[Basic loss in stator and rotor cores]
It is mainly generated when the main magnetic field changes in the iron core. Among them, the basic loss is the hysteresis loss and eddy current loss generated when the main magnetic field changes in the iron core. This change can be of an alternating magnetizing nature, such as occurs in the iron core of a transformer and in the stator or rotor teeth of an electric machine; or it can be of a rotating magnetizing nature, such as occurs in the stator or rotor yoke of an electric machine. which contains,
l Hysteresis loss: All ferromagnetic materials have hysteresis, which will result in hysteresis loss.
l Eddy current loss: When the magnetic field in the iron core changes, an electromotive force will be induced in the iron core, and the corresponding induced current is called eddy current, and the loss caused by it.
l Basic loss of yoke (gear yoke) and tooth: The basic iron loss in the iron core is mainly related to the magnetic flux density, material thickness and performance of the iron core under the condition of a certain frequency. At the same time, the core stacking process level and The processing method also has a greater impact on the loss
[Additional loss in iron core at no-load]
It is mainly due to the surface loss of the air-gap magnetic permeability harmonic magnetic field caused by the slotting of the stator and the rotor on the surface of the opposite iron core and the pulse vibration loss caused by the change of the magnetic flux in the opposite teeth due to the rotation of the motor due to the slotting.
At no-load, the additional loss in the iron core mainly refers to the surface loss of the iron core and the pulse vibration loss in the teeth, which is caused by the harmonic magnetic field in the air gap. There are 2 reasons for this harmonic magnetic field:
l The slotting of the motor core leads to the uneven permeability of the air gap;
l There are harmonics in the spatial distribution curve of no-load excitation magnetomotive force;
【Electrical Loss】
He refers to the loss caused by the working current in the winding (copper or aluminum), and also includes the contact loss of the brush on the commutator and the collector ring.
l Electrical loss of the winding: The electrical loss of the winding is equal to the product of the square of the current in the winding and the resistance.
l Contact loss of brush/collector ring: The contact voltage drop between the brush and the collector ring or commutator is mainly related to the type of brush selected, and has nothing to do with the size of the current.
[Additional loss at load]
This is due to various losses caused by the leakage magnetic field and harmonic magnetic field generated by the working current of the stator or rotor in the stator and rotor windings and in the iron core and structure.
Due to the leakage magnetic field around the windings, additional losses occur when loaded. These leakage fields create eddy current losses in the windings and all nearby metallic structures. The harmonic magnetic field generated by the harmonic magnetomotive force established in the air gap of the stator and rotor windings moves relative to the rotor and stator at different speeds, which induces eddy currents in the iron core and cage windings, resulting in additional losses.
【Mechanical loss】
It includes ventilation losses, bearing friction losses and friction losses between brushes and commutators or collector rings.
The friction loss of the bearing is related to the pressure on the friction surface, the friction coefficient and the relative motion speed between the friction surfaces. It is difficult to determine the coefficient of friction because it is related to various factors, such as the smoothness of the friction surface, the type of lubricating oil and its working temperature, the processing quality of parts and the quality of the motor's final assembly, etc. Ventilation losses are also related to many factors that are difficult to calculate accurately, such as the motor structure, the type of fan, and the wind resistance of the ventilation system. Therefore, in practice, it is often estimated based on the experimental data of the built motor.
The point! The point! The point!
In low-power micromotors, only the basic losses, electrical losses, and mechanical losses in the stator and rotor cores are generally calculated.
There is no best motor, only the best motor for you. Motor technology changes the way of life, I am Lao Zhang, see you in the next issue.
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Efficiency is King - "First Look" Motor Loss and Heat
We finally finished the part of the magnetic field. Starting from this article, Lao Zhang wants to lead you to understand the efficiency of the motor from the macro and micro levels. The essence of the efficiency problem is to understand the loss and heat of the motor. In this article, Lao Zhang will take you to a preliminary understanding of the loss of the motor. First of all, I will show you what loss is, why there is loss, and what loss is there. In the follow-up, Lao Zhang plans to take everyone to understand the forms of various losses from a microscopic level. Finally, Lao Zhang hopes that he can still talk about the thoughts and problems about loss and heat generation at the motor application level based on the concept of "looking at the expert from the perspective of a layman".
The motor is an energy conservation system and obeys the law of energy conservation in the process of energy conversion. In steady state operation, the energy input to the motor is always equal to the energy output. In addition to the useful mechanical energy (motor) or electrical energy (generator), the output energy is the various losses of the motor, and the losses are eventually consumed in the form of heat energy.
【Principle of Conservation of Energy】
Everyone is familiar with the principle of conservation of energy. This principle can be expressed as: in a physical system with constant mass, energy is conserved, that is, energy will not be generated or disappeared out of thin air, but only change its form of existence. In the process of electromechanical energy conversion, the motor also obeys the law of energy conservation, that is,
From a macro perspective, there are four forms of energy in the motor during operation, namely electrical energy, mechanical energy, magnetic field energy, and thermal energy. Among them, electrical energy and mechanical energy are the input or output energy of the motor. The magnetic field energy is the energy stored in the motor magnetic field (mainly the air gap magnetic field), and the thermal energy is converted from various losses during the operation of the motor, then
Among them, the various losses converted into heat energy include three parts:
l Electrical loss (also called copper loss) caused by the current in the conductor in the resistance;
l Mechanical loss consumed in bearing friction and ventilation;
l Hysteresis loss and eddy current loss generated in the iron core by the magnetic field in the motor;
It should be emphasized that the loss of these conversions into heat energy is an irreversible process, that is to say, it is difficult or impossible for this part of the energy to be converted into electrical energy or mechanical energy.
The content of this article is relatively easy to understand. In this article, Lao Zhang hopes that the principle of energy conservation can be used as a basic theoretical framework, so that everyone can systematically understand the relationship between the loss of the motor, the efficiency of the motor, and the heating problem of the motor. At the end of this article, it is proposed that the motor loss is mainly composed of three parts. In the next article, the three parts will be refined into 5 categories, and the loss of each part will be explained in more detail.
