Two transmission lines (double-circuit 230 kV and single-circuit
525 kV) are near a Medical Building and Hospital in Northern Virginia.
The 230 kV lines (double-bundle) are only 80-100 feet from the Medical
Building while the 525 kV lines (triple-bundle) are 200-240 feet. Behind
the Medical Building is the emergency room and hospital (not shown in
picture).
The Profile Plot (see below) shows a 15.4 mG peak under
the 525 kV center conductor and a 12.5 mG peak beneath the outer 230
kV circuit (the other 230 kV circuit appears to be de-energized). Magnetic
field levels were between 2-6 mG inside the Medical Building and less
than 1 mG inside the hospital. The outside temperature was 94.5 degrees
(F) when the survey was performed. It should be noted that during seasonal
peak loads the magnetic field levels could easily double or triple since
these are high current transmission lines. Therefore, the levels within
the Medical Building could increase to between 6-18 mG under worst-case
conditions.
Magnetic Field Management Solution:
Install a Passive Wire Magnetic Field Cancellation System
around the transmission line right-of-way (ROW) to (mitigate) reduce
the magnetic fields inside the Medical Building and Hospital to less
than 2 mG and 1 mG, respectively. 
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