Optical Voltage Transducer Research Articles

AC zero crossing compensation for thermal stress linear birefringence in optical voltage transducer

The optical voltage transducer (OVT) based on the Pockels effect has a perennial issue of the thermal stress linear birefringence (TSLB) in the electro-optic crystal being overlapped with the electro-optic phase delay, which is difficult to be eliminated and seriously affects the measurement accuracy and reliability. In this paper an AC zero crossing compensation method for TSLB is proposed. It is based on that when the steady-state AC voltage crosses zero points the electric field is zero, and the electro-optic crystal does not have any electro-optic effect, so the electro-optic phase delay is zero. In this case, the output of the OVT is an additional phase delay caused by the TSLB, which can be separated and compensated by the linear demodulation OVT and the AC zero crossing detection circuit. The experimental results show that in the temperature range of −40 °C to 70 °C, the measurement accuracy of the OVT after TSLB compensation is improved from 0.5 class to 0.2 class. This method is helpful for the practicality of the OVT.

Modeling and minimization for thermal stress birefringence of an optical voltage transducer.

The thermal stress birefringence (TSB) is a big issue that destroys the sensing stability of the optical voltage transducer (OVT), and the existing research on the theoretical modeling and solution are not good enough to handle it. This paper presents a mathematical model of the TSB based on the photo-elastic effect, and then it is quantitatively calculated through the multiphysics coupling simulation. It shows that the asymmetric radial stresses in the electro-optic crystal are the root cause for the TSB, which results in a phase delay greater than 3.153°. On this basis, a method for TSB minimization to use the polyurethane buffer layer to enwrap around the crystal is proposed, which eliminates the random radial stress and improves the symmetry of stress distribution. Finally, the effectiveness of the proposed method is verified by simulation and experiment.

Introduction on Current Application of Voltage Transformer

As an important equipment, voltage transformer is widely used in power grid to obtain voltage signal and protect the system. In this paper, the voltage transformers in power system are classified according to the working principle. The working principle and characteristics of potential transformer (PT), capacitor voltage transformer (CVT), electronic voltage transformer (EVT) and optical voltage transducer (OVT) are briefly analyzed. Besides, this paper also introduces the principle, category and characteristics of voltage transformer, as well as the application and development of voltage transformer in power system.

Construction and Evaluation of an Optical Medium Voltage Transducer Module Aimed at a 132 kV Optical Voltage Sensor for WAMPAC Systems.

This paper reports on the construction and characterization of an optical voltage transducer module for applications in the field of wide-area monitoring, protection, and control (WAMPAC). The optical medium voltage transducer (MVT) module was designed to be combined with a capacitive voltage divider (CVD) to form a voltage sensor intended for 132 kV high voltage (HV) networks. The MVT module comprises a combination of a piezoelectric transducer (PZT) and a fiber Bragg grating (FBG) as a core optical sensing element. Changes in the input voltage across the PZT translate into strain being detected by the FBG. The resultant FBG peak wavelength can be calibrated in terms of the input voltage to obtain a precise voltage measurement. The module was experimentally evaluated in the laboratory, and its performance was assessed based on the requirements specified by the IEC standards for electronic voltage transformers and low power voltage transformers. The results of accuracy tests demonstrate that the MVT module is free from hysteresis, within the experimental error, and is capable of simultaneously meeting the requirements for 0.1 metering and 1P protection classes specified by the IEC 60044-7 and IEC 61869-11 standards.

Linear phase delay detection method for optical voltage transformer based on S-wave plate

To achieve linear measurement of electro-optic phase delay and improve the accuracy and measurement range of the optical voltage transducer (OVT), this paper proposes a linear phase delay detection method for an optical voltage transformer based on a strip S-wave plate. Using the strip S-wave plate, the phase delay can be directly converted into the displacement of the dark stripe of the strip spot, and the displacement is located by the dual-quadrant detector. Using the Jones matrix, we confirm the linear relationship between the position of the dark stripe and the phase delay, and propose a positioning method and error compensation scheme of the dark stripe and set up an experimental system to verify its performance. The experimental results show that the OVT realizes the measurement of the electro-optic phase delay; the measuring range of the phase delay is up to ±40°, and the measurement error is less than 0.5%.

A Grating to Transfer Polarization Rotation to Straight Line Movement - Designs and Applications

This paper presents a grating be used to transfer a polarization rotation to a straight moving facula, so the rotation can be detected by locating the facula displacement with a line array image sensor. It can be used to build a new type of polarimeter with no mechanical rotating device, or an optical current or voltage transducer applied for electrical power systems with no rotary translation converter. The grating is a subwavelength radial polarization one, which is made of aluminum and fabricated by nano-electron beam direct write lithography. It consists of 12,000 units arranged in a line array, and each unit has a $1~\mu \text{m}$ width and a $30^\prime $ angle difference from adjacent ones. Its polarization and temperature characteristics are simulated and experimented. The TM wave transmittance is greater than 78%, and the extinction ratio is better than 27dB.

An optical voltage transducer based on radial polarization demodulation and four quadrant detection

This paper proposes an optical voltage transducer based on radial polarization demodulation and a four-quadrant detector (FQD). The voltage has been sensed linearly using an annular radial polarization grating to convert the electro-optical (EO) phase delay into the synchronous rotation of a spot. The FQD is employed to locate the spot to achieve voltage measurement. Compared with the charge coupled device camera employed before for the spot positioning, the measurement resolution is improved by nearly 100 times in the range of ±40°, the EO phase delay and the measurement accuracy is improved from class 0.5 to class 0.2, and the cost of the image unit is greatly reduced by 95%.

Defects and Improvements of Pockels Transducer Voltage Segmentation

The sensing range and sensitivity of optical voltage transducer are badly limited by the inherent half-wave voltage of the electro-optic crystals and a nonlinear polarization demodulation based on Malus’ law. A multi-segmented structure can meet the requirement of the half-wave voltage but is only suitable for 500 kV and above voltage levels with incident wavelength of 632.8 nm, but it is not suitable for all voltage levels if the incident wavelength is greater than 1330 nm. By the way in the multi-segmented structure its optical path and devices are deviated easily by vibrations and thermal expansion and contraction. In this paper, the multi-segmented structure is improved to be suitable for various high-voltage levels with the wavelength of 632.8 nm or greater, and moreover, a new approach is presented to use MgTiO3 ceramics to enwrap around BGO (Bi4Ge3O12) crystal to reduce the integral voltage errors from 0.260% to 0.012%.

Traveling-Wave-Based Fault-Location Algorithm for Hybrid Multiterminal Circuits

This paper presents a traveling-wave-based fault-location algorithm for hybrid multiterminal transmission systems that consist of one onshore overhead lines and multiple offshore submarine cables. Such hybrid transmission systems are common for interconnection of offshore wind farms to the main grid. The input to the algorithm is synchronized transient voltage measurements from all of the receiving ends. These measurements are obtained by optical voltage transducers equipped with global positioning system receivers for time synchronization. The discrete wavelet transformation is utilized to decompose the mode-1 voltages at the receiving ends. The first wave arrival times are then obtained by observing the squares of the wavelet transformation coefficient (WTC 2 ). The transient simulations and the postfault analysis are carried out using EMTP-RV and MATLAB Wavelet Toolbox, respectively. The accuracy, limitations, and capabilities of the proposed algorithm are presented and discussed for different fault conditions.

An OVT Based on Conoscopic Interference and Position Sensitive Detector

The measurement mode of the existing optical voltage transducer (OVT) is mostly based on light intensity detection. In such a way, the OVT has some big issues, such as a light intensity dependency, a temperature drift, an additional birefringence in the crystal and a half-wave voltage limitation to its measurement range. A new OVT based on conoscopic interference and bi-dimensional position sensitive detector (PSD) is proposed in the paper, which can convert the electro-optical phase delay of the crystal to a rotation angle of spot pattern, and therefore, a high voltage can be measured by the PSD. Compared with the existing OVT, the measurement mode of the new one is independent of light intensity, capable of measuring the electro-optical phase delay from 0° to 180° linearly and directly, and has a wide measurement range with no restriction of the half-wave voltage. The rotation angle of the spot pattern is positioned by a bi-dimensional PSD and the new OVT has a good linearity better than 0.5%.

Polymeric Integrated-Optic Bias Chip for Optical Voltage Transducers

The operating bias point of optical voltage transducers (OVTs) must be adjusted to a quadrature phase point through the compensation of residual birefringence induced by the optical fiber and sensor head. An integrated optical device consisting of a polymeric waveguide 3-dB coupler, TE-pass polarizer, thermo-optic phase modulator, and polarization converter was proposed for adjusting the operating bias point. A high-voltage sensor probe was prepared with a LiTaO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> electro-optic crystal sandwiched by Teflon spacers. The operating point control was confirmed by measuring the output polarization change on the Poincaré sphere. Preliminary OVT experiment was performed by applying a high-voltage signal of 60 Hz, 4 kV <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">pp</sub> , and the sensor exhibited linear response with a sensitivity of 9.4 mrad/kV.

Novel Optimization Algorithm to Demodulate a PZT-FBG Sensor in AC High Voltage Measurements

The application of optical fiber sensors in high-voltage environments has long been recognized as being useful, due to many properties of silica, such as insulation and electromagnetic induction immunity. Thus, optical voltage transducers offer many improvements on traditional inductive and capacitive voltage transformers, such as linear performance, wider dynamic range, lighter weight, smaller size, and improved safety. In this paper, we aim toward a power-line voltage transformer application by using a piezoelectric ceramic crystal stack together with a fiber Bragg grating (FBG) sensor to construct the core of a potential transformer for 13.8 kV class. For the AC demodulation process, we develop a mathematical model to identify the optimization parameters through a novel algorithm to improve sensitivity on FBG demodulation. This new scheme is simple, reduces the cost of the setup implementation and shows a solution to circumvent the temperature drift of the system.

Noise Suppression of Optical Voltage Transducer by a Robust Control

This paper investigates an H∞ robust controller for improving the measurement accuracy of the Optical Voltage Transducer with noise and parameter uncertainty. Firstly, the optical voltage transducer based on closed-loop detection is analyzed, and the model of the system is established concerning noise and uncertainty. Secondly, according to the model, this paper is theoretically devoted to the study of the Robust control for meeting the design target, while guarantees that the closed-loop system is asymptotically stable. Furthermore, we give a design criterion in terms of linear matrix inequality for the Robust control in the presence of noise and uncertainty. Finally, the experimental results demonstrate the effectiveness and feasibility of the robust controller.

Optical High-Voltage Sensor Based on Fiber Bragg Grating and PZT Piezoelectric Ceramics

Electric power facilities, such as substations, rely on voltage transformers (VTs) for measurement and protection. These pieces of equipment are bulky and heavy and tend to explode, destroying nearby equipment and posing a threat to substation personnel. Optical voltage transducers offer many improvements on traditional inductive and capacitive VTs, such as linear performance, wider dynamic range, lighter weight, smaller size, and improved safety. This paper relates to the development of a high-voltage sensor system using a PZT piezoelectric crystal as a transducer and a fiber Bragg grating as a sensor for an optical VT for a 13.8-kV class. The results show that the developed sensor is capable of attaining the International Electrotechnical Commission 0.2%-accuracy class for the revenue metering system.

双孔光子晶体光纤光学电压传感方案研究

双孔光子晶体光纤光学电压传感方案研究

基于椭圆芯保偏光纤模间干涉的光学电压互感器

基于椭圆芯保偏光纤模间干涉的光学电压互感器

Modified quadrature method for accurate voltage measurement in optical voltage transducer

There are fewer problems encountered with optical voltage transducers in comparison with their inductive and capacitive counterparts. As a result they are considered as proper candidates for replacing conventional inductive and capacitive transformers. Lighter weight, smaller size, larger dynamic range, wider bandwidth, insensitivity to electromagnetic interference, stability over temperature change, absence of iron core saturation, low maintenance and replacement cost, are some of the advantages of optical voltage transducers over inductive and capacitive transformers. A modified quadrature method is introduced to measure the voltage with the minimum number of sensors. Another advantage of this method is the possibility of improving the accuracy of the measurement by using a correction factor. The correction factor is determined by considering the level of accuracy, environmental conditions and the number of sensors. Simulation results show the validity and effectiveness of this method over a wide range of variation.

Accurate voltage measurement by the quadrature method

This paper introduces the quadrature method for measuring voltage using one or more electric field sensors. To date, all high-voltage sensors, from conventional inductive transformers to modern optical voltage transducers, have one or more of the following traits in common: large size and weight, high-voltage electrodes in close proximity, expensive and potentially hazardous insulation, and capacitive voltage division. Combined with the use of small electro-optic field sensors, the quadrature method enables voltage sensor designs that are free of these traits and that are, therefore, particularly ideal for high-voltage applications. It also allows for a trade-off between the accuracy of the voltage measurement and the number of required electric field sensors. Numerical simulations demonstrate the effectiveness of this technique.

Accurate Voltage Measurement by the Quadrature Method

This paper introduces the quadrature method for measuring voltage using one or more electric field sensors. To date, all high-voltage sensors, from conventional inductive transformers to modern optical voltage transducers, have one or more of the following traits in common: large size and weight, high-voltage electrodes in close proximity, expensive and potentially hazardous insulation, and capacitive voltage division. Combined with the use of small electro-optic field sensors, the quadrature method enables voltage sensor designs that are free of these traits and that are, therefore, particularly ideal for high-voltage applications. It also allows for a trade-off between the accuracy of the voltage measurement and the number of required electric field sensors. Numerical simulations demonstrate the effectiveness of this technique.

Linearization of Chromatic Change in a Polychromatic Current Transformer

This paper introduces permittivity shielding. Permittivity shielding enables the measurement of voltage with very few electric field sensors. Voltage sensor designs using permittivity shielding can exploit existing optical sensor technology without the need for the expensive and potentially hazardous insulation found in many modem optical voltage transducers. Numerical simulations demonstrate that a voltage sensor consisting of 100 MΩ shielding and six electric field sensors, or less, mounted inside an "off-the-shelf" stand-off insulator can achieve Class 1 metering accuracies (< 0.3 % magnitude error and < 8 min phase error) even in the presence of strong stray field effects.