Recently, optical voltage and current measuring methods based on a principle different from that of the existing apparatus have been developed. As the most promising method among them, a voltage measuring method which uses an electrooptic effect called the Pockels effect and a current measuring method which uses a magnetooptic effect called the Faraday effect have been proposed. The authors have developed an optical voltage measuring system based on the electrooptic effect in bismuth germanium oxide Bi4Ge3O12 and a current measuring system based on the magnetooptic effect of borosilicate crown glass for the purpose of utilization in electric power systems. As a result of the development, high accurate voltage and current measuring systems such as non linearity error less than ±0.4% and temperature stability less than ±1.0% were obtained. Furthermore, short-circuit current was measured with the current measuring system, and an accuracy within 0 to -4% in the range of 30 kApeak to 150 kApeak was obtained. When the measuring systems were mounted on the model of 70 kV class gas insulated switchgears, it was verified that the measuring systems had satisfactory linearity and temperature stability.

Optical Voltage and Current Measuring System for Electric Power Systems

Drift compensation is provided for the output signal of a magneto-optic current measuring system using a current sensor with a magneto optic element wherein current through a conductor which is proximate to the magneto optic element is measured; the compensation is achieved through the use of two light emitting sources, each at a different frequency, to generate two alternating optical input signals to the current sensor to establish a signal refer­ence in order to compensate for signal drift caused by variable attenuator characteristics of the optical elements in the system.

Drift compensation technique for a magneto-optic current sensor

By using Faraday and Pockels' effects of a Bi 12 GeO 20 (BGO) single crystal, two kinds of fiber-optic sensors for electric current and voltage were tentatively fabricated. The optimum design of these sensors and their performances were investigated. It was verified that the BGO crystal is very available for either of the current and voltage sensors with regard to their sensitivity and stability. As for the experimental results, the minimum detectable magnetic field of 10-2Oe and the temperature dependence within ±2 percent in the temperature range of -25 to 85°C was obtained for the current sensor, while for the voltage sensor the sensitivity of 10-3V and the temperature dependence within ± 0.5 percent was in the same temperature range.

Fiber-optic current and voltage sensors using a Bi 12 GeO 20 single crystal

The dielectric tensor of an anisotropic crystal with multiple perturbations is presented to include the effects of multiple perturbations. To study electromagnetic wave propagation in anisotropic crystals subject to various influences the perturbed dielectric tensor is substituted into Maxwell’s equation. Then, a 2 × 2 transmission matrix formalism, based on a normal-mode approach, is extended to anisotropic crystals possessing multiple birefringences to develop compensation schemes for ac optical sensors employing the crystal. It is shown that a new compensation method utilizing two analyzers can eliminate the effects of both unwanted linear birefringences and unwanted circular birefringences on the stability of the ac bulk polarimetric optical sensor. The conditions (here referred to as the quenching condition) in which the compensation method becomes important are also derived for both the voltage (or electric field) and current (or magnetic field) sensors.

New compensation method for bulk optical sensors with multiple birefringences

Symmetry properties of the converse piezoelectric effect are investigated for their use in fiber-optic sensing of individual electric field components. Three basic sensor designs are analyzed in detail. Suitable sensor materials are identified and relevant material properties are discussed. The sensitivity of the sensor to a specified field component is experimentally verified. A dynamic range of approximately 5 orders of magnitude is found for frequencies in the kilohertz range. The sensor concept is compared to electrooptic sensors.

Fiber-optic sensing of electric field components

A practical fiber optic measuring system for heavy electric current was developed by using the magnetooptic (Faraday) material. In order to obtain better SNR and smaller temperature dependence, the most suitable combination of the light source and Faraday material was experimentally and theoretically determined. Consequently, it was emphasized that an LED and diamagnetic SF-6 flint glass gave the superiority of overall system capability over LD's and para- or ferromagnetics. A novel type of fiber optic current sensor was constructed of the Faraday rotator of SF-6 flint glass with two thin-film polarizers. By using this sensor and a high radiance LED, high accuracy within ±0.5 percent was obtained for magnetic field between 20 and 500 Oe, and at temperatures from -25°C up to 80°C.

Fiber optic measuring system for electric current by using a magnetooptic sensor

A practical fiber optic measuring system for heavy electric current was developed by using the magnetooptic (Faraday) material. In order to obtain better SNR and smaller temperature dependence, the most suitable combination of the light source and Faraday material was experimentally and theoretically determined. Consequently, it was emphasized that an LED and magnetic SF-6 flint glass gave the superiority of overall system capability over LD's and para- or ferro-magnetic. A novel type of fiber optic current sensor was constructed of the Faraday rotator of SF-6 flint glass with two thin-film polarizers. By using this sensor and a high radiance LED, high accuracy within +-0.5 percent was obtained for magnetic field between 20 and 500 Oe, and at temperatures from -25°C up to 80°C.

Y. Ida

Papers

Fiber-optic current and voltage sensors using a Bi 12 GeO 20 single crystal

Fiber optic measuring system for electric current by using a magnetooptic sensor

Fiber Optic Measuring System for Electric Current by Using a Magnetooptic Sensor