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.
1 . 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.
2 . A current determining device as claimed in claim 1 , wherein the flat-sided primary conductor has a polygonal or substantially polygonal cross-section lateral to the flow direction at at least the sensing coil.
3 . A current determining device as claimed in claim 1 , wherein the flat-sided primary conductor has a rectangular or substantially rectangular cross-section lateral to the flow direction at at least the sensing coil.
4 . A current determining device as claimed in claim 1 , wherein the flat-sided primary conductor is a busbar, the busbar forms part of an electrical disconnect switch.
5 . A current determining device as claimed in claim 1 , wherein the first and second field-modifying elements are plates.
6 . A current determining device as claimed in claim 1 , wherein the first and second field-modifying elements are formed from a magnetisable material.
7 . A current determining device as claimed in claim 1 , wherein the first and second field-modifying elements are formed from a permanent magnetic material.
8 . A current determining device as claimed in claim 1 , wherein the first and second field-modifying elements are spaced from the flat-sided primary conductor.
9 . A current determining device as claimed in claim 1 , further comprising a second 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.
10 . A current determining device as claimed in claim 9 , wherein the first said sensing coil and the second sensing coil are positioned on opposite sides of the flat-sided primary conductor.
11 . A current determining device as claimed in claim 1 , wherein the said at least one sensing coil has a polygonal or substantially polygonal cross-section lateral to the coil axis.
12 . A current determining device as claimed in claim 1 , wherein the said at least one sensing coil has a rectangular or substantially rectangular cross-section lateral to the coil axis.
13 . A current determining device as claimed in claim 1 , wherein the said at least one sensing coil includes a hanger by which the or each sensing coil is engagable with the flat-sided primary conductor.
14 . A current determining device as claimed in claim 13 , wherein the hanger is a clip.
15 . A current determining device as claimed in claim 13 , wherein the said at least one sensing coil includes two said hangers.
16 . A current determining device as claimed in claim 1 , wherein the said at least one sensing coil includes a holder for holding the first and second field-modifying elements in spaced relationship with the flat-sided primary conductor.
17 . A current determining device as claimed in claim 16 , wherein the holder is a recess at each end of the at least one sensing coil in which a respective end of the first and second field-modifying elements is receivable.
18 . A corrector circuit in combination with a current determining device,
wherein the current determining device comprises:
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; and
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.
19 . A combination as claimed in claim 18 , wherein 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.
20 . A method of improving current determination using a current determining device,
wherein the current determining device comprises:
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; and
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.