Slip-ring induction motors starting

Starting and Control of Slip-ring Induction Motors... 

Starting and control of slip-ring induction motors 5/85... 

This is a vital relationship, which reveals that during start-up and until such speed, the reactance of the motor windings / 2> the rotor current will also remain almost the same as the starting current and will fall only at near the rated speed. (Refer to the current curves in Figures 1.5(a) and (b)). The initial inrush current in a squirrel cage induction motor is very high. In a slip-ring motor, however, it can be controlled to a desired level. (Refer to Section 5.2.1.)... 

ACl Noninductive or slightly inductive loads AC2 Starting of slip-ring motors... 

There are two types of induction motor rotor - the wound rotor and the cage rotor. The cage rotor consists of a laminated cylinder of silicon steel with copper or aluminium bars slotted into holes around the circumference and short-circuited at each end of the cylinder, as shown in Fig. 3.23. In small motors the rotor is cast in aluminium. Better starting and quieter running are achieved if the bars are slightly skewed. This type of rotor is extremely robust and since there are no external connections there is no need for slip rings or brushes. A machine... 

There are three ways to overcome this problem first, by matching the motor to the load torque as shown by cun/e (b) in Fig. 3.25 second, by connecting the load after the load has run up to full speed or third, extra resistance can be added to a wound rotor induction motor through slip rings and brushes. The extra resistance of the rotor increases the starting torque, as shown by curve (c) in Fig. 3.25. 

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