DD228908A1 - MEASURING ARRANGEMENT FOR ELECTRIC STROEME - Google Patents

Abstract

The invention is based on a known measuring arrangement which consists of an iron core, a primary winding, an indicator winding and a secondary winding. The indicator winding supplies a signal to a differential amplifier and the same drives such a current through the secondary winding and Burden that quasi a flux compensation takes place in the iron core. According to the invention, the iron core still carries a fourth compensation winding, which is operated in a short circuit and the number of turns is dimensioned so that the caused by them flooding is almost as large as the flooding that generates the primary winding. This ensures that the per se large number of turns of the secondary winding is reduced.

Description

embodiment

In the following an embodiment of the invention will be explained in more detail with reference to a circuit diagram.

In the accompanying drawing, the figure shows a circuit arrangement according to the invention. Here is an iron core of a transformer designated 1, which couples four windings. A primary winding 2 is traversed by the current to be measured and expediently consists of at least a few turns. An indicator coil 3 which is typical of zero-flux converter arrangements operates on a differential amplifier 4. It drives a current through a secondary winding 5, which adjusts in terms of sealing and size so that the magnetic flux produced by the winding of the winding 1 is almost compensated. In series with the secondary winding 5, the burden is 7th

Another winding 6, which works as a compensation winding, is short-circuited. As a result of a residual flux in the iron core 1 is formed at the winding output of the winding 6, a voltage which drives a current in the winding. The same leads to a counter-flow, so that only a smaller current is necessary to produce flooding equilibrium in the winding 5. If the transmission ratio is predetermined as the ratio of the current in the primary winding 2 to the current in the secondary winding 5, this leads to a reduction in the necessary number of turns of the winding 5.

The effect of the arrangement of the compensation winding 6 on the number of turns of the secondary winding 5 is shown below:

Designating the current in the winding 2 with i _P , the current in the winding 5 with i _s and the current in the winding 6 with i _K , so applies due to the flooding equilibrium

ip W ₂ = i _s ^ W ₅ + i _K · W ₆ , followed by i _s = K-i _P

i _s _ W ₂ - KW ₆

ip W ₅

This means that with a corresponding dimensioning even with a small number of turns of the winding 5, but a small counter, a large transmission ratio can be realized.

Claims (1)

-1- 689 34 Claim: Measuring arrangement for electrical currents comprising an iron core (1) and a primary winding (2) carrying the current to be measured, an indicator winding (3) which drives a differential amplifier (4), and a secondary winding which is driven by the differential amplifier and the primary current represented secondary current is flowed through, characterized in that the iron core (1) carries a fourth compensation winding (6), which is quasi shorted and whose product current times number of turns slightly deviates from the product current times number of turns in the primary winding (2). For this 1 page drawing The invention relates to a measuring arrangement for electrical currents, wherein the arrangement consists of an iron core and a primary winding, which carries the current to be measured, and an indicator winding and a secondary winding. The indicator winding drives a differential amplifier which drives a current through the secondary winding and a load representing the primary current. Such measuring arrangements are referred to as Nullflußwandler and lead in particular in the medium voltage range and low voltage range to arrangements with greatly reduced cost of materials. Characteristic of the known technical solutions The traditionally constructed current transformer consists of two windings and an iron core, wherein the transmission ratio of the primary current to the measuring current is determined by the transmission ratio of the windings. Since the power of the measuring circuit is transmitted from the high voltage circuit, it requires a not inconsiderable core cross-section, which in turn determines the mean turn length. In order to reduce the use of materials leads, among other effects, a known arrangement, where as transducer a transformer with three windings application applies. The first winding of this arrangement is traversed by the primary current here. A second winding - the indicator winding operates on a differential amplifier whose output is in series with the third winding. The current driven by this winding from the differential amplifier is an image of the primary current. The gear ratio is determined by the number of turns of the primary winding to the third winding (Lisser, Ribbernik "zero-flow current transformer for measuring DC and AC currents" ETZ Bd. 100 (1979) H. 24 pp 1390-1394, US Patent 2 428 613). In such a converter - which is also referred to as a zero-flux converter - the cross-section of the iron core can be made very small, but it is disadvantageous that the desired large gear ratios require a large number of turns of the third winding, but turns with a large number of turns are uneconomical in their manufacture and / or often associated with large manufacturing tolerances. Furthermore, a measuring arrangement for electrical currents is known, which consists aus.zwei transformers with at least similar transmission behavior. The secondary winding of the two transformers work against each other, and the primary winding of a transformer is traversed by the current to be measured, while the primary winding of the second transformer is traversed by a current representing the current to be measured, one controlled by a difference in the magnitude of the secondary windings active Four-pole drives (DD-D 157981). Even with this arrangement, as in the zero-flux converter, a very small iron cross-section can be used, because here too the measuring power is not transmitted. Although a magnetic flux is generated in the iron core, which leads depending on the design to a different induction in the core. However, this has no effect on the measurement accuracy as long as the iron cores consist of the same material and are dimensioned accordingly. However, this arrangement also initially has the disadvantage that the often desired large transmission ratio, ie the ratio of primary current to secondary current also requires a large number of turns. In this, also referred to as a bridge converter arrangement (Brendler "The bridge converter, a novel single-ended current transformer with minimal errors" Scientific and technical communication of the institute test field for high-performance electrical engineering IPH "No. 24 from 1983), it is already known to remedy this disadvantage to apply in each case a two-winding transformer and a three-winding transformer, of which in each case a first winding is connected in series through which the current to be measured flows, while a second winding of the transformer works on each other and between the connections of the second windings of the two transformers is a differential amplifier whose output current depicts the current to be measured and is in series with a third winding of the three-winding transformer (DD-PS159370). In the embodiment is shown there that z. B. by 10% different numbers of turns in the windings to a tenfold of the natural gear ratio W _Pr to W _sec leads. The described arrangement also has drawbacks compared with the solutions specified in the prior art in terms of disadvantages, because it is subject to a larger measuring error. This is because the three-winding transformer operates as a zero flux converter, while the two-winding transformer has a dependent on the modulation induction. In this respect, the arrangement is not applicable for all purposes. It also does not constitute a further development of a zero-flow converter and requires two transformers per measuring arrangement. Object of the invention The invention aims to reduce the manufacturing costs for the production of the transmitter for measuring arrangements, which operate on the Nullflußprinzip and should have a large transmission ratio. Explanation of the essence of the invention The invention has the object of providing a measuring arrangement for electrical currents, which consists of a transformer and having a differential amplifier and operates on the Nullflußprinzip, such that without accepting errors in the transmission behavior windings can be used with greatly reduced number of turns with the same translation. This object is achieved according to the invention in that in a measuring arrangement for electrical currents having an iron core and a primary winding, an indicator winding and a secondary winding, a fourth winding is provided according to the invention, which is operated quasi short-circuited, and the number of turns is dimensioned in that the ampere-turn number of this winding deviates only slightly from the ampere-turn number of the primary winding.