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Questions and Answers
What determines the direction of rotation in a reluctance-start motor?
What determines the direction of rotation in a reluctance-start motor?
- The narrow air gap
- The pole flux components
- The wide air gap (correct)
- The direction of the AC source
Why does a reluctance-start motor develop starting torque?
Why does a reluctance-start motor develop starting torque?
- Due to the single-phase AC source
- Because the pole flux has two in-phase components
- Because the pole flux has two out-of-phase components (correct)
- Due to the difference in air gaps
What is a characteristic of reluctance-start motors?
What is a characteristic of reluctance-start motors?
- They are made in large sizes
- They have high starting and overload torque requirements
- They are made in small sizes only (correct)
- They can be reversed
How is speed control accomplished in a reluctance-start motor?
How is speed control accomplished in a reluctance-start motor?
What type of machine is a split-phase motor?
What type of machine is a split-phase motor?
What is a characteristic of split-phase motors?
What is a characteristic of split-phase motors?
What is a characteristic of the flux in a magnetic circuit containing no iron?
What is a characteristic of the flux in a magnetic circuit containing no iron?
What happens to the flux when the mmf of a coil produces flux in a magnetic circuit made entirely of iron?
What happens to the flux when the mmf of a coil produces flux in a magnetic circuit made entirely of iron?
What is the main difference between a capacitor-start motor and a standard split-phase motor?
What is the main difference between a capacitor-start motor and a standard split-phase motor?
What is the primary application of a capacitor-start split-phase motor?
What is the primary application of a capacitor-start split-phase motor?
What is the main advantage of a two-value capacitor motor?
What is the main advantage of a two-value capacitor motor?
What is the typical starting torque of a single-value capacitor motor?
What is the typical starting torque of a single-value capacitor motor?
What is the main characteristic of a single-value capacitor motor that makes it suitable for applications requiring frequent back-and-forth movement?
What is the main characteristic of a single-value capacitor motor that makes it suitable for applications requiring frequent back-and-forth movement?
What type of capacitor is used in a two-value capacitor motor?
What type of capacitor is used in a two-value capacitor motor?
What is the primary advantage of a capacitor-start motor over a reluctance-start motor?
What is the primary advantage of a capacitor-start motor over a reluctance-start motor?
What type of applications are single-value capacitor motors commonly used in?
What type of applications are single-value capacitor motors commonly used in?
What is the primary function of a centrifugal device in a split-phase motor?
What is the primary function of a centrifugal device in a split-phase motor?
What is the typical current inrush when starting a split-phase motor directly from the line?
What is the typical current inrush when starting a split-phase motor directly from the line?
What is the purpose of the capacitor in a capacitor-start motor?
What is the purpose of the capacitor in a capacitor-start motor?
What is the typical application of standard split-phase motors?
What is the typical application of standard split-phase motors?
What is the effectiveness of speed control in split-phase motors?
What is the effectiveness of speed control in split-phase motors?
What is the primary advantage of using a capacitor in a capacitor-start motor?
What is the primary advantage of using a capacitor in a capacitor-start motor?
What is the speed variation of split-phase motors between no load and full load?
What is the speed variation of split-phase motors between no load and full load?
What is the key factor in determining the direction of rotation in a split-phase motor?
What is the key factor in determining the direction of rotation in a split-phase motor?
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Study Notes
Capacitor-Start Motor
- Develops more starting torque with a lower inrush current compared to standard split-phase motor
- Suitable for small portable hoist applications, requiring a control circuit for instant reversal of direction
Two-Value Capacitor Motor
- Uses an autotransformer and a single capacitor unit
- Appears to the primary as having a value of (a²)C, where 'a' is the transformation ratio
- Retains benefits of a capacitor during both normal running and starting periods
Single-Value Capacitor Motor
- Has a permanently connected capacitor in the auxiliary winding circuit
- Frequently used in air-moving equipment like fans and blowers, or in applications requiring quiet operation
- Starting torque between 50 to 100 percent of rated torque
- Ease of reversing by simply swapping the two identical windings
Reluctance-Start Motor
- Direction of rotation is always from the wide air gap to the narrow air gap
- Starting torque is developed due to two out-of-phase components of flux
- Not as widely used as shaded-pole motors, made in small sizes only, and applied where starting and overload torque requirements are low
- Cannot be reversed and must be assembled so that the rotor shaft extends from the motor to drive the load in the proper direction
- Speed control is accomplished by varying the voltage across the motor
Split-Phase Motor
- One of the most widely used types of single-phase motor
- Fundamentally an induction machine, as the rotor power is received inductively
- Mechanism actuated by a centrifugal device or an electromagnetic relay is used to cut out the auxiliary winding at the proper time
- Direction of rotation is determined by the connection of the main and auxiliary windings to the source and with respect to each other
- Starting current inrush may be 4 to 6 times the rated value
- Speed control is difficult and requires special windings to change the speed
- Speed regulation is similar to polyphase motors, with a speed variation of about 2.5 to 5 percent between no load and full load
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