What is generator demagnetization
Generator loss of excitation is one of the common faults in the power system. It refers to the phenomenon that the generator loses excitation current during operation, resulting in the inability to maintain normal power generation. Loss of excitation may cause serious consequences such as unit oscillation, voltage collapse, or even system disconnection. This article will combine the hot topics on the entire network in the past 10 days to conduct a structured analysis of the principles, performance and countermeasures of generator demagnetization.
1. Analysis of the causes of generator demagnetization
According to recent hot discussions in the power industry, the main reasons for magnetic field loss can be summarized into the following three categories:
| Type | specific reasons | Proportion (industry data) |
|---|---|---|
| Excitation system failure | Excitation winding short circuit/open circuit, rectifier device failure | 68% |
| Operation error | Incorrect excitation switch switching, wrong parameter setting | 22% |
| external factors | Power grid voltage sag and lightning overvoltage | 10% |
2. Typical characteristics of loss of excitation faults
Based on a recent actual case of a power plant (reported on October 15, 2023), the following phenomena will occur when magnetism is lost:
| Monitoring parameters | normal range | Changes during demagnetization |
|---|---|---|
| Excitation current | 300-500A | Drops to 0A |
| Machine terminal voltage | 10.5-13.8kV | Decrease 30%-50% |
| Reactive power | ±50MVar | Reverse absorption of reactive power |
3. The latest response strategies (refer to the 2023 industry white paper)
1.Immediate measures:
• Start the backup excitation system (modern units are equipped with dual-channel excitation)
• Adjust reactive output compensation of other units
2.mid- to long-term improvements:
• Install a loss-of-excitation protection device (action time ≤ 0.5s)
• Promote AI-based predictive maintenance technology for excitation systems (Huawei’s digital energy solution has attracted attention recently)
4. Hotspot related events
Relevant events that have triggered industry discussions recently:
| Date | event | Technical inspiration |
|---|---|---|
| 2023-10-18 | A collective loss of magnetism accident in a wind farm | Revealing the special risk of demagnetization of doubly-fed units |
| 2023-10-21 | New solid state excitation device released | Response speed increased to 10ms level |
5. In-depth technical analysis
1.Loss of magnetization dynamic process:
• 0-2 seconds: Enter asynchronous running state
• 2-5 seconds: Overheating of the rotor accumulates (temperature rise rate is about 15°C/s)
• >5 seconds: May cause stator overcurrent (up to 1.5 times rated value)
2.New detection technology:
• PMU-based wide-area monitoring system (recent State Grid patent hotspot)
• RF signal analysis method (can give 30ms warning in advance)
Conclusion
Generator demagnetization remains a hot topic in the field of power safety. With the large-scale integration of new energy into the grid (according to the National Energy Administration's October report, 120GW of new energy installed capacity will be added in 2023), its prevention and control technology continues to iterate. It is recommended to pay attention to the new regulations on loss of excitation protection in the latest PES-2023 standard released by IEEE, as well as the revision trend of the domestic "Power System Safety and Stability Guidelines".
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