Ying Na Li

On-Line Monitoring of Air Cooler in Transformer by Using Fiber Bragg Grating Temperature Sensors

The air cooler reduce the working temperature of the transformer, high temperature will reduce the transformers life, and even make insulation overheating, aging, then the transformer will be damaged. The air cooler which is forced oil circulation in transformer outdoor in substation has been monitored. The real-time monitoring of 24-hours indicates that the temperature changes in the range of 3°C. The ambient temperature is lower than the temperature of fan about 1°C. At the long-term of 479 days, the average daily temperature range of fan is 35.32°C, the maximum temperature is 50.25°C on August 18,2011, and the maximum temperature is 14.93°C on January 17, 2011. The daily average of ambient temperature range is 37.59°C, the maximum temperature is 51.16°C on August 17, 2011,and the minimum temperature is 13.57°C on January 17, 2011. The maximum difference between the temperature of fan and the ambient temperature is 12.48°C on September 15, 2011. According to the relevant standards and monitoring results, the maximum threshold of fan temperature is defined to 80°C, and the threshold of temperature rise is 20°C.

Spring-Steel Pipe Fiber Bragg Grating Strain Sensor

Structure’s strain reflects the stability of the project, the excessive structural strain will destroy the stability of the structure. Fiber Bragg Grating has many features, such as, strong anti-interference ability, low optical loss, and it can be used for a long time in the project, etc. Base on the features, the Fiber Bragg Grating Strain Sensor can be used in slope and other projects for the long-term monitoring. In this paper, we develop a Fiber Bragg Grating Strain Sensor based on the spring-steel pipe, FBG be fixed to the inner of the steel pipe by epoxy glue, it is protected by a stainless steel pipe outside, the Flange be fixed to the both side of the spring-steel pipe. When the tension acting one the flanges, the spring-steel pipe occurs an axial strain, this axial strain makes the center wavelength of the Fiber Bragg Grating change, measuring the wavelength shift amount of the Fiber Bragg Grating can calculate the strain. The loading experiment indicates that the sensitivity of the Spring-steel pipe Fiber Bragg Grating Strain Sensor is 0.81pm/με, the linearity of the sensor is 2.1%FS, and the repeatability error of the sensor is 2.29%FS.

Study on FEM Numerical Simulation and Strain Monitoring of Tunnel Secondary Lining

Safety of secondary lining is of utmost importance to tunnel engineering quality as the main load-bearing structure and the last waterproof line of rock tunnel under type III. The comparative study of strain state results from FEM numerical simulation and on-site monitoring in Yunnan Tianxin Tunnel was conducted to obtain the stress regularity of tunnel lining. The results showed that except vault, the strain states of secondary lining obtained by numerical simulation and on-site monitoring were consistent. The strain value of on-site monitoring was approximately 60%~70% to the simulation value. And the strain value of right side was greater than the value of the corresponding location on the left side. It’s noticed that high strain were found in tunnel haunch and arch springing. Great attention should be paid to arch springing for the largest strain value. The strain monitoring value of vault (309.83με~327.23με) has been detected larger than simulation value (209.37με), which matches well the crack phenomenon of vault. Therefore it’s significant to focus on the long-term monitoring of vault. The defects of single on-site monitoring method such as poor predictability were made up effectively by comparative study. The results achieved can be recommended for similar projects.

Testing Research of Fiber Bragg Grating Strain Sensor Embedded in Bored Pile

Reinforced concrete piles are used when structures are constructed on soft ground, because it is necessary to transfer the loads into deeper strata with a sufficient bearing capacity. With the purpose of receiving more precise information about the pile features, four fiber Bragg grating strain sensors are embedded at different levels of the pile to measure the strain distribution during straining and pull-out tests. Test Pile vertical uplift static load test results show that, settlement of the test pile is steep variations, the steep rise starting point corresponding to the load of 3300 kN for the Uplift Ultimate Bearing capacity, the corresponding uplift amount is 12.45 mm; 4.4 m, 7.2 m, 11.0 m and 14.5 m sections axial strain were 115 με, 42 με, 6 με and-3 με. Maximum loading capacity is 3600 kN, the corresponding uplift amount is 30.13mm; 4.4 m, 7.2 m, 11.0 m and 14.5 m sections axial strain were 142 με, 61 με, 7 με and-1 με.

Blind Pipe Type Fiber Bragg Grating Hydrostatic Gauge

A blind pipe type fiber Bragg grating hydrostatic gauge is developed to measure the pressure of liquid. In the hydrostatic gauge, the inside of elastic tube is suffered by the pressure of liquid and drives the wavelength shift of a fiber Bragg grating mounted on the outside of elastic tube. For eliminating the disturbance of temperature variation, the other grating is mounted on the n type sheet metal and is immune to the applied stress strain of elastic tube. The hydrostatic experiment indicates that the pressure sensitivity of the hydrostatic gauge is 0.425 nm/MPa, when the original Bragg wavelength of pressure-sensitized grating is 1557.510 nm.

Monitoring of Tunnel Second Lining and Steel Lining by Using Fiber Bragg Grating Strain Sensor

Dong Yang Tunnel is located in the low mountains and hilly areas with tectonic denudation, where the tunnel of K147+535~K147+575 passes mainly through the maroon and purple red completely weathered mudstone. A differential fiber Bragg grating strain sensor is developed for monitoring the surface strain of tunnel lining. By converting the strain of gauge rod into the strain of beam, two fiber Bragg gratings are separately mounted on the top and bottom surfaces of beam, and as a result shifts its Bragg wavelength. The difference of relative Bragg wavelength shifts of the sensing gratings is 1.05×10-6 /. Grating sensors are installed on the tunnel lining of K147+540~K147+610. Especially, the second lining of K147+592~K147+598 is enhanced by the steel plate. The strains of >100 occur on the lining of K147+560 and K147+590 in the reinforcing period of 20 days. Following a 160 days operation period, the measurement results indicate that the tunnel structures are gradually tending towards stability.

Temperature Researches of Porcelain Insulator

When porcelain insulator operates in a harsh environment for a long time, it will cause leakage current increase, and lead to heating phenomenon. As a result, the temperature of porcelain insulator can be changed, which probably due to crack, breakdown or other factors. In order to reflect the working state of the porcelain insulator, to monitor the temperature of porcelain insulator, optical fiber Bragg grating temperature sensors are installed respectively on the steel cap and the porcelain of porcelain insulator. In the interaction of industrial frequency voltage test of 15kV, thus the temperature of porcelain insulator can be distributed. The temperature of the porcelain insulator affects the center wavelength of optical fiber Bragg grating temperature sensors, which are installed on porcelain insulator. The tests show that in the pure condition, the temperature of porcelain insulators steel cap and porcelain respectively rise 1.4°C and 1.5°C, in the polluted condition, the temperature of porcelain insulators steel cap and porcelain respectively rise 5.8°C and 6.3°C, in the pollution level II condition, the temperature of Porcelain insulators steel cap and porcelain respectively rise 6.8°C and 7.2°C. Therefore, by using optical fiber Bragg grating temperature sensors to monitor the change of porcelain insulators temperature, combined with the researches of temperature characteristics, can directly reflect the porcelain insulators working situation and real-time online monitoring.

Application Research of Fiber Bragg Grating for Sensing Finger Pressure Detection on High Voltage Isolate Switch

The sensing finger pressure does not meet the requirements can cause isolation switch overheating, even lead to accident in the operation of high voltage isolate switch. According to the structure of isolating switch, FBG pressure sensor and FBG displacement sensor are installed on isolate switch, which constitute the sensing finger pressure detection system. The sensing finger pressure detection experiments indicate that, when the moving contact’s closing position of isolate switch changes from 0.267mm to 29.040mm, the sensing finger pressure ranges from 30.378N to 32.970N.However, when spring pressure changes from 42.776N to163.827N, the sensing finger pressure ranges from 29.033N to 111.193N.The sensing finger pressure measuring system can realize real-time and online monitoring of the sensing finger pressure.

Application of Fiber Bragg Grating Earth Pressure Sensor in Safety Monitoring for Electric Steel Tower Foundation

Power transmission tower is an important part of power transmission equipment. The tower foundation is suffered by landslides, debris flows, erections of foundation settlement and so on. The power transmission tower near Yanjin transformer substation is selected to be measured. By using fiber Bragg grating (FBG) earth pressure sensor, the earth pressure of tower foundation is measured. The long-term monitoring data indicate that the #1 sensor daily variations amplitude of earth pressure is 7.22KPa, and the #2 sensor daily variations amplitude of earth pressure is 4.69KPa. In the 479 days, the rangeability of average data is 61.55KPa in sensor #1 and 64.05KPa in sensor #2. Compared with the local precipitation, the earth pressure of tower foundation is seasonal change. According to the history data, the warning threshold value is set as 280KPa.

On-Line Monitoring of Charge Unit by Using Fiber Bragg Grating Temperature Sensors

The charge unit supply power when the power is cut off. It has been the necessary components in every type of substations to ensure the continuous operations of electric relays, automatic devices and circuit breakers. By using contacting electrical insulating Fiber Bragg Grating temperature sensor, the monitored equipment can be measured and controlled under the safe temperature. The temperatures of three fans and environment have been surveyed since June 6, 2010, in the charge unit of Yanjin substation’s main control room. The real-time monitoring of 24-hours indicates that the temperature changes in the range of 1°C. At the long-term of 479 days, the average daily minimum temperature range of three fans is 12.48°C, and the maximum range is 23.07°C. The maximum temperature is 39.14°C on April 30, 2011, and the minimum temperature is 23.98°C on January 10, 2011. The daily average of ambient temperature range is 12.04 °C, the maximum temperature is 38.38 °C on July 16, 2010, and the minimum temperature is 26.34 °C on January 9, 2011. The maximum difference between the temperature of fan and the ambient temperature is 7.60 °C on October 23, 2010. According to the relevant standards and monitoring results, the maximum threshold of fan temperature is defined to 85°C, and the threshold of temperature rise is 20°C.