Application Of Current Transformers Research Articles

C37.110 guide for the application of current transformers used for protective relaying purposes

Relay engineers have had to rely on many sources to compile information on current transformer application. Typically, they have drawn on relay application and transformer textbooks, manufacturer publications, and standards. Recognizing the need for a comprehensive one source document, the power system relaying committee has produced the C37.110-1996 guide for the application of current transformers used for protective relay purposes.

Development of optical current transformers and application to fault location systems for substations

The authors report on an optical current transformer (CT) based on the principle of the Faraday effect. The information measured by the optical CT is transmitted to the ground side through optical fibers contained in an insulator. An application of the optical CT, a new fault location system, is described.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Design Considerations in the Application of Current Transformers for Protective Relaying Purposes

A procedure is presented which enables one to design a current transformer (CT) to meet arbitrary specifications on the required number of cycles of accurate secondary current following a system short circuit which results in a fully offset short circuit current waveform. The procedure enables one to relate the resulting current transformer design to its physical characteristics and to its accuracy classification. The procedure also enables one to account for an arbitrary amount of remanent flux in the current transformer resulting from previous short circuit currents.

Transient Characteristics or Current Transformers During Faults-II

The range of application of current transformers in bus differential protective systems is limited by saturation in the transformer cores under fault conditions, which may sometimes result in improper relay operations. It is shown that the addition of impedance in the relay circuit will reduce the relay current under fault conditions so as to increase the range of applications for which standard current transformers may be used.

Instrument transformers

The paper deals in a general way with the whole field of instrument transformer work, and in a more extensive manner with certain developmets and views for which the authors are more particularly responsible. Among these are the following:—Current Transformers.— (i) Short-circuit limitations are described, the conclusion reached being that reduction of ampere-turns is the only real means of increasing the short-circuit capacity.(ii). Accurate transformers for metering.—The conclusions reached are that high accuracy can and should be obtained without recourse to a large number of ampereturns, and that single-turn or bar-primary transformers with compensating windings should be used on all heavy-duty circuits.(iii). The design and application of current transformers for Protective-gear systems.— The conclusions reached are that current transformers are not necessarily the limiting features in the performance of protective gear; but that transformers for protective systems can and should be designed to be “ideal transformers” as far as the requirements of the protective systems are concerned.Voltage Transformers.—(i) General features are described, the conclusions being that voltage transformers on low voltage circuits are a satisfactory proposition subject to suitable provision of protective fuses and resistors.(ii) On high-voltage circuits means of eliminating voltage transformers are described, by utilizing an existing power transformer, and connecting the voltage transformer to the low-votltage side and compensating for regulation of the power transformer.Special-purpose Instrument Transformers.— Design and application of current and voltage transformers with varying ratio characteristics are described, especially in regard to voltage or current-change amplifiers for the more sensitive operation of relays, voltage regulators, etc.

Discussion on “the application of current transformers to three-phase circuit,” “cost of transformer losses.” Chicago, June 30, 1911. (see proceedings for June, 1911)

Discussion on “the application of current transformers to three-phase circuit,” “cost of transformer losses.” Chicago, June 30, 1911. (see proceedings for June, 1911)

The Application of Current Transformers to Three-Phase Circuits

The performance of current transformers when their secondaries supply simple series loads, and the methods of test for determining the errors introduced by the transformer when used with known secondary connected loads have been considered in previous papers. The secondaries of two or three current transformers whose primaries are supplied from the lines of a three-phase circuit, are, however, frequently interconnected to save room, simplify wiring, and diminish cost. In this case the equivalent load carried by the current transformer secondary can not be determined in the simple manner that applies to an ordinary series connection, since the devices used in a series circuit may constitute a very different equivalent load when used in an interconnected circuit. An understanding of the equivalent load carried by each transformer is necessary in order to determine suitable limits of load from results of tests made in the ordinary manner. The term “equivalent load” is here used to indicate the load carried by the secondary of a current transformer where this may differ from that obtained by combining in series the resistances and reactances of the devices used.

The application of current transformers to three-phase circuits

The performance of current transformers when their secondaries supply simple series loads, and the methods of test for determining the errors introduced by the transformer when used with known secondary connected loads have been considered in previous papers. The secondaries of two or three current transformers whose primaries are supplied from the lines of a three-phase circuit, are, however, frequently interconnected to save room, simplify wiring, and diminish cost. In this case the equivalent load carried by the current transformer secondary can not be determined in the simple manner that applies to an ordinary series connection, since the devices used in a series circuit may constitute a very different equivalent load when used in an interconnected circuit. An understanding of the equivalent load carried by each transformer is necessary in order to determine suitable limits of load from results of tests made in the ordinary manner. The term “equivalent load” is here used to indicate the load carried by the secondary of a current transformer where this may differ from that obtained by combining in series the resistances and reactances of the devices used.

Discussion on ``The Application of Current Transformers to Three-Phase Circuits,'' ``Cost of Transformer Losses.'' Chicago, June 30, 1911

Discussion on ``The Application of Current Transformers to Three-Phase Circuits,'' ``Cost of Transformer Losses.'' Chicago, June 30, 1911