Motor efficiency determination method and classification
There are several methods for determining the efficiency of three-phase asynchronous motors, which can be roughly divided into three categories: the first type of direct measurement method, the second type of indirect measurement method (also known as loss analysis method), and the third type is after simple test. Reuse the method of theoretical calculation. Today, Xiaobian conducts a brief analysis of different test methods, focusing on the A test.
Characteristics and applicability of various test methods
The first type of method is intuitive, simple, and relatively accurate, but it is not conducive to the specific analysis of the motor performance and targeted improvement; the second type of method has many test items, time-consuming and laborious, and more calculations. The overall accuracy is not as good as the first one, but it can show the specific conditions that determine the main components of the motor efficiency, so as to facilitate the targeted analysis of the problems in the motor design, process and manufacturing, and improve the motor performance through improvement. Requirements or further improvement; the third type is the method used when the test equipment is insufficient, and the accuracy is the worst. The efficiency limits specified in the technical conditions of most current motors require efficiency determination using the second type of method (loss analysis).
Test method classification
GB/T1032 refers to the relevant standards of IEC and NEMA, and further classifies the method for determining the efficiency of three-phase asynchronous motor, and uses the code name.
Method A - input-output method. Usually only for motors with rated power ≤ lkW or efficiency index ≤ 80%.
Method B - Input and output loss analysis method to measure stray loss. High accuracy requirements for measuring instrumentation (generally required to be no less than 0.2)
C method - loss analysis indirect method (feedback) measured stray loss
E method - loss analysis method and measured stray loss
E1 method - loss analysis method recommends stray loss
F method - equivalent circuit method and measured stray loss
F1 method - equivalent circuit method and recommended stray loss
G method - reducing voltage load method and measured stray loss
G1 method - reducing voltage load method and recommended stray loss
H method - circle chart calculation method
A method for measuring efficiency - direct measurement of efficiency
The A method is called the “direct measurement method of efficiency” and is often referred to as the “input-output method”. Since the test can directly obtain two data for the efficiency of the input—the input power rate P1 and the output mechanical power P2. Named after.
●Test equipment requirements
The key to this method is to have a dynamometer that can directly measure the mechanical power (or torque) of the motor output. The power of the dynamometer used (or the nominal torque of the torque sensor) shall not exceed 2 times the rated power (or torque) of the motor under test at the same speed as the motor under test.
When using a calibrated DC motor, the calibration of the DC motor used should be performed in the generator state. During the test, the steering and excitation current of the DC motor should be the same as during calibration. The excitation current should remain constant during the test.
●Test method description
After the specified load is applied to the tested motor and the temperature rises to a stable or specified time (when the latter method is used, the difference between the temperature reached by the winding of the motor under test and the temperature reached by the actual temperature rise shall not exceed 5K. ), the adjustment load is varied within the range of 1.5-0.25 times the rated power, and the two operating characteristic curves when the load is decreased and rising are measured. Each curve is measured with no less than 6 readings. Each reading includes: three-phase line voltage (should be maintained), three-phase line current I1 (A), input power P1 (W), speed n (r/min) ), output torque T (N•m), and output power P2(W) should be recorded when conditions exist. Finally, the power is turned off, and the DC resistance R1 (Ω) of the stator winding is measured within the specified time (specified in the standard). Otherwise, the external resistance correction should be made according to the relevant provisions of the thermal resistance after the thermal test. When conditions permit, it is preferred to use a live measurement (superposition method) or a temperature sensor such as a thermocouple or a copper (platinum) thermal resistor embedded in the winding to obtain the temperature or resistance of the stator winding at each point. The ambient temperature θ (°C) should also be recorded during the test.
