Inspection test is to determine the conformity of electric motor performance through the main data relationship, different electric motor manufacturers have different ways to determine how to choose and judge for three phase ac motor.
It should be combined with their respective process characteristics.
Today we talk about the three phase asynchronous motor inspection test data and the main performance data relationship of the three phase ac motor and the principles of factory assessment to determine.
Relationship between inspection test data and main performance data of the electric motor
The inspection test data mentioned here refers to no-load current, no-load loss, blocking current and blocking loss, which are theoretically related to several main performance parameters of the electric motor as follows.
(1) No-load current is high, the power factor is low for induction motors.
(2) No-load loss is large, the efficiency is low for the three phase ac motor.
(3) large blocking current, the blocking current at rated voltage will probably exceed the assessment standard;
small blocking current, it may cause the blocking torque at rated voltage can not meet the standard requirements, because the blocking torque and blocking current is proportional to the relationship of three phase motors.
(4) The blocking loss is large, then the efficiency is low;
the blocking loss is small, then the maximum torque may not reach the standard requirements, because the maximum torque and blocking loss is proportional relationship.
2 Determination method of factory assessment
● Qualified area method
Using the electric motor principle and mathematical calculation method to derive a series of relationships, and then substitute the prototype test data and assessment standard values into these relationships to derive several control formulas.
When using, the actual measurement data is then substituted into the corresponding control formula to determine whether the electric motor is qualified or not, and this method is called the "qualified area method".
The method is theoretically more accurate control, but the calculation and use of more cumbersome, and sometimes due to the standard given a large range and cause misjudgment phenomenon, so it is rarely used.
● Upper and lower limit method
According to the test data of the qualified prototype and the test standard, the maximum and minimum limits of the factory test data are given, or the range of permissible fluctuations. It is called the single value "upper and lower limit method". Compared with the first method, although the control accuracy is slightly worse, but the calculation and use are much simpler, so it is more widely used. The following focuses on its development principles and development steps.
3. to develop the principles and steps of factory standards
(1) as much as possible to summarize the type test data of qualified prototypes, calculate the average value of the relevant items and fluctuations in the range (maximum and minimum values).
(2) for no-load current, if the maximum value corresponds to the power factor has reached the minimum limit of the assessment, the maximum value is the factory standard no-load current of the maximum limit.
No-load current may not set a minimum limit. If it is considered necessary (for example, to prevent the wrong rotor or air gap is too small to cause sweeping), then the above statistics of the no-load current minimum value is relaxed some (for example, relaxed 3%) as the factory standard no-load current minimum limit.
(3) no-load loss can only set the highest limit.
Considering the value in the simple factory test, by the operation time, test the natural environment (mainly ambient temperature) and other factors have a greater impact, so can be increased by about 10% on the basis of the maximum value of the above prototype data.
If the factory test is higher than the maximum standard given, the electric motor should be run for a longer period of time to get a more stable no-load loss before comparison and determination
(4) test environmental conditions on the blocking current and blocking loss of the two values of the size of the impact is small.
so It should be strictly in accordance with the fluctuations of the statistical value of the prototype to give the upper and lower limits of the control range.
If calculated according to the statistical average of the prototype, it is suggested that the blocking current is 95%~105% of the statistical average of the prototype; the blocking loss is 90%~110% of the statistical average of the prototype.
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