Patent Application
20200225066
Aspects of the present invention relate to a sensor for detecting an amount of current flowing in a wire, and more particularly, to a sensor that includes a magnetostrictive element located within a magnetic field formed by the wire wherein a position sensor detects a size increase of the magnetostrictive element and the size increase is amplified by a predetermined amplification factor by an amplifying device to provide an amplified size increase wherein the sensing mirror is displaced by an amount corresponding to the amplified size increase.
It is desirable to make flux, voltage or current measurements on high voltage components or devices. But the presence of high voltages complicates the installation of sensors used to make the measurements. An example is the measurement of the current needed by generator neutral grounding devices utilized in electrical power generators for power plants. In this regard, the entire disclosure of US Patent Publication No. 2016/0266206A1 entitled “Generator Neutral Ground Monitoring Device Utilizing Direct Current Component Measurement and Analysis” is incorporated herein by reference in its entirety.
Fiber optic devices are often utilized in high voltage environments due to the dielectric properties of the materials used to make the devices. Such devices may include fiber optic sensors made of fibers coated with magnetostrictive films that can be used to measure magnetic fields, thus enabling determination of the current in a conductor. But such devices are suitable for higher current and voltage applications ranging from household power all the way up to high voltage transmission lines, and thus lack the resolution to measure small currents.
In particular, the generator neutral ground current is carried in a large conductor and can be as low as 30 mA in operation, but at a voltage that could potentially increase up to line voltage (sometimes over 20 kV) during a generator fault. Thus, a sensor for this application must be designed to withstand over 20 kV in order to enhance safety and reduce the likelihood of generator damage and down time for generator repairs. But providing suitable voltage isolation for the sensor is expensive and undesirably increases the size and weight of the sensor. Alternatively, measurement locations may be used that are in a lower voltage environment or generally safer area. Unfortunately, the current reading must be undesirably inferred or calculated based on various configuration parameters and thus is prone to measurement error.
Aspects of the present invention relate to a sensor for detecting an amount of current flowing in a wire wherein displacement of a sensing mirror is used in an interferometer to enable determination of the amount of current. The sensor includes a magnetostrictive element located within a magnetic field formed by the wire. The sensor also includes a position sensor that detects a size increase of the magnetostrictive element. In addition, the sensor includes an amplifying device that amplifies the size increase of the magnetostrictive element by a predetermined amplification factor to provide an amplified size increase. Further, the sensor includes a displacement device that displaces the sensing mirror by an amount corresponding to the amplified size increase.
In another embodiment, the sensor includes a magnetostrictive element located within the magnetic field, wherein the magnetostrictive element includes a first rack gear. The sensor also includes a second rack gear that includes the sensing mirror. In addition, the sensor includes a gear set that engages the first and second rack gears wherein a size increase of the magnetostrictive element causes linear movement of the first rack gear and wherein the first and second rack gears and the gear set amplify the size increase of the magnetostrictive element by a predetermined amplification factor to provide an amplified size increase. Further, the second rack and sensing mirror are displaced by an amount corresponding to the amplified size increase.
Those skilled in the art may apply the respective features of the present invention jointly or severally in any combination or sub-combination.
The exemplary embodiments of the invention are further described in the following detailed description in conjunction with the accompanying drawings, in which:
To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. The figures are not drawn to scale.
Although various embodiments that incorporate the teachings of the present disclosure have been shown and described in detail herein, those skilled in the art can readily devise many other varied embodiments that still incorporate these teachings. The scope of the disclosure is not limited in its application to the exemplary embodiment details of construction and the arrangement of components set forth in the description or illustrated in the drawings. The disclosure encompasses other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Unless specified or limited otherwise, the terms “mounted,” “connected,” “supported,” and “coupled” and variations thereof are used broadly and encompass direct and indirect mountings, connections, supports, and couplings. Further, “connected” and “coupled” are not restricted to physical or mechanical connections or couplings.
Referring to
As will be described, the sensing mirror 16 can be moved by a gear train that is actuated by a rod element made of a magnetostrictive material. Referring to
Referring to
Further, the sensor 44 includes a gear train 78 having a first gear 80. The first gear 80 may be adapted such that it that engages the first rack 60, a second gear 82 that engages a third gear 84, a fourth gear 86 that engages a fifth gear 88 and a sixth gear 90 that engages a seventh gear 92 that in turn engages the second rack 72. The first gear 80 is attached to the second gear 82, the third gear 84 is attached to the fourth gear 86 and the fifth gear 88 is attached to the sixth gear 90.
Referring to
In accordance with an aspect, the frame 51 may be positioned sufficiently close to the wire 38 such that the magnetostrictive rod 46 is located within the magnetic field 36 generated by the current 40 flowing in the wire 38. This causes a size (i.e. length) of the magnetostrictive rod 46 oriented in the first direction 48 to expand or increase by a second length L2, thus causing linear movement of the first rack 60 in the first direction 48. The linear movement, in turn, causes rotation of the gears 80, 82, 84, 86, 88, 90, 92 as previously described and ultimately movement of the second rack 72 and sensing mirror 16 in the first direction 48 such that the distance between the sensing mirror 16 and the optical fiber end 74 is increased by a second distance D2. As a result, a length of the sensing path 26 can be increased by the second distance D2, thus increasing the distance which the second beam 34 travels which, in turn, causes a phase difference between the first 32 and second 34 beams and the generation of light and dark fringe patterns on the detector 18 in a known manner. Thus, elongation of the magnetostrictive rod 46 (i.e. the change in position of the second end 54 due to the second length L2) as a result of the magnetic field 36 is detected by the gear train 78. The gear train 78 then causes displacement of the sensing mirror 16 away from the optical fiber end 74.
In an exemplary embodiment, due to the relatively small current 40 in the wire 38, an increase in the length of the magnetostrictive rod 46, by itself, may not be sufficient to enable measurement of current 40. Thus, a gear ratio for the gear train 78 can be selected such that the amount of lengthening of the magnetostrictive rod 46, i.e. the size increase of the magnetostrictive rod 46, is sufficiently magnified or amplified by the gear train 78 to provide an amplified size increase which in turn provides sufficient displacement of the sensing mirror 16 to enable determination of the amount of current 40 in the wire 38. In an embodiment, the gear train 78 is selected to provide an amplification factor of 212, which corresponds to the optical path difference between the reference 24 and sensing 26 paths. It is understood that the amplification factor of 212 is exemplary and that other amplification factors may be used depending on other factors including the type of magnetostrictive material used for the magnetostrictive rod 46 and desired resolution.
Typical magnetostrictive materials may include, for example and not limitation, TbFe2, Tb0.5Zn0.5, TbxDy1-xFe2 (Terfenol-D), and Tb0.5DyxZn. Terfenol-D may be manufactured in rods with a diameter of approximately 10 mm up to 65 mm and 200 mm in length. It has been found by the inventors herein that Terfenol-D provides suitable resolution for the sensor 44. Table 1 shows selected properties for Terfenol-D and calculations for the sensor 44 when the magnetostrictive rod 46 is fabricated from Terfenol-D. It is understood that other magnetostrictive materials and configurations may be used for the magnetostrictive rod 46.
Thus, the invention provides a sensor 44 having a resolution of approximately 0.001 amps (1 mA) per fringe with a sensitivity of approximately 0.6 μT per fringe.
As the sensing mirror 16 moves and the distance between the sensing mirror 16 and the optical fiber end 74 increases by the second distance D2, the number of cycles wherein a fringe change occurs (i.e. from a bright fringe to dark fringe, for example) on the detector 18 is counted in a known manner. The number of fringe changes is then multiplied by the calculated Incremental Detectable Current from Table 1 (i.e. 0.001 amps/fringe) to determine the current 40 in the wire 38.
It is understood that other mechanical or electromechanical systems may be instead of, or in combination with, the gear train 78 to detect lengthening of the magnetostrictive rod 46, magnify or amplify the amount of lengthening to provide an amplified size increase and cause displacement of the sensing mirror 16 by an amount corresponding to the amplified size increase. These include systems having a wedge arrangement, levers, belts, cams, a pantograph arrangement, screw mechanism, crank-slider mechanism and others.
Referring to
In another embodiment, the displacement sensor 104 and controller 106 may be located in a first housing and the linear actuator 108 may be located in a separate second housing. In this embodiment, the controller 106 may communicate with the linear actuator 108 using known wireless methods. This enables a reduction in size of the first frame to facilitate positioning of the first frame adjacent the wire 38, or to provide improved access to confined areas adjacent the wire 38, such that the magnetostrictive rod 46 is located within the magnetic field 36 generated by the current 40 flowing in the wire 38.
An aspect of the invention provides a high resolution sensor 44 that utilizes standard components such as single mode fibers, the fiber optic coupler 20, light source 12 and detector 18. Conventional fiber optic current sensors involve geometries, polarization maintain fibers, heterodyne and homodyne demodulation and other features that add undesirable cost and complexity to a sensor. In another aspect of the invention, a sensor 44 is provided that can be used in many applications where current or magnetic field measurements are difficult to make due to a high voltage environment or physical space limitations. In addition, the sensor 44 may be used in dangerous environments having explosive atmospheres and nuclear radiation. In another aspect of the invention, a sensor 44 is provided that measures relatively small currents or voltages in large conductors wherein the conductors may also be subjected to carrying large currents and voltages due to a generator fault, for example.
While particular embodiments of the present disclosure have been illustrated and described, it would be obvious to those skilled in the art that various other changes and modifications can be made without departing from the spirit and scope of the disclosure. It is therefore intended to cover in the appended claims all such changes and modifications that are within the scope of this disclosure.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US2017/044844 | 8/1/2017 | WO | 00 |
