This document discusses concepts related to rotating machines including: 1. Physical concepts of force and torque production in rotating machines and general terms like generated EMF in full pitched and short pitched windings. 2. Definitions of terms like conductor, overhang, coil, pole pitch, coil span, full pitched and short pitched coils. 3. Advantages of using short pitched coils like reduced overhang and copper, lower distortions harmonics, reduced eddy current and hysteresis losses, and increased efficiency. 4. Disadvantage of short pitched coils is their total voltage is somewhat reduced due to voltages induced on two sides being slightly out of phase.

1. CONCEPT OF GENERAL TERMS
PERTAINING TO ROTATING
MACHINES

2.  Physical concept of force and torque production.
 Concept of general terms pertaining to rotating
machines.
 Generated emf in full pitched and short pitched
winding.

3.  The force on a moving particle of electric q in a
magnetic field is given by the Lorentz’s force law
F = q ( V × B ) Newtons
Where, v = velocity motion of conductor, m/s
B = flux density, Tesla
 The force acting on a current carrying conductor
can be directly form the equation

4. l = length of conductor
C = contour of the conductor
 For a homogeneous conductor of length l carrying
current I in a uniform magnetic field, the above
equation can be written as
 In a rotating magnetic field, the torque about an
axis is given by
Where, r = radius vector from the
axis towards conductor

5. 1) Electrical and mechanical degree
There is a definite relationship between and
mechanical rotation of a conductor in machine.
Electrical degrees
It is the degree or the cycle of emf induced in the
conductor of a machine.

10. 2) Conductor :
The active length of wire in which emf is induced
and embedded in the slot is called a conductor. In
shows fig. two active conductors ‘ab’ and ‘cd’.
3) Overhang :
The portion of coil which just provides a
connection between the two active conductors
and does not take part in energy conversion
process is called overhang.

11. 4) Coil :
The two active conductors ‘ab’ and ‘cd’ along with
overhang constitute one coil.
5) Pole pitch :
It is the peripheral distance between the two
adjacent poles.
The pole pitch is always expressed in electrical
degrees and it is always equal to 180° electrical.

12. 6) Coil span :
The distance between the two sides of a coil span.
7) Full pitched
The coils having span which is equal to one pole
pitch are called full pitched.
Short pitched coil
If the coils span is less than the pole pitch, the
coils are called short pitched coils.

13.  ADVANTAGES OF USING SHORT PITCHED
COILS
1. Overhang will reduce i.e. save copper of end
connections.
2. Distorting harmonics can be reduced or totally
eliminated.
3. Due to reduction of high frequency harmonics,
eddy current and hysteresis losses are
reduced.
4. Iron losses decrease & efficiency will increase.

14.  Disadvantage
1. total voltage around the coils is somewhat
reduced.
2. because the voltages induced in the two sides of
the short pitched coil are slightly out of phase,
their resultant vectorial sum is less than their
arithmetic sum.

15. Time for one revolution, dt =
Now, frequency of generated emf,
Speed of rotor , N =
Average generated emf/phase = 4f Ø Tph
1.11
Ep = 4.44 kw f Ø Tph ( kw = kc kp )

16. Let,
Z = number of conductors or coil sides in series per phase
Tph = no. of turns or coil per phase
Ø = flux per pole in Weber
P = number of rotor poles
N = speed of rotor, rpm
f = frequency of generated emf
kc = coil span
kp = pitch factor
kd = distribution factor of stator winding
kw = winding factor

17.  DC MACHINES AND TRANSFORMERS BOOK
( DR. J.G. JAMNANI)
 E DRAW MAX ( FOR DRAWING )

18. Thank You……