Shangpeng Sun

Intense transient electric field sensor based on the electro-optic effect of LiNbO3

Intense transient electric field measurements are widely applied in various research areas. An optical intense E-field sensor for time-domain measurements, based on the electro-optic effect of lithium niobate, has been studied in detail. Principles and key issues in the design of the sensor are presented. The sensor is insulated, small in size (65 mm × 15 mm × 15 mm), and suitable for high-intensity (<801 kV/m) electric field measurements over a wide frequency band (10 Hz–10 MHz). The input/output characteristics of the sensor were obtained and the sensor calibrated. Finally, an application using this sensor in testing laboratory lightning impulses and in measuring transient electric fields during switch-on of a disconnector confirmed that the sensor is expected to find widespread use in transient intense electric field measurement applications.

Temperature characteristics of Pockels electro-optic voltage sensor with double crystal compensation

Voltagesensors based on the Pockels electro-opticeffect in LiNbO3 crystals have been applied to practical engineering measurements because of their passive nature, wide operating bands, and low transmission loss. However, the temperature of the measurement environment can greatly affect the dynamic responses of these sensors because the natural birefringence of a single LiNbO3 crystal voltagesensor(SVS) is related to its temperature. To improve the stability of this sensor over a wide temperature range, a double crystal compensation method is introduced in this paper to compensate for the natural birefringence of the SVS. A double LiNbO3 crystal voltagesensor (DVS) was fabricated, and its working point drift characteristics and amplitude-frequency response were investigated over the temperature range from 0°C to 50°C. The effects of two intrinsic parameters of the LiNbO3 crystal were also investigated. Comparison between an existing SVS and the proposed DVS showed that the DVS resisted environmental temperature fluctuations more strongly.

Protection radius of bird-preventing installation design for 110 kV suspension insulators based on withstand tests

According to IEEE Guide for Reducing Bird-Related Outages, several types of transmission line faults could be induced by birds. The number of birds increases as human awareness of environmental protection increases. Thus, the probability of suspension insulator string flashover induced by bird streamer would also increase. Analysis of transmission line faults in Yunnan, China, shows that many transmission line faults occurred in the winter bird migration zone, and most of the towers affected are 110 kV transmission line towers. Hence, investigating the flashover process of the 110 kV transmission line suspension insulator strings induced by bird streamer and designing a well bird-preventing installation for 110 kV transmission line suspension insulator strings is necessary. In this study, a simplified, self-designed 110 kV transmission line tower is utilized to experiment on the three types of 110 kV transmission line suspension insulator string with bird simulation excrement. The analysis of withstand test results has revealed the mechanism of flashover caused by bird streamer of the three types of suspension insulator string, and the protection radius R of the three types of insulator string has been presented. The mechanism of flashover and test results have been testified by means of the distributions of electric field and potential calculated by FEM method. Thus, the bird streamer caused flashover could be classified as the shortest air gap breakdown. Hence, it is valuable for designing or selecting a well bird-preventing installation.

A non-contact electro-optic sensor for lightning overvoltage measurement

Measurement of Lightning overvoltage in high voltage power network is of great significance to the research on the characteristics of overvoltage and the design of insulation coordination. In this paper, an integrated passive sensor for overvoltage measurement is designed. A high voltage sensing unit is constituted by a capacitor with fixed value in series connected to the stray coupling capacitor between the high voltage transmission line and metal plate as a series capacitive divider. The electro-optic unit is designed based on the electro-optic effect of LiNbO3(LN) crystal. The voltage signal sensed by the front unit can be converted to an optical signal by electro-optic unit with no power supply at the installation site. The electro-optic unit is connected with control room by optical fibers. Tests on the new developed overvoltage sensor indicate that the sensor has not only a good linear operating region, but also a high precision and high frequency response speed under lightning and switching impulse. It can be applied to the non-contact passive measurement of lightning overvoltage in different voltage levels.

An optical fiber Bragg grating and piezoelectric ceramic voltage sensor

Voltage measurement is essential in many fields like power grids, telecommunications, metallurgy, railways, and oil production. A voltage-sensing unit, consisting of fiber Bragg gratings (FBGs) and piezoelectric ceramics, based on which an optical over-voltage sensor was proposed and fabricated in this paper. No demodulation devices like spectrometer or Fabry-Perot filter were needed to gain the voltage signal, and a relatively large sensing frequency range was acquired in this paper; thus, the cost of the sensing system is more acceptable in engineering application. The voltage to be measured was directly applied to the piezoelectric ceramic, and deformation of the ceramics and the grating would be caused because of the inverse piezoelectric effect. With a reference grating, the output light intensity change will be caused by the FBG center wavelength change; thus, the relationship between the applied voltage and the output light intensity was established. Validation of the sensor was accomplished in the frequency range from 50 Hz to 20 kHz and switching impulse waves with a test platform; good linearity of the input-output characteristic was achieved. A temperature validation test was completed, showing that the sensor maintains good temperature stability. Experimental results show that the optical over-voltage sensor can be used for voltage monitoring, and if applied with a voltage divider, the sensor can be used to measure high voltage.

Dual LiNbO3 Crystal-Based Batteryless and Contactless Optical Transient Overvoltage Sensor for Overhead Transmission Line and Substation Applications

Advanced high-voltage and overvoltage measurement techniques are required for smart grid construction. The existing overvoltage measurement methods that are currently used for power system measurements are mostly based on the use of electromagnetic voltage transformers and capacitive voltage transformers, which have contradiction in measuring accuracy, measuring distance, antijamming, and system compatibility. A batteryless sensor for contactless measurement of the overvoltage on overhead transmission lines based on a combination of the electrooptic effect in LiNbO3 with stray capacitance in the air is designed in this work. On the basis of this design, a dual-crystal structure-based electrooptic conversion unit is presented that eliminates the natural birefringence and improves the operating stability of the sensor. Testing platforms were set up to measure the characteristics of the sensor in thermal stability. In combination with a data acquisition device, the newly designed sensor was applied to online monitoring of the overvoltage in the ac bus and the overhead transmission lines of a 500-kV transformer station and a ±500-kV convertor station in the China Southern Power Grid.

Research and application of a non-contact optical voltage sensor for the monitoring of lightning and switching overvoltage in EHV power grid

In this paper, a type of sensor for the non-contact monitoring of lightning and switching overvoltage in power grid is presented. It is designed based on Pockels effect and stray-capacity coupling theory. Double-crystal structure is utilized to restrain the unwanted influence caused by natural birefringence. The transmission of the data is achieved by optical fibers which are immune to the electromagnetic interference in substation. This type of sensor is applied to an EHV transformer substation for on-line monitoring.

Overvoltage measurement based on the electro-optic E-field sensor

Overvoltage measurement has been an important field of high voltage engineering. In this paper, an optical intense E-field sensor which is based on the electro-optic effect of lithium niobate, has been studied comprehensively. First, the principles and key issues in sensor design are presented. Second, after fabrication, the input/output characteristics of the sensor are obtained and calibration under lightning impulse. Then, the designed electric field sensor is applied in overvoltage measurement.

Research on the measurement methods of half-voltage in LiNbO 3 crystal electro-optic modulation

In the optical voltage sensor based on first order electro-optic effects, the half-voltage of electro-optic crystal is one of the key factors influencing the input-output characteristic of sensors. With relative analysis of the electro-optic modulation mechanism, LiNbO3 crystal is chosen to set up the measurement system of half-voltage, measurement is done on half-voltage. Theoretical calculation of half-voltage is completed, comparison with the actual results is finished, factors influencing the LiNbO3 crystal half-voltage is discussed, and problems need to be taken into consideration in practical engineering application are pointed out.