Public Service Commission of Wisconsin

Public Service Commission of Wisconsin

Stray Voltage Phase I and Phase II

Combined Database Summary

January 26, 2006

Since 1988, the Public Service Commission (PSC) has been accepting data filed by the five major

investor-owned utilities (IOU¡¯s) regarding certain aspects of their stray voltage (SV) Phase I

investigations. Recently, the database has been expanded to include extra fields from their Phase II

investigations. The Wisconsin Electric Cooperative Association has also been submitting some data

on behalf of a number of its members in the last few years. Please refer to the glossary in Appendix A

for definitions of various terms and acronyms use in this document. All voltage and current data is

express as rms, 60-Hz, AC, steady state.

To date, the PSC SV database has entries from 7,441 farms. A separate database of Phase II primary

profiles now has data on 12,430 grounded distribution poles. The data from these databases is

summarized in this paper. A statistical summary for each parameter is presented along with

correlations and contrasts between some of the parameters. All of the submitted data is accepted as it

comes in. Some data are suspect as the magnitudes do not seem within a reasonable range, but are

included and will appear as statistical outliers. Entries of zero or blank fields are treated the same ¨C as

a ¡®no report¡¯ condition.

Farms reported per year in PSC database

800

700

600

500

400

300

farms

200

100

20

05

20

04

20

03

20

02

20

01

20

00

19

99

19

98

19

97

19

96

19

95

19

94

19

93

19

92

19

91

19

90

year

19

89

19

88

0

There were very few submissions to the database in the first five years of record keeping, but the last

thirteen years has shown a relatively steady level of submissions. Only half of the 2005 data had been

received by the time this report was prepared.

The data can be analyzed and presented using several statistical methods. Each numerical parameter

has an overall average along with a 5-number summary that lists the minimum value, the median

1

value, the maximum value along with the first and third quartile values. The distribution of values for

each parameter is summarized in a graph or a table that lists the percent of entries that fall within a

specific range of values. These statistics provide a standard yardstick against which any subsequent

data point collected in the field can be compared to see how it measures up and where it falls within

the known range of reported values.

A historic trend of the values versus the year they have been submitted is also presented in graphic

form. Lastly, a correlation is usually made with the most important parameter, the average cow

contact current, to see if the parameter in question may have any influence on the magnitude of current

that can be measured at the animal contact point or itself be influenced by the cow contact current.

Farm s in PSCW Utility Database - T rend

8000

7000

Database total

6000

5000

4000

3000

2000

2005

2004

2003

2002

2001

2000

1999

1998

1997

1996

1995

1994

1993

1992

1991

1990

YEAR

1989

0

1988

1000

The data are divided up into electrical and similar parameters and farm and miscellaneous parameters

as follows.

Electric parameters

Location within WI

Distance to substation

Grounds per mile

Rshunt

Vp Primary neutral-toreference voltage

Vs Secondary neutral-toreference voltage

End-of-line status

Vcc Cow contact voltage

Primary Voltage

Icc Cow contact current

Neutral Conductor

Resistance/mile

Vcc source on/off farm

status

Transformer kVA rating

As-found mitigation

Measured Vps drop

Secondary phase

arrangement

Rsource

Farm/misc. parameters

Recommended on-farm

mitigation

Recommended off-farm

mitigation

Recommended neutral

isolation

2

Load box test

Rprimary

Fencer status

Load box test Rfarm

Stanchion/other milking

Load box test K-factor

Pipeline/other delivery

Load box test CRR ¨C

current return ratio

Secondary neutral

voltage drop test

Vdrop

Primary profile current

Ipp

Primary profile

resistance Rpp

Primary profile voltage

Vne

Electric/pneumatic

pulsation

Herd size

Test program

Milk production level

Somatic cell count (SCC)

level

ELECTRICAL PARAMETERS

1) Distance to Substation

This parameter is defined as the circuit miles from the farm being investigated to its serving

distribution substation.

7 number

Distribution % in

summary

UNIT

Range

range

mile

Average

6

0.1 - 1.0

3.3

mile

Minimum

0.1

1.1 - 3.0

20.1

mile

1st quartile

3.5

3.1 - 6.0

39.6

mile

Median

5

6.1 - 10.0

25.5

mile

3rd quartile

7.8

10.1 - 15.0

9.1

mile

Maximum

55

15.1 - 21.0

2.0

Entries, N

7,068

21.1 & up

0.4

Average distance to substation trend

7.5

7

6.5

6

5.5

5

miles

4.5

4

3.5

year

19

88

19

89

19

90

19

91

19

92

19

93

19

94

19

95

19

96

19

97

19

98

19

99

20

00

20

01

20

02

20

03

20

04

20

05

3

The trend indicates that in the early years of the SV program at the PSC, most farms that were

investigated by the IOU¡¯s were closer to the substation. Recently, there is a trend to investigate farms

that are farther away from the substation. From 1988 to 2005, the average distance has increased 44%.

Avg. Icc vs. Dist. to substation

N = 6772

C orrel C oeff. = -0.04

1.4

1.2

1.18

1

0.94

0.92

0.84

0.78

0.8

0.67

0.71

0.6

0.4

mA

0.2

0

.1 - 1.0

1.1 - 3.0

3.1 - 6.0

6.1 - 10.0

M iles range

3

10.1 - 15.0 15.1 - 21.0 21.1 & up

There is a slight visual correlation between cow contact current levels and being too close or too far

from the substation. The data is skewed by the fact that early investigations (1988 ¨C 1993) found

higher levels of stray voltage than are found today and these farms were close to the substation. The

mathematical correlation coefficient indicates a very weak link between distance and cow contact

current.

2) Location

One of nine specific areas of the state where the farm is located is submitted as a data point. The areas

are named central, east central, north central, northeast, northwest, south central, southeast, southwest

and west central. They are determined by a table look-up based on the county in which the farmstead

is located. The average cow contact voltage and the average secondary neutral-to-reference voltage for

each of the nine locations is shown in the following table.

Avg Vcc

points

Avg Vcc

points

Avg Vcc

points

total points

Avg Vcc (Volts) vs. location:

0.47

0.28

0.33

315(NW)

645(NC)

428(NE)

0.38

0.33

0.30

362(WC)

824(C)

1,612(EC)

0.51

0.48

0.62

987(SW)

1,214(SC)

161(SE)

6,548

Avg Vs

points

Avg Vs

points

Avg Vs

points

total points

Avg Vs (Volts) vs. location:

1.42

1.07

1.19

320(NW)

645(NC)

427(NE)

1.29

1.18

1.03

369(WC)

827(C)

1,503(EC)

1.31

1.28

1.44

981(SW)

1,205(SC)

159(SE)

6,436

We can calculate an average K-factor (defined as Vcc/Vs) for each of the nine locations as follows:

Average K-factor (N = 6,079)

in percent from above data

Overall average = 29%

29(NW)

24(NC) 27(NE)

28(WC)

26(C)

27(EC)

32(SW)

33(SC)

37(SE)

The average K-factor for the state is therefore 29% which agrees well with the typical value of 33.3%

predicted by the PSC REPS team.

3) Grounds per mile

This parameter is defined as the average number of neutral-to-earth grounding electrode connections

on the primary distribution system per mile in the area of the farm towards the substation.

4

7 number

summary

Distribution

Range

UNIT

Grnds/mile

Grnds/mile

Grnds/mile

Grnds/mile

Grnds/mile

Grnds/mile

% in

range

Average

13

1-4

0.6

Minimum

1

5-8

5.0

1st quartile

9

9 - 12

53.7

Median

12

13 - 16

20.1

3rd quartile

15

17 - 20

11.1

Maximum

33

21 - 24

6.9

Entries, N

6,418

25 & up

2.6

Wisconsin has always required nine grounds per mile in any continuous one mile section for overhead

distribution systems and 4 grounds per mile for underground distribution systems. The measurement is

made starting at any point on the line to include at least one mile, if possible, or a prorating thereof.

Modified in 1996, PSC ch. 114.096C now requires a connection between the distribution neutral and a

grounding electrode at every pole for all new rural overhead construction.

Trend of average grounds/mile

17

16

15

14

gr / mi

13

12

11

20

05

20

04

20

03

20

02

20

01

20

00

19

99

19

98

19

97

19

96

19

95

19

94

19

93

19

92

19

91

19

90

year

19

89

19

88

10

No data for this parameter was submitted before 1992. The trend shows the effect of the 1996 change

in code, as there was an overall decrease in the recorded average grounds per mile between 1992 and

1996 of 2.5%. From 1996 to 2005, however, the average has increased 37%.

Avg. Icc vs. Gnds/mi.

C orrel C oeff. = -0.041

N = 6255

1.2

1.09

1

0.95

0.8

0.79

0.8

0.72

0.69

0.61

0.6

0.4

mA

0.2

0

1 - 4

5 - 8

9 - 12

13 - 16

Gnds/m i. range

5

17 - 20

21 - 24

25 & up

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