Discrimination of the same name end of the hottest

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Discrimination of the same name end of three-phase motor

in transformers and mutual inductors, there is a relationship between the same name end of inorganic and organic fibers on the primary side and the secondary side. The pre-test acceptance procedures strictly require that polarity tests must be carried out before operation and after maintenance. Similarly, in a three-phase motor, if the terminal with the same name is connected incorrectly, a big problem will occur. The three-phase current cannot form a rotating magnetic field in the motor. The motor not only cannot operate normally, but also the three-phase current is seriously asymmetric, which has a great impact on the motor, resulting in heating and even burning out the motor. On the contrary, as long as the terminals of the same name are not connected wrongly and the three-phase current is connected, there is only a difference between forward rotation and reverse rotation of the motor (the voltage is the rated voltage and frequency of the motor). As long as the ab (or BC, CA) second line is exchanged, it is estimated that the overall TPV latent demand in China can reach 300000 tons, and the motor will operate normally according to your requirements. Therefore, the homonymous end test of three-phase motor is very important

1. Test method

first measure A1, A2, B1, B2, C1, C2 of three-phase winding with Multimeter resistance gear. Connect the three wire ends of the same winding (such as A1, B1, C1) together, and then connect the wire ends of the other three different windings (such as A2, B2, C2) together. Then use the milliampere gear (DC) of the multimeter to lap the heads (A1, B1, C1) and (A2, B2, C2) together, and turn the rotor of the motor by hand to see whether the pointer of the milliampere meter swings. If there is a large swing, first exchange A1 and A2 and try again; If there is still a large swing, first replace A1 and A2, then replace B1, B2 (or C1, C2) and try again; If there is still a large swing, first replace the original wire head, and then replace the two wire heads that have not been replaced with necessary protective measures. Until the rotor rotates, the milliammeter has only a small swing. That is, the heads connected together are three terminals with the same name (the other three are also terminals with the same name)

2. Theoretical analysis

because the three windings of three-phase motor only differ by 1200/pole pairs in the arrangement of winding positions, the electrical parameters of the three windings are basically the same. In addition, the rotor of the three-phase motor has a certain residual magnetism. When the rotor rotates, the induced electromotive force will be generated on the three windings. The induced electromotive force is:

if x, y, Z are connected together, a, B, C are also connected together, and then the current flowing to (a, B, c) is measured with a milliampere meter (x, y, z), If the reactance of the three windings and the reactance of the milliammeter are combined as Z, then

if one of the same name is terminated reversely, set it as phase a connection reversely, then

because the rotor is driven to rotate by hand, Its (is relatively small, so the milliammeter will swing. The same B-phase or c-phase terminals with the same name are connected reversely, and the current flowing through the milliammeter is:,, which will also produce pointer swing.

3. Conclusion

if the same name end of the motor has clearly indicated that connect x, y, Z with a, B, C, and then measure the current flowing through the milliammeter. At this time, the smaller the pointer swing, the better the symmetry of its three-phase electrical parameters. ⊙ (end)

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