Emotron MSF 2.0 Softstarter

8.7.2 StartWith MSF 2.0, torque control, voltage control and directon-line are available as start methods. Torque control isavailable both for loads with a linear torque characteristiclike conveyors and planers and with square torque characteristicsfor pumps and fans. In general torque control isrecommended as a starting method; voltage control may beused when for some special reasons a linear voltage ramp isdesired. With Direct on-line (DOL) as a start method, neitherthe current nor the voltage will be controlled; full voltageis applied to the motor immediately. DOL can be usedto start the motor if the softstarter has been damaged andthe thyristors are short-circuited.All start methods can be combined with a current limit.However, only a properly configured torque-controlled startwill lead to constant acceleration. For this reason it is notrecommended to set a current limit for pump applications.With a proper set-up of the torque control parameters, thestarting current will be very low. For applications with variableload characteristics from start to start, the current limitfunctionality may be useful to avoid overloading the mainsfuses. However, as the motor torque is proportional to thesquare of the current, setting a low current limit will limitthe motor torque considerably. If the current limit is set toolow in relation to the application's requirements, the motorwill not be able to accelerate the load.Start method [310]In this menu the start method is chosen. The menus necessaryfor configuration of the start will be available dependingon the chosen start method.Torque controlThe default settings for initial torque at start is 10% and forend torque at start it is 150%. In Fig. 37 the resulting torquecurve is shown versus time for linear and square torque characteristics.TorqueFig. 37 Torque control at startA Properly configured torque-controlled start will lead to alinear speed increase and low starting current without currentpeaks.Current (A)End torqueNominal torqueInitial torque1 Linear2 SquareStart timeTime3 1 0Setting1Start methodDefault: 1Range: 1, 2, 3, 41 Linear torque control2 Square torque control3 Voltage control4 Direct on-line, DOLSpeedTimeTimeFig. 38 Current and speed in torque controlEmotron AB 01-4135-01r2 Functional description 57