FI78794C - WITH STROEMFOERDELARE FOERSEDD STROEMMAETTRANSFORMATOR. - Google Patents

Description

78794 1 Current transformer with current distributor Med strömdelare försedd strömmättransformator 5

The invention relates to a current measuring transformer provided with a current divider.

With regard to the prior art, reference is made to DE 27 34 729, DE 30 08 308 10 and US 4 240 059. In known transformers with a current divider of this type, the current to be measured is divided into two parts, one of which passes through the transformer. This makes the transformer operate at low flux densities and thus the transformer does not saturate even at high currents. The measuring range of the transformer can thus be extended.

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In known current transformers, an attempt has been made to dimension the shape of the current divider so that the current divider heating caused by the measuring current is as similar as possible in the current divider branch passing through the transformer and in the current divider branch passing through the transformer. EP 0111063, US 4 240 059, 20 DE 27 34 729 and EP 0123062 deal specifically with heating compensation. The above-mentioned reference publications have focused almost exclusively on achieving uniform warming of the current divider. In this case, the resistances of the branches of the current divider change relatively equally and the current distribution ratio remains constant despite the heating of the current divider.

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Due to the non-ideal properties of the current transformer, a phase difference is created between the primary current and the secondary current of the current transformer. This phase difference is quite detrimental, especially when a current transformer is used in an electrical energy measurement application. The false-30 error thus caused by the current transformer is detrimental, in particular because it is not of a constant magnitude, but its magnitude depends on the intensity of the current flowing through the current transformer. This phenomenon is due to the nonlinear magnetization of the transformer iron. The relative permeability of the transformer iron increases as the magnetic flux density of the transformer iron increases.

In the past, attempts have been made to correct the phase error of the current transformer by implementing the correction in a constant magnitude over the entire measuring current range.

35, 78794 2 1 With such a solution, the phase error of the current transformer is reset to zero at only one point. Elsewhere in the mitigation current range, there are still positive and negative phase errors, respectively.

It is an object of the invention to provide an improvement over the currently known current transducers with current divider. It is a detailed object of the invention to provide a current transducer in which the phase error of the current transducer is eliminated in the entire measuring current range in a considerably better way than previous solutions.

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The objects of the invention are achieved by a current transducer, which is mainly characterized in that the current divider is provided with a compensating piece for changing the phase error of the transducer due to a change in the measuring current of a magnetic material such that the relative permeability of said compensating piece changes with flux.

In a preferred embodiment of the invention, the current divider consists of two branches, the first branch passing through the current transformer 20 acting as a primary conductor of the current transformer and the second branch bypassing the current transformer acting as a bypass current branch.

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In another preferred embodiment of the invention, the current divider consists of two branches, the first branch passing through the current transformer acting as the primary conductor of the current transformer and the second branch bypassing the current transformer acting as the bypass current branch is made of a material whose permeability decreases as the measurement current increases.

The invention will be described in detail with reference to some preferred embodiments of the invention shown in the figures of the accompanying drawings, to which, however, the invention is not intended to be exclusively limited.

Figure 1 shows an axonometric view of a preferred embodiment of a current meter-5 transformer with a current divider according to the invention.

Figure 2 shows an axonometric view of another preferred embodiment of a current measuring transformer with a current divider according to the invention.

Figure 3 shows the dependence of the relative permeability of a steel on the magnetic flux density.

In the embodiment according to Fig. 1, the current divider is generally indicated by reference numeral 10. The current transformer is denoted by reference numeral 15 12. The current divider 10 consists of a conductor 11 having current 1 in its first branch 11a and current I2 in its second branch 11b »Iron core 13 of current transformer 12 and reference number 13 the secondary circuit of the current transformer 12 is generally indicated by the reference numeral 14. In the secondary circuit 14, the current 1 ^ · the windings of the secondary circuit 14 are denoted by the reference numeral 15 and the resistor by the reference numeral 16.

In this embodiment, the compensating piece 17 is located in the second branch 11b of the flow divider 10. The compensating piece 17 is of the same type as the iron core 13 of the current transformer 12.

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Thus, in the embodiment according to Fig. 1, the change in phase error due to the nonlinearity of the current transformer 12 can be reduced by means of a magnetic compensation piece 17 placed in the branch 11b of the current divider 10 passing the current transformer 12. The compensating piece 17 30 causes a phase difference between the different branches 11a and 11b of the current divider 10. Since the compensation piece 17 is chosen so that its magnetization is also non-linear, the phase error of the current divider 10 is also caused to change with the measurement current. The permeability of the compensating piece 17 will increase in the same proportion as the permeability of the iron core 13 of the transformer 12 increases as the current increases. The changes in the phase difference between the current transformer 12 and the current divider 10 are in the opposite direction, whereby the phase error caused by the current transformer 4 78794 1 12 and the current divider 10 together remains almost constant as the measurement current changes.

In the embodiment according to Figure 1, the magnetic circuit 5 of the compensating piece 17 consists of a magnetic material such as an iron part and an air gap 18. By changing the size of the air gap 18, the magnetic flux density of the compensating piece Such a rising part of the permeability curve is shown in Figure 3.

The embodiment shown in Fig. 2 is otherwise the same as the embodiment shown in Fig. 1, but in the embodiment according to Fig. 2 the compensating piece 17 'is placed on the first branch of the flow divider 10. The compen-15 chord piece 17 'is a ring of mucus air gap made of a material of high permeability. By changing the length of the ring, the desired flux density value can be set on the compensation piece 17 'so as to operate over the entire measuring range of the current transformer 12 with the descending part of the excitation curve. The descending part of the magnetization curve is shown in Figure 3.

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Only some preferred embodiments of the invention have been described above, and it will be clear to a person skilled in the art that numerous modifications can be made to them within the scope of the inventive idea set out in the appended claims.

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Claims (5)

5 78794 A current measuring transformer (12) provided with a current divider (10), characterized in that the current divider (10) is provided with a compensating piece (17, 17 ') for changing the false phase of the current transformer (12) due to a change in the measuring current 5. 17.17 ') the relative permeability changes as the flux density changes. 1 Claims Current transformer with current divider according to Claim 1, characterized in that the current divider (10) consists of two branches (11a, 11b) known per se, of which the first branch (11a) passes through the current transformer (12) acting as the primary conductor of the current transformer (12) and the second branch (11b) bypasses the current transformer (12) acting as a bypass current branch 15, and that the bypass current branch (11b) of the current divider (10) is provided with a magnetic compensation piece (17) to compensate for a change in the false phase of the current transformer (12). A current transformer with a current divider according to claim 2, characterized in that the magnetic circuit of the compensating piece (17) consists of a part of magnetic material and an air gap (18), and that the magnetic flux density of the compensating piece (18) varies is adjustable, whereby the flux density values of the compensating piece (17) are obtained for the rising part of the permeability curve over the entire measuring range of the current transformer (12). Current measuring transformer with current distributor according to Claim 1, characterized in that the current distributor (10) consists of two branches known per se, the first branch (11a) passing through the current transformer (12) acting as the primary conductor of the current transformer (12) and the second branch (11b) bypassing the current transformer (12) as a bypass current branch, and that to compensate for the change in false current of the current transformer (12), a compensating piece (17 ') of magnetic material is fitted to the first branch (11a) passing through the current transformer (12), and 17) 6 78794 Ί is made of a material whose pennability decreases as the measurement rate increases. A current meter-current transformer according to claim A, characterized in that the compensation piece (17 ') is a ring made of a high permeability material without an air gap, whereby changing the length of said ring the desired flux density value can be set in the compensation piece (17'). 17 ') flux density values are obtained for the descending part of the permeability curve 10 over the entire measuring range of the current transformer (12). 15 20 25 30 35 7 78794