When the motor converts electrical energy into mechanical energy, it also loses a part of the energy itself. Generally, the motor loss can be divided into three parts: variable loss, fixed loss and stray loss.

1. Variable losses vary with load, including stator resistance loss (copper loss), rotor resistance loss and brush resistance loss.

2. Fixed loss is independent of load, including core loss and mechanical loss. The iron loss is composed of hysteresis loss and eddy current loss, which is proportional to the square of the voltage, and the hysteresis loss is also inversely proportional to the frequency.

3. Other stray losses are mechanical losses and other losses, including friction losses of bearings and wind resistance losses caused by rotation of fans and rotors.

Motor Loss Classification

Several Measures to Reduce Motor Loss 

1 Stator losses

The main methods to reduce the I^2R loss of the motor stator are:

1. Increase the cross-sectional area of ​​the stator slot. Under the same outer diameter of the stator, increasing the cross-sectional area of ​​the stator slot will reduce the magnetic circuit area and increase the magnetic density of the teeth.

2. Increase the full slot ratio of the stator slots, which is better for low-voltage small motors. Applying the best winding and insulation size and large wire cross-sectional area can increase the full slot ratio of the stator.

3. Try to shorten the length of the stator winding end. The loss of the stator winding end accounts for 1/4 to 1/2 of the total winding loss. Reducing the length of the winding end can improve the efficiency of the motor. Experiments show that the end length is reduced by 20% and the loss is reduced by 10%.

2 Rotor losses

The I^2R loss of the motor rotor is mainly related to the rotor current and rotor resistance. The corresponding energy-saving methods are as follows:

1. Reduce the rotor current, which can be considered in terms of increasing the voltage and the motor power factor.

2. Increase the cross-sectional area of ​​the rotor slot.

3. Reduce the resistance of the rotor winding, such as using thick wires and materials with low resistance, which is more meaningful for small motors, because small motors are generally cast aluminum rotors, if cast copper rotors are used, the total loss of the motor can be reduced by 10% ～15%, but today’s cast copper rotor requires high manufacturing temperature and the technology is not yet popular, and its cost is 15% to 20% higher than that of cast aluminum rotor.

3 Core loss

The iron loss of the motor can be reduced by the following measures:

1. Reduce the magnetic density and increase the length of the iron core to reduce the magnetic flux density, but the amount of iron used in the motor increases accordingly.

2. Reduce the thickness of the iron sheet to reduce the loss of the induced current. For example, replacing the hot-rolled silicon steel sheet with a cold-rolled silicon steel sheet can reduce the thickness of the silicon steel sheet, but the thin iron sheet will increase the number of iron sheets and the manufacturing cost of the motor.

3. Use cold-rolled silicon steel sheet with good magnetic permeability to reduce hysteresis loss.

4. Adopt high-performance iron chip insulation coating.

5. Heat treatment and manufacturing technology, the residual stress after processing the iron core will seriously affect the loss of the motor. When processing the silicon steel sheet, the cutting direction and punching shear stress have a greater impact on the core loss. Cutting along the rolling direction of the silicon steel sheet and heat treatment of the silicon steel punching sheet can reduce the loss by 10% to 20%.

4 Stray loss

Today, the understanding of motor stray losses is still in the research stage. Some of the main methods to reduce stray losses today are:

1. Use heat treatment and finishing to reduce short-circuit on the rotor surface.

2. Insulation treatment on the inner surface of the rotor slot.

3. Reduce harmonics by improving the stator winding design.

4. Improve the design of rotor slot coordination and reduce harmonics, increase stator and rotor cogging, design the rotor slot shape as inclined slots, and use series-connected sinusoidal windings, scattered windings and short-distance windings to greatly reduce high-order harmonics; Using magnetic slot mud or magnetic slot wedge to replace the traditional insulating slot wedge and filling the slot of the motor stator iron core with magnetic slot mud is an effective method to reduce additional stray losses.

5 wind friction loss

The wind friction loss accounts for about 25% of the total loss of the motor, which should be given due attention. Friction losses are mainly caused by bearings and seals, which can be reduced by the following measures:

1. Minimize the size of the shaft, but meet the requirements of output torque and rotor dynamics.

2. Use high-efficiency bearings.

3. Use efficient lubrication system and lubricant.

4. Adopt advanced sealing technology.

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Post time: Jun-22-2022