Analysis and treatment of brushless excitation fau

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Analysis and treatment of brushless excitation fault of synchronous motor

the brushless excitation high voltage synchronous motor imported from Canada is used in the main oil refining unit of a factory. Figure 1 is the excitation circuit diagram of 4KV, 60Hz, 765hp hydrogen compressor motor in the refinery

1. The working principle is as follows: the rotating part is in the dotted box in the figure. A three-phase AC excitation generator is installed on the main shaft of the synchronous motor. Compared with the general alternator, the stator winding and rotor winding of the excitation generator are installed in reverse, that is, stator excitation and rotor power generation. The stator excitation winding JLQ is regulated by 120V, 60Hz power supply through voltage regulator ty, and then supplied with DC excitation power supply after rectification by silicon rectifier 1zl. The rotor winding JF rotating with the main shaft sends out three-phase alternating current, which is rectified by silicon rectifier 1D ~ 6D and then supplied with LQ excitation current of synchronous motor rotor winding. By adjusting the excitation current of the alternator stator excitation winding JLQ, the three-phase AC voltage emitted by the rotor of the excitation generator can be adjusted, thereby changing the excitation current of the synchronous motor rotor excitation winding LQ. The deexcitation link of synchronous motor when starting or stopping and the excitation link of synchronous motor are installed on the rotor and work in the rotating state. In this way, the excitation generator generates power from the rotor, and the rectifier rectifies in the rotating state to supply the excitation of the synchronous motor rotor, there is no need for the mutual contact and conduction between the stationary part and the rotating part, which completely eliminates the contact between the brush and the slip ring

2. Fault phenomenon: after a normal shutdown, it is found that the no-load current of the machine increases from the original 20a to 50A (the rated current is 78a) when it is restarted. After a little load is added, the current slowly increases by 20% - 80% humidity. After a few seconds, it is protected and shut down due to overcurrent. Check that the load is OK, the control of the high-voltage cabinet is normal, and the motor stator current decreases when the excitation current of JLQ excitation winding is increased

3. Fault analysis and treatment: since the motor can be started normally, it indicates that the motor control circuit is basically normal. The problem may lie in the excitation circuit, according to the characteristics of synchronous motor. If in the under excitation area, the excitation current increases and the motor stator current decreases, from the above phenomenon, it can be concluded that the motor operates in the under excitation state, but the measured JLQ excitation coil current is the normal value 5a, so the problem may be in the rotating rectifier

the processing process is briefly described as follows:

3.1. The power factor meter of the machine is broken. In order to determine whether there is excitation failure, it is learned from the outgoing line of 60Hz power supply (variable frequency generator) that the active power increases by 0.1MW, the reactive power increases by 0.3mvar, and the excitation generator works basically normally when the excitation current of JLQ winding of the synchronous machine increases to the rated value

3.2. Open the motor cover, check whether each winding of the motor has discoloration, mold break and other phenomena, and check the brushless excitation part. It is found that the voltage stabilizer 1wy is damaged, and the other lead is loose. It is restarted after replacement, and the fault is still not eliminated

3.3. Stop the machine and immediately check the heating condition of each part. It is found that the heating of thyristor 2kgz is slightly large. Disassemble the outgoing line of excitation generator and main excitation lead, and measure each element. It is found that 2kgz is damaged, which causes a phase short circuit of excitation generator and underexcitation, resulting in too small electromagnetic torque to be pulled into synchronization

3.4. The model of the thyristor is grwq59. Plastic materials and products in the EU market may be removed from the shelf because they do not meet the requirements of the new regulations or reported that there are no spare parts, and there is no purchase of this part in the local market. It is decided to use 500a/2kv domestic one-way thyristor with similar overall dimensions instead. After replacement, it operates normally

4. Summary

brushless excitation device, because it does not vibrate during operation, will affect the experimental data. You can check its voltage, waveform and other parameters. It is more troublesome to check the fault. You can only determine the approximate range from external parameters, and then use the static measurement method to check its fault point. Judging from the failure of the machine, it is because the voltage stabilizer is damaged, the thyristor does not conduct when starting, and the open circuit overvoltage of the main rotor cannot be eliminated, resulting in the breakdown and short circuit of the thyristor 2kg2. After the breakdown of the thyristor, it can be seen from the schematic diagram that it will cause the short circuit of one phase of the excitation generator JF, resulting in insufficient main excitation current, causing this fault. In order to prevent the motor workpiece from rusting due to poor environment and causing other faults, after this maintenance, a layer of insulating paint is painted on the surface of the rectifier to produce some small faults and protect these components from damage caused by poor environment. (end)

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