Types of DC Motor are classified on the basis of armature and field winding connection same as that of DC Generator. If armature and field is connected in shunt then this machine is called as dc shunt Motor. When armature and field are connected in series then it is called as dc series motor.
DC Shunt Motor
- In the shunt dc motor type motor, the armature and field winding are connected in parallel as shown in fig.
- The parallel combination of the two windings is connected across a common dc power supply.
- Resistance of the shunt field winding (Rsh) is always much higher than that of the armature winding (Ra).
- Current flow through the shunt field winding name indicated as Ish and current through armature winding name as Ia.
DC Series Motor
- In the D.C. series motor, the armature and field windings are connected in series with each other as shown in fig.
- The resistance of the series field winding (Rs) is much smaller as compared to that of the armature resistance (Ra).
- Current flowing though armature winding and field winding is same name as I=Ia=Ise.
Que. Series DC motor should never be started at no-load. Justify.
- At no load the field current (which is also the armature current) is very small and hence the useful air-gap field flux also very small.
- Therefore the speed rises to excessively high values and it is mechanically very harmful for machine.
- At high speeds due to centrifugal forces on the rotating parts they may get damaged. And also it may cause accident at work place.
- Hence DC series motor should never be started on no-load.
DC Compound Motors
The DC compound motors are classified into two types:
- Long shunt compound motor.
- Short shunt compound motor.
Long Shunt Compound Motor
- The connection of long shunt compound dc motor is shown in fig.
- Note that the shunt field winding is connected across the series combination of the armature and series field winding.
Short Shunt Compound Motor
- Interconnections between various windings of a DC short shunt compound motor are shown in fig.
- The armature and shunt field windings are connected in parallel with each other and this parallel connection combination is then connected in series with the series field winding.
Applications of DC Motors
Que. State at least four applications of Different types of dc motor.
Shunt Motor Applications:
- Lathe Machine
- Drilling Machine
- Milling Machine
- Printing Machine
Series Motor Applications:
Que. State at least four applications of D.C. series motor.
- Series motors are very widely used for the following applications:
- Electric trains,
- Diesel-electric locomotives,
- Trolley cars and trolley buses,
- Conveyers etc.
Cumulative Compound Motor Applications:
- Cumulative compound motors are used for the following applications:
- Rolling mills
Selection of DC Motors for a Particular Application:
D.C. shunt motor:
D.C. shunt motor is used to drive pumps, lathes machine tools, prime mover for generators due to constant speed characteristic.
D.C. series motor:
This has a very high starting torque. Hence it is used in applications like traction, cranes, and hoists etc. which require high starting torque.
D.C. compound motor:
Compound Motor has higher starting torque but has finite speed at no load. It is used to driving rolling mills, cutting tool etc.
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