Page 506 - Motor_protection_and_control_Manual_motor_starters_ contactors

Autotransformer starters

Contactor selection

General
Electrical distribution
An autotransformer starter allows to start a squirel cage motor
with a reduced starting current due to the reduced voltage
within the accelerating duration.
Unlike the star-delta wiring, this autotransformer starting
KM1 KM2
method needs three wires and three terminals on the motor.
At the starting period, the motor is wired to the autotrans-
former taps: the star contactor "KM3" and the autotransform-
er contactor "KM2" are closed, the motor is under reduced
T1
voltage. Consequently, the torque is reduced as the square Autotransformer
of the applied voltage. The autotransformers are generally
equipped of three taps at each phase in order to adapt the
5 starting parameters to the field requirements.
When the motor reaches 80...95 % of its nominal speed, the KM3
star contactor opens. Then, the line contactor "KM1" is mak-
ing and the autotransformer contactor is opening. This start-
ing process is done without any network interruption.

Selection Table (Id starting current / In nominal current < 8 - Acceleration time ≤ 20s - 30 cycles / h max.)
kW motor ratings 50/60 Hz Contactors
KM1 KM2 KM3
line autotransformer taps: star
220/240 V 380/400 V 415 V 440 V 690 V 90 % 80 % 70 % 60 %
4 7.5 7.5 7.5 9 AF16 AF16 AF12 AF09 AF09 AF09
6.5 11 11 11 15 AF26 AF26 AF16 AF16 AF09 AF16
11 18.5 18.5 18.5 22 AF38 AF30 AF26 AF26 AF16 AF26
15 22 30 30 30 AF52 AF52 AF38 AF30 AF26 AF30
18.5 30 37 37 37 AF65 AF52 AF40 AF30 AF26 AF38
22 37 45 45 45 AF80 AF65 AF52 AF40 AF30 AF40
25 45 55 55 55 AF96 AF80 AF65 AF52 AF38 AF52
30 55 55 75 55 AF116 AF116 AF80 AF65 AF52 AF65
37 75 75 90 75 AF140 AF140 AF96 AF80 AF65 AF65
45 75 75 90 90 AF146 AF140 AF96 AF80 AF65 AF65
55 90 90 110 132 AF190 AF146 AF116 AF96 AF65 AF80
55 110 110 132 160 AF205 AF190 AF140 AF116 AF80 AF96
75 132 132 160 200 AF265 AF265 AF190 AF140 AF96 AF116
90 160 160 160 250 AF305 AF265 AF205 AF190 AF116 AF140
110 200 200 200 315 AF370 AF370 AF265 AF190 AF140 AF190
132 250 250 250 355 AF460 AF400 AF305 AF265 AF190 AF205
160 315 355 355 500 AF580 AF580 AF400 AF305 AF205 AF305
220 400 425 450 600 AF750 AF750 AF580 AF400 AF305 AF400
257 475 500 560 900 AF1350 AF750 AF580 AF460 AF400 AF460
315 560 600 670 1000 AF1650 AF1350 AF750 AF580 AF460 AF580

1SBC101699S0201 - Rev. B

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