Service manual
5.1.5 Motor/Load Problems
Problems with the motor, motor wiring, or mechanical load
on the motor can develop in a number of ways. The motor
or motor wiring can develop a phase-to-phase or phase-to-
earth short resulting in an alarm indication. Checks must
be made to determine whether the problem is in the
motor wiring or the motor itself.
A motor with unbalanced, or unsymmetrical, impedances
on all three phases can result in uneven or rough
operation, or unbalanced output currents. For
measurements, use a clamp-on style ammeter to
determine whether the current is balanced on the three
output phases. See 6.4.6 Output Imbalance of Motor Supply
Voltage Test.
Usually a current limit warning indicates an incorrect
mechanical load. If possible, disconnect the motor from
the load to determine if the load is incorrect.
Quite often, the indications of motor problems are similar
to those of a defect in the frequency converter itself. To
determine whether the problem is internal or external to
the frequency converter, disconnect the motor from the
frequency converter output terminals. Perform 6.4.6 Output
Imbalance of Motor Supply Voltage Test procedure on all
three phases with an analog voltmeter. If the three voltage
measurements are balanced, the frequency converter is
functioning correctly. Hence, the problem is external to the
frequency converter.
If the voltage measurements are not balanced, the
frequency converter is malfunctioning. This typically means
that one or more output IGBTs are not switching on and
off correctly. This can be a result of a defective IGBT or
gate signal.
5.2
Internal Frequency Converter Problems
If an over temperature indication is displayed, determine
whether this condition actually exists within the frequency
converter or whether the thermal sensor is defective. If
not, the temperature sensor must be checked.
5.2.1
Current Sensor Faults
When a current sensor fails, it is indicated sometimes by
an over-current alarm that cannot be reset, even with the
motor cables disconnected. However, the frequency
converter experiences frequent false earth fault trips. This
is due to the DC offset failure mode of the sensors.
The simplest method of determining whether a current
sensor is defective is to disconnect the motor from the
frequency converter. Then observe the current in the
frequency converter display. With the motor disconnected,
the current should be zero. A frequency converter with a
defective current sensor indicates some current flow. An
indication of a fraction of one amp is tolerable. However,
that value should be considerably less than one amp. If the
display shows more than one amp of current, there is a
defective current sensor. All three current sensors in
FC 101 units are mounted on one circuit board (either
power card, SMPS card, or current transducer card). The
repair procedure is to replace all three current sensors at
the same time.
5.2.2 Signal and Power Wiring
Considerations for Electromagnetic
Compatibility
This section provides an overview of general signal and
power wiring considerations when addressing the Electro-
magnetic Compatibility (EMC) concerns for typical
commercial and industrial equipment. Only certain high-
frequency phenomena (such as RF emissions, RF immunity)
are discussed. Low-frequency phenomena (such as
harmonics, mains voltage imbalance, notching) are not
covered.
NOTE
Special installations or compliance to the European CE
EMC directives require strict adherence to relevant
standards and are not discussed here.
5.2.3 Effect of EMI
While electromagnetic interference (EMI) related distur-
bances to frequency converter operation are uncommon,
the following detrimental EMI effects may be seen:
•
Motor speed fluctuations
•
Serial communication transmission errors
•
Frequency converter CPU exception faults
•
Unexplained frequency converter trips
A disturbance resulting from other nearby equipment is
more common. Generally, other industrial control
equipment has a high level of EMI immunity. However,
non-industrial, commercial, and consumer equipment is
often susceptible to lower levels of EMI. Detrimental effects
to these systems may include the following:
•
Pressure/flow/temperature signal transmitter
signal distortion or aberrant behaviour
•
Radio and TV interference
•
Telephone interference
•
Computer network data loss
•
Digital control system faults
Frequency Converter and Mot...
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HVAC Basic Drive Service Manual
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