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Short Notes: DC Machines - Short Notes for Electrical Engineering - Electrical Engineering (EE)

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 Page 1


 
 
 
 
 
 Induced emf equation 
    
a
NZ P
E = 
60 A
?
??
??
??
 
               ? ? = flux per pole wb ? 
    ? ? N = speed of machine rpm 
    P = number of poles 
    A = number of paralled path 
    Z = number of conductors 
   A = 2   for wave winding 
   A = P for lap winding 
   If speed is given in rad/sec                
a
ZP
E = 
2A
?? ??
??
?
??
   where ? = speed (rad/s)  
                                                
? ?
m
PZ
  = K
2A
??
??
??
? ? ? ? ?
?
 
                                                            
m
PZ
K =  = machine constant
2A ?
 
Developed Torque 
    
ma
T = K I ? 
                     
m
PZ
K =  = machine constant
2A ?
 
                 = flux per pole ? 
                
a
I = armature current 
   
Page 2


 
 
 
 
 
 Induced emf equation 
    
a
NZ P
E = 
60 A
?
??
??
??
 
               ? ? = flux per pole wb ? 
    ? ? N = speed of machine rpm 
    P = number of poles 
    A = number of paralled path 
    Z = number of conductors 
   A = 2   for wave winding 
   A = P for lap winding 
   If speed is given in rad/sec                
a
ZP
E = 
2A
?? ??
??
?
??
   where ? = speed (rad/s)  
                                                
? ?
m
PZ
  = K
2A
??
??
??
? ? ? ? ?
?
 
                                                            
m
PZ
K =  = machine constant
2A ?
 
Developed Torque 
    
ma
T = K I ? 
                     
m
PZ
K =  = machine constant
2A ?
 
                 = flux per pole ? 
                
a
I = armature current 
   
 
 
 
 
 
Classification of DC Machine 
(i) Separately excited 
 
 
 
 
 
(ii) Shunt excited 
 
 
 
 
 
(iii) Series excited 
 
 
 
 
 
(iv) Compound Excited 
 
 
 
Page 3


 
 
 
 
 
 Induced emf equation 
    
a
NZ P
E = 
60 A
?
??
??
??
 
               ? ? = flux per pole wb ? 
    ? ? N = speed of machine rpm 
    P = number of poles 
    A = number of paralled path 
    Z = number of conductors 
   A = 2   for wave winding 
   A = P for lap winding 
   If speed is given in rad/sec                
a
ZP
E = 
2A
?? ??
??
?
??
   where ? = speed (rad/s)  
                                                
? ?
m
PZ
  = K
2A
??
??
??
? ? ? ? ?
?
 
                                                            
m
PZ
K =  = machine constant
2A ?
 
Developed Torque 
    
ma
T = K I ? 
                     
m
PZ
K =  = machine constant
2A ?
 
                 = flux per pole ? 
                
a
I = armature current 
   
 
 
 
 
 
Classification of DC Machine 
(i) Separately excited 
 
 
 
 
 
(ii) Shunt excited 
 
 
 
 
 
(iii) Series excited 
 
 
 
 
 
(iv) Compound Excited 
 
 
 
Page 4


 
 
 
 
 
 Induced emf equation 
    
a
NZ P
E = 
60 A
?
??
??
??
 
               ? ? = flux per pole wb ? 
    ? ? N = speed of machine rpm 
    P = number of poles 
    A = number of paralled path 
    Z = number of conductors 
   A = 2   for wave winding 
   A = P for lap winding 
   If speed is given in rad/sec                
a
ZP
E = 
2A
?? ??
??
?
??
   where ? = speed (rad/s)  
                                                
? ?
m
PZ
  = K
2A
??
??
??
? ? ? ? ?
?
 
                                                            
m
PZ
K =  = machine constant
2A ?
 
Developed Torque 
    
ma
T = K I ? 
                     
m
PZ
K =  = machine constant
2A ?
 
                 = flux per pole ? 
                
a
I = armature current 
   
 
 
 
 
 
Classification of DC Machine 
(i) Separately excited 
 
 
 
 
 
(ii) Shunt excited 
 
 
 
 
 
(iii) Series excited 
 
 
 
 
 
(iv) Compound Excited 
 
 
 
Page 5


 
 
 
 
 
 Induced emf equation 
    
a
NZ P
E = 
60 A
?
??
??
??
 
               ? ? = flux per pole wb ? 
    ? ? N = speed of machine rpm 
    P = number of poles 
    A = number of paralled path 
    Z = number of conductors 
   A = 2   for wave winding 
   A = P for lap winding 
   If speed is given in rad/sec                
a
ZP
E = 
2A
?? ??
??
?
??
   where ? = speed (rad/s)  
                                                
? ?
m
PZ
  = K
2A
??
??
??
? ? ? ? ?
?
 
                                                            
m
PZ
K =  = machine constant
2A ?
 
Developed Torque 
    
ma
T = K I ? 
                     
m
PZ
K =  = machine constant
2A ?
 
                 = flux per pole ? 
                
a
I = armature current 
   
 
 
 
 
 
Classification of DC Machine 
(i) Separately excited 
 
 
 
 
 
(ii) Shunt excited 
 
 
 
 
 
(iii) Series excited 
 
 
 
 
 
(iv) Compound Excited 
 
 
 
 
 
 
 
 
Characteristics of DC Generator 
External characteristics 
If no-load voltage is same for all types of generators: 
 
 
 
 
 
There are two categories of compound generators/motors 
  1.  Cumulative Compound     => If series field flux aids the shunt fields flux. 
  2.  Differentially Compound  => If ser es field flux opposes the shunt field flux. 
  If full – load voltage of all generators is kept same 
      1 ? series excited  5 ? separately excited 
   2 ? over compound   6 ? shunt excited 
  3 ? level compound 7 ? differentially compound 
     4 ? under compound 
 Conditions for voltage build-up in Shunt Generator 
1)   There must be residual flux. 
2) Correct polarity of field winding with respect to armature winding so that field flux aids 
residual flux for a given direction of rotation. 
3) Field Resistance must be less than critical value 
               
? ?
f f cr
R < R 
Critical resistance is equal to the slop of air-gap line. 
4) Speed of rotation should be more than critical value for a given field resistance
f
R . 
   
cr
N > N 
E y
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