Current Determining Device and Methods

A current determining device with a flat-sided primary conductor having two end faces between which a current can flow in a flow direction, and at least two flat sides in parallel with the flow direction. A first field-modifying element formed of a magnetic material is located at or adjacent to a first said flat side of the primary conductor, and a second field-modifying element formed of a magnetic material and located at or adjacent to the second said flat side of the primary conductor. At least one sensing coil is also provided at or adjacent to the primary conductor and the first and second field-modifying elements, and has a coil axis which extends between planes of the two flat sides. An electromagnetic field F formed by current flowing in the flat-sided primary conductor is modified by the first and second field-modifying elements to extend more in parallel or substantially in parallel with the coil axis of the sensing coil, whereby an induced electromotive-force at the sensing coil has improved proportionality with the current flowing in the flat-sided primary conductor.

CROSS REFERENCE TO RELATED APPLICATIONS

This non-provisional patent application claims priority under 35 U.S.C. §119(a) from Patent Application No. 1518372.6 filed in Britain on 16 Oct. 2015.

FIELD OF THE INVENTION

The present invention relates to a current determining device, to a corrector circuit in combination with such a device, and to a method of improving current determination using the device. Furthermore, the invention relates to a method of improving proportionality of an induced electromagnetic field in a sensing coil relative to a current flowing in a primary conductor using the current determining device, and to a method of improving sensing coil resolution when determining current flowing in a current-carrying primary conductor using such a current determining device.

BACKGROUND OF THE INVENTION

From classical principles of electromagnetic induction, it is understood that an electromagnetic field is generated by a current-carrying conductor, such as an electrical wire. It is also known that such an electromagnetic field will induce a measurable voltage signal in a neighbouring sensing coil. The signal outputable by the sensing coil is at least in part related to the magnitude of the current flowing in the current-carrying conductor.

It would be beneficial to be able to improve or optimise the association between the sensing coil and the current-carrying conductor, thereby allowing a size of the sensing coil to be reduced without adversely affecting a required resolution or accuracy of the outputted signal. This consequently enables a reduction in size not only of the sensing coil but also, if necessary, the current-carrying conductor being monitored. A size reduction without a reduction in accuracy translates into a material cost-saving.

SUMMARY OF THE INVENTION

The present invention therefore seeks to provide a solution to this problem.

According to a first aspect of the invention, there is provided a current determining device comprising: a flat-sided primary conductor having two end faces between which a current can flow in a flow direction and at least two flat sides in parallel with the flow direction; a first field-modifying element formed of a magnetic material and located at or adjacent to a first said flat side of the primary conductor; a second field-modifying element formed of a magnetic material and located at or adjacent to the second said flat side of the primary conductor; and at least one sensing coil at or adjacent to the primary conductor and the first and second field-modifying elements, and having a coil axis which extends between planes of the two flat sides, wherein an electromagnetic field formed by current flowing in the flat-sided primary conductor is modified by the first and second field-modifying elements to extend more in parallel or substantially in parallel with the coil axis of the sensing coil, whereby an induced-EMF at the sensing coil has improved proportionality with the current flowing in the flat-sided primary conductor.

There is also provided a current determining device comprising: a flat-sided primary conductor having two end faces between which a current can flow in a flow direction and at least two flat sides in parallel with the flow direction; a first field-modifying element formed of a magnetic material and located at or adjacent to a first said flat side of the primary conductor; a second field-modifying element formed of a magnetic material and located at or adjacent to the second said flat side of the primary conductor; and at least one sensing device at or adjacent to the primary conductor and the first and second field-modifying elements, and extending between or substantially between planes of the two flat sides, wherein an electromagnetic field formed by current flowing in the flat-sided primary conductor is modified by the first and second field-modifying elements to extend more in parallel or substantially in parallel with the sensing device, whereby an induced-EMF at the sensing device has improved proportionality with the current flowing in the flat-sided primary conductor.

According to a second aspect of the invention, there is provided a corrector circuit in combination with a current determining device according to the first aspect of the invention, the corrector circuit having an input for receiving an output signal corresponding to an induced-EMF from the or each sensing coil, and a differential-phase correction integrator circuit having an op-amp and which alters a phase-difference of the output signal, so that an altered output signal can be formed in-phase or substantially in-phase with the current in the primary conductor.

Preferably, the corrector circuit includes a scaling calibration circuit for calibrating and scaling the altered output signal, the scaling calibration circuit including a further op-amp.

According to a third aspect of the invention, there is provided a method of improving current determination using a current determining device, preferably in accordance with the first aspect of the invention, the method comprising the steps of modifying an electromagnetic field formed by a current-carrying primary conductor by utilising opposing flat sides on the current-carrying primary conductor and associated first and second field-modifying elements, whereby the electromagnetic field is more in parallel or substantially in parallel with a coil axis of an associated sensing coil, thereby improving the proportionality of the induced-EMF at the sensing coil relative to the current flowing in the flat-sided primary conductor.

According to a fourth aspect of the invention, there is provided a method of improving proportionality of an induced-EMF at a sensing coil relative to a current flowing in a primary conductor using a current determining device, preferably in accordance with the first aspect of the invention, the method comprising the steps of: providing opposing flat sides on the primary conductor; and modifying an electromagnetic field formed by the primary conductor when carrying a current by utilising first and second field-modifying elements associated with the said flat sides, whereby the electromagnetic field becomes more in parallel or substantially in parallel with a coil axis of the associated sensing coil.

According to a fifth aspect of the invention, there is provided a method of improving sensing coil accuracy when determining current flowing in a current-carrying primary conductor using a current determining device, preferably in accordance with the first aspect of the invention, the method comprising the steps of modifying an electromagnetic field formed by the current-carrying primary conductor by utilising first and second field-modifying elements associated with opposing flat sides on the current-carrying primary conductor, whereby the electromagnetic field becomes more in parallel or substantially in parallel with a coil axis of the associated sensing coil.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring firstly toFIGS. 1 to 3of the drawings, there is shown one embodiment of a current determining device10which comprises a primary conductor12, a first field-modifying element14, a second field-modifying element16, and two sensing devices18, which in this case are preferably sensing coils18a,18b.

The primary conductor12is advantageously a busbar, but may be any other suitable electrically conducting element. The busbar or other suitable primary conductor12is, in this case, rigid or at least stiff, and preferably forms part of an electrical disconnect switch or other suitable kind of switching contactor. The busbar12is elongate, preferably formed of metal, such as brass, steel or copper, and may be straight, curved or a combination thereof.

Preferably, the busbar12has a length L1having a first dimension which begins and ends at end faces20, a width W1having a second dimension, and a height H having a third dimension. The width W1and height H are preferably mutually perpendicular to each other as well as to the length L1, with the first dimension being greater than the second and third dimensions, and the second dimension being less than the third dimension. This consequently allows the busbar12or other suitable primary conductor to define a rectangular or substantially rectangular cross-section laterally to and along a portion, preferably being at least a major portion, of the longitudinal extent.

Although preferably rectangular or substantially rectangular, the primary conductor may be of another polygonal or substantially polygonal lateral cross-section. However, a rectangular or substantially rectangular lateral cross-section is most beneficial due to the cross-section being elongate thereby providing opposing flat or planar minor-sides22extending between the two opposing end faces20or at least along a portion of the longitudinal extent. The flat minor-sides22define the aforementioned width W1, in this case.

A further benefit of the rectangular or substantially rectangular lateral cross-section is the provision of the opposing flat or planar major-sides24extending between the two opposing end faces20or at least along a portion of the longitudinal extent, and preferably perpendicularly to the flat minor-sides22. The flat major-sides24define the aforementioned height H, in this case.

The first and second field-modifying elements14,16may conveniently be formed of magnetic material, and in this case are preferably rigid or stiff planar or substantially planar plates14a,16a. The plates14a,16ain this case may be formed from a magnetisable material, that is, a soft magnetic material such as iron, cobalt, nickel or steel. Equally, though, the plates14a,16amay be formed from a hard magnetic material, such as a permanent magnet, for instance a rare-earth magnet such as a neodymium iron boron or samarium cobalt magnet.

Although continuous or unbroken planar plates14a,16aare suggested, in this case being preferably rectangular, it may be feasible to utilise non-planar plates or to have at least a portion which is non-planar, which may allow for further modification of the induced-electromagnetic field when a current flows in the primary conductor12. This is described in further detail hereinafter.

Additionally or alternatively, the plates may be discontinuous or have openings, as may be required. Again, it may become apparent that this again allows for further tuning of the generated electromagnetic field.

To preferably support the first and second field-modifying elements14,16at or adjacent to the flat minor-sides22of the primary conductor12, and preferably overlapping or extending beyond the width W1of the flat minor-sides, the two said sensing coils18a,18bare provided, in this case preferably clipped in spaced relationship to the primary conductor12. The sensing coils18a,18bmay be provided with a bobbin former26around which electrically conductive wire28is coiled multiple times so as to be tightly packed, typically with a plurality of overlying turns or runs.

At each end of the former26may be provided a, preferably elongate, holder32for receiving ends or sides of the first and second field-modifying elements14,16. Generally, the holder32may conveniently include a recess34within the body of the holder32. The recess34may be slot shaped, and sufficiently dimensioned to receive a portion of one of first and second field-modifying elements14,16as a complementarily fit. The dimensions of the recess34may allow for a tolerance or close fit of the respective first and second field-modifying elements14,16.

With the first and second field-modifying elements14,16engaged with respective ends of the first and second sensing coils18a,18b, the coils18a,18bare then physically or mechanically connected directly to the primary conductor12via their hangers36, which as mentioned above may beneficially be in the form of clips or brackets36a.

The clips or brackets36aare in the form of elongate rigid or semi-rigid arms38, preferably cantilevered from the formers26to project towards an opposing sensing coil18a,18b. The clips or brackets36aare offset from each other, and are located over the minor-sides22to hold the sensing coils18a,18bin spaced relationship with their respective major-sides24.

Although an air gap is present between the sensing coils18a,18band the major-sides24of the primary conductor12, the sensing coils may be mounted directly to their respective major-sides. In this case, it is preferable that an electrically insulated layer or member is provided to electrically isolate each sensing device from the primary conductor to prevent or inhibit direct current flow thereto.

The hangers36are beneficial in that the sensing coils18a,18bmay thus be demountable from the primary conductor12. However, a permanent fastening may be considered, as necessity dictates, and which may, for example, take the form of a bracket which is permanently attached to the primary conductor12, such as by welding, bonding or via one or more screw-threaded fasteners.

Although two sensing coils18a,18bare preferred to provide improved resolution, only one sensing coil or other suitable sensing device or means may be utilised.

As best seen inFIG. 3, each sensing coil18a,18bhas a width W2which is preferably greater than its depth D. A length L2of the sensing coils18a,18b, and therefore the respective coil axes40, also extend to or substantially to planes42of the minor-sides22. A lateral extent of each sensing coil18a,18bis thus preferably polygonal or substantially polygonal, and more preferably rectangular or substantially rectangular, in this case uniformly or substantially uniformly along at least a majority of the coil length L2.

From each coil end, a secondary conductor44extends thereby allowing a voltage signal to be monitored based on an induced electromotive force, also referenced herein and throughout as ‘EMF’.

Although it has been suggested that a lateral cross-section of the busbar12or other primary conductor is rectangular or substantially rectangular, provided the minor-sides are utilised, it may be feasible that the major-sides are arcuate or partially arcuate, if required.

In use and with a current flowing between the end faces20of the flat-sided primary conductor12, thereby defining a flow direction46, an electromagnetic field F induced by the current in the flat-sided primary conductor12is modified by the first and second field-modifying elements14,16. As can be understood fromFIGS. 1and2, the electromagnetic field F is manipulated or re-shaped to extend more in parallel or substantially in parallel with the coil axes40of the sensing coils18a,18b. SeeFIG. 1, by way of example, which shows a representation of the field F with the sensing coils18a,18bdemounted.

With the sensing coils18a,18bmechanically connected to the primary conductor12, an induced electromotive force is realised, thereby allowing a voltage signal to be outputted. The induced electromotive force and thus the associated monitored voltage have improved proportionality with the current flowing in the primary conductor12, due to the combination of the rectangular or substantially rectangular lateral cross-section of the primary conductor12and the, preferably overhanging, first and second field-modifying elements14,16manipulating the produced field to, as mentioned above, extend more in parallel or substantially in parallel with the coil axes40of the sensing coils18a,18b. An improved resolution or accuracy of the monitored voltage being proportional to the current flowing in the primary conductor12is thus achieved.

As a consequence of this, to maintain a current or presently monitored voltage resolution or accuracy, which may in fact be sufficient or adequate for a required application, the sensing coils18a,18bcan actually be reduced in volume or size. This thereby enables not only material and manufacturing time and cost-saving during the production of the sensing coils18a,18b, but also the primary conductor12may also be reduced in size with similar benefits being achieved.

As shown inFIG. 4, a corrector circuit48may be utilised in combination with the current determining device10described above. This would be beneficial due to the output signal in the secondary conductors44being 90 degrees lagging and thus out of phase with the current to be measured or monitored in the primary conductor12.

To this end, the corrector circuit48preferably includes a signal input50for receiving an output signal from the sensing coils18a,18bcorresponding to an induced voltage, a differential-phase correction integrator circuit52having a first operational amplifier54, also called an op-amp, and a scaling calibration circuit56having a second operational amplifier58.

The differential-phase correction integrator circuit52preferably utilises the first operational amplifier54having its inputs connected to outputs of the sensing coils18a,18bthrough first and second resistors60,62. The sensing coils18a,18bare represented by differentially connected inductors. A first parallel RC-circuit64comprising a first capacitor66and a third resistor68is provided in a negative feedback loop of the first operational amplifier54. A second parallel RC-circuit70comprising a second capacitor72and fourth resistor74is connected between ground and the non-inverting input of the first operational amplifier54.

To allow for scaling, if required, the second operational amplifier58has an inverting input connected to the output of the first operational amplifier54through a fifth resistor76. A negative feedback loop of the second operational amplifier58comprises a sixth resistor78connected in parallel with a series RC-circuit80comprising a seventh resistor82and third capacitor84. The values of the circuitry components depends on the scaling calibration required.

Although it is suggested that the field-modifying elements are held in spaced relationship with the minor or narrower flat sides of the primary conductor, they may feasibly be mounted directly to the flat sides, for example, by utilising an electrically isolating layer interposed therebetween. Furthermore, although it is suggested that the field-modifying elements are positioned at or adjacent to the minor flat-sides, and the sensing device is position adjacent to one or more of the major flat-sides, this may feasibly be reversed, dependent on necessity.

The sensing means, which in this case is one or more coils, preferably provides an non-circular lateral cross-section along the axis of the former or bobbin. However, other cross-sectional winding shapes are feasible, such as circular. However, a benefit of the elongate wound cross-section is that an increased activate area or volume of the sensing means is achieved.

It is thus possible to provide a current determining device which better manipulates the induced magnetic field formed by a current carrying conductor, in this case being preferably a bulbar of a switch. This is achieved by having at least two opposing flat sides at or adjacent to which field-modifying elements can be located. Preferably, the opposing flat sides are minor or narrower sides of the current-carrying primary conductor to be monitored, forming part of a polygonal, preferably rectangular, cross-section. The current determining device enables a more parallel field to be achieved, thereby achieving a more accurate or higher resolution current measurement sensor within the active dimensions of the sensing coils. It is therefore possible to maintain an existing resolution or accuracy of the current determination within the in use primary conductor, whilst reducing the size of the sensing coils, if necessary. It is further possible to provide the at least one sensing device, which is preferably two sensing coils, in a demountable or removable clipped arrangement with the current-carrying primary conductor, thus enabling simple and time-efficient location and relocation during manufacture of the current determining device or retrospective addition to an existing busbar or other primary conductor. It is additionally possible to provide an improvement in current determination, accuracy, monitoring and/or resolution due to improved proportionality of the induced voltage in the sensing coil or other suitable induced-EMF sensing or monitoring device relative to the current flowing in the flat-sided primary conductor.

The words ‘comprises/comprising’ and the words ‘having/including’ when used herein with reference to the present invention are used to specify the presence of stated features, integers, steps or components, but do not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.

The embodiments described above are provided by way of examples only, and various other modifications will be apparent to persons skilled in the field without departing from the scope of the invention as defined by the appended claims.