Rotor Winding and Control Systems

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Questions and Answers

What is the primary purpose of the rheostat connected to the rotor in this motor design?

To maintain consistent speed under varying loads
To connect the rotor to a three-phase supply directly
To increase the starting torque during the starting period (correct)
To provide insulation for the rotor windings

How are the slip-rings modified during the motor's normal running conditions?

They are disconnected to prevent electrical faults
They are short-circuited by a metal collar (correct)
They are connected to a variable resistor
They are replaced with solid conductors

What characteristic of the rotor winding is noted in this design, even when the stator is two-phase?

It utilizes a single-layer configuration
It is wound for fewer poles than the stator
It has no external connections
It is always wound 3-phase (correct)

What effect does lifting the brushes from the slip-rings have on the motor's operation?

<p>Reduces frictional losses and wear and tear (C)</p> Signup and view all the answers

What happens to the rotor's winding terminals when the motor is started?

<p>They are connected to three insulated slip-rings (D)</p> Signup and view all the answers

Flashcards

Wound Rotor Winding

A type of rotor winding with three phases connected in a star configuration. It has as many poles as the stator and is always wound 3-phase, even if the stator is two-phase.

Slip Rings

Metal rings mounted on the rotor shaft that connect to the rotor winding terminals. They provide an electrical connection between the rotor and external circuits.

Rotor Rheostat

A variable resistor connected to the slip rings in the wound rotor motor. It allows control over the starting torque and speed by changing the rotor circuit resistance.

Short-Circuiting Collar

A metal collar that short-circuits the slip rings when the motor is running at normal operating speed. This reduces losses and wear.

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Adjustable Speed-Torque & Current Characteristics

The ability of a wound rotor motor to adjust its speed-torque and current characteristics by adding resistance to the rotor circuit using the rheostat.

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Study Notes

Rotor Winding Details

Rotor uses 3-phase, double-layer, distributed winding.
Rotor winding poles match stator poles.
Rotor winding is 3-phase, even if stator is 2-phase.
Internal rotor phases are connected in a star configuration.
External terminals of the three phases are connected to slip rings.
Slip rings are mounted on the shaft, with brushes contacting them.
Brushes are connected to an external 3-phase star-connected rheostat.

Starting Control

Rheostat allows variable resistance in rotor circuit during startup.
Increased resistance enhances starting torque.
This adjusts the speed-torque/current characteristics.

Running Conditions

Metal collar short-circuits slip rings during normal operation.
Brushes are lifted from slip rings to reduce friction and wear.
Under normal operation, the wound rotor is short-circuited like a squirrel-cage rotor.