Upon what does the amount of emf generated in alternator depend? A-the rate at which the lines of flux are being cut, B-the number of lines of flux per given area of pole face, C - the lenggth of the armature or stador conductors, D- all of the above In actual operation, which of these is a variable? A- the rate at which the lines of flux are being cut, B- the number of lines of flux per given area of pole face, C- the length of the armature or stator concuctors, D- all of the above Besides the fact that their phase sequence must be the same, what requirement(s) must be satisfied before AC genarators may be paralleled? A- their terminal voltage must be equal, B-their voltages must be in phase, C-their frequencies must be equal, D- all of the above.
Synchronous Generator
In comparison to an asynchronous generator, it is a machine where the rotor speed is equal to the rotating magnetic field produced by the stator, i.e., mechanical speed is equal to the electrical speed, thus called synchronous, and not asynchronous.
Salient Pole Rotor
Salient pole rotor includes a large number of exposed poles mounted on a magnetic wheel. The construction of a bright pole is as shown in the image on the left. The proposed poles are made of metal laminations. The rotor winding is provided on these poles and is supported by pole shoes.
Upon what does the amount of emf generated in alternator depend? A-the rate at which the lines of flux are being cut, B-the number of lines of flux per given area of pole face, C - the lenggth of the armature or stador conductors, D- all of the above
In actual operation, which of these is a variable? A- the rate at which the lines of flux are being cut, B- the number of lines of flux per given area of pole face, C- the length of the armature or stator concuctors, D- all of the above
Besides the fact that their phase sequence must be the same, what requirement(s) must be satisfied before AC genarators may be paralleled? A- their terminal voltage must be equal, B-their voltages must be in phase, C-their frequencies must be equal, D- all of the above.
EMF generated in an alternator is given by EMF equation
E = 4.44fфT Volts.
where P= No. of poles
Where T is the number of coils or turns per phase (Note that one turn or coil has two ends or sides)
f = frequency of induced EMF in Hz
ф = Flux per pole (Weber)
In one revolution of the rotor i.e. in 60/N seconds, each conductor is cut by a flux of Pф Webers.
So it depends on the rate at which the lines of flux are being cut,
also more the flux lines more the flux cut by each conductor in flux strength is high (Pф will be high).
we can also see from above equation EMF induced also depends upon number of turns of conductor more the number of turns more are number of conductors to cut the flux.
Hence all three options are correct hence for part A answer will be D - All of the above.
The rate at which the lines of flux are being cut depends upon speed of rotation of rotor. As speed of rotation can change hence it is not a constant .
In one revolution of the rotor i.e. in 60/N seconds, each conductor is cut by a flux of Pф Webers, if number of rotation changes rate of cutting of flux lines also changes.
Option A is correct for this question(Part B)
In option B the number of lines of flux per given area of pole face is constant as flux (ф) is constant as it is provided by external excitation source it is kept constant hence it is not a variable, hence option B is incorrect.
In option C : the length of the armature or stator conductors is fixed at the time of manufacturing it does not changes as users are not supposed to change number of conductors or its length. Hence it is also constant.
hence option C is incorrect.
As two options (B and C) are already incorrect option D (all of the above) is automatically incorrect
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