Is the no-load current of a motor always less than the load current ?

From the two intuitive states of no-load and load, it can basically be concluded that when the motor is under load, due to the actual situation of the load it drives, there will be a relatively large current, thus the load current of the motor will be greater than the no-load current.  However, this situation does not apply to all motors. There have some motors, the no-load current is greater than their load current.

The electrical functions of the stator part of an asynchronous motor are twofold: one is to input electrical energy, and the other is to establish the rotating magnetic field of the motor.

When the motor is in no-load condition, the main current component is the excitation current, and the active current corresponding to the no-load loss is relatively small.

That is, when no-load, the input electrical energy is small, and the stator current is mainly used to establish the magnetic field.

Under load conditions, more electrical energy needs to be input to drive the load. Generally, the main component of the current is the load current. Therefore, under normal circumstances, the load current is greater than the no-load current, which is only between one quarter and one half of the load current.

The electromechanical energy conversion inside a motor is a very complex process. Among them, the establishment of the magnetic field, which serves as the sole medium for electromechanical conversion, involves various factors, resulting in the no-load current of some specially designed or classified motors being greater than the load current.

For three-phase asynchronous motors, the three-phase windings are symmetrically distributed in space, the input three-phase currents are symmetrical, and the established magnetic field is always a circular magnetic field. Generally, the proportion of the excitation current to the load current does not change much, and the proportion has a certain regularity. However, for some specially designed motors, such as single-winding variable-pole multi-speed motors with a certain speed or pole number scheme, the leakage reactance or leakage flux is extremely large. The leakage reactance voltage drop caused by the load current is significant, resulting in the magnetic circuit saturation level under load being much lower than that under no-load, and the load excitation current being much smaller than the no-load excitation current, causing the no-load current to be greater than the load current.

The magnetic field of a single-phase motor is an elliptical magnetic field, and the ellipticity varies greatly when it is no-load and under load. Generally, the stator of a single-phase asynchronous motor has two sets of windings, the main winding and the auxiliary winding. Moreover, their axes are often 90° apart in space. After an appropriate capacitor is inserted in series in the auxiliary winding, it is connected in parallel with the main winding to the power grid. Due to the phase splitting effect of components like capacitors, the current in the main winding and the secondary winding differs by a phase Angle in time. The pulse magnetic potentials generated by the main winding and the secondary winding respectively are combined into a rotating magnetic potential, generating an induced current in the rotor and establishing an induced magnetic field. The interaction of the two magnetic fields produces the driving torque of the motor. Theoretical analysis proves that the elliptical synthetic rotating magnetic potential of a single-phase motor can be decomposed into two circular rotating magnetic potentials: positive sequence and negative sequence. The positive sequence rotating magnetic potential dominates the motor's rotation, while the negative sequence magnetic potential exerts a reverse braking effect on the motor, significantly affecting the magnitude of the driving torque.