FI107304B - Electric current transformer for medium or high voltage systems - Google Patents

Description

107304 Electric transformer for medium and high voltage

The present invention relates to an electric current transformer for a medium or high voltage power plant, provided with an annular bearing body 5 acting as a current sensor holder, wherein the current sensor attached to the bearing body is a tubular winding coil and,

The invention then refers to the state of the art disclosed e.g. in EP Publication 204082. The electric current transformer 10 shown in Figure 4 of this patent has a ring-shaped electric current transformer core of ferromagnetic material with a torus-shaped structure. The cores of the electric current transformer with the secondary windings mounted thereon are disposed coaxially with respect to the conductor of the electric current on the cable passage serving as the load bearing body of the plant. The secondary winding can receive signals from it which correspond to the current flowing in the electric current conductor. The current transformers are large in size and additionally contain extremely heavy ferromagnetic material. Therefore, the prior art electric transformer requires a large amount of subscriber and should also be built to be particularly stable due to its high weight.

Other prior art solutions are known, for example, from GB-1,453,679; J.A.J. Pettinga / J. Siersema: "A polyphase 500 kA current measuring system with Rogowski coils", IEE Proceedings, Vol 130, Pt. B, No. 5, September 1983; U.S. Pat. No. 4,471,333; U.S. Patent Nos. 3,990,001 and 4,611,191.

It is an object of the invention, as stated in claim 1, to provide an electric current transformer for a medium or high voltage power plant having small dimensions and whose current detector can be fitted without difficulty to the plant at desired locations. Characteristic features of the invention are set forth in the characterizing part of claim 1.

The electric current transformer according to the invention is characterized by low weight and low space requirement. Therefore, it can be easily installed in the plant at almost any desired location. In addition, it has a measuring range extending over several orders of magnitude and a high linearity within this measuring range. In addition, it does not require any magnetically impregnable components. The effect of unwanted magnetic fields is then decisively eliminated.

2,107,304

A preferred embodiment of the invention and other advantages thereto will be explained below with reference to the drawings.

An exemplary embodiment of the invention will be described in simplified form in the accompanying drawings, in which: FIG. and 2, a block diagram of a signal flow path.

Figure 1 shows a metal-encapsulated, gas-insulated medium voltage switchgear that can be used up to 24 kV. This plant has a shell 1, shown as a metal casing, which is filled with insulating gas, particularly 15 SF6, up to a pressure of a few bar. Inside the housing are high current components such as circuit breakers 2, isolation switches 3 and busbars 4. The high current component exams are connected in stages by means of electrical conductors 5. The cable through the ports 6 leads the electric current conductors 5 from the housing 1 to the cable 7. The electric current transformer detects the magnitude of the current flowing through the electric current conductors 5. Each of the electric current transformers 8 has a current detector 9 coaxially surrounding its associated electric conductor, as well as signal wires and measuring electronics 10 not shown herein, in which the measurement signals transmitted by the hazards 9 are analyzed.

Each of the current sensors 9 has small dimensions and can therefore be positioned in the plant at desired locations. It is preferable to consider the integration of the current detector 9 into the cable gland 6, since their threads have no effect therein, and since in this case the cable gland 6 acts as a load bearing body of the current sensor S, and an additional load bearing body is unnecessary.

Figure 2 shows the structure and arrangement of the current detector 9 of the electric current transformer 8. The magnified portion of the current detector 9 shown in this figure substantially includes a bearing body 13 formed by a ring cable entry 6, a toroidal coil 14 and a signal cable 15 and 16 introduced from the coil 14 to the measuring electronics 10 of the transducer. measured signals corresponding to the current flowing through the electric conductor 5.

The bearing body 13 includes an annular space 17 surrounding the electric conductor 5 in which the coil 14 is located. Space 17 is almost entirely delimited by interfering 5 electric fields with shielding 18, which is an electrically conductive material such as, in particular, copper or aluminum. The shield 18 is electrically conductive in communication with the casing 1 of the plant by means of a contact contact 19 and is thus contacted with the specified mass potential of the plant. Thus, space 17 is electrically shielded against interfering fields generated by undesirable, mainly transient events, such as switching action 10 or lightning strikes, and coils 14 therefore provide near-error-free signals when measured at the plant.

The shielding 18 consists essentially of two critically hollow cylindrical electrodes 20, 21 of which the electrode 20 is at the same time a control electrode for the cable gland 6 and the other electrode has a spherical shape. Each of the electrodes 15, 21 at the other end surface of the electrode 21 is electrically conductive and mechanically coupled to each other. At the other end surface of the electrode 21, they are electrically insulated from one another by means of an insulating point 22 surrounding the electric current conductor 5 in an annular fashion. Thus, space 17 becomes electrically shielded, thereby avoiding the generation of unwanted eddy currents.

Coil 14 is wound like a "Rogowski" coil on a non-ferromagnetic material annular core 23. The core 23 is substantially rectangular in cross section and is very small in size in terms of radius and axial extension. With a radius of e.g. 55 mm and an axial longitudinal extension of e.g. 30 mm, its thickness is typically only 2 mm. This compensates for the asymmetries in the magnetic field of the current being measured, while minimizing the effect of unwanted foreign fields. The space 17 comprising the coil 14 is filled with an annular insulator 24 which binds the coil 14 in place to the space 17 and also to the supporting body 13.

30 The core 23 of the insulator 24 and the reel 14 are made up of crucially isotropic material. This achieves that the insulator 24 and the core 23 are evenly stretched or shrunk in all directions. The geometry of the coil 14 therefore changes as the temperature changes linearly. This change can easily be compensated for by continuous temperature monitoring of the current detector 10 and by continuous adaptation of the resulting measuring electronics 35 10.

4 1073θ | 4

Extremely high measurement accuracy is achieved when the material 23 of the insulator 24 and the core 23 of the coil 14 has a cable entry 6 for the material of the carrier body 13, which is normally an epoxy resin-based cured insulating mass, and Sue 18. A very good material for insulation 5 24 and / or core 23 has proved to be a glass ball-filled insulating compound, which is particularly based on epoxy resin. Non-ferromagnetic metal may also be used as the material of the core 23. In particular, aluminum is suitable for this purpose because it strongly attenuates voltage peaks induced at high frequencies and because it also has corresponding thermal expansion coefficients for the insulating material used in the insulator 24 and the load-carrying run 10.

The current detector 10 can be manufactured in a simple manner by casting pre-assembled parts such as a shield 18 with a terminal contact 19, a coil 14 with an electric conductor 5 and signal lines 15, 16, and a shielded cable 25 the insulating material constituting the insulator 24 and the bearing range 13. If the current detector 9 is to be fabricated independently of the cable gland 6, then it is possible to mold the body 14 into a specific shape when insulator 24 is formed and then, after curing the insulator 24, is mounted on a coil 14 provided with mounting devices and 14, the insulator 24 is also molded directly into a bore 18 formed as a carrier body 13 as well.

The coil 14 produces signals proportional to the time change of the current flowing in the electric conductor 5. These signals are free from unwanted external field effects and transient events at the plant due to suitably positioned shields 18 and 25. They are integrated into the measurement as a signal corresponding to the current transmitted at ctro · ankle 10. As shown in Fig. 3, these signals are first digitized in an analog-to-digital converter 26, and the digitized signals are then integrated into an integrator 30 constructed as a digital integrator 27 as a signal corresponding to the current to be measured. This signal can then be converted into an analog display in the back-to-back digital analog converter 28 and / or fed to other operating units in the plant for further processing.

Claims (9)

1. Element transformer for en medel-eller högspänningsanläggning, innefat-15 tande en strömdetektor (9), som utformats som en tubularform birds Spole (14), en ringformad bärande stomme (13), som inrättats att uppbära strömdetektom (9), en elström (5) which surrounds the inner end centrer of the roll (14), mätelektronik (10) saint a protected mätkabel, som inrättats Leda in that the output signals fran the roll (14) account mätelcktro-Nike; of Vilka the roll (14) lindats som en Rogowski Spole NMT I annular XAMA 20 (23) of the icke-ferromagnetiskt material, wherein the Kaman is substantially rectangular i ax ial skäming, Science the roll (14) further placerats in a mot elfälten protection of the protected, cylitider -formigt utformad cavity (17) i den bärande stommen (13), bell net av att - den ringformade palm (23) radialmätt business jämfört med dess radie och Exiala dimension, 25. det mot elfälten skyddade rummet (17) fylls av en isolering (24), which faster the roll (14) och head plats 1 • m - of insulation (24) and the spool (14) of the stuff (23) is of decisive thing isotropiskt material. An electric current transformer for a medium or dummy power plant having a current sensor (9) constructed as a torus-shaped winding coil (14), an annular bearing body (13), which is provided to support a current sensor 5 (9), an electric conductor (5) surrounded by a coil (14) centrally, the measuring electronics (10) and a shielded measuring cable, which is tracked to supply output signals from the coil (14) to the measuring electronics; of which the coil (14) is wound like a Rogowski coil on an annular core (23) of non-ferromagnetic material, the core being substantially rectangular in cross section, and the coil (14) is further disposed in a hollow cylindrical structure protected against electric fields an empty space (17) of the bearing body (13), characterized in that: - the radial dimension of the annular core (23) is small compared to its radius and axial dimension, 15. the electric field protected space (17) is filled by an insulator (24) 14) the insulator (24) and the core (23) of the coil (14) are of crucial isotropic material. Elströmstransformator enligt patent krav 1, anchoring pads (24) and spolens (14) without attaching the material (11) to the material (s). • · 1 107304 Electric current transformer according to Claim 1, characterized in that the material of the insulator (24) and the core (23) of the coil (14) has a coefficient of thermal expansion 20 adapted to the coefficient of thermal expansion of the material of the carrier body (13). An elastic transformer enligt patent krav 1 eller 2, a turn-off fragment of an isolate ring material (23) utformats av en härd insulating ring av isoleringsmaterial fylld med spherical fragment. An electric current transformer according to claim 1 or 2, characterized in that at least the core (23) is formed of an illustrated insulating material filled with ball-like parts, of insulating material. An electrical transformer enligt patent krav 1, a rotary encoder av att kaman (23) 5 innehäller icke-ferromagnetic metal. Electric current transformer according to claim 1, characterized in that (23) contains a non-ferromagnetic metal. 5. Elströmstransformator enligt patentkrav 4, bellows av att den icke-ferromagnetic metal and aluminum. Electric transformer according to Claim 4, characterized in that the non-ferromagnetic metal is aluminum. 5 107304 6. Elströmstransformator enligt face av patentkraven 1-5, kännetecknad av attumummet (17) omges av en i jordpotentialen varande skärmning (18) av anläggningen 10 som ir elledande förbindelse med skärmningen (25) av den skyddade mätkabeln. Electric transformer according to one of Claims 1 to 5, characterized in that the space (17) is surrounded by a ground potential shield (18) of the apparatus, which is electrically conductive with the shielded measuring cable shield (25). 6 107304 Elströmstransformator enligt patent krav 6, bellows av att rummets (17) skärmning (18) bryts av en isoleringsunkt (22) som omger elströmsledaren (5) ringformigt. Electric current transformer according to Claim 6, characterized in that the shielding (18) of the space (17) is interrupted by an insulating point (22) around the electric current conductor (5). 8. Elströmstransformator enligt patent krav 6 eller 7, rotary knuckle av att rum-15 forest (17) skärmning (18) thin electrode head (20, 21), lively har avgörande formen av en ihälig cylinder och av lively en (20) inrättats att fungera som styrelektrod för en kabelgenomföming (6) i systemet. Electric current transformer according to Claim 6 or 7, characterized in that the shield (18) of the space (17) has two electrodes (20, 21) which are of a substantially hollow cylindrical shape and one of which (20) is operable to act on a cable entry (6) as a control electrode. Electric current transformer according to one of Claims 1 to 8, characterized in that the signals output from the coil (14) affect the integrating device in the measuring electronics (11), which is constructed as a digital integrator (27) preceded by an analog-to-digital transformer (26). is a capable digital-to-analog converter (28). 9. Elströmstransformator according to any one of claims 1-8, characterized in that utsignalema fran the roll (14) acts in opposition to integreringsapparat I i mätelektroniken (11) 20 which utformats som en digitalintegrator (27), in front of the vilken kopplats · I analogdigi-. talomvandlare (26) och bakom vilken kopplats en digitalanalogomvandlare (28). *, · 1 ·