5.2 Internal Frequency Converter Problems
The vast majority of problems related to failed frequency
converter power components can be identified by
performing a visual inspection and the static tests as
described in the test section. However, there are a number
of possible problems that must be diagnosed in a different
manner. The following discusses many of the most
common of these problems.
5.2.1 Overtemperature Faults
Overtemperature faults in the drive are typically the result
of blocked airflow or a faulty cooling fan. The overtem-
perature alarm message displayed indicates where the
fault exists.
Alarm 244,
Heatsink Overtemperature
. This normally
indicates a heatsink fan not functioning. While an overtem-
perature alarm message is displayed, all cooling fans
should be operating at full speed. Check the fans prior to
resetting the drive to determine the fault location.
Alarm 247,
Power Card Overtemperature
. This normally
indicates that the ambient temperature inside the drive
enclosure is too high. Check all air passages to ensure that
nothing is obstructing the air flow. Also check the filters
for the door fans and clean or replace if necessary.
With either of these alarms, the report value in the Alarm
Log displays which module experienced the overtem-
perature condition.
5.2.2 Open (Blown) Fuses
Open (Blown) Fuses
The frequency converter contains fuses protecting internal
circuits from excessive damage in the event of a
component failure. It must be emphasized that an open
fuse is an indication of a problem in that circuit. Do not
replace an open fuse and apply power to the drive
without checking for short circuits or component failures.
See the following descriptions for details.
Mains Input Fuses
An open mains input fuse typically indicates that there is a
shorted power component in either the rectifier or inverter
circuits. Perform the static test procedures to locate the
failed component(s).
Soft Charge Fuses
Each soft charge card contains three fuses which are in
series with the AC input to the card. This AC input powers
the soft charge circuit. It also connects to the power card
in each inverter module to supply power for the fans.
An open soft charge fuse can indicate a short in either the
soft charge rectifier or the fan transformer supplied by that
soft charge card. To locate the source of the problem,
perform the static test procedure for the soft charge
rectifier and the fan continuity test.
Fan Fuse
The fan fuse on each inverter module protects the fan
circuitry from excessive damage in the event of a failure in
the heatsink or door fans. Perform the fan continuity test
to determine the location of the defective fan.
DC Supply Fuse
The DC bus connection to each power card contains a fuse
in the positive DC lead. This is to protect the logic circuitry
from damage should a fault occur in the SMPS circuitry. It
is not recommended to replace an open DC supply fuse
without checking and possibly replacing the power card in
that module.
DC Bus Fuses
The DC bus connection to each inverter module is fused to
prevent excessive damage due to a shorted IGBT in the
inverter section. Typically, an open fuse indicates a shorted
or failed IGBT in the module.
Note, however, that an IGBT fault may fail the DC bus
fuses in adjacent inverter modules due to the quick
discharging of the DC capacitors through the shorted IGBT.
Perform a static test on all inverter modules if one or more
of these fuses are found to be open.
5.2.3 Current Sensor Faults
When a current sensor fails, it is indicated sometimes by
an overcurrent alarm that cannot be reset, even with the
motor leads disconnected.However, the frequency
converter will experience frequent false earth fault trips.
This is due to the DC offset failure mode of the sensors.
To explain this, it is necessary to investigate the internal
makeup of a Hall effect type current sensor. Included
inside the device is an op-amp to amplify the signal to
usable levels in the receiving circuitry. Like any op-amp,
the output at zero input level (zero current flow being
measured) should be zero volts, exactly halfway between
the plus and minus power supply voltages. A tolerance of
+/- 15mv is acceptable. In a three phase system that is
operating correctly, the sum of the three output currents
should always be zero.
When the sensor becomes defective, the output voltage
level varies by more than the 15mv. The defective current
sensor in that phase indicates current flow when there is
none. This results in the sum of the three output currents
being a value other than zero, which is an indication of
leakage current flowing. If the deviation from zero (current
amplitude) approaches a specific level, the frequency
converter assumes an earth fault and issues an alarm.
The simplest method of determining whether a current
sensor is defective is to disconnect the motor from the
frequency converter, and then observe the current in the
frequency converter display. With the motor disconnected,
Frequency Converter and Mot...
High Power Service Manual for Modular F Frame Drives
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