l Problem in dalher connection

Problem in dalher connection


QUESTION:

Contactors in a Dahlander connection are controlled by a PLC. Very often contactors are welding after a speed changeover commands. No transition times are parameterized into the PLC program. Contactors are electrically interlocked however.

ANSWER:

Enhanced by unfavorable configurations of line frequency and residual magnetic field of rotor, transient reactions inside the motor occur during a changeover of motor speeds. As a result current peaks arise higher than current peaks during ordinary DOL starting.

In the worst case the making capacity of contactors is exceeded with contact welding as a consequence.In order to allow the residual magnetic rotor field in to decay, a transition time of at least 50 ms has to be allowed before the line voltage is re-connected during speed changeovers



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