Symptoms of demagnetization of excitation generator set Jiangsu Haixing Power's wonderful hands return to spring

As a manufacturer specializing in the production and sales of generator sets , Jiangsu Haixing Power has been committed to the generator set industry for decades and is a 'old Chinese medicine doctor' in terms of technology. Listen to customers to show that the excitation generator set has demagnetization symptoms during regular use. After the pulse diagnosis of the Haixing generator set, the medical record details are as follows:

Symptoms:
The reactive power meter is reversed, the stator current swings periodically, the active load is slightly lower, the stator voltage is reduced, and the rotor voltage and current have different indications according to the fault point. When the rotor circuit is disconnected, the voltage rises and the current is zero; the excitation circuit or armature circuit of the excitation machine is disconnected, and the voltage and current are close to zero.
The demagnetized generator has a loss of the magnetic field and the electromagnetic torque decreases, while the prime mover torque does not change. Therefore, the unit speed increases, and the rotor and stator magnetic fields have a relative speed, that is, there is a slip between them and the disengagement and synchronization occurs. There is a slip between the rotor stators, and the generator generates asynchronous torque, which is balanced with the torque of the prime mover, and continues to send active power to the power grid. However, the demagnetized generator cannot send reactive power to the power grid, but instead absorbs reactive power from the power grid. We call this operating state the asynchronous operating state of the generator.

Symptoms:
The generator set loses magnetism, which will generate slip current on the rotor coil, rotor core surface, and damping system, causing additional temperature rise. Local high temperatures may occur between the groove wedge and the tooth wall, between the groove wedge and the ferrule, and on the contact surface between the teeth and the ferrule. In addition, the slip current in the stator will generate alternating mechanical torque, which may affect the safety of the unit.
After the generator loses magnetism, the original reactive power is sent to the grid to absorb reactive power. This will cause the voltage of the generator, factory electricity and nearby power grids to drop. Other generators may overcurrent. In severe cases, other generators may cause other generators to lose stability or voltage collapse.

Prescribe the right medicine:
As for how much load the generator can carry after demagnetization, it depends on the asynchronous torque characteristics of the generator and the speed regulation system characteristics, research and experiments have shown that after the generator is demagnetized, if the active load is rapidly reduced to 40-50% of the rated value, it may run in a low slip state for a short period of time (ten minutes), which will not damage the generator.
Therefore, there are currently two methods for generator demagnetization: if this type of unit performs a faulty magnetic test and proves that it can operate without excitation for a short time, the active power should be reduced to the specified value within the specified time after demagnetization. If the factory power voltage is too low, the factory load should be poured into the backup power strip, and then the cause of the demagnetization is quickly found and eliminated to restore synchronization; if the unit that has not been demagnetized or is not suitable for non-excitation operation after testing and demonstration, it should be cut off by demagnetization protection or manually de-stopped.

The reason for the use of medicine:
Why should the generator set be switched to the factory power supply by instantaneous shutdown after the magnetization is lost?
Answer: After the generator set loses magnetism, the system will not operate normally and the frequency and voltage will be affected. If the parallel method is used to switch factory power, it will affect the operation of non-faulting equipment and its system, and may also cause abnormal system operation, expanding the scope of abnormal system operation. Therefore, the instant shutdown method is used to switch factory power.
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