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Altistart 48 Enclosed Altistart 48 Soft Starters - Page 21 Selection Criteria


Altistart 48

soft starters for asynchronous motors Special Uses

Selection Criteria

Special uses

Additional criteria can influence the selection of the ATS48 soft starter: Shorting/Bypass Contactor Refer to the recommended wiring diagrams on pages 32-34. The soft starter can be bypassed by a contactor at the end of starting (to limit the heat dissipated by the soft starter). The shorting/bypass contactor is controlled by the soft starter and the current measurements. Thermal protection remains active when the soft starter is bypassed. Multiple Motors Motors may be connected in parallel provided that the power limit of the soft starter is not exceeded (the sum of the motor currents must not exceed the nominal current of the soft starter selected depending on the type of application). Individual thermal protection is required for each motor. Brush Motor The ATS48 soft starter can operate with a bypassed stator resistance motor or with a resistance lug. The starting torque is modified in accordance with the rotor resistance. If necessary, maintain a low resistance in order to obtain the required torque to overcome the resistive torque on starting. A bypassed brush motor has a very low starting torque. A high stator current is required to obtain the sufficient starting torque. Oversize the soft starter so that the value of the limiting current is 7 times that of the nominal current. NOTE: Ensure that the starting torque of the motor, equal to 7 times the nominal current, is greater than the resistive torque. NOTE: The ATS48 soft starter torque control enables excellent soft starting despite the limiting current being 7 times the nominal current required to start the motor. 2-Speed Motor The ATS48 soft starter can operate with a 2-speed motor. A motor demagnetization period must elapse before changing from low speed to high speed in order to avoid antiphase between the line supply and the motor, which would generate very high currents. Select the soft starter using the three main criteria, see pages 19-21. Long Motor Cable Lengths Very long motor cables cause voltage drops due to the resistance of the cable. If the voltage drop is significant, it could affect the current consumption and the available torque. This criteria must be taken into account when selecting the motor and the soft starter. Miscellaneous Application Precautions Do not use the ATS48 soft starter upstream of loads other than motors (for example transformer and resistor type loads). Do not connect power factor correction capacitors to the terminals of a motor controlled by an Altistart 48.

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