MAINTENANCE
Service Manual M4 - M10
24.01.2003
Page
21
6.2.2 Capacitors
Frequency converters have large aluminium electrolytic capacitors in DC –link
as PWM –type units use to have. Al electrolytic capacitors are commonly used
due the fact that they have very good capacitance value compared to the can
volume and also high ripple current capacity.
In normal operation leakage current of the capacitor are low based on
dielectric aluminium oxide layer (forming) on the foil. If capacitors or units
having capacitors are stored long period without applied voltage, the oxide
layer will not be homogenous anymore and when voltage is connected, the
high leakage current can exist and might damage capacitors. This is typical
feature of Al oxide type capacitors and is not depending on the manufacturers
of the capacitors. With converters it means that capacitors, charging
resistors, rectifier etc. might be destroyed if forming is not adequate after
long storage period and the unit is connected to the mains voltage.
6.2.3 Re-forming after long storage period
Complete units
When complete units are stored without voltage applied for example in sales
stock or as a spare units in the factory, the re-forming of the capacitors
should be done at least 12 month period by connecting the voltage into unit
and keep unit powered minimum 1 h.
If the storing time is much longer than a year since unit was energized last
time, the re-forming of the capacitors have to be done in a way that the
possible high leakage current through the capacitors is limited. Best
alternative is to use DC power supply provided with adjustable current
limitation. Current limit has to be set for example to 300…500 mA and DC
power supply has to be straight connected to the +/- terminals of the DC-link
or straight to the terminals of capacitors.
CXS models, which have no DC+ terminal, because having built in brake
chopper, can be energized as following:
•
Frame size M3; DC-supply is connected between two input phases.
•
Frame sizes M4b/M5b; DC-supply is connected to the +/- terminals
which are available on power board under the control board but are
reachable without removing the control board.
DC voltage has to be adjusted up to nominal DC voltage level of the unit
(1.35*Un ac) and has to be supplied at least 1h.
If DC –power supply is not available and unit has been stored much longer
