Analysis of the Causes of Large Loss of Motor Core
In the low-voltage high-power and high-voltage motor, the loss of the motor core is relatively large, which is one of the key factors affecting the efficiency of the motor. Ms. Reference analysis of the electromagnetic calculation of the single and type test results, look at the product map, found that the main cause of the abnormal iron loss test value is that the silicon steel sheet grade does not match the design.
The motor iron loss includes the basic iron loss caused by the change of the main magnetic field in the iron core, the additional (or stray) loss in the iron core at no load, and the leakage magnetic field and harmonic magnetic field generated by the operating current of the stator or rotor. Loss caused in the core. The latter two are generally classified into stray consumption that is difficult to accurately quantify. The test results are analyzed or calculated according to the recommended values or actual measurements given by the standard. They are closely related to the air gap size between the stator and rotor, and the iron loss analysis is not included.
Factors affecting basic iron consumption
The basic iron consumption is caused by the change of the main magnetic field in the iron core. Such variations may be alternating magnetization properties, as occurs in the stator or rotor teeth of the machine; they may also be of the so-called rotational magnetization properties, such as occurs in the stator or rotor yoke of the machine. Both alternating magnetization and rotational magnetization cause hysteresis and eddy current losses in the core.
Hysteresis loss
The hysteresis loss ph caused by the alternating magnetization in the unit ferromagnetic material is called the hysteresis loss coefficient, and is related to the frequency f of the alternating magnetization and the amplitude B of the magnetic flux density, and can be accurately expressed by the following formula:
Ph=(aB+bB2)f
Where a and b are the constants determined by the properties of the material.
When the magnetic flux density in the motor core is usually in the range of 1.0 to 1.6 Tesla or 10,000 to 16,000 Gauss, the coefficient a is close to 0, so
Ph=bB2f
The magnitude of hysteresis loss caused by rotational magnetization is different from that caused by alternating magnetization. Tests show that the silicon steel sheet has the following phenomena under the magnetization of two properties: when the magnetic flux density is below 1.7 Tesla, the hysteresis loss caused by the rotating magnetization is larger than that caused by the alternating magnetization; when it is higher than 1.7 Tesla When, the opposite is true. The magnetic flux density of the yoke of the motor is generally 1.0 to 1.5 Tesla, and the corresponding rotational magnetization hysteresis loss is about 45 to 65% larger than the alternating magnetization hysteresis loss.
Eddy current loss
When the magnetic field in the iron core changes, a current is induced in it, called eddy current, and the loss caused by it is called eddy current loss. In order to reduce the eddy current loss, the motor core is usually not made in one piece, and the steel sheets insulated from each other are axially laminated to block the flow of the eddy current.
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