30 Questions
What is the main advantage of AC motors over DC motors?
AC motors require less maintenance
Which of the following is a characteristic of AC synchronous motors?
They have a constant speed
What is the primary method used to control the speed of an AC motor?
Varying the frequency
Which of the following describes a method for producing a rotating magnetic field in an AC motor?
Using a capacitor
What type of AC motor is well-suited for constant-speed applications?
AC synchronous motor
Which characteristic of AC motors eliminates the problem of dangerous sparking?
The lack of brushes and commutators
What type of power systems are these motors designed for?
Polyphase or single-phase
Which type of AC motors are the most commonly used?
Induction motors
How are the rotors of synchronous motors energized?
By direct current (DC) voltage
What is the principle behind the operation of a three-phase induction motor?
A rotating magnetic field
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.
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
In a three-phase system, the resultant magnetic field rotates in which direction?
Clockwise
At which point in the rotation cycle is the magnetic field in coils 1-1A at its maximum?
Point 1
What happens when the three-phase voltage completes one full cycle?
The magnetic field rotates through 360 degrees
At point 2, which winding experiences the maximum negative voltage?
3-3A
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
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
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
What is the other type of rotor winding mentioned in the text?
Wound rotor
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
What materials are typically used for the conducting bars in a squirrel-cage rotor?
Copper or aluminium
How are the rotor bars connected in a squirrel-cage rotor?
They are short-circuited at each end by a solid ring
What is the typical construction of a squirrel-cage rotor?
A laminated cylinder with slots in its surface
What happens to the phase voltage when a motor is connected in delta configuration?
It increases by a ratio of √3
How does the phase current change when a motor is connected in delta mode?
It increases by a ratio of √3
What happens to the line current in a delta-connected motor compared to a star-connected motor?
It increases three times
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
How is voltage induced in the rotor of a single-phase induction motor?
As a result of magnetic induction
What happens to the push-pull along the line if an outside force rotates the rotor of a single-phase motor?
It is disturbed
Test your knowledge on the construction, operation, and characteristics of AC synchronous motors, AC induction motors, and single and polyphase AC motors. Also explore methods of speed control and controlling the direction of rotation.
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