Rotors slip-ring induction motors

The simplest method of achieving the effect is to insert extra resistance into the rotor circuit. The rotor of the induction motor has to be specially wound so the winding can be split into three sections. Each section is connected to shaft-mounted slip-rings. The conductors of the rotor winding are carefully insulated from the iron core and from each other. The extra resistance is an external static unit mounted near to the motor. 

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.)... 

This is a very useful nomogram to determine the performance of a motor with the help of only no-load and short-circuit test results. In slip-ring motors, it also helps to determine the external resistance required in the rotor circuit to control the speed of the motor and achieve the desired operating performance. Slip-ring motors are discussed in Chapter 5. The concept behind this nomogram is that the locus of the rotor and the stator currents is a circle. Consider the equivalent circuit of an induction motor as shown in Figure 1.15, where... 

Since the performance of an induction motor can be varied by altering the rotor parameters, a slip-ring motor, through its rotor circuit, can be made to suit any specific torque and speed requirement. 

The hoist drive solution presented in this work, which is based on the Ingedrive MVlOO medium voltage AG frequency converters, contains two completely independent Active Front End Rectifier and Inverter sets under the well-known AC-DC-AC topology. The entire drive system solution allows the operation at full speed and full load (then full hoist performance, with no limitation) even in the case that one frequency converter (AG-DC-AC set) is unavailable. The solution presents some extra benefits comparing to the original hoist system solution that was based on two slip ring rotor wound induction motors in which the speed control... 

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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