Electrical Machines 2 - Motors

Flashcards based on lecture notes about Synchronous, Induction, and Solid-State Induction Motors.

What is a synchronous motor?

An AC motor where the rotor's rotation period matches the supply current frequency, aligning with the rotating field.

What determines the speed of a synchronous motor?

Supply frequency.

What is the formula for synchronous speed (Ns)?

Ns = 120 * f / P (where f is frequency in Hz and P is the number of poles)

What are the two main parts of a synchronous motor?

Stator and Rotor.

What is the stator made of?

Thin laminated sheets of steel or cast iron of good magnetic quality.

What is the purpose of the stator's armature winding?

Generating the rotating magnetic field (RMF).

How is the rotor energized in a synchronous motor?

Using slip rings and a brush assembly, typically with a DC source.

What are three characteristics of synchronous motors?

1. Constant speed. 2. Not self-starting. 3. Operates under a wide range of power factors.

Name an application where synchronous motors are used.

Paper mills, textile mills, and power plants utilize them for driving compressors, blowers, and pumps.

Name an advantage of using a synchronous motor.

Constant Speed, High Efficiency, Power Factor Correction, High Torque

Name a disadvantage of using a synchronous motor.

Complex Starting Mechanism, Cost, Maintenance, Not Self-Starting

How does the physical stator of induction motor compare to that of a synchronous machine?

An induction motor has the same physical stator as a synchronous machine.

What are the two main types of induction motor rotors?

Cage rotor and wound rotor.

What does a cage rotor consist of?

A series of conducting bars laid into slots carved in the face of the rotor and shorted at either end by large shorting rings.

How are the three phases of the wound rotor windings connected?

Usually Y connected, and the ends of the three rotor wires are tied to slip rings on the rotor's shaft.

What is a benefit of wound-rotor induction motors?

Rotor currents are accessible at the stator brushes, where they can be examined and where extra resistance can be inserted into the rotor circuit to modify the torque-speed characteristics of the motor.

Are wound-rotor induction motors widely used?

No, wound-rotor induction motors are rarely used.

What is a key operating principle of induction motors?

Electromagnetic induction.

What is the typical efficiency of larger three-phase induction motors at full load?

Potentially reaching 95%.

Name an application where induction motors are used?

Fans, pumps, conveyors, compressors, and household appliances.

Name an advantage of using an induction motor?

Simple and rugged construction, low cost, high efficiency, low maintenance.

Name a disadvantage of using an induction motor?

Speed cannot be varied without sacrificing efficiency, speed decreases with increase in load, lower starting torque.

What do solid-state induction motor drives (VFDs) control?

The speed and torque of induction motors.

Name an advantage of a solid-state induction motor drive.

The flexibility of this drive is very high it can be connected with the one-phase or 3-phase supply, it can also connect with a system that has a frequency of either fifty or sixty hertz, and it can also operate on a voltage range from two-hundred-eight to two-thirty volts.

How can the output voltage of solid-state induction motor drives be varied?

By using PWM (pulse width modulation).

Where are VFDs (variable frequency drives) used?

Applications requiring variable speed control, energy savings, and process optimization.