AC Motors Construction and Operation

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What is the main advantage of AC motors over DC motors?

AC motors are more expensive

AC motors require less maintenance (correct)

AC motors are more efficient

AC motors are more powerful

Which of the following is a characteristic of AC synchronous motors?

They use brushes and commutators

They are single-phase motors

They have a variable speed

They have a constant speed (correct)

What is the primary method used to control the speed of an AC motor?

Using a variable resistance

Changing the number of poles

Varying the frequency (correct)

Adjusting the voltage

Which of the following describes a method for producing a rotating magnetic field in an AC motor?

Using a capacitor Signup and view all the answers

What type of AC motor is well-suited for constant-speed applications?

AC synchronous motor Signup and view all the answers

Which characteristic of AC motors eliminates the problem of dangerous sparking?

The lack of brushes and commutators Signup and view all the answers

What type of power systems are these motors designed for?

Polyphase or single-phase Signup and view all the answers

Which type of AC motors are the most commonly used?

Induction motors Signup and view all the answers

How are the rotors of synchronous motors energized?

By direct current (DC) voltage Signup and view all the answers

What is the principle behind the operation of a three-phase induction motor?

A rotating magnetic field Signup and view all the answers

How are the individual phase windings arranged in the stator of a three-phase induction motor?

They are equally spaced around the stator, 120° apart. Signup and view all the answers

Which rule is used to determine the electromagnetic polarity of the poles at any given instant in a three-phase induction motor?

The left-hand rule Signup and view all the answers

In a three-phase system, the resultant magnetic field rotates in which direction?

Clockwise Signup and view all the answers

At which point in the rotation cycle is the magnetic field in coils 1-1A at its maximum?

Point 1 Signup and view all the answers

What happens when the three-phase voltage completes one full cycle?

The magnetic field rotates through 360 degrees Signup and view all the answers

At point 2, which winding experiences the maximum negative voltage?

3-3A Signup and view all the answers

What is the effect of the weaker magnetic fields in windings 1-1A and 2-2A at point 2?

They aid the magnetic field in winding 3-3A Signup and view all the answers

What is the natural alignment of a bar magnet mounted in the center of the stator?

Its south pole aligns with the north pole of the stator field Signup and view all the answers

What is the purpose of having no insulation between the core and the bars in a squirrel-cage rotor?

To allow for maximum field strength in the small air gap Signup and view all the answers

What is the other type of rotor winding mentioned in the text?

Wound rotor Signup and view all the answers

What is the basic principle of operation for an induction motor, regardless of the rotor type?

The stator field induces a magnetic field in the rotor, causing the rotor to turn Signup and view all the answers

What materials are typically used for the conducting bars in a squirrel-cage rotor?

Copper or aluminium Signup and view all the answers

How are the rotor bars connected in a squirrel-cage rotor?

They are short-circuited at each end by a solid ring Signup and view all the answers

What is the typical construction of a squirrel-cage rotor?

A laminated cylinder with slots in its surface Signup and view all the answers

What happens to the phase voltage when a motor is connected in delta configuration?

It increases by a ratio of √3 Signup and view all the answers

How does the phase current change when a motor is connected in delta mode?

It increases by a ratio of √3 Signup and view all the answers

What happens to the line current in a delta-connected motor compared to a star-connected motor?

It increases three times Signup and view all the answers

What is the main difference in the stator field behavior between single-phase and polyphase induction motors?

The stator field does not rotate in single-phase motors and rotates in polyphase motors Signup and view all the answers

How is voltage induced in the rotor of a single-phase induction motor?

As a result of magnetic induction Signup and view all the answers

What happens to the push-pull along the line if an outside force rotates the rotor of a single-phase motor?

It is disturbed Signup and view all the answers