In the production and use of motors, we often test motors.
Today, I'll talk about why and how we test motors.
Three-phase asynchronous motor test purposes and projects
The test of three-phase asynchronous motor is divided into two kinds of inspection test and type test.
The inspection test is to check the quality of the finished products and repaired motors of the motor manufacturer.
Type test is a comprehensive test for each new product of the motor manufacturer according to the standard, to verify the design, technical problems in the process, to determine whether the new product meets the relevant standards.
The asynchronous motor after overhaul is usually only for inspection test.
Checking and testing method of three-phase asynchronous motor
(1) Appearance inspection:
check whether the appearance is complete, whether the mark of the outlet end is correct, whether the screws, bolts and nuts for fastening are tightened, whether the rotor rotation is flexible, whether the motor shaft extends radial deflection and how the vibration is.
For the winding rotor motor, the assembly quality of brush, brush holder and collector ring should be checked, and whether the contact between brush and collector ring is good. For the closed self-fan-cooled motor, the air exhaust system should be checked.
(2) Measurement of insulation resistance:
insulation resistance is divided into hot state and cold state. For the repaired motor and the factory motor, only the cold state (room temperature) insulation resistance of the winding phase to phase and phase to ground is measured.
The insulation resistance of the rotor winding should be measured for the wound rotor motor.
For multi-speed winding motor, the insulation resistance of each winding should be measured one by one. For large motors, the insulation resistance can be measured to determine whether the winding is damp or not.
For motors with rated motor below 500V, generally use 500V megohmmeter to measure; for motors between 500-3000V, use 1000V megohmmeter; for motors above 3000V, use 2500V megohmmeter. For motors below 500V, the insulation resistance should be not less than 0.5MΩ.
(3) The determination of DC resistance of motor winding,
it is generally carried out in cold state. Its measuring instrument is bridge, less than 1Ω apply double-arm bridge, more than 1Ω available single-arm bridge, the error between the measured resistance value of each phase and the ratio of the average value of three phases shall not be greater than 5%. (Rmax-Pmin)/R average value ≤ 5% in the formula, R average value = (Ru + Rv + Rw) / 3Ω .
If the difference in resistance value is too large, it means that there is a short circuit in the winding, a broken circuit, poor welding or contact, or the winding turns are wrong, etc.
If the three-phase resistance is beyond the specified range, it means that the winding wire is too thin.
(4) Withstand voltage test:
After the motor stator winding is insulated with phase and phase, phase and ground, it can withstand certain voltage without breaking down. When the rated voltage of high-voltage motor is 2000-10000V, the test voltage is 2.5 times of the rated voltage.
(5) Inter-turn insulation test:
Increase the power supply voltage to 130% of the rated voltage, make the motor idle for 5min, no short circuit should occur, called inter-turn insulation test, the purpose is to assess the insulation performance between turns.
(6) Determination of rotor open circuit voltage:
When measuring rotor open circuit voltage, rotor is stationary, rotor winding is open circuit, starting rheostat is disconnected, rated voltage is applied to stator winding, voltage between lines is measured between rotor collector rings, rated voltage is above 500V, voltage applied to stator winding can be reduced appropriately.
(7) No-load test:
No-load test is to apply three-phase balanced voltage on the stator winding of the motor and make the motor run without load, the purpose is to determine the no-load current and no-load loss, and to separate the iron consumption and mechanical loss (including wind friction consumption) from the no-load loss.
During the no-load test, the motor should be observed, listened to for any abnormal sound, whether the core is overheated, whether the temperature rise of the bearing and the operation are normal, and for the wire-wound rotor motor, the brush should be checked for spark and overheating. For the repaired asynchronous motor, when doing no-load test, usually only measure the no-load current to check the quality of the repaired motor. Only when necessary for no-load loss test.
(8) Short-circuit test (blocking test):
the motor will be stuck without turning, using the voltage regulator from zero value, gradually increase the voltage, so that the current of the stator winding reaches the rated value, the voltage applied to the stator winding at this time is called short-circuit voltage Uk.
Another method called fixed voltage measurement method, that is, the rotor does not move, to the fixed winding plus a constant voltage, generally between 95-100V, the measured current is called short-circuit current Ik, Ik The measured current is called short-circuit current Ik, Ik value between (1-1.4) IN can be regarded as qualified (the power of small motor is also small Ik). If the measured short-circuit current is too small.
It may be because the number of series turns is too small and the leakage resistance is small, then the no-load current of the motor is large, the starting current is large, the loss is large, the power factor and efficiency are not qualified, the temperature rise is higher and the output power is reduced. If the short-circuit current is unbalanced in three phases, it means the stator winding has short-circuit, wrong connection or rotor winding has broken circuit and other phenomena.
(9) Over-speed test:
Under no-load condition, the motor should be able to withstand 1.2 times of rated speed over-speed test for 2min. to assess the mechanical strength of the rotating part. Two methods are used to increase the speed.
a. Increase the power frequency of the motor under test.
b, using auxiliary motor to drag the motor under test, or the rotor can be taken out separately for over-speed test. After the overspeed test, the rotor should be checked for harmful deformation.
(10) Load test:
The load test is to determine the loss of each part of the motor, i.e. stator copper consumption, rotor copper (aluminum) consumption, iron consumption, mechanical consumption (including wind friction consumption) and additional loss.
(11) Temperature rise test:
The temperature rise test of the motor is an important item in the type test, because the output power of most motors is limited to the temperature rise, and the temperature rise is generally measured by two kinds of resistance method and thermometer method.
Hope the above information will be helpful for you.
If you have anything to add, feel free to leave a comment.
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2 Responses
Thank you for indicating that the winding rotor motor, brush, brush holder, and collector ring assembly quality should be examined. I recently purchased an electric motor rewind for my father’s birthday. I’ll take the electric motor rewind to an expert for inspection before giving it to my father.
GOOD !