Technical information

8 – THEORY OF OPERATION
Wye Delta Operation
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3. When the 2S contactor pulls in, resistors are inserted in the circuit and the 1S contactor is DE-energized.
4. When the 1S contactor drops out the 2M contactor is energized.
5. When the 2M contactor is pulled in, feedback can be sent to the MX control card to confirm that the transition sequence
to Delta is complete.
The starter remains in the Delta or running mode until the start command is removed or a fault occurs.
Usually the MX 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 occurs only after
the Up To Speed Time has expired. In order to reduce the current surge that can take place during the transition from Wye to Delta
mode, the Up To Speed Time parameter should be adjusted so that the transition occurs as close to full speed as possible within the
constraints of the load. If the Up To Speed Time is set too short, a large current and torque surge may occur during the transition. If
the Up To Speed 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 25.
Figure 25 – 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 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 Feedback Time parameter.
Note: When in Wye-Delta mode, the acceleration ramp, kick, and deceleration settings have no effect on motor operation.
Note: When in Wye-Delta mode, the SCR gate outputs are disabled.