DE1766446B2 - IRON CORE SYSTEM FOR A LINEARIZED CURRENT CONVERTER - Google Patents

Description

Current transformers in high-voltage networks for the operation of network protection devices must have a very large current range that transfers the primary currents to the secondary side with true form and phase. The performance required to respond to these protective devices must be sufficient be available. The constant increase in electrical energy consumption leads to increasing Meshing of the supply networks, which also have correspondingly greater short-circuit capacities.

Current transformers, whose iron cores are constructed in a conventional manner, come especially at high Short-circuit currents with a superimposed direct current element quickly reach the area of saturation, so that considerable Distortions of the secondary currents occur. The necessary distortion-free transmission of the Primary current to the secondary side at least for the duration of a few half-periods, during which then the protective devices respond, requires special measures. For this reason, the Iron core air gap is provided and thus the converter time constant is made small. This is a reduction of the induction increase otherwise caused by the direct current element is possible or the critical saturation value is only reached more slowly or not at all, so that the protective devices can be operated with safety. The disadvantage of this so-called linearized current transformer exists in that by reducing their main inductance, the no-load current rises sharply and thus large errors occur in the nominal current range, which are necessary for the supply of measuring and protective devices make it unsuitable in this area.

A switching arrangement is already known which avoids the specified disadvantages by providing two separate current transformers. Included one current transformer core is designed without an air gap and assigned to the lower part of the current range, in which it works with a small error for the upper part of the current range in which

ίο the normal magnetic material in the area of saturation a current transformer core with one or more air gaps is provided, which has a linear characteristic in the overcurrent area Switching from the current transformer with high accuracy on the linearized current transformer takes place at a certain size of the primary current through a relay. The disadvantage of this known arrangement is that two current transformers and one additional Relays are required.

ao In the older German patent 1 638 602 there is already a linear current transformer - these are current transformers with an iron core system, which has an iron core sheared by means of at least one air gap contains - has been proposed in the ne-

a5 beneath the air gap or gaps in the sheared iron core Iron bars are arranged with a considerably smaller cross-section compared to the sheared iron core are, so that a parallel connection of magnetic resistances with increasing the permeability of the iron core system in the nominal current range via the permeability of the sheared iron core results. The iron webs bridging the air gaps have the effect that at low field strengths the magnetic resistance in the magnetic circuit of the iron core system largely through the iron webs is determined, so that, as mentioned, an increase in the permeability of the iron core system results in the nominal current range via the permeability of the sheared iron core; at greater field strengths. which occur with shifted short-circuit currents, only the air gaps are effective, so that at Short-circuit currents in the desired manner the permeability of the sheared iron core alone Carry comes.

The invention is based on an iron core system for a linear current transformer according to this older one German patent. It is based on the task of determining the cross-sections of the sheared iron core parts and to dimension the iron bar (s) bridging the air gap so that the requirement - small error in stationary operation and linear characteristic in the overcurrent area - optimally fulfilled will. At the same time, the iron webs bridging the air gaps to hold the by means of the Air gaps sheared iron core parts are used.

This object is achieved according to the invention in that the core part sheared by means of air gaps is a wound body wound from tape and divided into segments, the segments of which are from a outside and / or inside the segments located closed iron ring are supported, wherein the cross section of the closed iron ring or rings and the cross section of the sheared by means of air gaps Core part is dimensioned so that the ratio of these cross-sections is about 1: 100 to 200. The invention is not only characterized by an optimal solution to the complexes mentioned above Task, but also by the fact that one

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1 sheet of drawings

Claims (2)

Patent claims: 1. Iron core system for a linearized current transformer, which consists of a means of at least an air gap sheared iron core consists, in addition to the air gap (s) of the sheared Iron core Iron bars with considerably less than the sheared iron core Cross-section are arranged so that there is a parallel connection of magnetic resistors while increasing the permeability of the iron core system in the nominal current range above the Permeability of the sheared iron core results, characterized in that the means Air gap (23) sheared core part wound from tape and divided into segments (22) Winding body is whose segments (22) from an outside and / or inside the segments (22) located closed iron ring (24, 25) are supported, the cross section of the or the closed iron rings (24, 25) and the cross section of the sheared by means of air gaps (23) Core part is dimensioned so that the ratio of these cross-sections is about 1: 100 to 200 amounts to. 2. iron core system for a linearized current transformer according to claim 1, characterized in that that one of the closed iron rings (24, 25) has a secondary winding to which Measuring devices for the nominal current range can be connected.