Triplett Mitigator Loop Coil – 3232 - Manual (Page 20)

If capacitor banks are creating a resonant condition at a harmonic frequency, it may be possible to move
the capacitor bank to a different location, thereby altering the power line inductance and changing the
resonant frequency. If the new resonant frequency is not at a 60Hz [50Hz] harmonic, then there will be
little current flow.
Sometimes capacitor banks can be changed in value or removed from circuit. These possibilities should
be discussed with the power engineer. Occasionally, the capacitor banks will be found to be an unnec-
essary leftover from a since modified power distribution scheme. Removing capacitors from circuit for
the purpose of testing or permanent noise reduction may be as simple as pulling their fuses.
14.4: “FLOATING” CAPACITOR BANKS
When all of the capacitor banks are removed from circuit for the purpose of testing, the craftsperson
usually finds that a significant reduction in Power Influence will occur on the affected telephone cable.
Reductions of 15 to 20dBrnC [P] are typical. If this were to translate into improvement in Circuit Noise,
as it often does, then Circuit Noise would also drop by 15 to 20dBrnC [P].
Unfortunately, the power lines cannot be operated efficiently without the capacitors connected. As
each capacitor is put back “on-line”, the exposed telephone cable’s Power Influence will rise back up to
the original level. It may be discovered, though, that 1 or 2 capacitor banks affect the Power Influence
significantly, and the rest have only a minor effect. Wouldn’t it be nice if there was some way to satisfy
the power company’s need to have these capacitors on-line but be able to prevent them from increasing
the phone cable’s Power Influence?
It just so happens that such a solution exists. And the best part is that, sometimes, no additional devices
need to be added to the power line or the telephone line. This magic technique is called “floating the
capacitor bank”.
Unfortunately, this technique ONLY works on 3 phase lines, and some power companies will not allow
their capacitors to be floated. Even so, this is a viable technique for the situations in which it can be
used.
So how does it work? Figure 9 shows an electrical diagram of a 3 phase capacitor bank connected to a
3 phase power line. Notice that one side of all 3 capacitors connect together to the “wye point”, and
that this is connected to the power line neutral. The neutral is also connected to earth ground. The wye
point is obviously held at earth ground potential.
Figure 9
19