Hong-yang Zhou

A Wireless and Passive Online Temperature Monitoring System for GIS Based on Surface-Acoustic-Wave Sensor

A novel temperature monitoring system for gas-insulated switchgears (GISs) based on surface-acoustic-wave (SAW) sensing is proposed in this paper. Compared with the existing systems, this system has several unique advantages, such as being wireless, passive, and at a proper cost with continuous monitoring. First, an accurate SAW temperature sensor is designed for the GIS conductor, where epoxy encapsulating and loop antennas are adopted in the SAW sensor to prohibit the potential partial discharge of the sensor itself. After that, a multifunctional reader antenna is developed, which can measure the conductor temperature and partial discharge by the time-division multiplexing technique. Experiments are carried out to examine the accuracy and response speed of the SAW sensors, and the results indicate that the uncertainty of the contact temperature measurement is smaller than 10 °C. Moreover, the insulation level and anti-interference ability are demonstrated based on experiments carried out on a 126-kV GIS. At last, temperature monitoring performance of the developed system is investigated by changing the current in the 126-kV GIS conductor. The experiment results prove that the developed system can meet the requirement of temperature monitoring in GIS.

The Reusable Load Cell with Protection Applied for Online Monitoring of Overhead Transmission Lines Based on Fiber Bragg Grating

Heavy ice coating of high–voltage overhead transmission lines may lead to conductor breakage and tower collapse causing the unexpected interrupt of power supply. The optical load cell applied in ice monitoring systems is immune to electromagnetic interference and has no need of a power supply on site. Therefore, it has become a hot research topic in China and other countries. In this paper, to solve the problem of eccentric load in measurement, we adopt the shearing structure with additional grooves to improve the strain distribution and acquire good repeatability. Then, the fiber Bragg grating (FBG) with a permanent weldable package are mounted onto the front/rear groove of the elastic element by spot welding, the direction deviation of FBGs is 90° from each other to achieve temperature compensation without an extra FBG. After that, protection parts are designed to guarantee high sensitivity for a light load condition and industrial safety under a heavy load up to 65 kN. The results of tension experiments indicate that the sensitivity and resolution of the load cell is 0.1285 pm/N and 7.782 N in the conventional measuring range (0–10 kN). Heavy load tension experiments prove that the protection structure works and the sensitivity and resolution are not changed after several high load (65 kN) cycles. In addition, the experiment shows that the resolution of the sensor is 87.79 N in the large load range, allowing the parameter to be used in heavy icing monitoring.

The online monitoring system of transmission lines weight based on fiber sensing technology

The online monitoring of ice load of transmission lines, which reflects the dynamic load of line, can alert the early stage ice in advance and guarantee the safety of power supply. However, the fiber sensors, which were used in ice online monitoring of overhead transmission lines, usually had low sensitivity and bad repeatability. And the capacity of sensor network was limited and it was difficult to provide hundreds of FBGs for optical sensing of overhead transmission lines in kilometers. In this paper, we proposed a novel load cell based on Fiber Bragg Grating (FBG) and presented the idea for high-capacity sensing network. Firstly, we adopted shearing structure with additional protection parts to reduce the influence of eccentric force. Then the FBG gauges were welded on the elastic element to avoid glue aging problem. After that, the FBGs were mounted at the front/rear slot with the direction deviation of 90° from the each other to eliminate the temperature effect in strain detection, and the extra FBG which usually used for temperature compensation is not necessary. The results of tension experiment indicate that the tension sensitivity and resolution of the load cell is 0.1285 pm/N and 7.78 N. Moreover, the expanded sensing network proposed can export consecutive modulating pulse as incoming signal for FBG sensors to detect the strain change result transmission line load.

Tracing methane dissolved in transformer oil by tunable diode laser absorption spectrum

Dissolved gas analysis (DGA)in power transformers is related to the degradation of insulation materials and dissolved methane (CH 4 )is a symbol gas of low energy electrical or thermal faults in power transformer oil. Conventional online DGA equipment suffers from problems such as cross sensitivity, electromagnetic compatibility and reliability. Based on tunable diode laser absorption spectroscopy (TDLAS) technique, a novel optical method is proposed to detect dissolved methane in transformer oil. Oil samples with fault gases are prepared and dissolved methane detection has been carried out in the laboratory. 1653.72 nm is selected as the central wavelength of tunable diode laser, moreover, a multipass gas cell and wavelength modulation strategy is utilized to trace methane dissolved in oil. Results show that the resolution of detection reaches 0.28 µL/L, and accuracy is less than 2 µL/L at low concentration. In addition, the detection cycle is so time-saving, less than 5 minutes. The proposed measurement method shows tremendous advantages, such as immediate response to concentration changes, no cross interference, no carrier gases, which is proved to be a promising maintain-free technique instead of conventional DGA equipment.

Note: Dissolved hydrogen detection in power transformer oil based on chemically etched fiber Bragg grating

A fiber Bragg grating (FBG) sensor based on chemically etched cladding to detect dissolved hydrogen is proposed and studied in this paper. Low hydrogen concentration tests have been carried out in mixed gases and transformer oil to investigate the repeatability and sensitivity. Moreover, to estimate the influence of etched cladding thickness, a physical model of FBG-based hydrogen sensor is analyzed. Experimental results prove that thin cladding chemically etched by HF acid solution improves the response to hydrogen detection in oil effectively. At last, the sensitivity of FBG sensor chemically etched 16 μm could be as high as 0.060 pm/(μl/l), increased by more than 30% in comparison to un-etched FBG.

Time and frequency characteristics of very fast transient overvoltage in ultra high voltage substation

Most work about the measurement of very fast transient overvoltage (VFTO) was carried out in the laboratory and test base. Because of the different GIS arrangement and power capacity, the time and frequency characteristics of VFTO in ultra high voltage (UHV) substation could be different with that obtained in the laboratory and test base. A series of VFTO measurements were carried out in two 1100 kV GIS substations to investigate the characteristics of on-site VFTO. The port-hole sensor based on surface-mounted device was chosen to measure the VFTO for its reliability and wide band-width. The whole measurement system was introduced and the schematic layout of each experiment was given. Measurement results of different switch conditions and measure points were presented for comprehensive understanding of the VFTO characteristics on site. The results indicated that the striking number during one operation was 16 (closing) and 14 (opening), similar to that obtained from test base result. Besides, single strike with front time 5.3 ns and voltage steepness 186.1 kV/ns was recorded, and the steepness was relatively higher than that gained in the test base. Moreover, the spectral analysis based on S transform was investigated to get the duration of different frequency components of VFTO waveform. Compared with the data obtained from the test base, the high frequency components of VFTO were reduced, while the lower frequency components lasted longer. The results provided references for the investigation of the electromagnetic interfere, the insulation coordination, and VFTO mitigation methods.

Characteristics of surface potential of disc spacers under different temperature

The problem of surface charge accumulation on gas-insulator interface is one of the critical factors for the insulation of DC-GIL. A GIL experiment platform which can heat central electrode with variable temperature is built to investigate the surface charge under different temperature. The surface potentials of insulator at different temperature under negative voltage are measured and the effect of temperature on the non-uniformity of potential distribution is discussed. The average potential at 70 °C is 231% higher than that at 30 °C. These data can be referred in the insulation design of DC-GIL.

A high humidity sensitive Fiber Bragg Grating for contamination measurement

In order to overcome the on-line monitoring systems technical problems for polluted insulators, which are susceptible to EMI(electromagnetic interference), on-site power supply required, poor accuracy and low reliability, this paper proposes an insulator surface ESDD (equivalent salt deposit density) detection scheme for contamination measure based on high humidity-sensitive PI-FBG (Fiber Bragg Grating coated by polyimide) sensor. First of all, through theoretical analysis and experimental verification, and based on the exploration of several aspects—PAA (polyamic acid) solution concentration, viscosity, PI (polyimide) film thickness — a high humidity-sensitive PI-FBG sensor was developed. Then, The ESDD sensing experiment was carried out based on the developed high humidity-sensitive PI-FBG. Finally, to test the sensors stability and life length, performance experiments were repeated after 6months from the time when the sensor was manufactured. By the developed high humidity-sensitive PI-FBG sensor and its result of experiment on salt sensitivity, the PI-FBG sensor was proved that, with its good stability, it can be used for the ESDD detection on the surface of insulator in the future.

Impact of temperature on surface charges accumulation on insulators in SF6-filled DC-GIL

With this expected future advance of HVDC, the use of gas insulated transmission lines (GIL) for dc application are getting increasingly interesting. For now, the problem of surface charge accumulation on gas-insulator interface is one of the critical factors for the development of DC-GIL. In many previous works, the model of surface charge accumulation on insulator was investigated. However, the quantitative relationship between temperature and surface charge accumulation on insulator was not exactly obtained since the lack of complicated heat transfer progress in the model. In this paper, the heat transfer surface charge accumulation model of operating DC-GIL was developed, including the nonlinear relationship between volume current in gas and electric field. Moreover, the space charge was also considered in the model. Based on the developed model, temperature distributions in DC-GIL insulator under different current are obtained. Afterwards, the temperature impact on space charge density in the insulator, the saturation time of surface charge accumulation, the surface charge on the insulator surface, and the electric field distribution on the insulator were investigated. It was proven that the tangential component of the electric field reaches to 5.3 kV/mm on lower interface and 5.0 kV/mm on upper interface for Ti=378 K. This value increase 17.8% on lower interface and 17.6% on upper interface along with the conductor temperature from 298 K to 378 K. The data can be referred in the insulation design of DC-GIL.

Impact of temperature on surface charges accumulation on insulator in gas insulated systems under DC voltage stresse

With this expected future advance of HVDC, the use of gas insulated transmission lines (GIL) for dc application are getting increasingly interesting. For now, the problem of surface charge accumulation on gas-insulator interface is one of the critical factors for the development of DC-GIL. In many previous works, the characteristics of surface charges accumulation on insulator was investigated. However, the impact of temperature was neglected in most studies. In fact, a heating phenomenon is known to occur in transmission channel. Due to the surface charge accumulation is closed to the conductivity of insulator and insulated gas, and the conductivity of insulated materials are influenced deeply by temperature. Thus, this paper describes an experimental setup with the ability to simulate the heat transfer progress in DC-GIL, for measuring surface charge of insulator. It is hoped to study the impact of temperature on surface charge accumulation on insulator in future work.