An Intelligent Sensor for the Ultra-High-Frequency Partial Discharge Online Monitoring of Power Transformers
Abstract
:1. Introduction
2. The Level Scanning Method
3. Implementation of the Intelligent Sensor
3.1. Ultra-High-Frequency Antanas
3.2. Hardware of the Data Processing Module
3.2.1. The Signal Pre-Processing Module
3.2.2. The Data Acquisition Module
3.3. Software of the Data Processing Module
- Step 1:
- Initialization. In this step, the signal channel, the gain of amplifier, the initial reference level, and the number of scanning cycles are set. Moreover, a frequency cycle is divided into several equal phase intervals, and the corresponding memory addresses to store the number of discharges within each phase interval are assigned in FPGA.
- Step 2:
- Signal comparison, data storage, and transmission. The start of the module is first triggered by the zero crossing point in the rising edge of the power frequency phase inference signal after being initialized, and the scanning time is counted from this moment. UHF PD signals are compared with the reference level and then scanned by FPGA, and the phase of UHF PD signals are calculated simultaneously. If the UHF PD signal is greater than the reference level, the number of discharges within the corresponding phase interval in the memory address add 1. If the counted scanning cycle reaches the set valve ts, stop scanning and transmitting the data to the PC or control center. The data is a row of numbers, which is shown in Table 1.
- Step 3:
- Comparison with variable reference level. FPGA automatically changes the value of the reference level according to the algorithm. Repeat Step 2.
- Step 4:
- Stop operation. Judge the number of discharges in each phase interval; if they are totally equal to zero, which means there is no discharge whose magnitude is greater than the reference level, stop scanning and exit the loop.
4. Experiment and Results
4.1. Experiment
4.2. Results
5. Discussion
5.1. The Influence Factors of the Number of Discharges
5.2. Methods to Improve the Performance of the Intelligent Sensor
- Increase the gain of the amplifier. For a UHF PD signal, the width of the discharge pulse becomes larger after being amplified, and the larger the gain of the amplifier is, the greater the width of the discharge pulse is, which makes the discharge pulse easier to detect.
- Increase the scanning frequency of the FPGA. Woff of the proposed intelligent sensor is decided by the scanning frequency used to count the square wave in the FPGA; the smaller the Woff is, the more accurate the data is. This method can be realized with the rapid development of the FPGA in the future.
- Decrease the step of the reference level. According to the theory of the level scanning method, the detection accuracy of the magnitude will increase with the decrease in the step of the reference level, especially when the reference level is near the peak of the discharge pulse.
5.3. The Use of the Intelligent Sensor for Ultra-High-Frequency Partial Discharge Detection in Other Electrical Components
6. Conclusions
- A new method to directly acquire the statistical characteristic quantities of UHF PD, namely the level scanning method, is proposed.
- The corresponding data processing module of the level canning method was designed, and a prototype was made. Combined with the antenna designed in our previous work, the intelligent sensor was made.
- Actual UHF PD experiments with three typical artificial defect models of power transformers were carried out to verify the performance of the intelligent sensor in a laboratory, and the waveform recording method and the intelligent sensor proposed were simultaneously used for UHF PD measurement. The results show that the intelligent sensor can accurately acquire statistical characteristic quantities of the UHF PD signal, which indicates the proposed intelligent sensor is qualified for UHF PD online monitoring.
- In order to improve the accuracy of the intelligent sensor, three methods to improve the performance of the intelligent sensor are proposed according to the principle of the proposed level scanning method.
Acknowledgments
Author Contributions
Conflicts of Interest
References
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Reference Level | Phase Interval | |||
---|---|---|---|---|
1 | 2 | … | j | |
V1 | n11 | n12 | … | n1j |
V2 | n21 | n22 | … | n2j |
V3 | n31 | n32 | … | n3j |
… | … | … | … | … |
Vi−1 | n(i−1)1 | n(i−1)2 | … | n(i−1)j |
Vi | ni1 | ni2 | … | nij |
Defect Model | Incepetion Voltage (kV) | Breakdown Voltage (kV) | Test Voltage (kV) |
---|---|---|---|
Air-void discharge | 6.1 | 12.3 | 9.7 |
Surface discharge | 8.4 | 13.2 | 10.5 |
Corona discharge | 5.7 | 12.5 | 9.0 |
Vt (mV) | f (MHz) | N1 | N2 | Voff (mV) | Woff (ns) |
---|---|---|---|---|---|
1000 | 100 | 312,500 | 312,508 | 725 | 2.4184 |
1000 | 80 | 250,000 | 250,007 | 785 | 2.6583 |
1000 | 50 | 156,250 | 156,255 | 870 | 3.2824 |
500 | 100 | 312,500 | 312,510 | 390 | 2.0483 |
500 | 80 | 250,000 | 250,005 | 420 | 2.2819 |
500 | 50 | 156,250 | 156,253 | 450 | 2.8713 |
250 | 100 | 312,500 | 312,506 | 190 | 2.2520 |
250 | 80 | 250,000 | 250,003 | 210 | 2.2819 |
250 | 50 | 156,250 | 156,253 | 230 | 2.5638 |
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Li, J.; Li, X.; Du, L.; Cao, M.; Qian, G. An Intelligent Sensor for the Ultra-High-Frequency Partial Discharge Online Monitoring of Power Transformers. Energies 2016, 9, 383. https://doi.org/10.3390/en9050383
Li J, Li X, Du L, Cao M, Qian G. An Intelligent Sensor for the Ultra-High-Frequency Partial Discharge Online Monitoring of Power Transformers. Energies. 2016; 9(5):383. https://doi.org/10.3390/en9050383
Chicago/Turabian StyleLi, Jian, Xudong Li, Lin Du, Min Cao, and Guochao Qian. 2016. "An Intelligent Sensor for the Ultra-High-Frequency Partial Discharge Online Monitoring of Power Transformers" Energies 9, no. 5: 383. https://doi.org/10.3390/en9050383