Selection of A.C. Motor Starter
Type
Starter type
 Range
Voltage
HP
Squirrel cage  Manual full volatge
110 - 550
1.5 - 7.5
. Manual Auto transformer
220 - 2500
5 - 150
. Manual full voltage
110 - 550
1.5 - 600
. Manual reduced
220 - 5000
5 - 1750
. Magnetic voltage resistor
220 - 550
5 - 600
Synchronous Reduced voltage magnetic
220 - 5000
25 - 3000
. Reduced semi-magnetic
220 - 2500
20 - 175
. Full voltage magnetic
220 - 5000
25 - 3000
Wound rotor Magnetic
220 - 4500
5 - 1000
High capacity induction Magnetic full voltage
2300 - 4600
upto 2250
High capacity synchronous Magnetic full voltage
2300 - 4600
upto 2250
. Reduced voltage
2300 - 4600
upto 2250

D.C MACHINES
Series wound motor :- As torque increases the speed fails rapidly. The load current is also the field current. The flux increases with load, so reducing the speed used for cranes.
Ia = It  = and E = V - I(Ra + Ri)
Shunt wound motor :- As load current rises the voltage drop in armature increases. The fall in speed is not very great and the motor is suitable for driving machinery at constant speed.
I = V/R1 and Ia = I - IfE = V - IaRa
Compound Wound Motor :- These have characteristics intermediate between those of series wound and shut wound machines.
   The output of a generator or motor is limited by the permissible increase of temperature and also by sparking 

Efficiency of D.C Machines :
Copper losses  :
Power used in armature windings I2a Ra
Power used in field windings 12fRf
Iron losses  :
Power consumed eddy currents
Power consumed by hysteresis
Mechanical losses :
Brush friction and resistance
Bearing  friction and windage

DIRECT CURRENT MOTOR STARTERS
Type of Starter
Uses
Reduced voltage manual Used for motor upto 50 hp
Reduced voltage, Multiple switch Motors of more than 50 hp
Reduced voltage drum Switch Large motors, frequent starting and stopping
Reduced voltage magnetic switch
 - do-

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