FI118142B - Insulator - Google Patents

Description

118142

Insulator

BACKGROUND OF THE INVENTION

The invention relates to an insulator comprising a body 5 molded from an insulating material, an opening for receiving a primary current conductor, and a current measuring element arranged around the opening, comprising a Rogowski sensor and a shielding housing structure surrounding the Ro-gowski sensor.

In the context of the present invention, an insulator comprising a body molded from an insulating material such as an epoxy resin and an opening for receiving a primary current conductor means various electrical distribution devices, in particular switchgear devices such as support insulators, lead-through insulators or circuit breakers. For the sake of simplicity, the invention will now be described only in connection with a lead-in insulator.

Especially in medium-voltage switchgear, the conventional current transformer to present-15 is often replaced by a Rogowski sensor because of its compact size, which can easily be fitted to various devices, such as bushing isolators, resulting in significant space savings. The Rogowski sensor typically comprises a single air core coil, but the coil may also be formed of a plurality of connected air core coils. The coil or coils are typically • · · · *. · *: 20 fitted to the surrounding shield, to reduce the error voltage induced by the surrounding wires and • · components.

EP 0917157 discloses a protective casing formed of two aluminum plates and a cross-formed half and designed so that the coils are positioned exactly to reduce external interference. - 25 clusters around the circumference of the circle and remain in place until the entire sensor is cast * ·>, In the resin. The halves of the protective housing are shaped so that there is at least one break point *: ** between the halves so that the housing does not form a closed-loop loop.

• · ·

US 4,611,191 discloses a Rogowski sensor 30 which is fitted with an electrostatic shield of a non-magnetic metal such as copper or aluminum. , which is shaped like a cylindrical ring and encircles the heart and winding of the Rogowski sensor on all sides,

In prior art solutions, alignment and positioning of the shielding housing, at least until the entire Rogowski sensor has been possibly molded into the insulating material, has been difficult to arrange. The Rogowski sensor is either supported by loose cardboard or pre-sponge pieces in the mold or in the primary power cable, or else the shield is welded with fixed supports that are welded at one end to, for example, the bushings of the insulator mounting screws.

BRIEF DESCRIPTION OF THE INVENTION

It is an object of the present invention to provide an insulator, in particular a gland insulator, which solves the above problems by providing simple support for the Rogowski sensor while minimizing the effect of interferences affecting the Rogowski sensor. This is accomplished by means of a structure which is characterized by what is stated in the independent claim 1. Preferred embodiments of the invention are set forth in the dependent claims.

The invention is based on a Rogowski transducer comprising either an annular coil or one or more air-core coils fitted in a non-* · *; a magnetic metal shield, which is preferably [? formed by two identical halves which are arranged · · · opposite to form a substantially enclosed closed shield • · ***. . ; · 25 Specifically, it should be noted that a dense metal housing without the .5 • · * being provided with a conventional breakpoint to form a closed loop is • · "·] thus electrically unidirectional because the solution attenuates the amplitude of the Rogowski • · · sensor output signal. The upper limit of the useful frequency range of the Rogowski sensor is thus lower than that of the • ·: 30 shielded interference protection structure, but for most power distribution measurements, the frequency response can be considered to be 118142: 3, however, lightweight, high-quality zinc. suitable for the solution according to the invention, in particular Zn Al 4 Cu 1.

The specific resistance of zinc is about 2.5 times that of aluminum, whereby the use of zinc or zinc alloy achieves sufficient interference suppression without, however, diminishing the magnetic field acting on the Rogowski sensor of the actual measured primary current.

By making the shield enclosure sealed, it is much more effective in suppressing crosstalk caused by adjacent voltages and interference caused by the electric field of the primary current conductor than a conventional structure provided with a break point. The most preferred embodiment for production control and fabrication is that the shield housing is made up of two identical castings, so that only one mold is needed and one component is sufficient. The same type of Rogowski-15 sensor shield can be used for different types of insulators, such as grommet insulators, support insulators and other insulators, because

the sensor can be fitted to different insulators. The adapter piece can easily be made so sturdy that it alone supports the Rogowski sensor and does not require more support arms welded to the housing as has often been known to be used. '[When using welded support arms, different shielding enclosures are required, depending on the mechanical dimensioning of the insulator. There are also * · · • s manufacturing techniques.

it is advantageous that no air gap is required in the screen. by casting

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·: ··· zinc provides a highly dimensional shield for shielding and, moreover, the surface of the zinc casting can be easily treated, for example by sandblasting! · · To obtain a surface roughness which is well adhered to by an insulating material such as a casting resin and does not form a harmful interface. DESCRIPTION OF THE FIGURES The invention will now be described in more detail in the following embodiments: with reference to the following forms, with reference to the following: patterns of which • · · ♦ #; ί '1 • ·' 1.

118142 4:

Figure 1 shows a swing section of an exemplary embodiment of the invention, a lead-in insulator; r

Figure 2 is a cross-sectional view A-A of the insulator of Figure 1;

Fig. 3 is a perspective view of the shield-5 housing shown in Figs. 1 and 2;

Figure 4 shows a partial perspective view of the inner surface of one half of the shield;

Figure 5 shows a half cross-section of the shield.

DETAILED DESCRIPTION OF THE INVENTION

Figures 1 and 2 show a bushing insulator for a medium voltage switchgear according to the invention comprising an insulating body (1) with a primary current conductor (2) centrally arranged therein. Typically, the primary current conductor (2) is installed in place before the casting of the insulating body, whereby the primary current conductor is an integral part of the bushing insulator. The coils (4) of the Rogowski sensor (3) are arranged inside a substantially closed shield (5) made of metal, preferably zinc or zinc alloy.

• · · · · ·: The shielding housing (5) is supported during molding by a fitting (6), which is respectively attached at one end to the earth connection (7). The adapter (6) is sized according to the dimensions of the respective insulator, so that the Rogowski sensor (3) is centrally located on the primary current conductor pair. The adapter piece (6) is made of an electrically conductive material that • # • a

*** separate earth conductor for shielding housing (5) and earthing terminal (7) I

25 is not required. The earthing connector (7) is arranged in the mold so that the

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The gowski sensor remains firmly and precisely in place during casting.

Figures 3 and 4 show a shield (5) consisting of two halves (5a, 5b), preferably two at the same time. * "'account cast identical pieces for easy storage and installation? * ·: 30 compared to using two different halves. The shield * * * \ roller (5) is preferably zinc or lightweight zinc alloy, but it may be of 5 118142 other electrically conductive materials, such as aluminum The shield screen (5) has an annular outer surface and is also substantially circular in cross-section The shield screen comprises at least one preferably protruding lug (8) projecting from the outer periphery (9) for receiving the fitting (6) 5. The bracket (8) further has a hole (10) for receiving a mounting device (6) for the fitting (6), such as a bolt and nut (not shown). order.

The mounting means (6) of the adapter (6), such as a bolt and a nut or rivet, is also adapted to fasten the halves (5a, 5b) of the shield housing 10 together to form the housing surrounding the coils (4) of

The outer surface of the shield halves (5a, 5b) can be roughened, for example by sandblasting, so that the epoxy resin adheres well to the outer surface and does not provide an interface where harmful partial discharges could occur under the influence of an electric field.

On the inside of the annular wall of the shielding housing are provided support flanges (11) for precisely positioning the cylindrical coils (4). The ends of the insulating coil bodies (4a) of the coils (4) are supported on the support flanges (11) so that the coils are in a plane perpendicular to the plane of the primary current conductor • M120. .> ·. · · '·? The coils (4b) of the current measuring coils (4) are wound onto the coil body (4a) and • · the coils are electrically connected in series and the conductor of one end of the last coil of the series is arranged in a so-called. as a return wire to be introduced through the centers of the hollow coil bodies out of the shield housing (5) of the first ··· Rogowski sensor. * Like 25 connecting cables through hole (12) in bracket (8). The hole (12) is formed by the presence of a semicircular cavity (13) in each of the halves (5a, 5b): * *:

• · «··. Fig. 5 shows the **** of the halves (5a, 5b) of the shielding housing (5). ' overlapping the edges such that the center of the lug (8) passes through the center; ) ·. On the first side of the 30 spring axis of symmetry, there is some distance • «·. ···. extended slightly less than half of the wall thickness of the inner and outer periphery • · · as an extension of the outer surface (14) and respectively on the other side of the jacket a 6; 118142 extends substantially less than half of the wall thickness of the inner and outer periphery of substantially equal length as an extension of the inner surface (15). When the two halves (5a, 5b) are joined together, the seam site overlaps to improve the level of shielding, and the halves i are easily mechanically aligned with each other so that the halves are fastened from one place to another. It is essential that the overlap is arranged on a ring-shaped portion of the current measurement coils (4), whereas there is less need to provide overlap for the latch (8).

Although only one embodiment has been described above, it should be understood that one skilled in the art can readily apply the invention to various electrical distribution devices.

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Claims (7)

An insulator, as a conductor insulator, comprising a dielectric body (1), an opening for receiving a primary current conduit (2), a Rogowski sensor (3) adapted around aperture, Rogowski sensor winding or coils (4) receiving interference protective cap (5) of conductive material, such as interference protective cap (5) adapted to provide a closed mesh of its cross profile characterized therein at least one bracket (8) is arranged on interference guard (5) to receive a passport (6) to support interference guard (5) on its; place. 2. An insulator according to claim 1, characterized in that the disturbance cover (5) is formed by two halves (5a, 5b). . . 3. An insulator according to claim 2, characterized in that the interference guard (5) half (5a, 5b) is formed of zinc or zinc alloy by casting. 4. Insulator according to claim 3, characterized in that the disturbance% apa protection cap (5) is specially made of zinc alloy Zn AI 4 Cu 1. 5. An insulator according to claims 2-4, characterized in that half (5a, 5b) of the interference protection cap (5a) are substantially similar in size. ϋ • · · · · · · φ.φ. 6. An insulator according to any one of claims 2-5, characterized in that the interference protection cap (5) part of the half (5a, 5b) which is arranged against one another is arranged by the essential part to partially adjust. cover each other. • ·· .2 ·. 7. Insulator according to any one of claims 1-6 characterized ···. hence, that the passport piece (6) is conductive of its material for grounding interference protection cap (5). • »• · ♦ 1 * 1 · _ _ ** · 1 30 • Λ · ♦ '-f. 2 * ·· -J: