# What happens when the motor torque is constant and the load torque suddenly decreases?

It is a situation where the load torque (Ta) suddenly decreases while rotating the shaft with a motor(PMSM) at a constant motor torque (Tm).

In my opinion, the rotational speed of the shaft (I-moment of inertia) and motor will be instantaneously increased by the torque difference, and then more power is consumed in proportion to the shaft speed, right?

Tm - Ta = I*wdot

before load decrease : Power = Tm * w
After load decrease :  Power = Tm * (w + wdot * dt)

• What do you understand by "at constant motor torque"? Is it a control system that keeps the torque constant? – AlexVB Mar 17 at 12:02
• yes , control system keeps the torque – Lee Mar 17 at 12:02