Wideband Transducer for Measuring a Broad Range of Currents in High Voltage Conductors
This patent describes an instrument that can measure currents almost anywhere but was invented primarily for electrical power systems. This instrument is called a magnetic field current sensor (MFCS). A website at www.frsconsulting.biz describes the instrument in detail and covers the development work done in a test laboratory, installation of a three phase power loss measuring system in a transformer manufacturing plant that has been in operation since mid 2013, and a 115 kV high voltage current transformer. The MFCS was invented to replace current transformer in electrical power systems because they have major technical shortcomings that result in serious problems and almost absurd solutions. In addition, current transformers are very costly to buy and operate. The low initial cost and efficiency would be enough to justify using this new technology, but there is much more. All of this is explained in the website that is abstracted in the following paragraphs that briefly describing construction and operation of the MFCS.
Iron core transformers work very well up to a point. That point is reached when the flux density in the core exceeds a magnitude described as the knee of the B-H curve. Above that point, the transformation is inaccurate at best and completely absent in many instances. Temporary or permanent magnetism left in the core may require corrective action (demagnification and recalibration) to restore normal operation. This condition frequently happens when there is a transient in the system that contains DC components.
Current transformers cannot measure DC currents even when they are only a component in AC systems. Serious consequence such as improper operation of protective relays can result from the failure to process the DC component. A large volume of literature exists that in large part applies band aids to the problem. There is no way to adequately replace the missing or incorrect information that comes from a saturated current transformer.
The magnetic field current sensor does not use the transformer principal but instead is a direct application of an electromagnetic law knows as Biot-Savart. The physical arrangement is a copper cylinder to which strips of a nickel-iron alloy know as mu metal are attached and this assembly is centered around the current carrying conductor. The purpose of this arrangement is to concentrate the magnetic field in air gaps between the strips of mu metal. Magnetometers such as Hall Effect Devices are used to measure the magnetic flux density that in both theory and practice is a perfect analog of the current in the conductor. It is shown in the website that the relationship between the current and the flux density is completely linear over a wide range of currents even though the mu metal characteristics are not linear but the B-H curve is mathematically smooth. There is a phase shift of a few degrees caused by the conductivity of the mu metal which is approximately 1.8 micro siemens/meter that produces small eddy currents in the strips. However, the shift is constant and can easily be corrected for in the signal processing. Therefore, the measuring system is inherently free of error and almost any level of both magnitude and phase angle accuracy can be achieved.
The R&D work is essentially complete and it is time work on production of the instruments that use this technology. We think a reasonable target for getting some high priority products ready for market is three years.
The next step is the detailed design stage of the development which is dependent on specific applications. There are several scenarios for moving forward including design, fabrication and testing by my associate, Messerstrom, Inc. In any event, we will provide to the new owner of the patent every relevant document, drawing and report in our files and offer our consulting services if that is desired.
US 85,759,182 issued 2013-11-05 [MORE INFO
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