3
Power Capacitors
for Power Factor Correction
Installation, Commissioning and Maintenance
The enclosures and control cabinets housing for power factor
correction systems must be dimensioned so that they can dissi-
pate the heat resulting from the capacitor power losses even at
the maximum permissible ambient temperature. The temperature
inside the enclosure or cabinet must also not exceed the maximum
allowable ambient temperature for the capacitors it contains.
Because of the their low power losses, the capacitors have a
high inrush current which can peak at values some 200 times the
nominal current. The capacitor and its switchgear must be able to
han dle this heavy current. Special contactors compatible with the
inrush current are therefore necessary for switching capacitors in
and out. Contactors with special precharge resistors in conjunc-
tion with pre-make contacts are able to limit the inrush current
effectively.
FRAKO
power capacitors exhibit a particularly high
switching endurance.
All
FRAKO
power capacitors have discharge resistors permanently
attached to their terminals for your personal safety, in compliance
with VDE regulations. These resistors discharge the capacitors
down to a residual voltage of less than 50 V in 60 seconds or less.
If a particular application calls for the capacitors to have faster
discharge times, additional bleed resistors or special discharge
chokes are required in addition to the permanently connected
discharge resistors. Discharge chokes are available in
FRAKO
‘s
range of accessories.
Harmonics
For many years now, the total harmonic distortion in public utility
and industrial networks has continued to rise. Harmonics are per-
turbations caused not only by electronically controlled devices such
as power converters, frequency converters and thyristor controllers,
but also by the AC adapters installed in PCs, television sets and
other electronic consumer goods. The operation of power capa-
citors can increase the level of harmonics and result in dangerous
network resonance. This can damage appliances connect ed to the
system or trip safety devices, thus causing power outages over
complete sectors. We have therefore developed special solutions
for the reliable operation of power capacitors in networks polluted
with harmonics. Please ask our specialists, who are always ready
to help you. Even in networks plagued with harmon ics, you are not
compelled to leave your power factor uncorrect ed!
Commissioning, operation and
maintenance
B efore the supply voltage is applied to the system, a visual check
should be carried out by a qualifi ed technician to verify that no
equipment or connections have worked loose during transport
and no mechanical damage can be identifi ed.
Damaged capacitors must not be put into service.
Capacitors and power factor correction systems should be che-
cked once every year in a systematic inspection by a specialist.
General
Please ensure that the capacitors are kept clean at all times, if
necessary having them cleaned without delay by skilled personnel.
During the annual inspection the capacitors themselves and the
complete power factor correction system must be given a visual
check by an electrician to verify good working order (sound electri-
cal contacts, no evidence of overheating, no blown fuses, etc.).
Capacitors
The capacitors must be checked visually during the annual inspec-
tion for any mechanical changes. Any variation in capacitance or
distortion by harmonics can be inferred from the operating currents
measured. There must always be good electrical contact at the
capacitor connections, which must remain clean and dry.
Fuses
LV HBC fuses undergo an ageing process when carrying the high
switched currents associated with capacitors. They should there-
fore be inspected at least once per year. We recommend replacing
the fuse links at the latest after ten years of service.
Contactors
Contactors that are specifi cally designed to switch capacitors in
and out must always be installed. Please therefore ensure when
replacing contactors that only the special capacitor-switching
type is fi tted.
The contacts of capacitor-switching contactors have a particularly
demanding duty. They should be tested for 100 000 switching cyc-
les and must be completely replaced once this number has been
reached. If the power factor correction system is controlled by a
FRAKO
control relay with a switching cycle counter (such as the
RM 9606, EMR 1100S, EMR 1100 or PQC), a separate message
is given for each stage after 80 000 switching cycles to inform
the operator that contactor replacement is imminent. The current
counter readings can be accessed via the
FRAKO
control relay
Note!
Wear and tear of the switching contacts has an adverse
effect on the service life of the capacitors!
Ventilation
In the case of power factor correction systems with forced ventila-
tion, it is essential to keep the air inlets and outlets clean to en sure
adequate cooling of the installed components. Cleaning may be
necessary at regular intervals throughout the year, the frequency
depending on the amount of dust that accumulates at the location
concerned. Filter mats must be carefully cleaned on a regular basis,
used mats being replaced.
