Symptoms of excitation generator set excitation loss: Jiangsu Haixing Power makes a comeback

Jiangsu Haixing Power is a professional manufacturer and sales companyGenerator setmanufacturers, committed to working withGenerator setHe has been in the industry for decades and can be called an 'old Chinese doctor' in terms of technology. I heard a customer show that the excitation generator set suffered from demagnetization during regular use. After taking the pulse and diagnosing the Haixing generator set, the details of the medical record are as follows:

Symptoms:
The reactive power meter indicates reversely, the stator current swings periodically, the active load is slightly lower, the stator voltage decreases, and the rotor voltage and current have different indications according to different fault points. When the rotor circuit is disconnected, the voltage rises and the current is zero; The excitation circuit or armature circuit of the exciter is disconnected, and the voltage and current are close to zero.
In a demagnetized generator, the rotor magnetic field disappears and the electromagnetic torque decreases, while the prime mover torque remains unchanged. Therefore, the unit speed increases, and the rotor and stator magnetic fields have relative speeds, that is, slip occurs between them and they are out of synchronization. There is a slip between the rotor and the stator, and the generator produces asynchronous torque, which is balanced with the torque of the prime mover, and continues to send active power to the grid. However, the demagnetized generator cannot deliver reactive power to the grid, and instead absorbs reactive power from the grid. achievement. We call this operating state the asynchronous operating state of the generator.

Symptoms impact:
The demagnetization of the generator set will produce slip current in the rotor coil, rotor core surface and damping system, causing additional temperature rise. Local high temperatures may occur on the contact surfaces between the slot wedge and the tooth wall, between the slot wedge and the ferrule, and on the contact surfaces between the tooth and the ferrule. In addition, the slip current in the stator will produce alternating mechanical torque, which may affect the safety of the unit.
After the generator loses magnetism, it changes from sending reactive power to the grid to absorbing reactive power from the grid. This will cause the voltage of the generator, factory power and nearby grids to drop. Other generators may have overcurrent, and in severe cases, other generators may 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 and speed regulation system characteristics of the generator. Research and tests have shown that after the generator loses magnetism, if the active load is quickly reduced to 40-50% of the rated value , it is possible to run for a short period of time (tens of minutes) in a low slip state without causing damage to the generator.
Therefore, there are currently two methods for dealing with generator loss of excitation: If this type of unit undergoes a loss of excitation test and proves that it can operate without excitation for a short period of time, the active power should be reduced to the specified value within the specified time after deexcitation. If the factory uses If the power voltage is too low, the plant load should be transferred to the backup power supply, and then the cause of the loss of excitation should be quickly found and eliminated to restore synchronization; if the unit has not been subjected to a fault loss test or is not suitable for non-excitation operation after testing and demonstration, the unit should be replaced by a loss of excitation test. Magnetic protection is cut off or manual decoupling is used to stop the machine.

Reason for taking medication:
Why is it necessary to use the instantaneous shutdown method to switch the plant's power supply after the generator set loses excitation?
Answer: After the generator set loses excitation, the system will not operate normally, and the frequency and voltage will be affected. If the parallel method is used to switch the plant's power supply, it will affect the operation of non-faulty equipment and its systems, and may also cause non-synchronous operation and expand the abnormal range of system operation. Therefore, the instantaneous power outage method is used to switch the plant's power supply.
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