earth

kΩ

156.65 With

Figure 5A0.217

~ 6 30645

1 Insulated

2

146.65 Without

Figure 5B0.182

~ 6 36538

16 Figure 5C 0 30504

3

166.65

None

WithFigure 5C

0.2180 30504

4

176.65 Without

Figure 5D0.179

Not applicable

37151

5

12C6.65

Bare

WithFigure 5A

0.196~ 6 33928

6

136.65 Without

Figure 5B0.181

~ 6 36740

6

Table 5High Voltage Tests without TPGs on Dry Pole, Pole 5 (Category 2 Tests)$ Capacitively coupled ambient current* RΦA-neutral or RΦA-remote earth = (VΦA-N)/ (I1013Ω)

Table 6High Voltage Tests without TPGs on Wet Pole 5 (Category 3 Tests)

Test

NEETRAC VΦA Downlead

Grounding Connectio

I5.67ΩmA

*RΦA-neutralor RΦA remote

Commentst

NoC

TestID

VΦA-

NkV

Downlead Connected to Neutral

Pole Band

Connection

Reference I1013ΩmA

mA or RΦA-remote

earthkΩ

1 18

6.8 With

Figure 5A

94 44

72.34 ~ 8mA capacitively coupled ambient

current in the I5.67Ω

Insulated circuit

2 19

6.8 Without

Figure 5B

39 17


current in the I5.67Ωcircuit

3 20

6.8

None

With

Figure 5C

89 44



4 21 Figure 5D Not 261.546.8 Without 26 applicabl

e

5 22

6.8 With

Figure 5A

90 37



Barecircuit

6 23

6.8 Without

Figure 5B

38 12



* RΦA-neutral or RΦA-remote earth = (VΦA-N)/ (I1013Ω)

Test 1Ifault ~2000-3000kA

TestNo

NEETRA

CTest ID

*Grounding Method/Configuration

Worker Between

WorkerExposure Voltage

(V) or Current (ma)

ΦA to Remote Earth Voltage

(V)

Neutral to Remote Earth

Voltage(V)

Current in TPGsAmps

ZTPGs Across the Worker

Tests with Pole Band

1 1 Worksite grounds on Pole 2ΦA- ΦB- ΦC-N-PB

ΦA & PBΦA & N (Pole 2)

9.28.9

153 147 2105 Z3TPGs=4.4 mΩZ3TPGs=4.2 mΩ

2 2 Worksite grounds on Pole 2ΦA- ΦB- ΦC-PB-N

ΦA & PBΦA & N

8.911 95

157 145 2172 Z3TPGs=4.1 mΩZ =5 5 mΩΦA ΦB ΦC PB N ΦA & N

(Pole 2)11.95 Z4TPGs 5.5 mΩ

3 5 Worksite grounds on Pole 2 ΦA- ΦB- ΦC-PB-N


21.22 154 139 2104 Z4TPGs=10 mΩ (Includes imp. of 10’ of phase and

neutral conductors)

4 6 Worksite grounds on Pole 2ΦA ΦB ΦC PB N

ΦA & N (10’ on load side of

12 154 142 2138 Z4TPGs=5.6 mΩΦA- ΦB- ΦC-PB-N on load side of

Pole 2)

Tests without Pole Band


ΦA & N(Pole 2)

9.3 156 146 2206 Z3TPGs=4.2 mΩ

6 4 Worksite grounds on Pole 2 ΦA & N 5 9 154 143 2150 Z =2 74 mΩ6 4 Worksite grounds on Pole 2ΦA- ΦB- ΦC & ΦB-N

ΦA & N(Pole 2)

5.9 154 143 2150 Z2TPGs=2.74 mΩ



18.9 157 141 2195 Z3TPGs=8.6 mΩ (Includes imp. of 10’ of phase and neutral conductors)

8 8 Worksite grounds on Pole 2ΦA ΦB ΦC N

ΦA & N (10’ L d Sid

9.4 153 143 2105 Z3TPGs=4.5 mΩΦA- ΦB- ΦC-N on Load Side

of Pole 2)


ΦA & N( Pole 2)

15.1 129 112 3417 Z3TPGs=4.4 mΩ


ΦA & N ( Pole 1)

15.1 - - 3417 Z3TPGs=4.4 mΩ

11 11 Bracket Grounds on Poles 1 & 3 (ΦA- ΦB- ΦC-N on each pole)

ΦA & N on Pole 2

6.72 123 115 3259 (Pole 3)104 (Pole 1)

-

*Voltage applied between φA and N

AEP Wood Pole DistributionJobsite Grounding Tests

Preliminary Resultsy

EEI Occupational Safety and Health Committee ConferenceConference

Grounding – Industry PanelTucson, AZ

October 2, 2007John M. Schneider, Dr. Eng.John M. Schneider, Dr. Eng.Technology ConsultantDistribution Engineering [email protected]

Di l iDisclaimerThe procedures, methods and results presented herein are for e p ocedu es, et ods a d esu ts p ese ted e e a e o

informational purposes only and do not represent an endorsement by American Electric Power Company of any particular

grounding practices.

American Electric Power Company and its affiliates, expressly disclaims all liability, both direct and indirect, arising from the use or

application of any of the information, methods, or procedures found i thi t tiin this presentation.

Additionally, American Electric Power Company and its affiliates, disclaim any and all warranties with respect to the accuracy or usedisclaim any and all warranties with respect to the accuracy or use

of the information, methods, or procedures found in this presentation, whether expressed or implied, including the implied warranties of merchantability and fitness for a particular purpose.

2

E i t ti l G diEquipotential GroundingOSHA 1910.269 (n)(3) “Equipotential Zone”OSHA 1910.269 (n)(3) Equipotential Zone

Safe PotentialDifference?

3

‘E ga Pape ’‘Erga Paper’Discussions with various cluster ground barDiscussions with various cluster ground bar manufacturers, consultants and users revealed that the ‘Erga Paper’ forms the basis of its g peffectiveness in equipotential grounding applications. J T Bonne B E g W W Gibb V MJ. T. Bonner, B. Erga, W. W. Gibbs, V. M. Gregorius, “Test Results of Personal Protective Grounding on Distribution Line Wood Pole gConstruction,” IEEE Transactions on Power Delivery,Vol. 4, No. 1, January 1989.

4

EPRI T i i T i i VidEPRI Transmission Training Video

Phase

ClusterBar

© 2005 EPRI

Ground

5

CEA R t 101 d 876CEA Report 101 d 876

“Safety Grounding Practices for Personnel Working on Distribution Systems Up to 50kV,” CEA December 1997CEA, December 1997. Review of published wood pole measurement data & extensive computer simulations.data & extensive computer simulations.

“Equipotential Bonding…the effectiveness of this practice can range from nil to order-of-magnitude reductions in the resulting body currents, depending on the relative values of the f ll i k i bl l l it di l i t itfollowing key variables:…pole longitudinal resistance per unit length.”Pole longitudinal resistance is strongly dependent upon wood moisture content and distribution, which is

6

indeterminate.

‘Utility A’ Wood Pole Cluster G dGround Bar Test

In early 1970’s ‘Utility A’ field tested theIn early 1970 s, Utility A field tested the effectiveness of cluster ground bar:

S t t d t d j i tl ith l tSome tests conducted jointly with a cluster ground bar manufacturer.Ground bar did not provide consistentGround bar did not provide consistent protection.Concluded that ground bar should not beConcluded that ground bar should not be adopted.

7

‘Utility B’ Wood Pole Cluster G d B TGround Bar Tests

Recently commissioned series of testsRecently commissioned series of tests conducted at an independent laboratory

Contact resistance between cluster groundContact resistance between cluster ground bar and wood pole too high to be effective.Currently, leaning towards recommendingCurrently, leaning towards recommending installation of full pole ground, before maintenance on ungrounded structures.

8

‘I iti l’ W d P l R i t T t‘Initial’ Wood Pole Resistance TestCreosote (aged), CCA (new), Penta (new)Creosote (aged), CCA (new), Penta (new)Both dry & wet (tap water) poles tested.Aged creosote pole produced the worst case g p presult (best conductor of electricity), it was selected for the subsequent high voltage testingtesting.

T kΩ/ftType kΩ/ft(Worst case)

Creosote 0.66

CCA 7 1

9

CCA 7.1

Penta 15.5

AEP Test Set pAEP Test Setup

Recloser Test Pole7620 V

19.9 kV7620 V

2400/480 V

BixbySubstation

0.175Ω

10

Simulated Line MechanicSimulated Line MechanicHV Probe

Line-ground voltage500 Ω Body Impedance

10 Ω ShuntLine mechanic current

SimulatedGaff

Many standards (IEEE Std 80 2000) typically use

SimulatedHand130 cm2

Many standards (IEEE Std 80-2000) typically use 1000Ω body impedance.Neglects insulation provided by work boots, gloves &

11

clothing.Simulated gaff’s penetrated ~3/4”.

AEP Sh k C it iAEP Shock Criteria60 Hz Threshold ReactionCurrent (mA) Reaction

1 Perception level

3 Painful shock*

10 Let Go

E t i i t t30 Extreme pain, respiratory arrest, severe muscular contraction

157 ** Ventricular fibrillationLimiting Criteria

* Startle response may result in a fall, dropped tool, … .

** Hand to foot path, 1 second duration, 99.5% probability of no ventricular fibrillation for 154 lbs. person (Dalziel).

12

A o d of ca tionA word of caution…Distribution system design, service history, y g , y,operating procedures and environmental factors present a wide range of variability. Key variables are unknown or indeterminate.Cannot test every conceivable ‘real world’ scenario.Tests are intended to be representative of worst case conditions.Hence, caution must be exercised in the

li ti f th lt t d13

application of the results presented.

Nomenclature:Li M h i G ffLine Mechanic on Gaffs

GroundingJumper

PhaseWire

Insulator

Hands

NeutralWire

Bare Pole Ground w/Staples Line

Mechanic

304/116 mA1’

MoldingExtrapolated to

34.5/12 kV

H i ht

Gaffs

Ground Rod

Height

14

Cluster Ground Bar‘D ’ A d C t P l‘Dry,’ Aged, Creosote Pole

219/79 A221/80 A* 219/79 mA

ClusterG d

17.5’

221/80 mA*19.5’

18.5’

GroundBar

* l d / k

9/3 mA

* Extrapolated to 34.5/12 kV

27/10 mA

Bare Pole Ground w/Clips & Nails

15

Major OutcomeMajor OutcomeThe cluster ground bar does not consistentlyThe cluster ground bar does not consistently achieve a sufficiently low resistance contact with the wood, to provide an effective equipotential zone for a line mechanic working on the pole.

High Contact

Resistance

16

‘Wet ’ Aged Creosote Pole TestsWet, Aged, Creosote Pole Tests33/12 mA343/129 mA*

23/9 mA19.5’

227/85 mA

Isolated


39/15 mA 46/18 mA

17.5’14.5’

-11.5’

-8.5’

26/10 mA 17.5’227/87 mA

15.5’

17.5’

17

‘Wet ’ Aged Penta Pole TestsWet, Aged, Penta Pole Tests684/231 mA*

19 5’19.5’

165/63 mA3’

15/1 mA10’


286/110 mA8’

42/16 mA13’10’ Ground

18

S mmaSummaryThe presence of a ground rod, eitherThe presence of a ground rod, either permanent or temporary, does not adequately reduce the line mechanicadequately reduce the line mechanic current.The equipotential zone established with aThe equipotential zone established with a single lag screw (spike) does not protect the line mechanic in all positions on thethe line mechanic in all positions on the pole.

19

S mma Cont’dSummary Cont’d.Current through the line mechanic can be greduced substantially by:

Applying a single-point or bracket ground at the jobsitejobsite … Insuring the integrity of the neutral conductor and connections in the vicinity…Creating an equipotential zone (EZ) by bonding the neutral to either:

A full, uninsulated pole ground nailed/stapled to the pole., p g / p pA partial (10’), uninsulated pole ground nailed/stapled to the pole. (Must be disconnected from neutral when not in use.)

20

S mma Cont’dSummary Cont’d.The effective EZ extends from the midpoint of the pole ground length to the highest attachment on the structure.

In some circumstances, steps must be taken to protect the line , p pmechanic when entering or exiting the EZ.

EZ*10’

5’EZ*

PoleGround

d

d/2Molding

21Partial Pole GroundFull Pole Ground

Questions?Questions?

22

Single-Point Ground Radial Distribution LinePotential Distributions & Current Paths

PhasePotential

CurrentPath

Vs

ØØ

N N

G

Neutral

G

23

Potential