This paper analyzes the response of optical fiber current sensors that are subjected to high electric fields, such as fields encountered in gas-insulated systems. This paper shows that through the electrooptic (EO) Kerr effect, these fields can cause harmonic distortion of the measured ac current waveform. This harmonic distortion was confirmed experimentally. Also, this paper shows that it is possible to simultaneously measure both current and voltage waveforms and the phase between them using this effect. To minimize the electrooptic Kerr effect, optical fiber current sensors must be screened from high-electric fields.

Optical fiber current sensors in high electric field environments

An optical fiber sensor is presented that allows current and voltage to be measured simultaneously by use of only one block of bismuth germanate crystal. The polarized light from the sensing crystal is split into two light beams: One beam is utilized for current measurement based on the Faraday effect, and the other one is utilized for voltage measurement based on the Pockels effect. Compared with the existing optical sensors that can measure current and voltage simultaneously, this sensor is simple and inexpensive and allows measurement of electric power. The simultaneous measurements of ac electric current from 0.05 to 10 A, voltage from 1 to 235 V, and power from 2 to 1000 W have been achieved with good linear-response characteristics. The input characteristics and measurement uncertainties that are due to the nonlinear error of the sensing system are also discussed.

Simultaneous measurement of current and voltage by use of one bismuth germanate crystal.

A high-voltage sensor was developed by driving optical fibre Bragg gratings, mechanically fixed along the radial direction, with a conventional piezoelectric disc. A wavelength shift modulation is obtained as a result of the converse piezoelectric effect. The measured output signal is linear. The voltage upper limit depends on the type and thickness of the piezoceramic. A sensor built with a disc of piezoelectric PZT-4 type, 6.33 mm thick, has a dynamic range of 6.33 kVrms, a sensitivity of ~0.108 mVp-p kV-1rms, and a resolution of ~0.15 kVrms, at 60 Hz. Changing the piezoelectric dimensions may enhance the sensitivity and resolution of the high-voltage sensor.

https://iopscience.iop.org/article/10.1088/0957-0233/10/9/303/pdf

Piezoelectric-modulated optical fibre Bragg grating high-voltage sensor

An optical electric-power sensor is presented that allows active and apparent powers to be measured simultaneously using one block of bismuth germanate (Bi/sub 4/Ge/sub 3/O/sub 12/) crystal as sensing element, which exhibits both the Faraday effect and the Pockels effect. It is based on the fact that the polarization-related intensity of the light wave passing through the crystal can be modulated by the product signal of applied electric and magnetic fields. When load current and voltage are simultaneously applied to the sensing crystal, the instantaneous electric power signal can be directly obtained from the intensity-modulated light wave. The simultaneous measurements of active power and apparent power, as well as the direction of power flow, have been carried out in experiments. Measurement uncertainty is theoretically analyzed. The potential applications of the proposed optical electric-power sensor are also discussed.

Optical electric-power sensor by use of one bismuth germanate crystal

An optical sensor is proposed which can perform the simultaneous measurements of voltage and current through single light path. This novel optical sensor makes use of an electrically switchable quarter waveplate to produce an alternating polarized light whose state of polarization alternately changes between linear and circular polarizations. By the use of the alternately polarized light and polarization multiplexing, we can simultaneously measure ac voltage and ac current through single light path. In addition, the output voltage and current sensing signals are free from the fluctuation of light intensity and have an enhanced immunity to electromagnetic interference due to the application of square wave modulation and lock-in amplification. The ac voltage and ac current with industrial frequency have been experimentally measured with good linearity within the ranges of 0.2–235 V and 0.05–10 A.

An optical voltage and current sensor with electrically switchable quarter waveplate

A sensor employing a single monomode low-birefringence fiber, excited with a 632.8-nm He–Ne laser, has been developed for the simultaneous measurement of current and voltage in an energy system. The piezoelectric effect for the voltage and the magnetic stress for the current are utilized. The current and voltage signals are separated at the detector end by suitable self-tracking tuned filters. Experimental results from a laboratory model demonstrate the feasibility of the sensor for field application in high-voltage systems.

N. Rajkumar

Papers

Fiber sensor for the simultaneous measurement of current and voltage in a high-voltage system