Emotron MSF 2.0 Softstarter

T/T n2,5TorqueT/T n2,5Torque221,51,5110,50,500 0,5 1n/n s00 0,5 1n/n sI/I n8CurrentI/I N8Current7766554433221100 0,5 1n/n s00 0,5 1n/n sFig. 10 Soft starting – torque controlFor optimal starting performance, correct setting of the softstarter’sparameters such as initial torque and end torque atstart and start time is important. The choice of parameters isexplained in detail in section 8.7, page 55.2.3 Other starting methodsIn contrast to the preceding sections of this chapter, whichfocused on squirrel-cage motors, slip-ring motors are dealtwith later on. A slip-ring motor is equipped with a woundrotor; one end of each rotor winding is available for externalconnection via slip-rings. These motors are often optimizedfor rotor resistance starting, i.e. with short-circuited rotorwindings they develop a very low torque at an extremelyhigh current. For starting external resistances are connectedto the rotor windings. During the start, the resistance valueis decreased in several steps until the rotor windings areshort-circuited at nominal speed. The following figureshows typical torque and current characteristics for a slipringmotor during the start with an external rotor-resistancestarter.Fig. 11 Rotor-resistance startingBecause of the low starting torque it is often not possible toshort-circuit the rotor windings and replace the rotor-resistancestarter with a softstarter. However, it is always possibleto use a frequency inverter instead. The following illustrationshows how the torque and current characteristics areaffected when the stator frequency is changed.12 Description Emotron AB 01-4135-01r2