Large-Volume E.L.F. Magnetic Field Compensation [LV-EMFC] Research Project - part 3

    Note excellent agreement of magnitude plots, good agreement of phase data and  negligible variance in either data set. Deviation of phase survey data from simulation values over the -20m to +30m interval has been found to agree with ground conductivity effects not modeled in the simulation program.

    Overall building dimensions are 42m [128'] x 5m [16']. A.c. magnetic field values ranging between 7 and 14 milligauss, rms have been recorded in rooms which face a nearby, roughly parallel 4-circuit 345 KV right-of-way. At its closest approach, the near edge of the right-of-way lies approximately 14m [46'] from the Site structure.

    Pointblock magnitudes (i.e., discrete ACMF values on grid of specified resolution) corresponding to the source field are calculated by the simulation program for a best fit to survey data. To generate field magnitudes and relative phases, our simulation model employs an accurate physical description of the 4-circuit transmission line array and its known phasing, and scales the overall line currents as required to best match actual survey data. Uncompensated fields average about 0.61 µT (6.1 mG), rms, over the first 20 m of the building nearest and perpendicular to the source transmission lines.

    Phase I evaluation of simulated active-feedback system for a building such as the Beta Site is multi-step process. First, a detailed magnetic field survey is made throughout a volume which includes the proposed site protected volume [PV]. Next, simulation models are created which produce a close approximation of the survey a.c. magnetic field data. Finally, the active-feedback components (sensors, transfer characteristic and driven coils) are added, along with initial and step parameters, and the optimization iterations are begun. In the proposed Phase II development, a pointblock data integration module permitting direct entry of survey data into the simulator will be added to the simulation code package.