emf equation of alternator, pitch factor & coil span factor

emf equation of alternator, pitch factor & coil span factor

1. Active Learning Assignment Semester : 4 th Branch : Electrical Engineering Subject : ACM ( ) Topic : “ emf equation of alternator, pitch factor & coil span factor ” Prepared by : Soham Gajjar (160120109007) Guided by : Prof. Hitesh Manani Gandhinagar Institute of Technology 1

2. INTRODUCTION emf equation of alternator emf equation of pitch factor emf equation of coil span factor

3. emf equation of alternator Let ,        Φ  = Flux per pole, in Wb               P  = Number of poles               N = Synchronous speed in r.p.m               f = Frequency of induced emf in Hz               Z = Total number of conductors               Zph  = Conductors per phase connected in series/phase =2T K d = distribution factor = sin m β /2 m sin β /2 Kf = from factor = 1.11

4. In one revolution of the rotor each stator conductor is cut by a flux of ɸp webers . dɸ = ɸp and dt =60/N second average e.m.f induced per conductor = = Now, we know that f=PN/120 or N=120f/p Substituiting this values of N above , we get Average e.m.f per conductor = * =2f ɸ volt If there are z conductors in series/ parallel,then average e.m.f /phase =2f ɸz volt =4fɸT volt R.M.S value of e.m.f /phase = 1.11*4f ɸT = 4.44fɸT volt Actually available voltage/ phae = 4.44kckdf ɸT = 4kfkckdfɸT volt  

5. emf equation of pitch factor In short pitched coil, the phase angle between the induced emf of two opposite coil sides is less than 180 o (electrical). But we know that, in full pitched coil, the phase angle between the induced emf of two coil sides is exactly 180 o (electrical ). Hence, the resultant emf of a full pitched coil is just the arithmetic sum of the emfs induced on both sides of the loop. We well know that vector sum or phasor sum of two quantities is always less than their arithmetic sum. The pitch factor is the measure of resultant emf of a short-pitched coil in comparison with resultant emf of a full pitched coil.

6.                                                                                                Now, as per definition of pitched factor ,

7. emf equation of coil span factor The  Coil Span Factor  or  Pitch Factor  K C  is defined as the ratio of the voltage generated in the short pitch coil to the voltage generated in the full pitch coil. The distance between he two sides of a coil is called the  Coil Span  or  Coil Pitch Factor . It is also known as  Chording Factor The angular distance between the central line of one pole to the central line of the next pole is called  Pole Pitch . A pole pitch is always 180 electrical degrees, regardless of the number of poles on the machine. A coil having a span equal to 180⁰ electrical is called a  full pitch coi l as shown in the figure below.

8. The coil span factor is represented as For full pitch coil, the value of α will be 0⁰, cos α/2 = 1 and  K C  = 1. For a short pitch coil  K C  < 1.

9. REFERNCES B.L THERAJA GOOGLE.COM ELECTRICAL4U.COM