Rockwell Automation Low-Voltage Switchgear and Controlgear - Manual (Page 97)

0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
0.0 0.2 0.4 0.6 0.8 1.0
n /n
s
T /T
e
T
av-acc
T
4
T
3
T
2
T
0 T
1
Fig. 3.8-1
Torque characteristic on starting of a slip-ring motor
T
0
… T
4
Torque characteristics of the individual starting steps
T
av-acc
Mean starting torque
A starter for a slip-ring motor can be equipped with one or more steps. On the one hand, this
allows the starting torque to adjust to the working machine and, on the other, the current peaks
to the supply conditions.
Half-load starting Full-load starting
Number of resistance steps 2 3 4 2 3 4
Max. starting current I
max
/I
e
2.2 1.7 1.3 2.8 2.3 1.8
Min. starting torque T
min
/T
e
0.5 0.5 0.5 1 1 1
Starting time s 4 … 60
Tab. 3.8-1
Example of application: Starting motors under load
Note
With slip-ring motors, also the speed can be controlled with the resistors in the rotor circuit
(resistance or slip control; e.g. for crane motors). This requires a correspondingly designed
control circuit and ratings of the contactors and resistors for variable speed operation.
Fig. 3.8-2
Circuit diagram with three-step, automatic shorting of external rotor resistors
LVSAM-WP001A-EN-P - April 2009 3-21