Fiber Bragg Grating Sensor for Hydrogen Detection in ... - IEEE Xplore

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Guo-M. Ma et al.: Fiber Bragg Grating Sensor for Hydrogen Detection in Power Transformers

Fiber Bragg Grating Sensor for Hydrogen Detection in Power Transformers Guo-Ming Ma, Cheng-Rong Li, Rui-Duo Mu, Jun Jiang Key Laboratory of Alternate Electrical Power System with Renewable Energy Sources Beijing Key Laboratory of High Voltage & EMC North China Electric Power University Beinong Road #2, Beijing, 102206, People’s Republic of China and Ying-Ting Luo Electric Power Research Institute of Guangdong Power Grid Corporation China Southern Power Grid Meihua Road #73, Guangzhou, 510600, People’s Republic of China

ABSTRACT A novel hydrogen sensor is designed on the basis of Fiber Bragg grating (FBG) sensing technique. The sensor can be arranged inside the transformer. It has several advantages, such as fast fault detection and location, immunity to electromagnetic interference, quasi-distribution measurement and real-time monitoring. The principle of the proposed FBG hydrogen sensor is based on changes of the physical properties of palladium films which absorb hydrogen. A thick palladium layer prepared by magnetron sputtering is used to achieve high sensitivity. Meanwhile, polyimide is added into the adhesive layer to improve the reliability of the sensor. Partial discharge experiments demonstrated that the wavelength shift of the FBG hydrogen sensor varies linearly with the concentration of hydrogen dissolved in the transformer oil. It is hardly disturbed by other factors. The hydrogen sensing experiment in oil at a temperature of 80˚C revealed that the sensitivity of the sensor remains same as the temperature varies, ranging from room temperature to operating temperature of the power transformer. Thus, the proposed sensor can work properly under the operating temperature of power transformers. Index Terms — hydrogen, dissolved gas analysis, fiber Bragg grating, quasi-distribution, palladium, high temperature.

1

INTRODUCTION

CONDITION monitoring and fault diagnosis of power transformer is an efficient way to predict and prevent the failure of power transformer [1]. In recent years, new condition monitoring techniques and devices have been proposed ceaselessly. The major condition monitoring techniques include frequency response analysis (FRA) [2], partial discharge (PD) detection[3-5], hotspot temperatures measurement [6], moisture analysis and so on. Dissolved gas analysis (DGA) is also one of the widely used diagnostic tools in fault analysis of transformer [7, 8]. As a result of chemical reactions (which involve steel, uncoated surfaces and protective paints) and decomposition of oil and cellulosic insulation, insulating materials within transformers liberate gases within the unit [9]. The composition of those Manuscript received on 9 September 2013, in final form 1 October 2013, accepted 5 October 2013.

gases allows for recognition of the type of electrical fault. Thus, dissolved gas concentration is an important indicator for fault diagnosis of power transformer. Off-line DGA consists of obtaining an oil sample from a transformer and analyzing the dissolved gases of the sample. In general, the sampling interval of off-line DGA might be up to 1 year. Thus, defects which happen during the interval may not be detected in time. Therefore, in recent years, more attention is paid to the on-line monitoring using DGA techniques. Most of the on-line DGA techniques are based on Gas Chromatography (GC) [8], Photo-Acoustic Gas Spectroscopy (PAS) [10], and near-infrared spectroscopy (NIR) [11] technique. However, although the on-line DGA techniques can monitor power transformers continuously, there is still a long time delay between the fault initiation and the fault detection. Moreover, it is not possible to locate the exact fault location [12].

DOI 10.1109/TDEI.2013.004381

IEEE Transactions on Dielectrics and Electrical Insulation

Vol. 21, No. 1; February 2014

One way to locate the fault quickly and accurately is to insert the gas sensors into the power transformer. Tao et al. have reported a carbon nanotube which is used to detect the dissolved gases in power transformers [13]. But, those carbon nanotubes are easily disturbed under strong electric magnetic field as it is a kind of electrical device. Therefore its usage is limited. Optical sensors are proved to be a good candidate for being placed into the power transformer due to their inherent immunity to electromagnetic interference. Hammon et al. have reported a temperatures measuring system for high voltage transformer winding based on optical gratings [14]. Deng et al and Yu et al. have developed a new optical acoustic sensor which is used for PD measurement [12, 15]. However, only limited amount of works has been carried out in the field of dissolved gas detection in power transformer based on optical technique.

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power transformer can cause various phenomena. This paper aims to study the influences of those phenomenon except hydrogen on the proposed sensor. Moreover, the sensitivity of the proposed sensor placed in transformer oil under operating temperature is also investigated.

2 PRINCIPLE OF FBG HYDROGEN SENSOR FBG is a type of distributed Bragg reflector constructed in a short segment of optical fiber that reflects particular wavelengths of light and transmits all others (illustrated in Figure 1).

Multiple gas detectors are required for diagnosis of the defect or fault in the power transformer. Thus we are aiming to develop FBG sensors for typical gases, e.g. H2, CH4, C2H2, C2H4, C2H6, CO, CO2 and construct a sensor array. At first, our work is aimed to detect the hydrogen with FBG technique. The author has proposed a Fiber Bragg grating (FBG) hydrogen sensor based on palladium film, which is highly sensitive and reliable [16]. But there is still a lot of works need to be done before it can be applied to the power transformers. It is also necessary to investigate the potential influences of the operating transformer to the FBG hydrogen sensor. The potential factors having effect on operation of a sensor inserted into the power transformer internal assembly mainly include: 1) High electric and magnetic field intensity induced by high voltage and current in the windings and leads; 2) Influences from other types of gases generated by insulation defect; 3) High temperature of the transformer oil. The insulation strength of the FBG sensor has been demonstrated by Teunissen [17], Because of its immunity to electromagnetic interference, the influence of high field intensity and electromagnetic interference on the FBG hydrogen sensor can be ignored. Most of the researches related to the FBG hydrogen sensor are carried out under room temperature at the present [18]. It is well known that high temperature benefits the hydrogen emitting process. Some literatures also indicate the absorption rate of hydrogen by palladium decreases with temperature[19]. Thus there is a possibility that the sensitivity of FBG sensor also decreases with temperature in transformer oil. Therefore, it is necessary to examine the sensitivity of the FBG hydrogen sensor under high temperature. In addition, the cross-sensitive problem of hydrogen and the influence of other types of gasses dissolved in transformer on the FBG hydrogen sensor also need to be taken into consideration. In this paper, the coating method of the fiber Bragg grating (FBG) hydrogen sensor is introduced. Defects in

Figure 1. FBG structure, with a refractive index profile and spectral response.

The Bragg wavelength ( B ) is in response to temperature and strain, as shown in equation (1) [20]. B  ( f   )T  (1  pe ) (1)

B

Where pe is the strain optic coefficient;  is the thermo-optic coefficient;  f is the thermal expansion coefficient of the optical fiber. Once the temperature is compensated, the wavelength shift of the reflected light is linear with the strain. The principle of the proposed FBG hydrogen sensor is based on the changes of the physical properties of the thin palladium films which is induced by hydrogen absorption. Several optical fiber sensors, based on FBG coated with palladium, were developed for hydrogen detection in air. However, the highest sensitivity of the above sensors is only around 0.1% [21-23], which could not meet the requirement for hydrogen detection in the transformer oil. The FBG hydrogen sensor proposed in our previous paper consists of fiber core, fiber cladding, polyimide layer, titanium (Ti) layer (20 nm) and palladium layer (560 nm). The thick palladium layer is used to absorb hydrogen, inducing strain change on the FBG, and both of the

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polyimide layer and titanium layer are worked as adhesion layers to prevent the palladium coating from being peeled off. The fabrication procedures are as follows: 1) Cover the naked FBG with the liquid polyimide; 2) Put the FBG with polyimide into a temperature-controlled oven. Increase the oven temperature from 60 to 150 ℃ with the step of 30 ℃, and every step takes 2 hours. Then cool the oven back to the room temperature and take the FBG out. Such procedure is aimed to strengthen the bond between fiber cladding and metal layers; 3) Coat Ti and palladium by using magnetron sputtering. A vacuum of 2×10-2 Pa is used during the sputtering coating process. The argon gas, with a flow rate of 20 sccm (standard-state cubic centimeter per minute), is also introduced. During the sputtering process, the pressure maintains at 1 Pa and the power is 60 W. Compared to the other classic coating technologies, magnetron sputtering is able to form a uniform metal layer. Moreover, compared with other methods, the working temperature of magnetron sputtering is lower, which can protect the FBG and improve the sensor’s sensitivity. The FBG hydrogen sensor has several advantages such as immunity to EMI, resistance to high temperature, and high dielectric strength [17]. Thus, it can be located placed close to the insulation of concern inside the transformer, provided that the tangential stress along the sensor is low and the creeping discharge is not probable. The sensors can be placed inside the transformer, close to its critical components, allowing for location of the defect in fast andaccurate manner. This represents a marked improvement when compared to the classical DGA method with which the exact location of defect cannot be accomplished. Since the FBGs can be connected in series and each FBG can be assigned a unique wavelength range, a quasi-distribution measurement can be achieved by the using FBG.

3 EXPERIMENT AND DISCUSSION 3.1 PARTIAL DISCHARGE EXPERIMENT The characteristics of the developed FBG hydrogen sensor were investigated by putting it into a ball to plate partial discharge model as PD is a common source of hydrogen in power transformers. The experiment setup is shown in Figure 2. The diameter of the copper ball is 40 mm, while the diameter of the plate is 75 mm. A 4 mm thick square board (100 mm x 100 mm) is placed between the ball and the plate electrode. Moreover, the PD model was put into a small glass test cell filled with transformer oil. A FBG hydrogen sensor was fixed on the inside wall of the cell. In order to eliminate the influence of the temperature, a packaged FBG sensor which is only sensitive to temperature is fixed beside the hydrogen sensor. To achieve accurate

measurement, a high precision FBG interrogator (SM-130) is used to demodulate the wavelength of the FBGs, and the resolution of the device is 1 pm (picometer). The experiment is carried out in room temperature. During the experiment, the oil was sampled three times, and the PD production was stopped prior to the third oil sampling. All of the oil samples were analyzed by using the chromatograph of DGA. After the experiment, the recorded wavelength shift of the FBG hydrogen sensor is compared with the hydrogen concentration gained from chromatograph, as shown in Figure 3.

Figure 2. Setup of partial discharge experiment.

Figure 3. Comparison of H2 concentration detected by DGA and wavelength shift of FBG hydrogen senor.

Figure 3 reveals that the wavelength shift increases with an increase in the concentration of hydrogen dissolved in transformer oil. Defects in power transformer can generate heat, electromagnetic wave, acoustic wave, and gas, etc. Moreover, the degree of each phenomenon varies with different kinds of defects. The wavelength shift caused by temperature variation can be easily eliminated by adding a temperature compensation FBG which is only sensitive to temperature. In order to check whether the other factors can disturb hydrogen gas sensing, two more types of partial discharge model were also investigated: 1) Needle to plate electrode, where the needle is close to the plate. 2) Needle to plate electrode, where the needle is a short distance (3 mm) away from the plate. The needle is made of tungsten, while the curvature radius and the taper of the needle is 25 μm and 15°. During the experiments, the oil was sampled several times, and the oil samples were analyzed by using the



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chromatograph of DGA, the results are shown in Table 1. In the table, every data was averaged from three readings to reduce reading error. The recorded wavelength shift of the FBG hydrogen sensor is compared with the hydrogen concentration and other gas concentrations gained from chromatograph. Table 1. Gas concentrations sampled from three experiments. Wavelength shift (pm)

Gas concentrations (ppm) H2

CO

CO2

CH4

C2H4

C2H6

C2H2

9

165.6

26.4

650.6

290.2

724.0

175.0

2031.4

14

204.1

17.2

583.1

264.0

657.6

156.3

2030.9

17

249.8

121.4

741.1

141.0

283.2

24.5

1619.7

21

375.5

48.7

571.8

165.1

466.0

128.7

1778.2

26

545.1

29.8

680.2

335.1

746.0

183.4

2029.8

42

868.9

36.2

504.8

397.2

673.5

158.6

2032.2

The dissolved gas concentration measurement results from the three experiments are shown in Table 1. Since each gas has its own maximum concentration, it is hard to clearly indicate concentration of each gas under different wavelength shift in a particular figure. Thus normalization processing was applied for each gas concentration. The P.U. value of each point in Figure 4 corresponds to the ratio of each gas concentration and its maximum concentration under different wavelength shift. From Figure 4 it can be seen that no clear relationships between the other gases’ concentrations and the wavelength shift of FBG hydrogen senor has been observed. As shown in Figure 5, the wavelength shift varies linearly with the hydrogen concentration dissolved in transformer oil. The fitted equation is ( pm)  0.042 H2 ( ppm)  4.253 , and the correlation coefficient is 0.9895, thus the sensitivity of the FBG hydrogen sensor under room temperature is 0.042 pm/ppm. The experiments demonstrated that the developed FBG sensor is sensitive to hydrogen gas and is hardly disturbed by the other factors, such as electromagnetic wave, acoustic wave, and other gases.

Figure 4. Gas concentrations verse wavelength shift of FBG hydrogen senor.

Figure 5. Wavelength shift of FBG hydrogen senor response to H2 concentration.

3.2 HYDROGEN SENSING IN OIL UNDER OPERATING TEMPERATURE For most hydrides, the temperature and the pressure of the hydrogen determine the reversible reaction between metal and hydrogen and metal hydride. If the hydrogen pressure is high and the temperature is low, absorption of hydrogen will take place. On the other hand, the reaction tends to separate metal and hydrogen with low pressure and high temperature [24]. The operating temperature of transformer oil is typically in the range of 60 to 90℃, which is much higher than room temperature. Therefore, it is necessary to study the sensitivity of the FBG hydrogen sensor under high temperature. The gas cell used in this experiment was made with a Teflon tube completely filled with oil. It had two ports, which were used for the gas mixture to flow in and out, as shown in Figure 6. Moreover, an FBG hydrogen sensor and a temperature compensation FBG were fixed at the bottom of the gas cell. The experiments were performed using a mixture of ultra-high purity (99.999%) hydrogen gas and nitrogen gas. Gas flow rates were measured and controlled separately by two flow meters. The mixture of nitrogen and hydrogen was inserted into fresh transformer oil through a perforated tube, which was placed near the center of the cell. Before the experiment, the temperature of the oil was increased to 80 ℃ by using a water bath, and the variation of the temperature was controlled within 1 ℃, by using a PID (proportional-integral-derivative) device. Pure nitrogen gas was then run through the oil for half an hour. Afterwards, a mixture of gas with 2% concentrations of hydrogen and 98% concentrations of nitrogen was applied. The wavelength shift of the FBG hydrogen sensor caused by hydrogen absorption is given in Figure 7. Figure 7 indicates that the wavelength shift increased rapidly after importing the mixed gas. After importing

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the mixture of gas for about half an hour, the wavelength shift achieves a stable state at 80 pm when hydrogen concentration in oil stopped increasing after reaching its saturation level. The hydrogen injection was stopped then the only oil sample was extracted. The oil was analyzed by using the chromatograph of DGA method. The results obtained from the chromatograph reveals that the hydrogen concentration of oil sample is 1791.46 ppm. In order to ensure the accuracy of the experiment, the experiment was repeated many times, and the results are nearly the same. The sensitivity of the FBG hydrogen sensor working at high temperature is 0.044 pm/ppm, which is nearly the same as that in room temperature (0.042 pm/ppm). Such stability of sensitivity to temperature variations is believed due to the stability of hydrogen absorption. It is well known that the energy of dissociation of the molecule and the energy of interaction between the dissolved hydrogen atoms, and between the hydrogen and the metal are key terms for the enthalpy of solution of hydrogen from the molecular gas into the metal [25]. In the air, the speed of hydrogen molecule increases with the temperature, resulting in the reduction of hydrogen absorption rate. But compared with the hydrogen speed in the air, due to the larger molecule of transformer oil and higher pressure [26], the increment rate of hydrogen speed is much smaller in transformer oil. Thus both of the collision possibility and the interaction energy between the hydrogen molecule and the palladium molecule are not change seriously. Therefore, compared with air, the effect of temperature on the sensitivity of the sensor is much less in the transformer oil. The hydrogen absorption rate remains the same as the temperature varies, ranging from room temperature to operating temperature of power transformer. In conclusion, the hydrogen sensing experiment in oil with operating temperature indicated that the sensitivity of the developed sensor remains the same as the temperature varies, ranging from room temperature to operating temperature of power transformer.

Figure 7. Wavelength shift of the FBG hydrogen sensor caused by hydrogen absorption under 80 ℃ (the maximum hydrogen concentration of oil is 1791.46 ppm).

4 CONCLUSIONS 1) A novel hydrogen sensor is designed on the basis of FBG sensing technique. The sensors can be placed inside the transformer, close to its critical components, allowing for location of the defect in fast and accurate manner. This represents a marked improvement when compared to the classical DGA method with which the exact location of defect cannot be accomplished. 2) The experiment demonstrated that the developed FBG sensor is sensitive to hydrogen gas. No clear relationships have been observed between the other gases’ concentrations and the wavelength shift of FBG hydrogen senor. 3) The hydrogen sensing experiment in 80 ℃ oil demonstrated that the developed FBG hydrogen sensor can work properly in power transformers with operating temperature. The sensitivity of the FBG hydrogen is nearly the same at room temperature and operating temperature.

ACKNOWLEDGMENT This work was supported in part by the National Basic Research Program of China (973 Program) (2009CB724508), Fundamental Research Funds for the Central Universities, Research Fund for the Doctoral Program of Higher Education of China (RFDP), National Natural Science Foundation of China (Grant No. 51307052 ) and China South Grid and State Grid Corporation of China.

REFERENCES

Figure 6. Experiment setup of hydrogen sensing in operating temperature oil.

[1] J. Singh, Y. R. Sood, and R. K. Jarial, "Condition Monitoring of Power Transformers-Bibliography Survey," IEEE Electr. Insul. Mag., Vol. 24, No. 3, pp. 11-25, 2008. [2] J. A. S. B. Jayasinghe, Z. D. Wang, P. N. Jarman, and A. W. Darwin, "Winding movement in power transformers: a comparison of FRA measurement connection methods," IEEE Trans. Dielectr. Electr. Insul., Vol. 13, pp. 1342-1349, 2006. [3] H. Okubo and N. Hayakawa, "A novel technique for partial discharge and breakdown investigation based on current pulse waveform analysis," IEEE Trans. Dielectr. Electr. Insul., Vol.12, pp. 736-744, 2005.



[4] M. D. Judd, Y. Li, and I. B. B. Hunter, "Partial discharge monitoring for power transformer using UHF sensors. Part 2: field experience," IEEE Electr. Insul. Mag., Vol. 21, No. 3, pp. 5-13, 2005. [5] M. D. Judd, Y. Li, and I. B. B. Hunter, "Partial discharge monitoring of power transformers using UHF sensors. Part I: sensors and signal interpretation," IEEE Electr. Insul. Mag., Vol. 21, No. 2, pp. 5-14, 2005. [6] G. Betta, A. Pietrosanto, and A. Scaglione, "An enhanced fiber-optic temperature sensor system for power transformer monitoring," IEEE Trans. Instrum. Measurem., Vol. 50, pp. 1138-1143, 2001. [7] T. Cargol, "An Overview of Online Oil Monitoring Technologies," 4th Weidmann-ACTI Technical Conf., San Antonio, USA, pp. 1-6, 2005. [8] M. Duval, "A review of faults detectable by gas-in-oil analysis in transformers," IEEE Electr. Insul. Mag., Vol. 18, No. 3, pp. 8-17, 2002. [9] IEC-60599, "Mineral oil-impregnated electrical equipment in service-guide to the interpretation of dissolved and free gases Analysis," 2007. [10]Y. Yun, W. Chen, Y. Wang, and C. Pan, "Photoacoustic detection of dissolved gases in transformer oil," European Trans. Electr. Power, vol. 18, pp. 562-576, 2008. [11] M. Benounis, T. Aka-Ngnui, N. Jaffrezic, and J. P. Dutasta, "NIR and optical fiber sensor for gases detection produced by transformation oil degradation," Sensors and Actuators A: Phys., Vol. 141, pp. 76-83, 2008. [12] J. Deng, H. Xiao, W. Huo, M. Luo, R. May, A. Wang, and Y. Liu, "Optical fiber sensor-based detection of partial discharges in power transformers," Optics & Laser Technology, vol. 33, pp. 305-311, 2001. [13] C. Tao, Z. Xiaoxing, L. Wangting, and S. Caixin, "Detecting oil dissolved gases using carbon nanotubes sensor," Int’l. Conf. High Voltage Eng. Application (ICHVE), pp. 645-648. 2010. [14] T. E. Hammon and A. D. Stokes, "Optical fibre Bragg grating temperature sensor measurements in an electrical power transformer using a temperature compensated optical fibre Bragg grating as a reference," 11th Int’l. Conf. Optical Fiber Sensors, Tokyo, Japan, pp. 566-569, 1996. [15] B. Yu, D. W. Kim, J. Deng, H. Xiao, and A. Wang, "Fiber Fabry-Perot sensors for detection of partial discharges in power transformers," Appl. Optics, Vol. 42, pp. 3241-3250, 2003. [16] G.-m. Ma, C.-r. Li, Y.-t. Luo, R.-d. Mu, and L. Wang, "High sensitive and reliable fiber Bragg grating hydrogen sensor for fault detection of power transformer," Sensors and Actuators B: Chemical, Vol. 169, pp. 195-198, 2012. [17] J. Teunissen, R. Merte, and D. Peier, "Stability of fiber Bragg grating sensors for integration into high-voltage transformers for online monitoring," 15th Optical Fiber Sensors Conf. pp. 541-544, Vol.1, 2002. [18] T. Hübert, L. Boon-Brett, G. Black, and U. Banach, "Hydrogen sensors – A review," Sensors and Actuators B: Chem., Vol. 157, pp. 329-352, 2011. [19] T. B. Flanagan and W. Oates, "The palladium-hydrogen system," Annual Review of Materials Science, Vol. 21, pp. 269-304, 1991. [20] H. Kenneth and O. M. Gerald, “Fiber Bragg grating technology fundamentals and overview”, J. Lightwave Techn., 1997, Vol. 15, No.8, pp. 1263-1276, 1997. [21] S. F. Silva, L. Coelho, O. Frazao, J. L. Santos, and F. X. Malcata, "A Review of Palladium-Based Fiber-Optic Sensors for Molecular Hydrogen Detection," IEEE J. Sensors, Vol. 12, pp. 93-102, 2012. [22] T. Hübert, L. Boon-Brett, G. Black, and U. Banach, "Hydrogen sensors – A review," Sensors and Actuators B: Chem., Vol. 157, pp. 329-352, 2011. [23] B. Sutapun, M. Tabib-Azar, and A. Kazemi, "Pd-coated elastooptic fiber optic Bragg grating sensors for multiplexed hydrogen sensing," Sensors and Actuators B: Chem., Vol. 60, pp. 27-34, 1999. [24] G. Kruijtzer, Hydrogen in Magnesium Palladium Thin Layer Structures, Ph.D. thesis, Utrecht University, Utrecht, Netherland, 2008. [25] R. Oriani, "The physical and metallurgical aspects of hydrogen in metals," Fusion Techn., Vol. 26, pp. 235-266, 1994. [26] T. Rouse, "Mineral insulating oil in transformers," Electrical Insulation Magazine, IEEE, vol. 14, No. 3, pp. 6-16, 1998.

385 Guo-Ming Ma (M’10) was born in Hebei, China, in 1984. He received the B.S. and Ph.D. degrees in electrical engineering from North China Electric Power University (NCEPU), Beijing, China, in 2006 and 2011, respectively. Currently, he is a Lecturer with NCEPU. His research interests are condition monitoring of power apparatus and fiber-optical sensors.

Cheng-Rong Li (SM’03) was born in Xi’an city, China, in 1957. He received the B.S. and M.S. degrees in electrical engineering from North China Electric Power University in 1982 and 1984, respectively. He received the Ph.D. degree in electrical engineering from Tsinghua University in 1989. He joined the University of South Carolina, Columbia, in 1992 as a Postdoctoral Research Fellow. He joined NCEPU in 1995. Currently, he is a Professor with the Beijing Key Laboratory of High Voltage and EMC. His current research interests include gas discharges, electrical insulation and materials, and condition monitoring of power apparatus. Dr. LI is a Fellow of the Institute of Electrical Engineers.

Ruiduo Mu was born in Tianjin province, China, in 1988. He received the B.S. degree in electrical engineering from North China Electric Power University (NCEPU) in 2011. He is now working for the Master degree in electrical engineering in North China Electric Power University, Beijing, China. His current research interest is condition monitoring of power apparatus and fiber optical sensors.

Ying-Ting Luo was born in Jiangxi province, China, in 1988. She received the B.S. degree in automation (2009) and M.S. degree in electrical engineering (2011) form North China Electric Power University (NCEPU), Beijing, China. She joined Electric Power Research Institute of Guangdong Power Grid Corporation (Guangzhou, P.R.China) in 2011. Her current research interest is condition monitoring of power apparatus.

Jun Jiang was born in Anhui province, China, in 1988. He received the B.S. degree in electrical engineering and automation from China Agricultural University (CAU) in 2011. He is now working for the Master degree in electrical engineering in North China Electric Power University, Beijing, China. His current research interest is condition monitoring of power apparatus and fiber optical sensors.