Troubleshooting
40
All phases should be checked for correct, clean, zero crossing.
If a waveform appears to be regular and sinusoidal over consecutive half periods, but does
not cross through zero, it is likely that the zero crossing detection hardware is defective and
the unit should be replaced. If however, the waveform is irregular the problem could lie
with the sensors. In this case check all cabling and power supply connections. If these are
satisfactory, return the unit if the problem lies with a voltage channel. For current channels,
try replacing or swapping the sensor with another one. If the new sensor does not work the
problem is internal to the AMU unit and it should be returned to Artesis.
If any phase has a marked difference in amplitude to other similar phases, the calibration
constant for that phase should be checked. If no external sensor is attached (i.e. for low
voltage motors) the calibration constant should be 1. If the calibration is correct, the sensor
may be defective and should be changed.
Check the current balance levels using the AMU front panel. A value below 15% is
acceptable, but above 15%, the Total Harmonic Distortion (THD) on all current phases
should be checked. Normal levels for THD can be up to 6% depending on conditions.
For values higher than this level check whether the distortion originates from the motor or
the line, by measuring the THD present at other motors connected to the same supply. If
the same level for THD is measured at other motors, the line supply is suspect and should
be investigated as high levels can damage motors in the long term.
Otherwise, the motor is probably already damaged in some way and should be investigated.
Check the voltage imbalance levels using the front panel. A value below 5% is deemed
satisfactory. Above this level, check the THD levels on each voltage phase. Levels above 5%
should be investigated. The ability of AMU to detect faults will be reduced as voltage
imbalance increases.
Check that all waveforms disappear when power is removed from the motor.
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