Rockwell Automation Low-Voltage Switchgear and Controlgear - Manual (Page 94)

Tab. 3.7-1
Pole-changing motors with 2 speeds
Tab. 3.7-2
Pole-changing motors with 3 or 4 speeds
3.7.2 Ratings of starters for pole changing
Pole-changing motors often have, especially at lower speeds, considerably less favorable
efficiency and power factors (cos
φ) than standard motors. The intake current is therefore
usually higher than that assigned to the corresponding power in the selection tables. Therefore
the feeding contactors of the individual steps (
Fig. 3.7-1 ) for all arrangements and circuit layouts
(separate windings, Dahlander, PAM, phase modulation circuits) should not be rated according
to the rated operational powers, but according to the rated operational currents specified by the
motor manufacturer. Selection is in accordance with utilization category AC-3; for steps with
inching operations, the supply contactor should be suitable for AC-4.
The star point contactor of the YY-step (K3) in Dahlander circuits, carries, depending on the
circuit variation, exactly or approximately half the current of the feeding contactor for this step:
I
eK3
= I
eYY
/2 [A]
Selection is always in accordance with AC-3;
LVSAM-WP001A-EN-P - April 2009 3-18