Because when a motor is running steadily, the rotor speed remains constant, which means that the electromagnetic drive torque and the load torque (which is the actual output torque) are equal and in a state of equilibrium.

If the electromagnetic drive torque is greater than the load torque, the rotor will also accelerate; if the electromagnetic drive torque is less than the load torque, the rotor will reduce speed. In both cases the rotor is in an unbalanced transition state.

Expanded information:

Types of torque:

The torque can be categorized into static and dynamic torque.

Static torque is a torque whose value does not change with time or changes very little and slowly, including static torque, constant torque, slowly varying torque and micro-pulsating torque.

The value of static torque is constant, and the drive shaft does not rotate.

The value of constant torque is constant, but the drive shaft rotates at a constant speed, such as the torque when the motor is working steadily.

A slowly varying torque has a value that changes slowly over time, but the value of the torque can be considered constant over a short period of time.

Micro-pulsating torque has a pulsating change in instantaneous value of modest amplitude.

Dynamic torque is a torque whose value changes greatly with time, including vibration torque, transition torque and random torque.

The value of vibration torque is periodic fluctuation; transition torque is the torque change process of machinery from one operating condition to another; random torque is a kind of uncertainty, change irregular torque.

Based on the different conditions of the torque, different torque measurement methods can be taken. Torque = 9550 * power / speed of the same power = speed * torque / 9550 balanced equation: the unit of power (kW); speed of the unit (r/min); torque unit (N.m); 9550 is the calculation coefficient.

Baidu Encyclopedia - Electromagnetic Torque

Baidu Encyclopedia - Output Torque