Electricity: measuring and testing – Measuring – testing – or sensing electricity – per se – With coupling means
Reexamination Certificate
2000-02-03
2001-11-06
Metjahic, Safet (Department: 2858)
Electricity: measuring and testing
Measuring, testing, or sensing electricity, per se
With coupling means
Reexamination Certificate
active
06313623
ABSTRACT:
BACKGROUND
Rogowski coils measure magnetic fields. Early Rogowski coils could not be used for current measurements since the coil output voltage and power were not sufficient to drive measuring equipment. With the introduction of microprocessor-based protection and measurement equipment, Rogowski coils have become more suitable for use in such equipment. Prior to the advent of microprocessor-based equipment, current transformers (CTs) had been used for protection and measurement applications in part because of their ability to produce the high power output needed by electromechanical equipment.
SUMMARY
In one general aspect, a Rogowski coil measures a current in a conductor and includes first and second loops electrically connected in series with each other. The first loop is wound with a substantially constant winding density in a first direction around a first core that has a substantially constant cross section. The second loop is wound with a substantially constant winding density in a second direction around a second core that has a substantially constant cross section. The directions of the loops are substantially perpendicular to the normal of the core cross sections.
Implementations may include one or more of the following features. For example, a voltage induced in a Rogowski coil placed around an electrical conductor may be measured across the first and second loops of the coil.
The first loop may be wound by tracing the first loop on a first printed circuit board and the second loop may be wound by tracing the second loop on a second printed circuit board. The first and second loops may make up a first set of loops, and the Rogowski coil may further include one or more second sets of loops that are identical in design to the first set of loops. The one or more second sets of loops may be traced on a respective set of printed circuit boards and may be connected in series to the first and second loops of the first set of loops.
The first and second cores may be non-magnetic.
The first and second loops may be variable in shape. The first loop may be wound by tracing the first loop on a first variably-shaped core on a first printed circuit board, and the second loop may be wound by tracing the second loop on a second variably-shaped core on a second printed circuit board. Alternatively, the first and second loops may be traced on a variably-shaped core on a single printed circuit board. A variably-shaped core includes two or more straight sections coupled by two or more rounded sections. A rounded section may span between around 0° to 360° of a complete circle.
For example, the first and second loops may be rectangular in shape. The first loop may be wound by tracing the first loop on a first rectangular core on a first printed circuit board, and the second loop may be wound by tracing the second loop on a second rectangular core on a second printed circuit board. Alternatively, the first and second loops may be traced on a single printed circuit board. A rectangular core includes four straight sections coupled by four rounded sections. A rounded section may span about 90° of a complete circle.
Similarly, the first and second loops may be elliptical in shape. The first loop may be wound by tracing the first loop on a first elliptical core on a first printed circuit board, and the second loop may be wound by tracing the second loop on a second elliptical core on a second printed circuit board. Likewise, the first and second loops may be traced on an elliptical core on a single printed circuit board. An elliptical core includes two straight sections coupled by two rounded sections. A rounded section may span about 180° of a complete circle.
Additionally, the first and second loops may be triangular in shape. The first loop may be wound by tracing the first loop on a first triangular core on a first printed circuit board, and the second loop may be wound by tracing the second loop on a second triangular core on a second printed circuit board. Likewise, the first and second loops may be traced on a triangular core on a single printed circuit board. A triangular core includes three straight sections coupled by three rounded sections. A rounded section may span between around 0° to 180° of a complete circle.
The first and second loops may be traced on a variably-shaped core on a single printed circuit board, the variably-shaped core including two or more straight sections coupled by two or more magnetically shielded joints. Alternatively, the first loop may be traced on a first variably-shaped core on a first printed circuit board, and the second loop may be traced on a second variably-shaped core on a second printed circuit board. The first and second variably-shaped cores include two or more straight sections coupled by two or more magnetically shielded joints.
The first and second loops may be a first set of loops, and the Rogowski coil may further include one or more additional sets of loops. Each additional set of loops is designed identically to the first set of loops. Each set of loops may measure a current through an electrical conductor that is placed within the set of loops. The Rogowski coil may be used to measure phase currents in a multi-phase electrical circuit, where each phase current is determined by measurement across a set of loops. This design is referred to as an integrated Rogowski coil system.
In the integrated Rogowski coil system, the first loop in a set of loops may be wound by tracing the first loop on a first printed circuit board, while the second loop in a set of loops may be wound by tracing the second loop on a second printed circuit board. The integrated Rogowski coil system may further include a first perimeter loop traced on an outer perimeter of the first printed circuit board, and a second perimeter loop traced on an outer perimeter of the second printed circuit board. The first and second perimeter loops measure residual current through electrical conductors placed within the sets of loops.
In the integrated Rogowski coil system, both loops in a set of loops may be traced on a single printed circuit board. The integrated Rogowski coil system may further include first and second perimeter loops traced on an outer perimeter of the printed circuit board. The perimeter loops measure residual current through electrical conductors placed within the sets of loops.
Rogowski coils have many advantages over conventional CTs. For example, Rogowski coils provide high measurement precision because they can be designed to measure currents to better than 0.1% precision, with a typical precision of around 1-3%. Rogowski coils also offer wide measurement range. For example, the same coil can be used to measure currents ranging from several amps to several hundred thousand amps. In addition, Rogowski coils are operable over a wide frequency range, such as from around 0.1 Hz to over around 1 MHz (depending on the design of the coil). Rogowski coils also can be designed to provide a bandpass frequency response of up to around 200 MHz.
Rogowski coils can precisely measure currents that have a large dc component because, unlike CTs, they do not include an iron core that can saturate. Moreover, Rogowski coils can withstand unlimited short-circuit currents.
Rogowski coils can be designed to be very small to permit measurement of currents in restricted areas. Likewise, they can be designed to be either flexible or rigid depending on application requirements.
Rogowski coils can be used to measure current distributions in circuits having very small impedances without affecting the circuits. Rogowski coils are galvanically isolated from the primary conductor. Furthermore, Rogowski coils have relatively low production cost.
Rogowski coils are also suitable for measuring current in a variety of other applications, including, for example, measuring the current distribution in parallel fuses or in parallel bus bars. Rogowski coils can be designed to be long enough to encircle a communication tower or an arc furnace, and therefore can be used to measure the total curren
Kojovic Ljubomir A.
Skendzic Veselin
Williams Stephen E.
Fish & Richardson P.C.
LeRoux Etienne
McGraw-Edison Company
Metjahic Safet
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