When the motor converts electrical energy into mechanical energy, it also loses a part of its energy. The loss of the motor can generally be divided into three parts: variable loss, fixed loss, and stray loss.
Motor Loss Classification
(1). Variable loss varies with load, including stator resistance loss (copper loss), rotor resistance loss, and brush resistance loss.
(2). Fixed loss has nothing to do with 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 windage losses caused by the rotation of fans and rotors, etc.
Several Measures to Reduce Motor Loss
1. Stator loss
The main methods to reduce motor stator loss 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 area of the magnetic circuit and increase the magnetic density of the teeth.
② Increase the full slot rate of the stator slot, which is better for low-voltage small motors. Applying the best winding and insulation dimensions, and a large cross-sectional area of the wire can increase the full slot rate of the stator.
③ Minimize the length of the end of the stator winding. The loss at the end of the stator winding accounts for 1/4 to 1/2 of the total loss of the winding. Reducing the length of the end of the winding can improve the efficiency of the motor. Experiments have shown that the end length is reduced by 20%, and the loss is reduced by 10%.
2. Rotor loss
The rotor loss of the motor is mainly related to the rotor current and rotor resistance, and the corresponding energy-saving methods mainly include:
① Reduce the rotor current, which can be considered from two aspects increasing the voltage and the power factor of the motor.
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% to 15%, but today's cast copper rotors require high manufacturing temperatures and the technology has not yet been popularized, and their cost is 15% to 20% higher than that of cast aluminum rotors.
3. Core loss
Motor iron loss 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 will increase accordingly.
② Reduce the thickness of the iron chips to reduce the loss of induced current. For example, replacing hot-rolled silicon steel sheets with cold-rolled silicon steel sheets can reduce the thickness of silicon steel sheets, but thin iron chips will increase the number of iron chips and the manufacturing cost of the motor.
③ Use cold-rolled silicon steel sheets with good magnetic permeability to reduce hysteresis loss.
④ Adopt high-performance iron chip insulation coating.
⑤Heat treatment and manufacturing technology. The residual stress after the iron chip processing will seriously affect the loss of the motor. When the silicon steel sheet is processed, 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-treating the silicon steel sheet can reduce the loss by 10% to 20%.
4. Stray loss
Today's understanding of the stray loss of the motor is still in the research stage. Some of the main methods to reduce the stray loss are:
① Use heat treatment and finishing to reduce the short circuit on the rotor surface.
② The inner surface of the rotor slot is insulated.
③ Reduce harmonics by improving stator winding design.
④ Improve the rotor slot matching design and reduce harmonics, increase the stator and rotor slots, design the rotor slots as inclined slots, and use series-connected sinusoidal windings, scattered windings and short-pitch windings to greatly reduce the use of high-order harmonics It is an effective method to reduce additional stray loss by using magnetic slot mud or magnetic slot wedge to replace traditional insulating slot wedge, and to fill up the notch of motor stator core with magnetic slot mud.
5. Wind friction loss
Wind friction loss accounts for about 25% of the total loss of the motor, and should be paid attention to by people. Friction loss is mainly caused by bearings and seals, which can be reduced by the following measures:
① Minimize the size of the shaft as much as possible, 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.