DE3243274C2 - Device for adapting the measuring current to a measuring device for measuring electrical currents - Google Patents

Abstract

The device for adapting the electrical measuring current to a measuring device with a primary and secondary circuit arranged on a magnetic core has in the primary circuit (5) n parallel-connected sub-conductors (1 ... n) arranged on n outer legs (K1 ... Kn) on, with each sub-conductor (1 ... n) being assigned only a single outer leg (K1 ... Kn). The secondary circuit (6) is formed by a single winding (Ns) on a single common middle limb (Ks) assigned to the n outer limbs (K1 ... Kn). The outer legs (K1 ... Kn) and the middle leg (Ks) are connected on both sides with yoke plates (8, 9). The magnetic core (7) can be replaced by a laminated core (21) with bent ends. When operating as a current divider, the secondary winding (Ns), which has the opposite direction of winding, is galvanically connected to the power supply line. The ohmic resistances of the sub-conductors (1 ... n) and the secondary winding (Ns) have resistances that are dimensioned according to the division ratio.

Description

The invention relates to a device for adapting the measuring current to a measuring device Measurement of electrical currents, in particular at an electricity switch, according to the preamble of Claim 1.

Such devices in the form of current transformers and current dividers are known. They essentially consist from a magnetic core and from a primary winding, which carries the current to be measured, and from a secondary winding which delivers a current adapted to the measuring device. The ratio of the number of turns of primary and secondary winding determines the transformation ratio. A great gear ratio requires a high number of turns in the secondary winding, which, however, usually results in a greater cost of materials as well as an undesirably large one, which adversely affects the accuracy of the device Winding capacity leads. The known current transformers are sensitive to direct current. To a lesser extent To achieve direct current sensitivity, the current measurement is also done with the help of parallel connected ohmic resistances carried out This current division is, however, from the geometry and from the thermal Conditions dependent. In the case of precise measurements, possible temperature differences in the individual current paths as well as the inductive component of the resistors.

There are also current transformers of the type mentioned in the preamble of claim 1 known (DE-PS 1 88-243 and GB-PS 1118 537), the primary circuit of which consists of several sub-conductors, which can be made either in parallel or in series to set the desired transformation ratio .
The invention is based on the object of creating a device of the type mentioned at the outset which requires a lower number of turns in the secondary winding and a smaller amount of material, without thereby increasing the dependence on the geometry and on the thermal conditions.

The invention is characterized in claim 1. Advantageous developments result from the Subclaims

Some exemplary embodiments of the invention are explained in more detail below with reference to the drawings shows

F i g. 1 shows a current transformer in perspective with detached top,

F i g. 2 the same current transformer in plan view with the upper part removed,

F i g. 3 another embodiment of the magnetic core and

F i g. 4 shows a circuit arrangement of the current transformer when it is operated as a current divider.

The current transformer according to FIGS. 1 and 2 have a primary circuit 5 consisting of four parallel-connected, four partial paths forming partial conductors 1 to 4 and a secondary circuit 6 consisting of a single winding Wj, which are arranged on a magnetic core 7. The magnetic core 7 consists of four outer legs K \ to K ^ which are connected to a common center leg K on both ends with two yoke plates 8, 9. The sub-conductors 1 to 4 connected to a current terminal 10 for the supply of the entire current to be measured / connected in the exemplary embodiment are arranged so that each sub-conductor 1 to 4 surrounds a single outer leg from the inside and the other outer legs from the outside of the current transformer. In this way, each sub-conductor 1 to 4 is a 50-single outer leg z. B. assigned to the sub-conductor 1 of the outer leg Ki. It is also possible that each conductor 1 to 4 only its associated outer legs K \ to Ki wraps. The only secondary winding N _s is arranged on the common center leg K _s .

A total current / = i _p supplied to the current terminal 10 is distributed by the magnetic coupling between the sub-conductors 1 to 4 and between the secondary winding Ns in equal parts i \ = / 2 = / 3 = A. The secondary winding N ₅ namely only "sees" the fourth part i _p : 4 of the total current i _p = i.

Compared with a conventional current transformer, the number of turns of the secondary winding N ₃ can thus be kept four times smaller for the same division ratio i _p : i, which requires correspondingly less material. Conversely, a four times greater division ratio i _p : i _s can be achieved with the same material expenditure. This leads to significant material savings

The exemplary embodiment described has four partial paths in the primary circuit 5. Other designs with several partial paths, generally with π paths and with a corresponding number of outer legs assigned to the partial conductors, are also possible. Theoretically, so many partial paths could be used in the primary circuit 5 until a single turn is sufficient for the secondary circuit 6

The magnetic core 7 described can be formed by a laminated magnetic core. Such a magnetic core 21 with ten bent outer legs ^ i ι to K ₂ D is shown in FIG. 3 can be seen. The bent outer legs K \ \ to K20 are provided with partial conductors 11 to 20 and the common middle leg K _s with a secondary winding N ₅ . The total current to be measured is again denoted by / = i _p and the current through the secondary winding N ₅ is denoted by U

The current transformer according to FIGS. 1, 2 and 3 can be operated as a current divider. The corresponding circuit arrangement with the total current i to be measured, with the primary current i _p and with its partial currents / 1, h ■ ■ ■ in as well as with the secondary _{current Z 5} and with the secondary winding N ₁ is shown in FIG. In contrast to the described power converter, the common Mittelschenkl K is here _s of the magnetic core 7 and 11 surrounding the secondary winding N ₅ galvanically connected to the supply line of the total current / and has opposite the from part conductors 1 ... n to corresponding outer legs K \ ... K _n existing primary circuit 5 has a reverse direction of winding. The measuring current i _m for the measuring device is then taken off with the aid of a converter located in the secondary circuit 6 and provided with a secondary winding N _n . Due to the magnetic coupling between the subconductors 1 to η and between the secondary winding N _s , the primary current i _p on the subconductors 1 to π is distributed in equal parts / j = h = ■ -, in comparison with a conventional current divider also applies here that for the same division ratio ipli _s the number of turns in the secondary circuit 6 requires correspondingly less material.

If the flow divider according to FIG. 4 must be insensitive to a superimposed direct current, the ohmic resistances of the individual current paths must be dimensioned according to the division ratio i _p : i _s. The following must therefore apply: R ₅ : R _P = i _P : k and R \ = Ri =. -. Rn, where R ₅ , Rp, Ru R ₂ ... R _{n are} the resistances of the corresponding current paths.

The device according to the invention in the form of a current transformer or current divider with primary current division In comparison with conventional devices of this type, it has a lower cost of materials. the Stromtsilung is due to the geometry and thermal changes no or significantly less addicted. The primary and secondary number of turns determine the division ratio essentially independently of material and manufacturing tolerances. If the resistance ratio is correctly selected, the Current divider insensitive to direct current.

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For this purpose 2 sheets of drawings

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Claims (6)

Patent claims: 1. Device for adapting the measuring current to a measuring device for measuring electrical currents, in particular to an electricity meter, consisting of a primary circuit and a secondary circuit, which are arranged on a magnetic core, the primary circuit consisting of a plurality of parallel-connected partial conductors and the Secondary circuit is formed by a winding arranged on a single central limb of the magnetic core, characterized in that the magnetic core (7; 21) has a plurality of outer limbs (K \ ... K ") to which the single central limb (Ks) is assigned, and that each of the parallel-connected sub-conductors (1 .. n) of the primary circuit (5) is assigned to a single one of the outer legs (K \ ... K _n ) . 2. Device according to claim 1, characterized in that the sub-conductors (1 ... n) of the primary circuit (5) each have a single turn and the secondary circuit is formed by a single winding (N ₅ ) 3. Apparatus according to claim 1 or 2, characterized in that the outer legs (K \ ... K _n ) of the magnetic core (7) are connected to the common central leg (Ks) by yoke plates (8,9) arranged on both sides. 4. Apparatus according to claim 1, characterized in that the magnetic core (21) consists of a plurality of individual lamellae with bent outer legs (Κι ι— K ₂₀ ) 5. Device according to one of the preceding claims for operation as a power divider, characterized in that the winding (N ₁ ) of the secondary circuit (6) is galvanically connected to the supply line of the total current to be measured (i) and one opposite to the sub-conductors (1 ... n) of the primary circuit (5) has the opposite direction of winding 6. Apparatus according to claim 5, characterized in that the ohmic resistances of the sub-conductors (1 ...) of the primary circuit (5) and the winding (Ν,) of the secondary circuit (6) are dimensioned according to the division ratio ip: / j.