Triplett Mitigator Loop Coil – 3232 - Manual (Page 25)

If the harmonic currents could be confined to the area where there is no exposure, then no noise would
be induced into the phone line. So how do we trap the harmonic currents in the “No Exposure” zone?
By using a capacitor bank...
Since harmonics like to flow through capacitors, we can take advantage of this effect and force the
factory’s harmonic currents to flow in a localized loop in the No Exposure Zone. The capacitor bank is
placed on the power line after it diverges from the phone line. Consequently, the harmonic currents will
be “trapped” on the section of power line between the factory and the capacitor bank.
It is likely that some of the harmonic current will escape the trap and flow on the power line back to the
substation. If the level of the harmonic currents are low enough, they may not cause any undue rise in
noise on the exposed phone line. If, however, the induced noise is still a problem, the trap can be made
more effective by placing an appropriately sized inductor at the capacitor bank location. By tuning the
trapped circuit to some degree of resonance, by using the proper value inductor, more of the harmonic
current can be trapped in the No Exposure Zone.
This is essentially opposite to the approach taken with the HSR. But in the case of the HSR, the power
line in question was exposed to the phone line along its entire length.
Actually, an HSR could be used as the inductor used to trap the harmonic currents, as long as the
current through the HSR is below its maximum current rating. Sometimes, a special inductor is used
instead of an HSR.
SECTION 15: SUMMARY
The techniques and procedures outlined in this manual are not meant to be an in depth examination of
Loop Coil use or harmonic current problems. This text only takes a superficial look at these issues.
There is more information available on these topics. Various telephone company (Bell, AT&T, etc.) and
government (REA) Methods and Practices detail individual test techniques and solutions. On the power
company side, the Westinghouse Transmission and Distribution manual is the handbook of the industry.
Using the Triplett 3232 Loop Coil, a Triplett MITIGATOR, and some knowledge and experience, a
craftsperson should be able to fix harmonic noise problems that have gone unsolved for years.
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