Fiber-optic sensing of electric field components

Optical high-voltage sensor based on fiber Bragg gratings and stacked piezoelectric actuators for a.c. measurements

In this paper, we present the design and fabrication of a compact, modular optical high-voltage sensor (OHVS) based on fiber Bragg gratings (FBG) for a.c. distribution and transmission lines. The proposed OHVS is composed by a stack of piezoelectric transducers that transfer mechanical strain to a sensing FBG. A prototype was tested in the laboratory and showed a maximum linearity error of less than 3% of full-scale range (FSR) for input voltages up to ${14\,\,{\rm kV}_{\rm rms}}$14kV_rms with a signal-to-noise ratio of 55 dB, allowing measurements with a resolution of less than 0.2% of FSR. Transient response of the developed OHVS was preliminarily investigated, and a response time of less than 1 ms was observed. The results obtained allow us to conclude that the developed OHVS may also be used for the detection of transient events.

Power-Frequency Electric Field Sensing Utilizing a Twin-FBG Fabry⁻Perot Interferometer and Polyimide Tubing with Space Charge as Field Sensing Element

A novel fiber-optic sensor based on the alternating electric field force actions on polyimide tubing with space charge for power-frequency electric field sensing is presented. In structure, the sensor consists of a lightweight fiber cantilever beam covered with a length of electrically charged polyimide tubing as the field sensing element. A twin-FBG based Fabry⁻Perot interferometer is embedded in this fiber beam to detect the beam vibrations excited by the force of power-frequency electric field to be sensed. Space charge in polyimide tubing is formed through a dielectric charging process. The basic concept, structure, fabrication and operation principle of the sensor are introduced with detailed theoretical analyses. The comprehensive experiments with two sensor prototypes are carried out, in which a sensor exhibits a high sensitivity of 173.65 μV/(V/m) with a minimal detectable field strength of 0.162 V/m, and another has a durability of continuous operation for over a year.

High-finesse Fabry-Perot electro-optic sensors with enhanced sensitivity and high spatial resolution

We present a high-finesse optical cavity containing a LiTaO(3) electro-optic crystal, devoted to free-space electric field characterization. Theoretical considerations will show that the modulation depth is directly related to the transversal components of the field to be measured, thus opening the way to vectorial mapping of the electric field using a single electro-optic crystal. Also, a discussion about noise and sensitivity will be given. As the latter increases with the effective cavity length, and bandwidth decreases, a trade-off is realized, allowing us to measure an electric field of 60 mV/m/ sqrt[Hz] in a 110 MHz bandwidth. Cavity dimensions are less than 8 mm(3), giving an inner-crystal transverse spatial resolution of 70 microm and allowing pigtailed systems to integrate.

Fiber-optic voltage sensor for SF6 gas-insulated high-voltage switchgear

We present an optical-fiber voltage sensor for 170-kV gas-insulated high-voltage switchgear. The sensor is based on the converse piezoelectric effect of quartz. The full voltage is applied to a cylinder-shaped quartz crystal. The resulting alternating piezoelectric deformation of the crystal is sensed by an elliptical-core dual-mode fiber, which is wound onto the circumferential crystal surface. The fiber is interrogated by low-coherence interferometry. We address the dielectric design of the sensor and verify its dielectric reliability under ac overvoltages and lightning impulse voltages. We then investigate the sensor performance, including accuracy, dynamic range, bandwidth, and temperature dependence.

Optical fiber sensor for electric field and electric charge using low-coherence, Fabry-Perot interferometry

An optical fiber sensor for electric field and electric charge, based on the deflection of a small cantilever, has been developed. When the sensor head is placed in an electric field, induced charging produces deflection of the cantilever, which is measured using low-coherence, Fabry-Perot interferometry. The sensor has been used to measure the electric field in the vicinity of a Van de Graaff generator, in the range 135-650 V/cm. The measured deflections are in good agreement with the predictions of a simple model equating the electrostatic and mechanical forces acting on the cantilever.

Fiber-optic sensing of voltages by line integration of the electric field

A fiber-optic sensor that is sensitive to the line integral of the electric field is presented. The sensor detects electric-potential differences by adding the scalar products of the local electric fields along the integration path times the path-segment vectors. This is achieved by exploiting symmetry properties of the converse piezoelectric effect. The sensor principle is experimentally demonstrated. Important performance parameters including integration accuracy, dynamic range, linearity, and bandwidth are examined.