IOMM Starter 39
The starter will remain in the Delta or running mode until the start command is removed or a
fault occurs.
Usually the D3 intelligent Wye to Delta transition algorithm provides an optimal transition
point that minimizes the transient current and torque surges that can occur. However
sometimes, based on the motor and loading, the Wye to Delta transition will occur only after
the Transition Time has expired. In order to reduce the current surge that can take place
during the transition from Wye to Delta mode, the Transition Time parameter (QST 09, P9)
should be adjusted so that the transition occurs as close to full speed as possible within the
constraints of the load. If the transition time is set too short, a large current and torque surge
may occur during the transition. If the transition time is set too long, the motor may not have
sufficient torque to continue accelerating when in Wye mode and may stop accelerating at a
low speed until the transition to Delta mode occurs. If this occurs, the start is unnecessarily
prolonged and motor heating is increased.
A typical closed transition Wye-Delta starting current profile is shown in Figure 11.
Figure 11, Wye Delta Profile
100%
200%
300%
400%
500%
600%
0%
100%
% speed
Wye-Delta Closed Transition Current Profile
% Full
Load
Motor
Current
Transition from Wye to Delta mode
A digital input (I/O 01-03, P39-41) can be programmed as a 2M contactor feedback input.
This input provides verification that the 2M contactor has fully closed preventing operation
when the transition resistors are still connected in the motor circuit. The use of this feedback
is recommended to prevent the overheating of the transition resistors if the 2M contactor does
not close properly. The 2M confirmation trip time can be adjusted by modifying the Bypass /
2M Confirm parameter (I/O 16, P54).
Note: When in Wye-Delta mode, the acceleration ramp, kick, and deceleration
settings have no effect on motor operation and the SCR gate outputs are disabled.
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