Triplett Mitigator Loop Coil – 3232 - Manual (Page 19)

suggest that there aren’t pieces of test equipment that the power company can use to measure har-
monic currents. There are. Two of the more common brand names are Dranetz and BMI. However, the
local power company may not have one of these available. Even if they do, their equipment is designed
to measure harmonic current flow in the power lines, not the magnetic fields produced by these cur-
rents. The actual magnetic fields, while closely related to the current flowing in the power lines, is
affected by various other factors, like power line geometry (spacing, height, etc.), magnetic field cancel-
lation, magnetic field distortion caused by metallic objects in the vicinity, Ground Return Current, etc.
Since the telephone lines respond to the induction produced by the magnetic fields, it is more appropri-
ate to examine the fields rather than the current flowing in the power lines.
SECTION 13: “FIRST TIMERS”
Solving a harmonic noise problem will require a coordinated effort. And since the power company may
be unfamiliar with causes and fixes for harmonic problems, they may end up relying upon the telephone
craftsperson to tell them what to do.
For those just embarking upon this adventure with no prior experience and no power company con-
tacts, it would be wise to “study up” on the things that we’ve just briefly mentioned. Various training
sessions and seminars are put on by consultants who are intimately familiar with the problems and are
well versed in the solutions. These “experts” could do a lot to improve your understanding of noise
mitigation and give you the confidence to tackle a noise problem that requires coordination.
Many states have started associations where power and telephone people get together and informally
discuss their problems and try to decide on a plan of action for solving them. Their names often end in
the letters . . . PCA, which means Power and Communications Association. For example, Missouri has
the MPCA and Oklahoma has the OPCA.
SECTION 14: SOLVING THE PROBLEM
14.1: OVER-EXCITED TRANSFORMERS
The obvious thing to do when transformers are over-excited is simply to turn down the voltage. The
power company can do this, and by making some other changes, still supply their customers with the
necessary 120 volts of power. Since the propensity for a transformer to produce harmonic currents is
determined by its construction, a different transformer may produce less harmonic currents. The prob-
lem transformer could be “changed out” with a lower distortion transformer. Beware, however, that if
the power company “turns down” the voltage where you are having problems, that they may have to
boost the voltage somewhere else, which means that instead of solving the noise problem, you might be
transferring your noise problem down the road.
14.2: VOLTAGE REGULATORS
Voltage regulators have a range of approximately ±10%. This amount of adjustment can obviously over-
excite down-line transformers. The power company can adjust the regulator so that when it is turned up
all the way, its output voltage is low enough that it won’t over-excite down-line transformers. It may also
be possible to re-distribute some of the loads so that a much smaller adjustment range is required.
14.3: RELOCATING TRANSFORMERS AND CAPACITOR BANKS
Because harmonic currents often develop between transformers and capacitors, it makes sense that
relocating the transformer, capacitor, or both, could alter the flow of harmonic currents so as to reduce
the severity of the noise induced into the telephone lines. Sometimes, it is not possible to reduce the
harmonic currents themselves, but it may be possible to re-route the currents in such a way so as to
reduce the exposure to the telephone cable.
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