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23. INSPECTION AND MAIN'TEMNCE
23.3
Replacing P a m
The inverter consists of a number of electronic component parts such
as
semiconductor devices.
Due
to their p h y s i c a l properties, it is anticipated that the following component
patts will deteriorate
with time,
kadw
to troubles or h e r e d performance of the inverter. They should be rephced
at regular Intervals for preventive maintenance.
(1) Cooling fan
A cooling fan is used to cool heat generating parts such as semiconductor devices in the
main circuit. Although the service life
of
the bearing used in the cooling fan is, under normal
operating conditions,
20,000
hours, it will vary in the range of 10,OOO to
35,000
hours
depending on ambient temperatures.
Therefore, if the system is continuously operated, it is necessary to replace the cooling fan
assembly every two to three years. Beside this regular replacement, if abnormal noise or
vibration is detecled during inspection, the cooling fan assembly should
be
replaced imme-
diately.
A large capacity aluminum electrolytic capacitor for smoothing the current is used in me direct
current circuit in the main circuit.
The
performance of the capacitor
is
degraded due to the
influence of ripple, etc. Although the service life of the capacitor varies depending on the am-
bient temperatures and operating conditions, the capacitor should be replaced
every five
years assuming that the parameter unit is used within specified environmental limits.
Since the deterioration of a capacitor accelerates over lime, it should be checked
at least
once a year. As it approaches the end of service life, it should be checked every six months
or at shorter intenals. The inspection items and defects which require the capacitor to be
replaced are summarized below.
1) Case conditions: Expansion
of
the case at the side and bottom
2) Sealing conditions: Excessive curvature or cracks
3) Safety valve conditions: Excessive expansion of the valve or an actuated valve
4) Others:
(2) Smoothing wpncltor
Check for
cracks, discoloration, leakage, or other
defects. Measure the
capacity. If
measured capacity is less than 85% of rated, the capacitor should
be
replaced.
(3) Relays
Relay contacts deteriorate with use. Relays should be replaced according to the total number
of makebreak operations (service life).
The following table shows the part replacement intervals. In addition to the parts given in this
table, lamps and other component parts having shorter service life should be inspected
at
regular intervals.
(4) Replacemsnt criterb
I
Part name
I
Typlcal nplllcrment
Intervals
[
Ropl-t
proodur
C o o l i n g Ian
Smoothing
capacitor
2
to 3
years
-
RelaV5
Replace
on
evidence of
deterioration
5
years
-99-
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