November 13, 2001
Dear Mr. Reines,
I am sorry that you feel that I misunderstood you when you meant to refer to the increase in lightening storms in California relative to Wisconsin and I understood you to say that the number of lightening strikes in Wisconsin had increased. Unfortunately, none of the other people present at the meeting with whom I have conferred remember California being mentioned, so you will have to admit the mistake was understandable. Further, since the question you were answering at the time was regarding why the Wisconsin PSC had felt it necessary to allow the utilities to ground the neutral at every pole in Wisconsin my error should be doubly understandable. However, if the supposed increase in lightening storms in California affected the PSC decision to allow grounding of the neutral at every pole in Wisconsin, I would still like to see the data that necessitated that move. If it did not, I would like to know why the PSC decided to allow grounding of the neutral at every pole and the evidence that supports that as a positive solution.
You mention that the PSC allows the utilities to ground the neutral at every pole in order to lower the neutral to earth voltages. The Handbook for the Assessment and Management of Magnetic Fields Caused by Distribution Lines EPRI TR-106003 Project 3959-07 by EPRI, with which you are doubtless familiar, mentions many ways to do that; none of which is adding grounding rods at every pole. I suspect that this is because they are aware that this reduces the neutral to earth voltage by allowing current to flow down the grounding wires and across the earth to the substation. This is forbidden by the National Electrical Safety Code (NESC) 92D, so they have ignored it as an option. They mention other possibilities including; increasing the size of the neutral to make "the neutral the lowest possible impedance path and conversely, the ground the highest possible impedance path", adding an additional neutral wire in parallel to make the neutral the lowest impedance path, and finally they say "A method that practically eliminates ground currents associated with primary distribution lines and still maintains the advantages of a four-wire multi-grounded system, is the five-wire system, shown in Figure 6-7." Has the PSC ordered the utilities to take any of the measures identified by EPRI for the elimination of ground currents? If not, why not? Why has the PSC not ordered the discontinuation of a practice which can only lead to more electrical ground currents, now that reliable methods for decreasing ground currents and neutral to earth voltage have been identified.
The "Survey to Determine the Age and Condition of Electric Distribution Facilities in Minnesota: Report 1: Analysis of Overhead Distribution Feeder Testing Data" has data that shows that in some of the distribution system over 70% of the power is returning to the substation via the earth. Ohm's Law, which says that current takes the path of least resistance (I=VR), proves that the neutrals must be overloaded if that much current finds the earth to be of lower resistance than the wire. It is possible for the wires to be sized as you say "such that all the loads, even at peak times, demand a fraction of the maximum current carrying capacity of that wire" and still not be able to carry all the current back to the substation. This can occur if you are sizing the wires with linear loads in mind and then the wires end up serving mostly non-linear loads. The high frequencies created by non-linear loads can overload lines sized for linear loads, as mentioned in EPRI report "Harmonics and Electrical Noise in Distribution Systems Measurements and Analysis" EPRI EL/EM 4290, as well as the IEEE 519-1992.
While it is true that "Grounding rods carry the current that the physics of their location dictates", they are supposed to be calibrated to have a higher resistance than the line. The only way they should be experiencing current flow is if the line is overloaded and therefore has a higher resistance than the grounding rod. Therefore, if they are carrying current on a regular basis they are functioning as "a conduit for "overload" current" and the earth is being used as part of the return path. I will bring to your attention again that it is forbidden by the National Electrical Safety Code (NESC) 92D for the earth to be used as the neutral return.
You state "Over 175 load box tests on Wisconsin farms for 7200-Volt and above primary systems gives an average of 68 percent current return on the neutral wire at the point of common coupling." This does not, however, address the question of how much of the current that leaves each substation returns to that substation on the neutral wire. Kirchoff's Law requires that an electron return to the substation for each electron that leaves the substation. Therefore, if you measure the net current flow on the phase conductors leaving the sub-station, it should be equal to the net current flow returning to the sub-station on the neutral wire. Please let me know what percent of the current returns on the neutral wire. The fact that you only have 68% return at the point of common coupling does not bode well for the numbers you would get if you measured at the sub-station. Your numbers suggest you must have lost 32% down the very first grounding rod. In all probability more was lost down each successive grounding rod on the way to the substation. This would violate National Electrical Safety Code (NESC) 92D which forbids the earth to be used as the neutral return.
You state in your reply "Your example of kilowatt-hours (energy) returning through the earth is not based on good engineering practice. It is the electric current that can return through the earth, as it is an integral part of the distribution system." The implication that number of kilowatt-hours sold bears no relation to the current is not true. Kilowatt-hours are directly related to watts. Since we know the time period the data represent we can calculate watts. The number of watts used is directly related to current and voltage. The number of watts is equal to the current times the voltage. If one knows the voltage at which the kilowatts were delivered one can calculate the current. Therefore the numbers I used are very representative of the severity of the problem.
There is no law of physics that requires the current to travel predominantly beneath the distribution line. According to Ohm's law current travels the path of least resistance and in some places it is possible that is beneath the line. You are correct that "The current flows through a three-dimensional structure of varying resistivity" because the resisitivity varies from point to point on the ground and current takes the path of least resistance it is impossible to say the current generally follows the line.
Please send me the data on the increase in lightening storms in California, if that played a role in the PSC's decision to allow grounding of the neutral on every pole. Please also let me know which of the EPRI identified solutions for ground currents the PSC has required to be implemented and the time frame for them to be implemented statewide. Please also let me know why the PSC has not discontinued the practice of grounding the neutral at every pole when the result so clearly violates National Electrical Safety Code (NESC) 92D and EPRI has identified other reliable alternatives. Please perform the return current tests at the substations and let me know what percentage of the return current returns to the substations on the neutral wire.
cc: Ave Bie, Public Service Commission
Mark Cook, Public Service Commission
Jim Loock, Public Service Commission
William Fannucchi, Public Service Commission
Secretary Harsdorf, DATCP
Secretary Phyllis Dube, Health & Family Services
Governor Scott McCallum
Randy Romanski, Office of the Attorney General
United States Senator Russell Feingold
Tom Still, Editor, Wisconsin State Journal
John Nichols, Editor, The Capitol Times
Gil Halsted, Wisconsin Public Radio
Chris Hardie, LaCrosse Tribune
Kurt Gutknecht, Wisconsin Agriculturist