air condi: Recent Episodes

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Little S is in charge of product development, and recently asked Ms. to help analyze the core loss of the motor. The reason is that the experimental value of low-power high-power motors with small S-led planning is too large, and it is unclear what caused it. Among the many losses of low-voltage high-power and high-voltage motors, the core loss of the motor accounts for a large proportion, which is one of the key factors affecting the efficiency of the motor. Ms. analyzed the results of electromagnetic calculation sheets and type experiments in a controlled manner, checked the product map, and found that the main reason for the abnormal value of the iron consumption experiment value was that the trademark of the silicon steel sheet did not match the plan. Motor iron loss includes the basic iron loss caused by 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 due to the working current of the stator or rotor.

Loss caused in the core. The latter two items are generally classified as stray losses that are difficult to accurately quantify. In the analysis and calculation of experimental results or according to the recommended value or actual measurement given by the standard, they are closely related to the air gap between the stator and the rotor, and the iron loss analysis is not included. Factors Affecting Basic Iron Consumption Basic iron consumption occurs due to changes in the main magnetic field in the iron core. This change can be of an alternating magnetizing nature, such as occurs in the stator or rotor teeth of a motor; it can also be of a so-called rotating magnetizing property, such as in the stator or rotor iron yoke of a motor. Whether it is alternating magnetization or rotational magnetization, it will cause hysteresis and eddy current loss in the iron core. Hysteresis loss unit The hysteresis loss ph caused by alternating magnetization in a ferromagnetic material is called the hysteresis loss coefficient, which is related to the frequency f of the alternating magnetization and the amplitude B of the magnetic flux density. It can be accurately expressed by the following formula: ph = (aB + bB2) In formula f, a and b are constants determined by the data function. The scale of the magnetic flux density in the core of a motor is generally 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 the hysteresis loss caused by rotating magnetization is different from that caused by alternating magnetization caused. Experiments have shown that silicon steel sheets have the following phenomena under two types of magnetization: when the magnetic flux density is below 1.7 Tesla, the hysteresis loss caused by rotating magnetization is greater than that caused by alternating magnetization; when it is higher than 1.7 Tesla , 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 hysteresis loss of the rotating magnetization is about 45 to 65% larger than the hysteresis loss of the alternating magnetization.

Eddy current loss: When a magnetic field in an iron core changes, an electric current is induced in it, which is called eddy current, and the loss caused by it is called eddy current loss. In order to reduce the eddy current loss, the iron core of the motor can not be made into a single piece, and steel sheets insulated from each other are stacked in the axial direction to hinder the flow of eddy current. Generally, 0.5 or 0.35 electrical steel sheet is used as the core material. Regarding the frequency scale encountered in general motors, the magnetic field can be considered to be uniformly distributed on the cross section of the steel sheet. At this moment, the eddy current loss of the steel sheet can theoretically be accurately calculated according to the formula: pe = ?; 2 (?feBf) 2 / (6 \u0026 rho ; dfe) Ventilation fan motor suppliers in the formula, pe-eddy current loss coefficient, ?fe-silicon steel sheet thickness, B-magnetic flux density, f-frequency, \u0026 rho; -resistivity, dfe-silicon steel sheet density. As can be seen from the above formula, the eddy current loss is proportional to the magnetic flux density, frequency, and the square of the thickness of the data. Analysis of the reasons for the high core loss The core loss depends primarily on the basic iron loss. The core loss is too high or the magnetic flux density is high due to the violation of the raw materials or the production of many unfavorable factors. The short circuit between the silicon steel sheets causes the silicon steel sheets. Thickness increases in disguise. The quality of the silicon steel sheet does not meet the requirements. The silicon steel sheet is the primary magnetically permeable material of the motor. Its functional compliance greatly affects the function of the motor. If the trademark of the silicon steel sheet meets the planning requirements, the other is the information of different manufacturers of the silicon steel sheet with the same trademark. There are some differences in functions, so you should try to choose the materials of good silicon steel manufacturers when you choose the materials.? Poor insulation between stator iron chips There are many factors that lead to poor insulation between chips. There are quality problems of silicon steel sheets themselves, as well as human factors caused during the production process of iron cores. ? The silicon steel sheet is not insulated or not treated well. This is a raw material problem of silicon steel sheets. Such problems can be found during the testing process of silicon steel sheets, but not all motor manufacturers have this test item. This problem is often not recognized by motor manufacturers. ? The insulation between the chips is damaged or the chip is short-circuited. This type of problem occurs during the manufacturing process of the iron core. If the pressure during lamination is too large, the insulation between the wafers will be damaged; or the burr will be too large after punching, and the burr will be removed by sanding, which will cause severe damage to the insulation on the surface of the punch;

The rear slot is not full, and the file repair method is adopted; or because the stator bore is not full, and the stator bore is not concentric with the base stop, the turning method is used to correct it. The customary usage of these motors in the process of production actually has a great impact on the function of the motor, especially the iron loss. When the winding is dismantled by fire or electric heating, the core becomes overheated, which reduces the magnetic permeability and damages the insulation between the sheets. This problem mainly occurs in the repair of windings and the repair of motors during the production process.Such processes as stacking welding will also cause insulation damage between the laminations and add eddy current loss. Iron weight is not compacted between tablets. The final result is the lack of weight of the iron core, which will most directly lead to the excess current and the fact that the iron loss exceeds the standard. The silicon steel sheet is painted too thick, which makes the magnetic circuit too full. At this moment, the curve of the relationship between no-load current and voltage is more severe. This is also a key element in the production process of silicon steel sheets. During the production and processing of iron cores, the grain orientation of the silicon steel sheet punching and shearing surface will be damaged, resulting in the addition of iron loss under the same magnetic induction. Regarding frequency conversion motors, the rated iron loss caused by harmonics is also considered; this is the planning link Elements to consider should be summarized. Other. In addition to the above factors, the planned value of the motor iron loss should be summarized in the practice of iron core production and processing, and the theoretical value and the practical value should be strived for. The characteristic curve provided by the general data supplier is measured according to the Epstein square circle method, and the magnetization directions of different parts in the motor are different. This special rotating iron consumption cannot be considered at present. This will lead to inconsistencies between the calculated and measured values ??to varying degrees.

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In order to ensure the normal operation of the production line, speculative protection is particularly important. The artificially scheduled maintenance is to prevent the motor from being shut down unexpectedly, resulting in the huge loss of the production line. Many companies will do speculative insulation protection regularly, but although there is a regular insulation test, the motor will still be damaged due to insulation problems. Why is this? Let's take a closer look. Setting introduction The production department of a water service group in a city in Fujian is responsible for the production safety of water supply in each city, county, and district. The production department will check the conventional temperature and insulation function before the motor is put into operation.

But this routine inspection did not prevent accidental incineration of the motor. The motors of the device were burned in 2012 for 6 years in 2005, and the motors of the device were burned in June 2018 for 6 years in 2012. Both of the motors had burned out windings. The windings of these two motors are burned out. Why can't the traditional insulation tester find the insulation problem of the motor windings? Let's take a look at the voltage at the output of the inverter and the motor at the scene. The actual measurement example uses the FlukeMDA-550 test. ?-? The test is a power frequency motor. The cable length between the inverter and the motor is 20m.

As can be seen from the figure above, the burr at the motor end is obvious, and the peak value increases, from the original 1240V to 1790V. The overshoot has changed from the original 14.7% to 80.1%. ? The waveform analysis of the output and motor ends of the inverter is also a power frequency motor, which is the motor repaired after being burned in June 2018. This motor is insulated The material's heat resistance grade is F, the maximum allowable working temperature is 155 ° C, the cable length between the inverter and the motor is 2m, and after MDA-500 analysis, the peak voltage of the motor end reaches 900V, and the overshoot coefficient is 67%. This pulse impacts The voltage has reached the 'harsh' level of the IEC standard. An analysis of the case shows from the measurement results in Fig. 5 that the peak-to-peak voltage of this motor is 1640V, and the 'maximum IVICA \u0026 rdquo; inverter-grade special motor with an insulation level has a maximum allowable value of 1254V. It Purifier motor manufacturers is this long-term pulse overvoltage that causes the motor's inter-turn insulation function to decline, and finally to cause a breakdown short circuit and the motor to burn down. For this working condition, it is advisable to choose a special frequency conversion motor with a pulse insulation level of at least 'medium IVICB'. The traditional insulation resistance tester can only measure the phase-to-ground, phase-to-phase insulation function, and the phase itself Interturn insulation cannot be evaluated, which is why even if there is traditional timing insulation detection, the motor burns out due to insulation problems. For this reason, the pulse voltage and overshoot coefficient detection at the motor end are particularly important. The above test can achieve the purpose of speculative protection and prevent huge economic loss caused by production line shutdown.