http://robots.iopscience.iop.org/article/10.1088/1757-899X/177/1/012099/pdf

Studies in electromagnetic compatibility of optical and digital current and voltage transformers

Innovative development of electric power systems is aimed at creating active-adaptive networks. Control of active-adaptive networks is based on usage of primary data measured at voltage and current transformers. In particular, the voltage transformers can be a source of information for devices determining fault location. The problem of fault location (FL) has always been and remains relevant because its solution may improve reliability of power supply. Overhead and cable high voltage power lines are most often-damageable elements of the electric power system. Power line cut-off is always accompanied by power undersupply or reduction of its reliability and quality. The paper investigates possibility of using transient voltage parameters obtained by digital voltage transformers for the FL on the cable lines.

Study of possibility of digital voltage transformers usage in fault location determination

Transmission lines are the most extended and least reliable elements of the electric power system. Failure of the overhead power line is accompanied by either under-discharge of electricity, or a decrease in reliability, quality and cost of power supply. Improving the accuracy of automatic devices of distant fault localization (DFL), as well as the development of new algorithms and devices of DFL, including methods of self-removing short circuits location, is an urgent task. In Ivanovo State Power Engineering University (ISPU) developed one-side and two-side DFL methods using digital current transformers and voltage transformers (DCT and DVT). The article is dedicated to the results of the study of two-side synchronized DFL method, including the study of the prototype DFL device as part of a multifunctional system.

Research of the Algorithm and the Prototype Device for Fault Location Based on Synchronized Two-Side Measurement

At present, active work is under way to develop and introduce digital substations based on modern micro-processing control and relay modules with digital current and voltage instrument (optical) transformers [1]–[3]. Leading relay protection manufacturers have already successfully developed and launched production of microprocessor relay protection modules adapted to work with digital flows, using process buses according to Standard 61850-9-2LE. A somewhat more complicated task is the implementation of current and voltage instrument transformers. The simplest form is to use standard current and voltage transformers provided with measuring merging devices (Stand Alone Merging Units). This approach, however, does not fully resolve the problems of standard current and voltage transformers, such as core saturation. Because of their high price, the use of optical transformers is warranted only at voltages exceeding 110–220 kV. Using digital (unconventional) transformers opens the possibility of operating them in a wide voltage range, from 6 to 220 kV.

Specific Features of Digital Current and Voltage Transformers for Relay Protection, Automation and Commercial Electric Power Metering

The high-voltage power lines are quite often damaged parts of the energy system. Line outage is always accompanied by undersupply of energy and decrease of reliability, cost, and quality of electric supply. That is why one of the important tasks of line maintenance is quick looking for location of the damage and organization of the rehabilitation. The main part of this work includes development and research of the methods and algorithms for fault location based on one-sided measurement and the ways to increase their accuracy. This type of measurement uses signals from digital current and voltage transformers as input. The influence of the basic distorting factors on the accuracy of the fault location determination methods is also considered.

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Increase of Accuracy of the Fault Location Methods for Overhead Electrical Power Lines

The article describes the possibilities of using the non-traditional current and voltage sensors to solve the problem of fault location in terms of digital transformers developed at the Ivanovo State Power Engineering University (ISPEU). Frequency and metrological characteristics of current and voltage sensors are given.

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Using of non-traditional current and voltage sensors for the fault location

Most of the works devoted to the study of measuring current and voltage transformers are focused on defining the characteristics of transformers in steady-state conditions to determine whether the transformers satisfy the metrological requirements. Such studies are often carried out using a chain of equivalent circuits or on the basis of field calculation methods. Field calculations methods definitely allow more precisely measuring the leakage field and the distribution of magnetic flux in the magnetic circuit. The study of transformers in dynamic modes is also of much interest. Nonlinearity of the core magnetization of measuring transformers leads to the need to create mathematical models that contain not only a model of the transformer itself, but also the model of circuits connected to it. In particular, of practical interest is the study of the stability of the voltage transformer to ferroresonance phenomena, when the transformer resonates with elements of the primary network connected to it. Thus, it is necessary to develop a mathematical tool allowing to create field models of instrument transformers connected to the primary and secondary circuits allow modeling not only steady modes, but transients ones as well. Problem solving in this formulation became possible after emerging of powerful computers and development of software packages capable to integrate for solving the problems.

Modeling of measuring current and voltage transformers in dynamic modes

The article examines the methods of calculating capacitive currents in a measuring transformer based on a resistive voltage divider. The developed methods may be used to optimize the design of resistive dividers.

Analysing the Impact of Electrical Displacement and Leakage Currents in Transformer Insulation on Voltage Measurement Accuracy

Power facilities are now implementing the concept of smart grid and its essential elements – high-voltage digital current and voltage transformers. However, the implementation of digital technologies is slowed down by the lack of operation experience and reliability indicators. One of the main causes of high-voltage equipment failures is insulation damage. The most informative parameters determined by insulation evaluation are partial discharge characteristics. There are rated values of these characteristics for rotating electrical machines and power transformers measured by external equipment. But the existing method of partial discharge analysis cannot be applied to digital current and voltage transformers as there are no criteria for tripping of the innovative equipment with comprehensive insulation. All this urges us to study the possibility to determine experimentally the characteristics of partial discharges in the insulation of digital current and voltage transformers by using embedded inductive sensors in order to develop a method for condition monitoring of digital current and voltage transformers and improving of their reliability. In this work, we have used a model of digital current and voltage transformers, a high-voltage test unit, a digital multi-input oscciloscope and inductive sensors. The experiment includes: detecting partial discharges in the model of digital current and voltage transformers by the external bridge connection, recording the voltage at which partial discharges occur in the simulated fault area, measuring the corresponding value of the apparent charge of the partial discharge, detecting partial discharges in the model of digital current and voltage transformers by a differential method with the help of embedded inductive sensors. The characteristics of partial discharges in the simulated fault area have been experimentally determined on a model of digital current and voltage transformers. The pulse voltage on the embedded inductive sensor corresponding to the apparent charge of 80 pC was equal to 600 mV at the test voltage of 2,7 kV. Embedded inductive sensors allow implementing the method of insulation condition monitoring for digital current and voltage transformers in accordance with the partial discharge characteristics both at the stages of production and operation extending the potential of the electronic (microprocessor) module and increasing the reliability of digital current and voltage transformers.

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Experimental determination of partial discharges in a model of a digital instrument transformer by differential method

Vladimir Lebedev1, Arkadiy Makarov2 1Department of Electric power systems automatic control, 2Department of electrotechnics foundations Ivanovo State Power University Ivanovo, Russia vd_lebedev@mail.ru, makarov1955@list.ru Andrey Yablokov, Galina Filatova Department of Electric power systems automatic control Ivanovo State Power University Ivanovo, Russia AndrewYablokov@yandex.ru, filatova2505@gmail.ru

Andrey Yablokov

Papers

Using of non-traditional current and voltage sensors for the fault location

Modeling of measuring current and voltage transformers in dynamic modes

Analysing the Impact of Electrical Displacement and Leakage Currents in Transformer Insulation on Voltage Measurement Accuracy

Experimental determination of partial discharges in a model of a digital instrument transformer by differential method

Modeling of magnetization reversal processes in magnetic circuits of measuring transformers