Combined Instrument Transformer Research Articles

Proposal of Testing Procedure for Resonance and Ferroresonance Inception Possibility in Instrument Transformers

This paper deals with the possibility of ferroresonance occurence in the interaction between circuit breakers and inductive instrument transformers. Existing standards lack guidance on testing for ferroresonant behaviour. The paper proposes a standardized testing procedure and presents measurements on a full-scale system. EMTP simulations complement the measurements for a broader network topology analysis, i.e. circuit breaker capacitance combinations. EMTP simulations are validated for a 170 kV voltage transformer and a combined instrument transformer, showing accuracy within 10%. The paper also extends the EMTP modelling application to a 420 kV voltage power transformer during design phase, ensuring it doesn't experience ferroresonance. This study offers a practical approach for testing and simulating ferroresonance in inductive instrument transformers, contributing to the safe operation of power networks.

Development of Combined Instrument Transformer for Gas-Insulated Switchgears

Accurate measurement of current and voltage information is essential to the safe reliable operation of railway substations. This paper dealt with a combined instrument transformer (CIT) built in a spacer for the purpose of miniaturization and eco-friendliness of a GIS, rated 72.5 kV and 2,000 A. A D-dot sensor and a Rogowski current sensor were applied to voltage and current measurement, respectively, to secure the insulation of the CIT in high-voltage and high-current conditions. As a result of an evaluation based on IEC 60044-7 and IEC 60044-8, the performance of the prototype CIT was found to sufficiently satisfy Class 0.5. When the CIT proposed in this paper was applied to a GIS of rated 72.5 kV, it was possible to reduce the size by 33% in length, 11% in height and 90% in weight per bay of the GIS compared to conventional iron-core transformers. In addition, since the amount of SF6 will be reduced by 15% in terms of volume, it is expected that this method can be used for the digitization, miniaturization and eco-friendliness of railway substations.

Using the next generation combined digital transformers

The paper considers and analyzes the use of new generation combined digital instrument transformers (DIT) with an optoelectronic conversion unit and a combining module or a stand-alone combining module, an external synchronization source or an internal clock generator and digital interfaces.

Improvement of the Insulation System of Unconventional Combined Instrument Transformer Using 3-D Electric-Field Analysis

This paper presents the new printed-circuit board (PCB) technology medium voltage combined instrument transformer. The capacitors of the voltage transformer and coils of the current-to-voltage transducers are designed and manufactured using PCB technology. The design of the insulation system of the combined transformer was carried out using electric field analysis. The electric field distributions, computed by applying the 3-D finite-element numerical method, are presented. The results for several different applications were compared with tests of real-life models.

Digital combined instrument transformer for automated electric power supply control systems of mining companies

The present paper discusses ways to solve the problem of enhancing operating efficiency of automated electric power supply control systems of mining companies. According to the authors, one of the ways to solve this problem is intellectualization of the electric power supply control system equipment. To enhance efficiency of electric power supply control and electricity metering, it is proposed to use specially designed digital combined instrument current and voltage transformers. This equipment conforms to IEC 61850 international standard and is adapted for integration into the digital substation structure. Tests were performed to check conformity of an experimental prototype of the digital combined instrument current and voltage transformer with IEC 61850 standard. The test results have shown that the considered equipment meets the requirements of the standard.

Application of optimization methods for improved electrical metrology

<p class="Abstract"><span lang="EN-US">In electrical quantities metrology numerous examples of stochastic processes exist and a need for optimal solutions is posed. Here stochastic genetic algorithm optimization is used for solving two typical metrological problems: 1) minimization of the metrological parameters (final accuracy) in the design process of instruments and 2) predicting metrological reference standard’s time-drift, i.e. re-calibration interval. The first case is the optimal metrological design of a combined instrument transformer and the second case is the analysis of resistance standard time-drift.</span></p>

Electric stress grading on bushings of combined instrument transformers using high permittivity polymeric composites

Bushings are used in high voltage equipment to bring the high voltage conductors through a grounded structure. Due to the high electric field around the area next to the grounded structure it is required to keep the intensity of the field as low as possible in order to avoid surface discharges. In this paper, it is discussed how high permittivity composites prepared with doped and functionalized barium titanate powder can be used to control the electric stress on the surface of a polymeric bushing which is used in a combined instrument transformer with two central conductors, one at high voltage and the other at ground potential. First, it is described how the properties of the filler were improved and then it is shown how the prepared polymer/ceramic composite can modify the voltage profile along the surface of a prepared sample. By using three dimensional finite element simulations the performance of the composite bushing is compared with the stress grading obtained in a ceramic bushing with capacitive grading. According to the results, by using composite materials of increased permittivity, the electric stress on the surface of the bushing can be reduced to acceptable values without need of conductive foils.

Optimization of the magnetic circuits of the column voltage transformers using the field‐circuit method

PurposeThe purpose of this paper is to consider a constructional solution of the combined instrument transformer: constructed so that the voltage part is a column transformer, which means that the magnetic circuit of it is open and situated into a composite insulator. The aim of this research was to achieve optimal configuration of open magnetic circuit of the column voltage transformer.Design/methodology/approachThe authors made analyses of electromagnetic field distribution and computed the voltage error and phase displacement for many different cases of magnetic circuits of the column voltage transformers. The analyses of the electromagnetic field distribution and computations were carried out using the 3D field‐circuit method based on the finite‐element numerical method. The results were compared with tests of a real‐life model.FindingsThe result of research is the selection of the best constructional version of the column voltage transformer; the research also gives some guidelines for design and manufacture of this construction of combined transformers.Originality/valueThe paper is meant for constructors of instrument transformers and presents results of research into new constructional solutions of combined transformer.

Electromagnetic transient analysis of combined instrument transformer with embedded 3D-finite element

In the paper a thorough electromagnetic transient analysis of a combined instrument transformer will be given. A CAD procedure for transformer optimal design by using a genetic algorithm original program will be accomplished. The transient analysis will be fulfilled for the initial and opti mal design as well as for a realised transformer prototype. The transient analysis will be non-linear, since the results from previou s FEM-3D electromagnetic field study as well as the non-linea rity of the two transformer measurement cores will be incorporated.

An innovative combined electronic instrument transformer applied in high voltage lines

For better performances, electronic instrument transformers are used to replace conventional electro-magnetic inductive current or potential transformers based on ferrous cores and windings to measure heavy current and high voltage in power system. But unpredictable stability, high price and unsatisfactory life hold back their industrializations. Employing the simple but reliable insulation structure of conventional transformer and the unconventional sensing methods of electronic transformers at the same time, an innovative combined electronic instrument transformer is presented in this paper. Performances of the prototype are estimated through relative tests, and the novel design has low price, high accuracy, satisfactory stability, very wide frequency response and long operation life, and therefore is well adapted to any voltage level up to 750 kV.

Computer aided techniques for estimation and reduction of electromagnetic measurement devices uncertainties

At non-linear electromagnetic measurement systems, the finite element method is the most convenient tool for the system analysis and measurement uncertainties budget estimation. Two non-linear devices will be analyzed by finite element method: electrical steel sheet testing device-Epstein frame and combined current-voltage instrument transformer. The Epstein frame must comply with the standard IEC 60404-2:1996+A1:2008, and the combined instrument transformer with the IEC 60044-3: 2002. The Epstein frame forms an unloaded transformer and the analytical transformer theory introduces some approximations. The main approximation is introduced by the standard IEC 60404-2 (through the presumption of constant, invariant to the specimen grade effective magnetic path length). The finite element method results will enable an Epstein frame and combined current-voltage instrument transformer prototype design (by using a computer program based on genetic algorithm with minimal uncertainty budget as goal function) with reduced measurement uncertainty, which will be experimentally verified in the Metrological Laboratory for Electromagnetic Quantities at the Faculty of Electrical Engineering and Information Technologies-Skopje.

Influence of the interaction of voltage and current parts of a combined instrument transformer on its measurement properties

A method of avoidance of mutual influences in a designed combined instrument transformer is presented. The combined instrument transformer comprises a current and voltage transformer in the same housing. Because of a low rated frequency, the main influences are: the current transformer on the voltage transformer through the magnetic field and inversely through the electric field. The mutual reactance and capacitance were determined based on 3D field distributions obtained by the numerical field method.

The use of 3-D electric field analysis and the analytical approach for improvement of a combined instrument transformer insulation system

In this paper, the algorithm of design for an insulation system of a high-voltage combined instrument transformer using the field method is considered. The commercial software OPERA 3D was used to compute field distribution and the author's software SHIELDS was used to optimize the number, dimensions, and position of each electrostatic control shield in the insulation of the voltage and current parts. The programs interact with each other. This work presents the results of the use of numerical methods in the designing process.

Application of 3D field analysis for modelling the electric field distribution in ceramic insulator of HV combined instrument transformer

The general analysis of the electric field in the whole ceramic insulator of the combined transformer is presented in the paper. The author has done the computer model very closely to a very geometrically complicated object. The field analysis answered the questions of the maximum value and distribution of electric field strength in the whole object, composed of different insulating materials, and is necessary in designing high voltage devices.