9-4 Diagnostics
1560D-UM051D-EN-P – February 2005
Fault Definitions (cont.) Voltage Unbalance Z
Voltage unbalance is detected by monitoring the three-phase supply voltages.
The formula used to calculate the percentage voltage unbalance is as follows:
V
u
= 100 (V
d
/ V
a
)
V
u
: Percent voltage unbalance
V
d
: Maximum voltage deviation from the average voltage
V
a
: Average voltage
The controller will shut down when the calculated voltage unbalance
reaches the user-programmed trip percentages.
Stall Protection
Stall protection is enabled at the end of the programmed ramp time after a
motor has been started. If the controller senses that the motor is not up to
speed at the end of ramp, it will shut down after the user-selected delay
time has elapsed.
Jam Detection [
Jam detection operates when the SMC Dialog Plus™ controller status is "at
speed". The controller will shut down when the motor current reaches the
user-defined trip level, which is based on a percentage of the programmed
motor full-load current rating.
Overload Protection
Overload protection is enabled in the Calibration group by programming the:
• Overload class
• Overload reset
• Motor FLC
• Service factor
Refer to Chapter 5 for more information on calibration.
Underload Z[
Underload protection is available for undercurrent monitoring. The con-
troller will shut down when the motor current drops below the trip level.
This trip level, a percentage of the motor's full-load current rating, can be
programmed.
Z Voltage unbalance protection is disabled during braking operation.
[ Jam detection and underload protection are disabled during slow speed and braking operation.
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