Briefly, in practice, the locked rotor torque needs to be as high as is feasible, so that the rotor can overcome the initial inertia of the load and can accelerate it rapidly, especially if the starting becomes less tension . The minimum torque is the smallest torque developed by the engine when accelerating from zero speed to the speed corresponding to the maximum torque.
Therefore, this value can not be very low, ie the curve should never present a marked depression in the acceleration process, so that the start is not very long and can result in overheating of the electric motor, especially in cases of high inertia Or starting with reduced voltage.
The maximum torque is the largest torque developed by the motor, under nominal voltage and frequency, without any possibility of extreme speed drop. In practice, the maximum torque must be as high as possible, for two main reasons, and the motor must be capable of overcoming any load peaks that may occur, as in specific applications. The engine can not lower, ie abruptly lose speed if excessive voltage drops occur.