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Questions and Answers
Why should the power be turned OFF after completing each individual measurement?
Why should the power be turned OFF after completing each individual measurement?
- To demonstrate the power of the generator
- To save electricity
- To ensure safety and prevent accidents (correct)
- To increase the voltage output
What is the primary function of the rotor in an ac generator?
What is the primary function of the rotor in an ac generator?
- To rotate within a set of conductors (correct)
- To generate an induced EMF
- To provide mechanical input
- To wind coils on an iron core
What precaution is advised with respect to connections and power in this experiment?
What precaution is advised with respect to connections and power in this experiment?
- Make connections only when the power is ON
- Do not make or break any connections with the power ON (correct)
- Make or break connections with the power ON
- Break connections only when the power is ON
What causes an electromotive force (EMF) to be induced in a conductor in an ac generator?
What causes an electromotive force (EMF) to be induced in a conductor in an ac generator?
Why is it important to check the connection with the instructor before turning the power ON?
Why is it important to check the connection with the instructor before turning the power ON?
What is the primary function of the rotor in an alternator?
What is the primary function of the rotor in an alternator?
What is the relationship between the frequency of the induced voltage, the rotor speed, and the number of poles in an alternator?
What is the relationship between the frequency of the induced voltage, the rotor speed, and the number of poles in an alternator?
How are the stator windings of a three-phase alternator physically arranged?
How are the stator windings of a three-phase alternator physically arranged?
What is the purpose of the brushless DC exciter in an alternator?
What is the purpose of the brushless DC exciter in an alternator?
What is the purpose of the 'prime mover' in an alternator system?
What is the purpose of the 'prime mover' in an alternator system?
Why are the armature windings in an alternator often 'short' (fractional) pitched and distributed?
Why are the armature windings in an alternator often 'short' (fractional) pitched and distributed?
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Study Notes
Safety Precautions
- Do not make or break connections with the power ON
- Turn off the power after completing each individual measurement
- Check connections with the help of an instructor before turning the power ON
Objective
- Verify the generated voltage equation of an ac generator
- Obtain the frequency of the generated voltage
- Obtain the no-load saturation curve
Theory of Alternating Voltage Generation
- Electromotive force (EMF) is induced in a conductor when the magnetic field around it changes
- In an ac generator/alternator, a rotating magnet (rotor) turns within a stationary set of conductors (stator) generating an induced EMF
- The rotor contains a coil with a dc current that produces an electromagnet
- The dc current for the rotor can be injected directly from a dc source or by a brushless dc exciter
Alternator Structure
- A three-phase alternator has three sets of stator windings physically spaced 120° from each other
- The armature windings are often short (fractional) pitched and distributed for better performance
Frequency of Induced Voltage
- The voltage induced in the phase windings of an alternator has the same frequency
- Frequency (f) of induced voltage is dependent on rotor speed and number of rotor poles
- The frequency in Hz is related to the rotor speed by the equation: N = 120f/P
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