AS 1202.3-1976

This Part of the specification applies to two-step autotransformer starters for industrial use, intended to start in the starting position, accelerate an induction motor to normal speed, provide means for the protection of the motor and its associated circuits against operating overloads, and cause the motor to stop intentionally.NOTE: Autotransformer starters with more than two steps are considered as special cases subject to agreement between purchaser and manufacturer.The autotransformer starters dealt with in this Part are not intended for reversing motors rapidly and, therefore, utilization category AC-4 included in Part 1* does not appear. Moreover, they are not normally designed to interrupt short-circuit currents; therefore, suitable short-circuit protection should form part of the installation but not necessarily in the starter (see Appendix C of Part 1).This Part applies only to starters, the main contacts of which are intended to be connected to circuits the rated voltage of which does not exceed 1000 V a.c.The clauses of this Part relating to overload protection are not applicable to starters operating in conjunction with over-temperature devices built into the motors (see AS 1023, Part 1).NOTES:1. In the starting position, the current in the line and the torque of the motor related to the motor starting with rated voltage are reduced approximately as the square of the ratio (starting voltage)/(rated voltage). Therefore, auto-transformer starters are used when the inrush current due to the starting is to be limited, or when the driven machine requires a limited torque for starting. Typical curves for starting current, of starting torque of the motor, and of torque of the driven machine are shown in Fig. F1).2. In order to avoid too large a peak of current or torque when changing the connection from start to run, it is recommended that this changeover occur only when the motor has reached a speed higher than 80 percent of its rated speed (see Appendix F).

Under Revision See DR 94015