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 600 V so there is 200 V across each DC motor.
- When the coupling drops and there is no load, does the current result in excessive torque and increase the DC motor's RPM?
- As the motor's RPM increases, does the back EMF increase, resulting in a reduction in the current in the motor armature?
- What is happening to the voltage across the motor? Increasing or decreasing? Is it P=VI, so current decreases due to back EMF, so the voltage across that motor increases? Where does the back EMF come into play mathematically?