How to determine the factory test control standard of the motor
A friend who worked on the motor test suddenly called and said that he had just had a fight with the person in charge of the assembly shop because he blocked a group of motors that were urgently needed to be sent to customers. He said that he only judged according to the standard, but the leader said that he was rigid and dogmatic.
The scope of the test data of the factory test is too narrow, and the qualified product may be blocked. On the contrary, the unqualified motor may be released. Today we will talk about the method of determining the assessment criteria.
Motor inspection test evaluation criteria
The qualified area method is based on the prototype test data, and is obtained by the motor principle and mathematical calculation method. The technical condition limit value and the prototype test value of the motor are used in the calculation, and the limit value of the assessment range is calculated according to the 100% eating tolerance. This method is called the "Qualified Area Method". In principle, the qualified area method has high control precision. Because there is no relevant document to calculate the calculation method, many motor manufacturers do not calculate and judge according to this method; however, this method is still used by older motor companies.
The upper and lower limits method gives the highest and lowest limit values of the test data of the inspection test according to the test data and the evaluation standard of the qualified prototype, or the allowable fluctuation range. It becomes a single value "upper and lower limit method". The upper and lower limits are less accurate than the qualified zone method, but the calculation and use are relatively simple. Most new motor manufacturers use this method.
Regardless of the upper and lower limits method or the qualified area method, the basic basis is the type test result of the prototype and the technical conditions corresponding to the product. Due to material and process differences, the mass produced products will more or less deviate from the prototype test data. Especially when the test data tolerance of the prototype exceeds 50%, the scope of assessment determined by reference to the data will be largely unreasonable. From the perspective of performance qualitative judgment, the author still prefers the qualified area method, but most enterprises lack empirical calculation formulas.
Principles and steps for developing assessment criteria
(1) Calculate the average value and fluctuation range (maximum and minimum values) of various related items by counting and summarizing the type test data of the qualified prototype as much as possible.
(2) For the no-load current, if the power factor corresponding to the above maximum value has reached the minimum limit of the assessment, the maximum value is the highest limit of the factory standard hollow load current.
The no-load current can be set without a minimum limit. If it is deemed necessary (for example, to prevent the use of the wrong rotor or the air gap is too small to cause the broom), the minimum value of the above-mentioned statistical no-load current can be relaxed (for example, 3-5%) as the minimum of the factory standard no-load current. Limit.
(3) The no-load loss can only set the maximum limit. Considering that this value is greatly affected by factors such as running time and test environment (mainly ambient temperature) in a simple factory test, it can be increased by about 10% based on the maximum value of the above-mentioned prototype data.
If the factory test is higher than the given maximum value, the running time of the motor should be extended appropriately to obtain a more stable no-load loss before comparison and judgment. Another problem is that many motor factories do not have a fan when inspecting the test, but the prototype referenced by the test data is tested with a fan, which requires that this factor be considered when determining the no-load loss standard.
(4) The test environmental conditions have little effect on the two values of the stall current and the stall loss. Therefore, the control range of the upper and lower limits of the factory should be given strictly according to the fluctuation statistics of the prototype. If the calculation is based on the statistical average of the prototype, it is recommended that the deviation between the locked current and the statistical average of the prototype is plus or minus 5%; the deviation between the stall loss and the statistical average of the prototype is plus or minus 10%.
The above is the method for determining the evaluation criteria of the ordinary squirrel cage rotor motor. There are some differences in the inconsistency of the performance indicators of different series of products. We will gradually introduce this content.
