The locked-rotation test is a key item of the three-phase asynchronous motor inspection test and type test. Through the locked-rotation test, what performance indicators can be determined for the motor? What manufacturing or design defects of the motor can be found? Today, the editor of Dalan Motor will answer your questions.
During the inspection test, the locked rotor test can be used to assess the welding quality of the motor windings, check whether the stator and rotor reactances are normal, check whether the cage rotor is broken, and also check whether the number of rotor poles used is appropriate.
1. Common methods of stall test:
The voltage value of the locked-rotation test can be selected according to the rated voltage of the motor. The constant-voltage method is used to measure the locked-rotor current Ik and the locked-rotor loss TK, and then the motor impedance Zd is calculated; the constant current method (according to the rated current equal to the locked-rotor Current) to do the test, measure the locked-rotor voltage Uk, the locked-rotor current Ik and the locked-rotor loss Pk, and then calculate the motor impedance value Zd.
2. Analysis of the magnitude of the locked-rotor current and the cause of unbalance:
The stall current Ik of motors of the same specification generally differs by only 3% -6%. It is required that any one phase of the three-phase stall current and the average value of the three phases should not exceed 2% -3% of the average value.
Reasons for too small stall current:
1) The iron core is eccentric or bored, the outer diameter of the rotor is small or the air gap of the stator inner bore is increased, making Ik too small.
2) The welding quality is not good, which increases the rotor resistance.
3) The cast aluminum rotor is defective (rotor thin bar, insufficient aluminum purity, etc.).
4) The coil size is enlarged or the winding is too chaotic, which increases the leakage reactance and causes Ik to be too small.
3. Reasons for excessive stall current
1) The core notch file is large.
2) The center line of the fixed rotor core is misaligned (intuitively, the fixed rotor axial misalignment).
3) The less winding turns of the coil reduce the reactance and increase Ik.
4) The size of the coil end is reduced.
4. Reasons for three-phase imbalance of locked-rotor current
1) The stator winding has a short circuit (to ground, interturn or interphase) fault.
2) Broken rotor winding or poor welding quality.
3) Defects in the cast aluminum rotor motor (uneven thin strips, broken strips), etc.
----- Responsible Editor: Dalan Oil Pump Motor 02-Procurement Consultant
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