Use of mains filters:
Radio interference filters and mains filters (combination of radio interference filter and one mains
choke) serve for protection against high-frequency disturbances, which are sent out via the power
cable or the radiation of the power cable. The high-frequency disturbances should be limited to a
mandatory or legal degree. Mains filters should possibly be mounted close to the thyristor controller
and moreover it is necessary to ensure that the connecting cable between the thyristor controller and
the mains filter is as short as possible.
CAUTION: The mounting surfaces of the thyristor controllers and the radio interference filters have to
be free from paint and well conducting in the high-frequency range.
Furthermore, mains filters have leakage currents, which may become significantly larger than the
nominal values in case of failure (phase failure, unbalanced load). To avoid dangerous voltages, the
mains filters have to be grounded. As the leakage currents are high-frequent disturbances, the
grounding measures have to be low-resistance and extensive.
With leakage currents, which exceed the value of 3,5mA, VDE 0160 or EN 60335 specify that either:
Ÿ
the cross section of the protective conductor has to be
≥
10mm²,
Ÿ
the protective conductor has to be monitored on interruption or
Ÿ
a second protective conductor has to be laid.
Shielding measures:
Shielding measures help to reduce the radiated interference energy. Electrical lines between thyristor
controller and load can be laid shielded. Thereby the shield must not replace the PE line. Four-wire
cables (three PE), whose shield is double-sided and extensive laid on earth potential (PES),
are recommended. The shield must not be applied over the connecting wires. Interruptions of the
shielding e.g. in the case of clamps, contactors, mains chokes etc. have to be bridged with low-resis-
tance and appropriate space considerations.
In practice this can be done for example by interrupting the shield close to the assembly and then
connecting it extensively with the earth potential (PES, shield clamp). The free cables, which are not
shielded, should not be longer than 100mm.
Grounding measures:
Grounding measures are absolutely necessary to fulfil legal provisions. They constitute a prerequisite
for an efficient use of further measures such as filters and shielding. All conductive, metallic housing
components have to be electroconductive connected with the earth potential. For the EMC-measure,
the important factor is not the cable´s crosssection, but its surface, since this is where high frequency
current flows to earth. Once again, all grounding points have to be led directly, extensively and with low-
resistance to the central grounding point (equipotential bonding bar, star-shaped grounding system).
The contact points have to be free from paint and corrosion (use galvanized mounting plate and
materials).
7
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Thermokon Sensortechnik GmbH - Thyristor controller TS1 3Ph, TS1 SP 3Ph