List the main components of a wound-rotor, polyphase induction motor. • describe how the Starting Theory of Wound-Rotor Induction Motors. To start the motor. Wound-rotor motors deliver speed control of heavy and high-torque 's special about the wound-rotor motor? This type of 3-phase induction motor has. A wound-rotor motor is a type of induction motor where the rotor windings are connected through slip rings to external resistance. Adjusting the resistance allows.


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Interchanging any two stator voltage supply leads reverses the direction of rotation.

Three-Phase Wound-Rotor Induction Motor

A wound-rotor motor is used for constant-speed applications requiring a heavier starting torque than is obtain able with the squirrel-cage wound rotor motor theory. With a high-inertia load a standard cage induction motor may suffer rotor damage on starting due to the power dissipated by the rotor.

With the wound rotor motor, the secondary resistors can be selected to provide the optimum torque curves and they can be sized to withstand the load energy without failure.

For this reason, wound rotor types are frequently used wound rotor motor theory of the squirrel-cage types in larger sizes.

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Wound-rotor motors are also used for variable speed service. To use a wound-rotor motor as a variable speed drivethe rotor control resistors must be rated for continuous current. If the generator over-speeds, resistance placed in the rotor circuit will absorb excess energy while the stator feeds constant 60 Wound rotor motor theory to the power line.

Figure above In the case of under-speed, negative resistance inserted into the rotor circuit can make up the energy deficit, still allowing the stator to feed the power line with 60 Hz power.

Converter recovers energy from rotor of doubly-fed induction generator. In actual practice, the rotor resistance may be replaced by a converter Figure above absorbing power from the rotor, and feeding power into the power line instead of dissipating it. This wound rotor motor theory the efficiency of the generator.

Converter borrows energy from power line for rotor of doubly fed induction generator, allowing it to function well under synchronous speed. Figure above The borrowed power, along with the larger wound rotor motor theory energy, passes to the stator which is connected to the power line.

Wound rotor induction motor qualities.

Wound Rotor Induction Motor

Excellent starting torque for high inertia loads. Low starting current compared to squirrel cage induction motor. Certain types of variable-speed drives recover slip-frequency power from wound rotor motor theory rotor circuit and feed it back to the supply, allowing wide speed range with high energy efficiency.

Doubly fed electric machines use the slip rings to supply external power to the rotor circuit, allowing wide-range speed control.

Wound Rotor Induction Motors | AC Motors | Electronics Textbook

Today speed control by wound rotor motor theory of slip ring motor is mostly superseded by induction motors with variable-frequency drives. The speed of a wound-rotor motor can be controlled manually or automatically with timing relays, contactors, and pushbutton speed selection.


Torque Performance As a load is applied to the motor, both the percent slip of the rotor and the torque developed in the rotor increase.

As shown in wound rotor motor theory graph in figure 6, the relationship between the torque and percent slip is practically a straight line.

Wound Rotor Induction Motors

The large amount of resistance in the rotor circuit causes the rotor current to be almost in phase with the induced voltage of the rotor. As a result, the field set up by the rotor current is almost in phase with the stator field.

If the two fields reach a maximum value at the same instant, there will wound rotor motor theory a strong magnetic reaction resulting in a high torque output. However, if all of the speed controller resistance is removed from the rotor circuit and the motor is started, the torque performance is poor.

The rotor circuit minus the speed controller resistance wound rotor motor theory largely of inductive reactance. This means that the rotor cur rent lags behind the induced voltage of the rotor andthus, the rotor current lags behind the stator current.

As a result, the rotor field set up by the rotor current lags behind the stator field which is set up by the stator current.


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