Efficiency is an important assessment index of three-phase asynchronous motors, especially after the release and implementation of the national energy saving and emission reduction policy.
The determination of efficiency has become a topic of special concern for various motor manufacturers. In order to standardize and unify, the Institute of Electrical Machinery Industry has also organized some relevant training, which promotes the objectivity of test data from the perspective of test standardization.
For different motors, the methods used are not the same, but also with the motor manufacturers equipped with test equipment has a greater relationship. Today we will determine the efficiency of the method of generalized run through, a little open the background of energy-saving emission reduction policy of the hottest words "efficiency" of the veil of mystery.
Classification of efficiency determination methods
● Direct determination method. This method is intuitive, simple, and relatively accurate, but it is not conducive to specific analysis of motor performance and targeted improvement.
● Indirect determination method, also known as loss analysis method. The method of testing more items, time-consuming and laborious, there are more calculations, the comprehensive accuracy to be worse, but it can show the decision of the efficiency of the motor of the main components of the specific situation, thus facilitating the design of the motor, process and manufacturing problems targeted analysis, and through improvements to make the motor performance to meet the requirements or to further improve.
● Method of using theoretical calculations after a simple test. This method is used when the test equipment configuration is insufficient, and the accuracy is the worst.
At present, the efficiency limits specified in the technical conditions of most motors require the use of the loss analysis method for efficiency determination.
Classification of test methods
GB/T 1032 refers to the relevant standards of IEC and NEMA, and categorizes the methods for determining the efficiency of three-phase asynchronous motors and indicates them with codes.
Method A - Input-output method. Usually limited to motors with rated power ≤ 1kW or efficiency index ≤ 80%.
Method B - input - output loss analysis method of actual measurement of stray loss. Higher accuracy requirements for measuring instruments and meters (generally require not less than 0.2 level).
C method - loss analysis indirect method (feedback) measured stray loss.
E method - loss analysis method and measured stray loss.
E1 method - loss analysis method recommended stray loss.
F method - equivalent circuit method and measured spurious loss.
F1 method - equivalent circuit method and recommended spurious loss.
G method - Reduced voltage load method and measured spurious loss.
G1 method - reduced voltage load method and recommended spurious loss.
H method - circle diagram calculation method
Brief description of common test methods
Method A - Input-Output Method
A method is called "direct determination of efficiency", often referred to as "input - output method", because the test can be directly obtained to obtain the efficiency of the two data - input electric power and output mechanical power, so called. It is also known as the "Input-Output Method" because the test can directly obtain two data for efficiency - input electric power and output mechanical power.
Method B - Input-Output Loss Analysis Method
B method is called "input-output loss analysis method", is the efficiency of the motor for efficiency certification (mainly assess the efficiency of high-efficiency motors), requires the use of a kind of efficiency test method. GB18613 on the efficiency of the test to make specific requirements.
B method to find the efficiency of the rated voltage and rated frequency under direct load test and no-load test to obtain a number of groups of input current, output power, output power (or torque), speed, and core loss and mechanical loss values, and then the relevant test values of the relevant corrections (mainly for the temperature correction of the thermal losses and the correction of the output torque) and find the corrected input power and output power, and finally Finally, the output power compared with the input power to find out the efficiency of the test points, and draw the efficiency and output power of the relationship between the curve, in the curve to check the rated output power when the efficiency value, that is, the "full load efficiency".
C method - dual machine to drag feedback method
C method test, with a same specification or different specifications but synchronous speed and the same motor being tested, the power is not less than the motor being tested other three-phase asynchronous motor (customarily referred to as "accompanying motor") and the motor being tested with a coupling connection. The motor under test is connected to a power supply of rated frequency; the test motor is connected to a power supply of variable frequency (whose frequency is adjustable within the range of at least 90%-110% of its rated value).
In the test, there is always a motor running as an asynchronous generator, the output of which is fed back to the grid or to another motor via a variable frequency power supply (unit or electronic). This is referred to as the "feedback method".
E-method for determining efficiency - loss analysis method
This method requires the determination of the input power of the motor under test, subtract the losses from this power to obtain the output power, and then use the ratio of the two to obtain the efficiency. The method of obtaining each loss is as follows:
(1) The core loss and mechanical loss are obtained from the motor no-load test.
(2) In the specified temperature fixed, rotor copper loss determination method with C method.
(3) Load stray loss determination method in accordance with the following provisions: E method, should be measured; E1 method, should be used to recommend the value.
F method--Equivalent circuit method
Equivalent circuit calculation method, is based on the motor no-load and plugging test part of the data, the use of motor equivalent circuit in the relationship between the relevant parameters to indirectly obtain the motor efficiency and other parts of the characteristics of the data, is one of the methods of indirectly obtaining the efficiency of three-phase asynchronous motors.
This method is employed when the capacity of the motor under test is large and the capacity of the test equipment is insufficient, and may also be borrowed when certain parameters (such as the control parameter setting of the variable frequency power supply) are to be provided for the motor control system.
G method - reduced voltage load method
This measurement method is the "reduced voltage load method" and is one of the indirect methods for measuring efficiency. It is used when the power supply or load capacity does not allow full voltage and full load testing.
Method H - Circular Calculation Method
This method calculates the full-load efficiency and power factor from the data of winding resistance, no-load current, no-load input power, blocking current, and blocking input power.
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