Current transformer for a metal-encapsulated gas-insulated high voltage installation

TECHNICAL FIELD

In the invention, it is assumed that a current transformer for a metal-enclosed gas-insulated high-voltage installation according the preamble of claim 1.

STATE OF THE ART

The invention makes reference to a prior art, as for example from the document EP-A2-0 522 303 results. The combined transducer described therein is for a metal-enclosed, gas-insulated high-voltage installation certainly. It has a current and voltage sensor and a the current and voltage sensor downstream signal processing device on. As current sensor is a Rogowski coil, the non-ferromagnetic to an annular core, predominantly isotropic material is wound. When voltage sensor there is provided a hollow-cylindrical measurement electrode. After installation of the current and voltage sensor in the Metal enclosure surrounding the coil and the measuring electrode a Conductor of the gas-insulated switchgear concentrically.

The Rogowski coil is embedded in an annular insulator, which is arranged in an annular space. The Walls of the room are made of electrically conductive material, preferably made of an aluminum alloy. The insulating body is fixed in this space. The room is on its the current conductor facing lateral surface of a planar, annular Shield limited. The one end side of this Shield electrode is in electrically conductive manner with the Wall on one side of the annular space, whereas the opposite this end face in an electrically insulating Manner with the wall on the other side of the annular connected space. As proof link is here a comparatively narrow, complete with insulation filled gap provided. The walls of the annular space form with the shield an electrically conductive Shielding. This shield protects the annular space against the influence of electrical interference. When measuring in the High-voltage system under operating conditions are therefore of leave the Rogowski coil signals that are free of interference by electrical interference. The Rogowski coil provides the magnitude and rate of change of the current conductor the gas insulated switchgear current flowing proportional signals arranged due to the suitable Shielding almost free from the influences of electrical Foreign fields. likely a For many practical applications constructed in this way quite sufficient current transformer.

The filled with insulating gap in the Rogowski coil However, surrounding shield is the reason that fast and very fast transient electrical disturbances, for example in a frequency range of greater than 1 MHz to about several GHz, are not kept away from the Rogowski coil. Such disturbances falsify the measuring signal, they can also be the cause that the always existing overvoltage protection at the input of the signal processing device is overstressed.

SUMMARY OF THE INVENTION

The invention as in the independent claims is specified, the task is based on a current transformer specify for metal gas-insulated high-voltage equipment, which radio-frequency electrical noise is insensitive, is at what cost to create, and which by small dimensions and a high Accuracy distinguished.

The current transformer according to the invention is characterized, that it is protected against high-frequency interference. The current transformer has a torus formed, a current path enclosing current sensor and a downstream thereof Signal processing device. He also has a the Current sensor and surrounding by a shield enclosed annular cavity in which a mass is filled. The shield is as least one electrically conductive or semiconductive at least one layer containing film formed. This transducer is especially for metal, gas insulated High-voltage equipment, the relatively less intense high-frequency disturbances are subject to appropriate it is in terms of cost to produce particularly low, also he is particularly easy to install in the equipment because he a has a small footprint.

The other embodiments of the invention are articles of dependent claims.

The invention, its development and the achievable Advantages are described with reference to the drawing which illustrates only one possible execution path, closer explained.

BRIEF DESCRIPTION OF THE DRAWING

Show it:<sl><li>1 shows a section through a schematically illustrated Power converter, which is considered as prior art, and</li><li>2 shows a section schematically represented by a Embodiment of an inventive current transformer.</li></sl>

Both figures are equivalent elements with the same Reference numerals. All for the immediate understanding the invention is not necessary elements are not shown.

WAYS OF IMPLEMENTING THE INVENTION

The Fig.1 shows a section through a schematically illustrated, annular shaped current transformer 1 which acts as State of the art is considered. This surrounds CT 1 a conductor of the metal-enclosed gas-insulated switchgear concentric. From this current conductor only is the Central axis 2 is shown that metal-encapsulated in a single phase gas-insulated switchgear same time the central axis the metal enclosure is. As current sensor serves a Rogowski coil 3, designated by an annular, not Core of non-ferromagnetic, predominantly isotropic material wound. However, also other toroidally trained current sensors are used at this point. The not shown by the Rogowski coil 3 away in a Signal processing apparatus leading signal lines also not shown. The Rogowski coil 3 is in a filled with an electrically insulating compound 4, annular cavity formed with a rectangular cross-section arranged. The boundary of the cavity is carried out by a Shield acting electrically conductive walls 5,6,7,8, the are indicated by lines that a somewhat larger line thickness exhibit. The structural design of the walls 5,6,7,8-forming components should not be described in more detail will. These components may, for example, formed similar be, as shown in EP-A2-0 522 303. Is in the metal-enclosed gas-insulated switchgear more provided as a conductor, so surround the current transformer and the possibly associated with these tension sensors to respectively assigned conductor concentrically, then have but not the same central axis as the metal.

Between the wall 8 and the wall 5 remains in this embodiment of the current transformer 1, a comparatively narrow gap 9, of this current transformer 1 runs around the entire circumference. This gap 9 is also filled with the insulating mass. 4 Through the gap 9 is prevented by the can flow shield induced stray currents, whereby the falsifies the Rogowski coil 3 penetrating magnetic field would, leading to a deterioration of the measurement accuracy of the would result in the current transformer. If the shield electrically conductively connected to the metallic enclosure of the gas-insulated Switchgear is connected, preventing the gap 9 also that Parts of the metal enclosure of the gas-insulated switchgear flowing Kapselungsstroms, flow through the wall 8 can, which is also an impairment of measurement accuracy the current transformer would result. The metal walls of the gap 9 should also penetration of electrical interference in the prevent immediate area of ​​the Rogowski coil. 3 speed and very fast transient electromagnetic interference, such in a frequency range of greater than 1 MHz to about more However GHz, be not of the Rogowski coil kept.

The Figure 2 shows a section through a schematically illustrated embodiment of an inventive Power converter 1. In this current transformer 1 which is the Rogowski coil 3 surrounding annular cavity completely with the insulating compound 4 completed. The outer sides of the insulating compound 4 are complete with a by a Serpentine shown, electrically conductive metal foil 12 plated, a gap is not provided here. The fat the metal foil 12 is dependent on the conductivity of the for it determines the material used, for highly conductive metals such as Ag, Cu or Al and alloys based these metals, it is about 3.5 .mu.m, for Ti or constantan is it about 80 microns and a chrome-nickel alloy 80/20 is it about 180 microns. This thickness depends on the Penetration of high-frequency currents in the respective metal. This current transformer needs when installed in the metal-enclosed gas-insulated switchgear is not of the metallic enclosure be isolated, since the metal film 12, which inner the Surface 13 of the current transformer 1 forms, such a low Cross section and thus such a low current-carrying capacity Having that the current flowing through it in the normal operating current no appreciable distortion of the Rogowski coil 3 can cause the recorded measurement value. This current transformer 1 can be made very simple and inexpensive and can without complex installation fittings in each metal-enclosed gas-insulated switchgear are installed.

In normal operation of the switchgear shields the metal thin film 12 acting on the Rogowski coil 3 electric fields not decrease, since in this case their electrical conductivity to is low, so that a correct current measurement ensures is. If the switchgear and with it the Rogowski coil 3 with applied high-frequency interference, so the shields appropriately dimensioned metal foil 12, the Rogowski coil 3 from so that their current measurements by these disorders can be falsified.

Instead of a metal foil but can also be a conductive or semiconducting film of an appropriate plastic be used. These films may one or more layers be carried out, wherein, in the multilayer embodiment, the individual layers may have different compositions. By this way, the effectiveness of the shield optimally placed on the to the current transformer 1 Operational requirements, but particularly to those in the respective metal-enclosed gas-insulated switchgear to expected frequency interference, be adapted so that influencing its accuracy by such interference can be neglected.

Current transformers, the principle described herein in accordance with the are constructed, can be modified accordingly, in Outdoor switchgear, the high and the highest operating voltages are designed and used in medium-voltage systems, in particular they can be used in switchgear, with comparatively large currents are operated. Further let to such current transformers with relatively little effort combined with capacitive voltage transformers, so that a easy and cheap to be manufactured combined current and Voltage converter is produced. For metal-enclosed, gas-insulated High Voltage Switchgear are such combined electricity and Voltage converter particularly suitable because they comparatively have small dimensions.

LIST OF REFERENCE NUMBERS

<dl tsize="8" compact="compact"><dt>1</dt><dd>current transformers</dd><dt>2</dt><dd>central axis</dd><dt>3</dt><dd>Rogowski</dd><dt>4</dt><dd>Dimensions</dd><dt>5,6,7,8</dt><dd>walls</dd><dt>9</dt><dd>gap</dd><dt>11</dt><dd>semiconducting bulk</dd><dt>12</dt><dd>metal foil</dd><dt>13</dt><dd>inner surface</dd></dl>