I have three DC shunt wound motors in series. Each motor has a coupling to a transmission. I am trying to work out (mathematically, as opposed to intuitively), what happens if the coupling was to drop in one motor (motor 2) resulting in no load on that motor.
Intuitively I know that that motor will speed up and eventually the centrifugal force will result in destruction of that motor if the supply isn't shut off in time.
The supply voltage is 600V so there is 200V across each DC motor.
- When the coupling drops and there is no load, does the current result in excessive torque and accelerates the DC motor RPM?
- As the motor RPM increases the back EMF increases resulting in a reduction in the current in the motor armature decreasing?
- What is happening to the voltage across the motor? Increasing or decreasing? Is it P=VI, so current decreases due to back EMF so voltage across that motor increases? Where does the back EMF mathematically come into play?