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Wind facility transmission line interference with telephone lines  

Author:  | Impacts, Minnesota

In the Matter of the AWA Goodhue Wind, LLC, Applications for a Certificate of Need and large wind Energy Conversion System Site Permit for the 78 MW Goodhue Wind Farm in Goodhue County, Docket Numbers IP-6701/CN-09-1186 and IP-6701/WS-08-1233.

I, Robert C. Weiss, General Manager of Hector Communications Corporation submit these written comments on behalf of the Sleepy Eye Telephone Company, a subsidiary of Hector Communications Corporation.

Sleepy Eye Telephone Company is a rural telephone company providing telecommunication services in Goodhue County since 1968. In order to provide these services, Sleepy Eye Telephone Company has buried copper cables and fiber optic cables in the right of ways of Goodhue County roads. This was done with the permission of the county through its permitting process. These cables were manufactured according to IEEE standards and placed underground according to Rural Utility Service specifications.

Sleepy Eye Telephone Company is concerned that there is a possibility that the transmission lines carrying the 34.5 kV wind generated electricity may induce electrical interference into the underground copper telephone cables presently in place, rendering them unusable. This has happened in other parts of the Midwest . In 2005, this problem was discovered by Interstate Telecommunications Cooperative, Inc., in their facilities near Lake Benton Minnesota on what is known as the Buffalo Ridge. This is the site of numerous wind generators. Tests performed at several customer premises in the Lake Benton area by Mr. Barry Dardis of Dardis.com concluded that where copper telephone lines parallel the transmission lines for than 1/2 mile, the magnetic fields couple to the telephone circuits and longitudinal currents are induced into the cable pairs. Some of this current is converted to telephone circuit noise. I have attached copy of Mr. Dardis’ test information and conclusions to these comments as Appendix A. The affected copper cables had to be replaced with fiber optic cables and the necessary electronics to make them work.

The wind generation project proposed by AWA Goodhue Wind LLC in Goodhue County is going to cover a large part of the same area served by Sleepy Eye Telephone Company. Because of this, Sleepy Eye Telephone Company is concerned that there will be many areas where the transmission lines carrying the 34.5KV electricity from wind generators to the substations will parallel our cable routes for more than 1/2 mile, increasing the possibility of this noise problem. Since Sleepy Eye Telephone Company has constructed its cable routes in Goodhue County road right of ways with Goodhue County’s permission, in accordance with the County’s permitting process, and in accordance with Rural Utility Service specifications, it is Sleepy Eye Telephone Company’s contention that any costs to mitigate or eliminate noise problems on the company’s cable plant proven to be caused by the wind generation transmission lines be the full responsibility of the wind farm and transmission line developers and owners. This would include any costs to re-route the copper cables or replacement of the copper cables with fiber optic cables and the necessary electronics.

I have included the following information for your reference:

Appendix A: Dardis.com Inductive Interference Report, Lake Benton Minnesota.

In conclusion, Sleepy Eye Telephone Company does not oppose the development of wind generation facilities. However, if the proposed facilities will interfere with our commitment to provide the best telecommunication services to our customers, then the electrical noise and interference issue needs to be addressed in the final order issued by the Minnesota Public Utilities Commission.

I am available for any questions you may have pertaining to these comments.

Sincerely,
~~~
Robert C. Weiss
General Manger
Hector Communications Corporation

[[[[ ]]]]

APPENDIX A

Dardis.com
Barry Dardis
220 29th Ave NE
Great Falls, MT 59404
406-868-0697 cell
406-453-6995
dardis@dardis.com

7/29/2010
Inductive Interference Report
Lake Benton MN

Some of the telephone facilities in the Lake Benton telephone exchange area are exposed to inductive interference from 34.5 Kv wind generation transmission lines. Where the telephone lines parallel the transmission lines, the magnetic fields couple to the telephone circuits and longitudinal currents are induced into the cable pairs. Some of this current is converted to telephone circuit noise.

This will happen to some extent on all telephone circuits that parallel power facilities, transmission or distribution. It is the intensity of the magnetic field that determines the amount of interference. It is common for telephone and power companies to work together to mitigate these problems.

Definitions:

Power Influence. Harmonic currents induced into the telephone circuit. Measurements are in dBrnc.

Circuit Noise. Power influence, which has been converted to noise by imperfections in the telephone circuit. Measurements are in dBrnc.

Circuit balances. a number representing the quality of the telephone pair. A balance of 60 dB is the industry standard.

Power exposure. a uniform section of power where the power and telephone remain about the same distance from each other.

Ground Return IT. Current Tif, telephone influence factor, weighted, returning to the sub-station in the earth. If currents return in the earth there is no cancellation in the phase wires.

Ground Return IT measurement indicators:

0 to 500 – minimal interference
500 to 1000 – some interference
Over 1000 – major interference
Over 2000 – severe interference.

Test Equipment:

Triplett Mitigator Noise Test set and spectrum analyzer
CMC PairChek noise and telephone line test set
CMC My Helper 8370 remote tester and tone generator
ExTech digital clamp on amp meter

Testing Buffalo Ridge Area 6-14-05

Wind in the Buffalo Ridge area was very high. A set of noise measurements were taken at a customer’s NID and Green Window 100′ probe wire at location 200 yds North of the test residence on 160th Ave. This customer’s telephone cable had a 2 mile exposure to a 34.5Kv wind generator transmission line

Test from customer’s NID

Power Influence. 105 dBrnc
Circuit Noise. 45 dBrnc. this is an out of service level.
Balance. 60 dB. Telephone pair quality is good

Green Window Test

Green Window 100′ probe test
Ground return IT. 7150. this will cause severe induction .
60 Hz volt per mile. 13.9 volts
Cmsg noise per mile 100 dBrnc

Note: All of the displayed frequencies added together, equals the total power influence.

Conclusion

1. The telephone plant is in good condition indicated by high longitudinal balance.

2. The loop length has been reduced by the installation of Digital Carrier Systems.

3. All loops tested were under 18 Kft.

4. The cable shield is bonded for continuity and ground connections have been made at exposure changes.

5. Induction Neutralizing Transformers are being used in an attempt to cancel low frequency harmonics. They cannot be used in all cases because of distributed cable counts.

6. D′′ loading is being employed on some loops to improve signal to noise ratios.

7. The power transmission system is changing from day to day. There are multiple resonant conditions creating an extremely high ground return IT.

8. The wind turbines using pulse width modulation create high frequency harmonics. This adds to the high ground return IT numbers. These frequencies cannot always be shielded by the telephone plant because of the availability of shielding conductors on some routes.

9. The Telephone Company has done everything conceivable to mitigate the noise trouble on the existing plant. The best mitigation techniques will not solve an induction problem this severe. Ground return IT measurements exceeding 2000 are very difficult. Those exceeding 6000 are next to impossible.

10. I have been in touch with Dr Dave Hartmann a consulting engineer at Portland OR, 503-244-0767, and Einar Larson with Control Development at GE, 518-385-1883. I inquired about filtration of the collector ring transmission circuits. It can be done, but the expense would be very high. The equipment for each lead would be in excess of $100,000.00. The engineering study would also be very expensive. Filtration of the high harmonics would not prevent the transmission lines from going resonant at lower frequencies.

11. The expanse of the transmission lines and their changing character makes the reduction of the Ground Return IT most difficult, if not impossible. The only practical solution would be a fiber to the curb telephone system. This would reduce the exposure lengths to just a few feet and render the facilities impervious to induced noise.

Barry Dardis

This article is the work of the author(s) indicated. Any opinions expressed in it are not necessarily those of National Wind Watch.

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