Triplett Mitigator Loop Coil – 3232 - Manual (Page 24)

Note: SNC is a manufacturer of HSRs and is very knowledgeable about their use. They offer a “white
paper” and a video tape that describes HSR applications and installation methods. For the craftsperson
considering the use of HSRs, their paper and video tape is very informative and is highly recommended.
14.6: FUSES
Capacitor banks are usually fused. On a three phase capacitor bank, there are three fuses, one on each
phase. For various reasons, such as a lightning strike, one or more of the fuses may open. If this occurs,
a sudden increase in noise on a nearby telephone line may occur. Removing capacitor banks from a
power line will not always cause a reduction in telephone noise. It may cause the noise to increase!
If one or two fuses in a three phase capacitor bank open, the capacitor bank itself will be unbalanced.
Some harmonic frequencies do benefit from magnetic field cancellation (the odd “non-triple” harmon-
ics). Since harmonic frequencies tend to flow readily through capacitors, in the process creating can-
celing magnetic fields, open fuses will prevent the current flow and the subsequent beneficial fields.
Solving this problem is as easy as replacing the fuses. Open fuses are easily identified from the ground
because they “hang open” when they blow.
14.7: BAD CAPACITORS
Capacitors can go bad. You can’t tell by looking at the capacitor if it’s bad. In a three phase capacitor
bank, the three capacitors need to be of the same value. Sometimes, a capacitor will go bad and
change value. In all other aspects, it will look OK.
This problem can be identified by examining the 60Hz [50Hz] current through each capacitor. The 60Hz
[50Hz] current through each capacitor should be similar. If a significant difference in current is found,
the capacitors should be removed from circuit and tested. Don’t go by the markings on the capacitors.
These have been known to be wrong! They sometimes get mis-marked by the manufacturer.
Another problem to be wary of. The KVAR rating on the capacitor is ONLY VALID if the power line and
the capacitor are of the same voltage rating. If the ratings are different, be suspicious. The KVAR rating
was probably “sized” to provide a certain degree of power factor correction. Since the KVAR rating of
the capacitor depends on its voltage rating, if it is connected to a different line voltage than it is rated for,
its KVAR value is different! This means that the power company may not be providing the amount of
correction to the line that they thought they were. Consequently, they may opt to re-size the capacitor
bank, and in the process, the telephone noise may be abated (or it may get worse).
14.8: “TRAPPING” HARMONICS
Sometimes, noise can be reduced by INCREASING the flow of harmonic currents. This technique is
based upon attempting to control the telephone line exposure to the harmonic currents. Consider a
situation in which an isolated (no telephone lines in the vicinity) transformer and capacitor create a
resonant circuit. Even though the harmonic current flow may be very high, and the magnetic fields
generated very strong, if there are no telephone lines in which to induce noise...then no noise will be
forthcoming.
Now, consider a situation in which a power line runs parallel to telephone line for several spans and then
diverges from the telephone cable’s path. Perhaps the power line runs from a substation to an industrial
facility (factory) that has harmonic generating equipment. Let’s say that the power line diverges from the
phone line before going into the factory. Because of the harmonic currents drawn by the factory, mag-
netic fields will be created down the entire length of the power line back to the substation. So, in the
area where the power line parallels the phone lines, the exposure will allow noise to be induced onto the
phone lines.
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