11. What is distributed winding?
When coil-sides belonging to each phase are housed or distributed in more than one slot under each pole region then the winding is called distributed winding
A full pitch coil has width of coil otherwise called coil-span as 180ยบ
Where - angle between adjacent slots in electrical degree and x=
1,2,3…
12. Why is short pitch winding preferred over full-pitch winding ?
Advantages
• Waveform of the emf can be approximately made to a sine wave and distorting harmonics can be reduced or totally eliminated.
• Conductor material , copper , is saved in the back and front end connections due to less coil-span.
• Fractional slot winding with fractional number of slots/phase can be used which in turn reduces the tooth ripples.
• Mechanical strength of the coil is increased.
13. Write down the formula for distribution factor.
Kd = sin(m b /2) / m sin(b /2) or Kdn = sin(mn b /2) / m sin(n b/2)
m= number of slots/ pole/ phase
b- angle between adjacent slots in electrical degree
n = order of harmonic
A full pitch coil has width of coil otherwise called coil-span as 180ยบ
Where - angle between adjacent slots in electrical degree and x=
1,2,3…
12. Why is short pitch winding preferred over full-pitch winding ?
Advantages
• Waveform of the emf can be approximately made to a sine wave and distorting harmonics can be reduced or totally eliminated.
• Conductor material , copper , is saved in the back and front end connections due to less coil-span.
• Fractional slot winding with fractional number of slots/phase can be used which in turn reduces the tooth ripples.
• Mechanical strength of the coil is increased.
13. Write down the formula for distribution factor.
Kd = sin(m b /2) / m sin(b /2) or Kdn = sin(mn b /2) / m sin(n b/2)
m= number of slots/ pole/ phase
b- angle between adjacent slots in electrical degree
n = order of harmonic
14. Define winding factor.
The winding factor Kd is defined as the ratio of phasor addition of emf induced in all the coils belonging to each phase winding to their arithmetic addition.
The winding factor Kd is defined as the ratio of phasor addition of emf induced in all the coils belonging to each phase winding to their arithmetic addition.
15. Why are Alternators rated in kVA and not in kW?
The continuous power rating of any machine is generally defined as the power the machine or apparatus can deliver for a continuous period so that the losses incurred in the machine gives rise to a steady temperature rise not exceeding the limit prescribed by the insulation class.
Apart from the constant loss incurred in Alternators is the copper loss, occurring
in the 3 –phase winding which depends on I2 R, the square of the current delivered by the generator. As the current is directly related to apparent – power delivered
by the generator , the Alternators have only their apparent power in
VA/kVA/MVA as their power rating.
16. What are the causes of changes in voltage in Alternators when loaded?
Variations in terminal voltage in Alternators on load condition are due to the following three causes:
• Voltage variation due to the resistance of the winding, R
• Voltage variation due to the leakage reactance of the winding, Xt
• Voltage variation due to the armature reaction effect, Xa
Apart from the constant loss incurred in Alternators is the copper loss, occurring
in the 3 –phase winding which depends on I2 R, the square of the current delivered by the generator. As the current is directly related to apparent – power delivered
by the generator , the Alternators have only their apparent power in
VA/kVA/MVA as their power rating.
16. What are the causes of changes in voltage in Alternators when loaded?
Variations in terminal voltage in Alternators on load condition are due to the following three causes:
• Voltage variation due to the resistance of the winding, R
• Voltage variation due to the leakage reactance of the winding, Xt
• Voltage variation due to the armature reaction effect, Xa
17. What is meant by armature reaction in Alternators?
The interaction between flux set up by the current carrying armature
conductors a and the main field flux m is defined as the armature reaction.
The interaction between flux set up by the current carrying armature
conductors a and the main field flux m is defined as the armature reaction.
18. What do you mean by synchronous reactance?
Synchronous reactance X s= (Xl + Xa)
The value of leakage reactance Xl is constant for a machine based on its
construction. Xa depends on saturating condition of the machine. It is the
addition of Xa , which represent the armature reaction effect between two
synchronously acting magnetic fields that makes the total reactance Xa to be called syncheornous reactance.
The value of leakage reactance Xl is constant for a machine based on its
construction. Xa depends on saturating condition of the machine. It is the
addition of Xa , which represent the armature reaction effect between two
synchronously acting magnetic fields that makes the total reactance Xa to be called syncheornous reactance.
19. What is meant by synchronous impedance of an Alternator?
The complex addition of resistance, R and synchronous reactance , jXs can be represented together by a single complex impedance Zs called synchronous impedance.
In complex form Zs = (R + jXs )
The complex addition of resistance, R and synchronous reactance , jXs can be represented together by a single complex impedance Zs called synchronous impedance.
In complex form Zs = (R + jXs )
In polar form Zs = | Zs | <
Where | Zs | = ¥(52 + X2 )
Where | Zs | = ¥(52 + X2 )
And tan-i (Xs /R)
20. What is meant by load angle of an Alternator?
The phase angle introduced between the induced emf phasor, E and terminal voltage phasor , U during the load condition of an Alternator is called load angle.
The phase angle introduced between the induced emf phasor, E and terminal voltage phasor , U during the load condition of an Alternator is called load angle.
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