Induction motors Wound rotor

AC methods include standard squirrel-cage induction motors, wound rotor induction motors, synchronous motors and commutator motors. Speed variation is obtained by the control of applied voltage to the stator or the control of current and voltage in the rotor by external circuit connections. 

Unhke squirrel-cage induction motors, wound-rotor motors have controllable speed and torque. Their application is considerably different from squirrel-cage motors because of the accessibility of the rotor circuit. Various performance characteristics can be obtained by inserting different resistances in the rotor circuit. 

Alternating-Current Motors, Wound-Rotor Induction. 29-7... 

Most chemical-plant-size compressors are electrically driven [43]. Moore [25] discusses the characteristics of squirrel-cage induction and synchronous electrical motors. Wound rotor induction motors have not been used for compressor drives. For 370 to 4500 kW (500 to 6,000 hp), the induction motors are the first choice. The squirrel-cage induction motor is the most coimnonly used driver in the process industries from 1/8 to 1,5000 hp (0.0932 to 1,120 kW [25]. From 15,000 hp (149 to 11,200 kw) the synchronous motor could be used [25]. If the compressor is operated at 7,500, 11,000, and 23,000 rad/s (1,200, 1,800 and 3,600 rpm), no step-up gears are required. The least costly speed for an induction motor is 1,000 rad/s (1800 rpm) so that this speed is usually selected. Step-up gears are used to obtain higher speeds. 

Three-Phase Induction Wound-Rotor Motors. Wound-rotor motors offer more speed and torque control than squirrel-cage induction motors, as well as the major advantage of accessibility of the rotor circuit. Performance characteristics can be varied merely by inserting different values of resistance in the rotor circuit. 

FIG. 29-3 Typical speed versus torque curves for a wound-rotor induction motor with varying amounts of external secondary (rotor) resistance. Resistance values are based on resistance at 100 percent torque and zero speed = 100 percent. 

Today s standard motor enclosure for indoor applications is the open, drip-proof enclosure for induction and high-speed synchronous motors. For large motors, open, drip-proof construction is available up to about 20,000 hp and is used for squirrel-cage, synchronous, and wound-rotor motors. 

Wound-Rotor Induction Motor. A wound-rotor induction motor is an induction motor in which the secondary circuit consists of a polyphase winding or coils whose terminals are either short circuited or closed through suitable circuits. 

Use of wound-rotor induction motors has been largely in continuous-duty constant-speed supplications where particularly high starting torques and low starting currents are required simultaneously, such as in reciprocating pumps and compressors. These motors are also used where only alternating current is available to drive machines that require speed adjustment, such as types of fans and conveyors. 

Wound-Rotor Motor Drives. The wound-rotor induction motor, using adjustable rotor-circuit resistance, is rarely used. However, two versions that use solid-state auxiliary equipment are finding limited application. 

Various standard types AC motors are used e.g. squirrel-cage and wound rotor induction motors, variable speed commutator AC 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. 

During the 1980 s attention turned to AC machines technology with both synchronous and induction being successfully applied. Variable speed and torque control was made possible by variable rotor resistance in the form of Wound Rotor Induction Motors and then the Cyclo Convertor which applied thyristor technology to produce low frequency ac output suitable for the driving large AC machines. 

Below, some engineering features including are highlighted and briefly summarized. Beyond the benefit obtained by the fact of using a frequency converter solution instead of the original solution (based on two rotor-wound induction motors with external resistances and reduction gearbox) in terms of energy efficiency, other specific benefits are obtained ... 

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... 

Ganapathi, Moger, Murthy, Udayakumar. Experimental Study on Energy Consumption of Wound Rotor Induction Motor in Mine Applications. International Journal of Engineering Science and Innovative Technology (IJESIT), Vol. 2 (5), pp. 363-369,2013. 

Figure 9. Comparison of indicative investment cost for electrical equipment of conveyor drive (Wound Rotor Induction iVlotor WRIM, Geared Drive VFD controlled, GCD conventional, and GCD with Permanent iVlagnet Motor PMSM)...

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 in holes around the circumference and short-circuited at each end of the cylinder, as shown in Fig. 2.50. 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... 

The generator is a wound rotor induction motor, which acts as a generator when it is turning at speeds greater than 1,500 rpm. 

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