Optical methods to measure electric parameters and transmit the information from high voltage circuits to ground potential are described and evaluated in the light of the specific requirements of high-voltage measurement applications. The history and physics of a variety of optoelectrical methods found suitable for electrical measurement applications are introduced. Existing optical devices for measuring alternating, direct, and impulse currents and voltages in high-voltage circuits are reviewed with emphasis on the operation and features of several selected methods. The use of these techniques in industrial systems, in research laboratory apparatus, and in reference standards laboratories is discussed.

Optical methods of electrical measurement at high voltage levels

The technology of the optical measurement of current is reviewed. Several fundamentallydifferent approaches are described. Implementations from a number of manufacturers are examinedso as to highlight the similarities and the differences. Experience with optical current transducers isreported. The question of interfacing to an optical current transducer is discussed. The specialproblems posed by calibration of this kind of instrument are reviewed.

Optical Current Transducers for Power Systems: A Review

A prerequisite for safe and stable operation of an electric power system is the accurate and reliable measurement of the system parameters, in particular, current and voltage. Conventionally, this has been achieved on High Voltage (H.V.) systems by expensive, bulky iron-core transformers and also by capacitor transformers. Both of them are increasingly coming under review (chapter 1) in modern power system due to their cost, safety implications for personnel and surrounding plant if failure occurs, installation time and indeed substation land requirements. Research effort into viable alternatives to instrument transformers has been ongoing for many years to reduce the cost and improve the safety and accuracy of this devices. In the last years, this research has accelerated due to the new requirements of the modern metering and protection systems based on electronic and microprocessor devices. This trend in the modern systems has allowed the development of novel transducers where the accuracy, the reliability and the safety has been significantly improved. The main alternative incorporate optic fibre viewed as the most realistic method of providing cheap and safe isolation between the chosen sensor at phase potential and earth. The sensor itself is, in the case of current measurement, based on the Faraday effect while in the case of the voltage measurement is generally a Pockels or Kerr effect device measuring a fraction of the actual phase voltage by employing a capacitive voltage divider. In parallel to the development of the optical alternative other different transducers have been studied based on the properties offer for new materials and technologies developed in the last years. A clear example of new emergent technologies is found in the piezoelectricity (chapter 2). In just over 100 years piezoelectricity has moved from a laboratory curiosity to big business. During this period, several technologies have been developed to utilise the piezoelectric effect. In turn, each of these technologies has become an essential component in many kinds of electronic products. The U.S. piezoelectric industry, good mirror for analyse the international technologic development, has gone through several boom and bust cycles. However, new applications are emerging for piezoelectricity because of the developments in piezoelectric ceramics and polymers. Even though piezoelectric quartz crystal still holds the largest market segment, several new piezoelectric ceramic and piezoelectric polymer materials are being developed that represent good, attractive market segments in terms of growth, competition, and investment. This thesis proposes an alternative for the measurement in High Voltage environments by using the piezoelectric technology. The thesis was initially concentrated in the alternative of the voltage measurement, but the successfully results in this field have open the way to propose alternatives for measuring current. Accordingly, the present thesis develops a novel instrument transformer based on the mechanical forces developed for the piezoelectric materials under the influence of an electric field. The transformer consists of an actuator piezoelectric column and a sensor piezoelectric column. The actuator column is connected to the a.c. High Voltage to be measured. This electrical voltage produces the generation of mechanical forces within the material. The forces can be measured by means of the piezoelectric sensor and convert it back into a low electrical signal which can drive an electronic protection or measuring system. The novel piezoelectric transformer herein treated is of wide application in electrical networks for measuring, providing both advantageous accuracy and large transformation ratio. Furthermore, It is expected to reduce the volume, weight and manufacturing cost of the traditional electromagnetic transformers.

Novel piezoelectric transducers for high voltage measurements

An overview of the development of instrumentation and measurement techniques at the National Research Council of Canada, based on current comparator technology, for calibration of nonconventional instrument transformers with nonstandard rated outputs, is presented. The instruments include: (1) a wide-dynamic-range transimpedance amplifier for operation of input currents from 1 A to 1000 A with means for modifying the in-phase and quadrature components of the output voltage (rated 10 V) within a +or-10% range; (2) a high-voltage high-current transconductance amplifier with output current ranges of 10 A, 100 A, and 1000 A; and (3) a voltage ratio standard also with means for modifying the in-phase and quadrature components of the output voltage (rated 100 V) within a +or-10% range. The current comparator technique is used to obtain accuracies of better than 20 parts per million in both magnitude and phase of the associated outputs of these instruments. >

The application of the current-comparator technique in instrumentation and measurement equipment for the calibration of non-conventional instrument transformers with non-standard rated outputs

Fig 5 (21,22,23); with by separate current sensor means (27,29,31,49,51,53) for generating separate polarized light outputs [Fig. 6 (69)] representative of voltage and current passing through the conductor, electronic means [35,37,39)] for receiving and transforming the voltage and current outputs into power, voltage, and current signals.

Metering system for measuring parameters of high ac electric energy flowing in an electric conductor

A method is described for testing precision current transformers, particularly devices with very high values of rated primary current and rated secondary currents up to 200 A. It makes use of the well-known differential method (Arnold, Hohle), substituting, however, the common resistor with an electronic operational amplifier, thus yielding an almost negligible resistance and a very high sensitivity of 0.01 ppm. Results of ratio error measurements are reported at values of primary currents between 500 and 100 000 A.

Determination of Current Transformer Errors at Primary Currents up to 100 000 A

An intercomparison of the ratio errors of the national power frequency current-ratio standards of the National Research Council of Canada and the Physikalisch-Technische Bundesanstalt of Germany has been carried out by means of transfer standard current transformers at ratios of 60 000 A : 5 A, 50 000 A : 5 A, 40 000 A : 5 A. Typical agreement between calibrations at both laboratories is of the order of 0.5 to 1.5 ppm. Details of the transfer standards are given.

An International Comparison of 50-60-Hz Current-Ratio Standards at Currents up to 60000 A

A new method has been developed for measuring the power on high-voltage lines. It involves determining the power directly on the high-voltage line and transmitting the measured values to the ground potential side by the aid of infrared light pulses. Two electromechanical counters at ground side, one for each direction of energy flow, record the transported electrical energy. The measuring error of the device is of the order of 0.2 percent. The small number of active electronic components should result in satisfactory reliability.

Optoelectronic Electricity Meter for High-Voltage Lines

Improvements in the accuracy of determining standard voltage transformer errors by the utilization of specially developed amplifiers are described. Results of recently evaluated measurements in the fundamental parallel-series step-up method of the Physikalisch-Technische Bundesanstalt (PTB) are reported. The overall limit of uncertainty in the calibration of high voltage ratios has been improved by a factor of ten as compared with previous results at power frequencies.

Determination of Voltage Transformer Errors by Means of a Parallel-Series Step-Up Method

A method is proposed for the self-calibration of a compensated current comparator. At first, with a unity ratio (5A:5A), an interrelation is established between the errors and the remaining magnetic fluxes, both in the compensated comparator configuration and in the current transformer configuration. These errors can be measured directly and the fluxes can be observed by means of a detection winding voltage. For the nonunity ratios (>5A:5A), the knowledge about this interrelation is incorporated to determine the errors with a measurement uncertainty of less than 5 × 10-7.

Andreas Braun

Papers

Determination of Current Transformer Errors at Primary Currents up to 100 000 A

An International Comparison of 50-60-Hz Current-Ratio Standards at Currents up to 60000 A

Optoelectronic Electricity Meter for High-Voltage Lines

Determination of Voltage Transformer Errors by Means of a Parallel-Series Step-Up Method

A New Method for the Calibration of a National Current Ratio Standard