Typical neighborhood in Northern Virginia (less than 15
years old) with single-phase 34.5 kV underground residential distribution
(URD) line and 100 KVA ground mounted distribution transformer(large
green box in picture). The URD is normally buried 3-6 feet below the
surface and runs from transformer to transformer supplying the primary
power. Each 100 KVA transformer provides electrical power to 4-6 homes
depending on the anticipated demand - all electric homes require more
power than fossil fuel (gas/oil) heated homes.
The Profile Plot (see below) shows a 22.1 mG peak directly
over the URD and elevated levels between 7-22 mG around the front yard.
This data was recorded during a summer seasonal peak load on 30 July
1994. Magnetic field (actually magnetic flux density) levels within the
house were between 3-6 mG and vertically polarized (notice the elevated
levels were in the Bz direction).
Unfortunately, there is a significant Net Current (calculated
to be 14.9 amps) on the URD which generates the magnetic field. If the
URD was balanced - that means the current on the "hot" 34.5 kV inner
core wire is equal to the current on the "multigrounded neutral" outer
sheath - the magnetic fields around the URD would be nearly zero. On
top of the transformer box there are elevated levels ranging between
50-250 mG. Keep children off and away from the transformer. Magnetic
fields quickly diminish to less than 3 mG about 4-6 feet away from most
transformer sources.
Magnetic Field Management Solution:
Install an Active Magnetic Field Cancellation System around the house
to (mitigate) reduce the magnetic field levels inside the house to less than
2 mG.
Install a ring of thorny shrubs around the transformer
to discourage children from sitting and playing on the transformer.
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