SMJE 2103 DC Motors

DC Motor Discussion topics: 1.Basic structure 2.Field circuit connections 3.Equivalent circuit 4.Induced torque 5.Terminal characteristics 6.Speed

DC Motor - basic structure -

DC Motor - field circuit connections - shuntcompound Separate excitation series

DC Motor - equivalent circuit -

DC Motor - equivalent circuit (separate)- Separate power supply for field circuit

DC Motor - equivalent circuit (shunt)- Power supply for field circuit directly from terminal

DC Motor - equivalent circuit (series)-

DC Motor - equivalent circuit (compound)- long-shunt connection

DC Motor - equivalent circuit (compound)- Short-shunt connection

DC Motor - induced torque (series)- As the load increases, its flux increases and proportional to armature current. So, the motor decreases in speed. A series dc motor has sharply drooping torque-speed characteristic. The application requiring very high torque, such starter motor in cars, elevator motor etc.

DC Motor - induced torque (compound)- It has a component of flux in constant. Also, another component in proportional to its armature current. So, higher starting torque than a shunt and lower than a series motors.

DC Motor - induced torque (compound)-

DC Motor - terminal characteristics (separate/shunt)- A plot of the machine’s output quantities between torque and speed. Load increase, load torque  load will exceed induced torque  ind, the motor will start slow down. Internal generated voltage drops, Armature current will increase, Induced torque increases and equal to load torque,

DC Motor - terminal characteristics (separate/shunt)-

DC Motor - terminal characteristics (series)-

DC Motor - terminal characteristics (compound)-

DC Motor - speed (shunt) - Two common methods: 1.Adjusting the filed resistance R F, then field flux. 2.Adjusting the terminal voltage applied to the armature. Less common method: 1.Inserting a resistor in series with the armature circuit.

DC Motor - speed (shunt) - R F changing

Voltage changing DC Motor - speed (shunt) -

DC Motor - speed (series) - The way how to change the speed of dc motor. By changing the terminal voltage of the motor. If terminal voltage is increased, the speed will increase for any given torque.

DC Motor - speed (compound) - Same as for a shunt motor