IS 8544 Pt.4-1979
Specification for starters for motors with voltages not exceeding 1000 V Part IV Step-down AC starters: Two-step autotransformer starters

Standard No.

IS 8544 Pt.4-1979

Release Date

1979

Published By

IN-BIS

Latest

IS 8544 Pt.4-1979

Scope

1.1 This standard (Part IV) applies to two-step auto-transformer starters for industrial use, intended to start, in the starting position, and accele-rate an ac induction motor to normal speed and to provide means for the protection of the motor and its associated circuits against operating overloads, and to cause the motor to stop intentionally. Note — Auto-transformer starters with more than two steps are considered as special cases subject to agreement between the manufacturer and the user. 1.2 The auto-transformer starters dealt with in this standard are not intended for inching duty or reversing motors rapidly and, therfore, utilization category AC-4 does not appear. Moreover, they are not 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 A of IS : 8544 ( Part I )-1977〓 ]. 1.3 This standard applies only to starters the main contacts of which are intended to be connected to circuits the rated voltage of which does not exceed 1 000 V ac. 1.4 The clauses of this standard relating to overload protection are not applicable to starters operating in conjunction with overtemperature protective devices built into the motors. Note — 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 of starting voltage to rated voltage. Therefore, auto-trans-former 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. Figure 2 gives typical curves of starting current, of starting torque of the motor, and of torque of the driven machine.

IS 8544 Pt.4-1979 history

• 1979 IS 8544 Pt.4-1979 Specification for starters for motors with voltages not exceeding 1000 V Part IV Step-down AC starters: Two-step autotransformer starters