Discussion Group 3-57, Magnetic Fields of Underground Cables, met with 28 members and guests present on Monday afternoon.
As in the past, the meeting started with a discussion of current events related to magnetic field concerns in general, and more specifically magnetic fields of underground cable systems. I made the observation that the concerns about possible health effects of magnetic fields seemed to be somewhat less of a hot topic in the eastern US; however, several members stated that magnetic fields are still used as a basis to oppose the installation of new transmission lines. Mike Foty of Ontairo Hydro reported that plans for a proposed overhead 115-kV transmission line in Windsor, Canada were rejected due to magnetic field concerns. The 115-kV line will now be installed as a 115-kV pipe-type underground transmission line.
There was also some discussion that while there may be some diminishing of public concerns about health effects due to magnetic fields in the US, possibly as a result of a recent report by the US National Research council, there appears to be an increasing level of concern about magnetic fields from transmission lines in Europe and the far east.
The chairman summarized recent CIGRE activities related to magnetic fields of underground transmission cables. A joint study committee has recently completed two papers concerning magnetic fields of underground transmission that will be published in the CIGRE magazine ELECTRA. One paper describes calculation procedures for underground transmission lines without ferromagnetic components, and the second paper deals with calculation procedures for magnetic fields produced by underground cables with ferromagnetic components.
Brian Cramer of ComEd then gave a presentation titled "Discerning Low Level Magnetic Field Contributions from Background Levels". Mr. Cramer's presentation described a proposed method for quantifying the magnetic field produced by a power cable when there are appreciable background levels of magnetic field produced by other sources. The proposed method consists of making magnetic field measurements with and without current in the cables that are of interest, and a method of using the orthogonal components of the background field to determine the magnitude of the magnetic field produced by the cables. Tests were performed by ComEd to try out the proposed method, and it appears that the method yielded results that compared well with calculated values for the power cables.
The meeting concluded with a discussion of the procedure proposed by Mr. Cramer.
Discussion Group 3-57, met on Tuesday morning with 36 members and guests present. The discussion group has experienced a decline in attendance in recent years. The meeting started with a discussion of whether magnetic fields produced by underground cables is no longer an important issue or whether we need to refocus the objectives of the group.
The first part of our meeting consisted of a review of our activities since the group was first formed in 1989. This discussion also summarized the progress that has been made in calculation procedures for magnetic fields for cables and whether or not there are generally accepted procedures for performing the calculations. Two CIGRE documents that have been prepared by CIGRE joint task force of study committees 36 and 2l. One of these documents, which was published in ELECTRA, describes calculation procedures for underground cables systems without erromagnetic components. The second document, which has not been published, describes the use of finite element analysis programs to calculate magnetic fields in the vicinity of power cables when there are ferromagnetic components.
A suggestion was made that the group should give some attention to magnetic fields produced by cables in commercial buildings. There are numerous problems with magnetic interference with video display terminals.
Several utility members reported that there is general concem by the public concerning proposed transmission lines. However, magnetic fields is only a part of their concern. In many cases this concern has significantly diminished when the line is installed underground.
Steven Au of Toronto Hydo reported that a multidisciplinary group had been formed in Ontario to establish provincial magnetic field guidelines for power lines.
The group also discussed whether or not there is a need for an ICC guide on magnetic field calculation procedures for underground cables. Steve Swingler of the National Power Grid in the UK said that the recent publication of A CIGRE document on calculation procedures for underground cables without for magnetic components had been helpful when applying for permits to build a fine. Steve pointed out that the public sometimes questions the accuracy and objectivity of-magnetic field calculations that are performed-by engineers associated with an electric company. Being able to state that calculations have been performed according to a recognized publication or standard reduces requests for calculations to be verified by at our party. However, Mr. Swingler was of the opinion that developing an ICC standard isn't necessary since it would most likely be a duplication of effort. We decided to review the existing CIGRE publication at our next meeting.
There was a discussion of whether the group should document typical magnetic fields produced by power cables compared to typical residential magnetic field levels. The majority of those that expressed an opinion thought that this was not an appropriate objective for 3-57.
