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A wound-rotor motor, also known as slip ring-rotor motor, is a type of induction motor where the rotor windings are connected through slip rings to external resistance. Adjusting the resistance allows control of the speed/torque characteristic of the motor.
For example; a single-phase motor with 3 north and 3 south poles, having 6 poles per phase, is a 6-pole motor. A three-phase motor with 18 north and 18 south poles, having 6 poles per phase, is also a 6-pole motor. This industry standard method of counting poles results in the same synchronous speed for a given frequency regardless of polarity.
The same basic design is used for both single-phase and three-phase motors over a wide range of sizes. Rotors for three-phase will have variations in the depth and shape of bars to suit the design classification. Generally, thick bars have good torque and are efficient at low slip, since they present lower resistance to the EMF.
As an example, consider the use of a 10 hp, 1760 r/min, 440 V, three-phase induction motor (a.k.a. induction electrical machine in an asynchronous generator regime) as asynchronous generator. The full-load current of the motor is 10 A and the full-load power factor is 0.8. Required capacitance per phase if capacitors are connected in delta:
In vector control, an AC induction or synchronous motor is controlled under all operating conditions like a separately excited DC motor. [21] That is, the AC motor behaves like a DC motor in which the field flux linkage and armature flux linkage created by the respective field and armature (or torque component) currents are orthogonally aligned such that, when torque is controlled, the field ...
The synchronous stator winding consists of a 3 phase winding. It is provided with a 3 phase supply, and the rotor is provided with a DC supply. DC excited motors require brushes and slip rings to connect to the excitation supply. [30] The field winding can be excited by a brushless exciter. [31]
Direct torque control (DTC) is one method used in variable-frequency drives to control the torque (and thus finally the speed) of three-phase AC electric motors.This involves calculating an estimate of the motor's magnetic flux and torque based on the measured voltage and current of the motor.
Some motor variants run on 3-phase AC power (see the synchronous reluctance variant below). Most modern designs are of the switched reluctance type, because electronic commutation gives significant control advantages for motor starting, speed control and smooth operation (low torque ripple).