EP0940834A2 - Multi-range fuse with metallic screen - Google Patents

Abstract

The fuse consists of two sub-fuses in an insulating sleeve (17). A fusible wire (2a,b) is wound round a support body (1a,b). A metal screen (20) is attached in the region of the low current side fusible wire (2a) to the insulating sleeve, such that it partially overlaps the high current side fusible wire (2b).

Description

The invention relates to a multi-area fuse for an electrical connecting line, in particular a cable line between a transformer and a switchgear, with at least two partial fuses housed covered in an insulating sheath each with at least one fuse element wound on a support body, the Multi-range fuse on both your low-current side and your high-current side End is closed with a cap.

Series-connected fuses of the type mentioned above are known. At A two-range fuse has two fusible conductors connected in series, from which depending on the size of the current to be switched off one or the other partial fuse takes over all switching work. Each incremental fuse is on a support body at least one, but usually several fuse links connected in parallel. By doing Known case of the two-range fuse is a partial backup from a band or wire-shaped fuse element made of silver (or copper), the respective fuse element is modulated by cross-sectional constrictions. The second incremental backup consists of a or several wire-shaped fusible conductors made of a material with a low melting point, preferably tin. These fusible conductors are in silicone hoses with a reinforcement provided to increase the pressure resistance. The fuse element made of silver has a high Melting point, which made tin a lower melting point. With the latter, therefore preferably switched low currents, while higher currents, for example short-circuit currents, through the silver fuse with the high melting point. By The arrangement of two partial fuses in series can be the opening area of the entire Multi-area protection can be enlarged.

In confined spaces, for example in a transformer under oil due to small distances to neighboring components of different potential (for example grounded housing parts) partial discharges occur on the tin fusible conductors. Their cause lies in the high electric field strength of the air gap between the surface of the Tin wire and the inner wall of the silicone tube. Because this air gap in comparison to the surrounding insulation layers has the lowest dielectric constant, it is by the highest field strength of the arrangement is claimed. The field strength can be so great the dielectric strength of the air is exceeded and partial discharges occur comes within the described air gap. These partial discharges can both Tin fusible link as well as the surrounding silicone hose will erode over time make it inoperable. In addition, the partial discharges when testing the equipment, in which the fuses are installed, disturbing by providing a reliable Do not allow a statement about the insulation of this equipment.

On the other hand, the air gap between the tin wire and the silicone tube is easy Assembly absolutely necessary. The partial fuse with the tin fuse can be used as Low-current fuse, which designate the silver as a high-current fuse.

In the known case, the fusible conductors are used in the area of the high-current partial fuse helically wound around an insulating winding or support body and are directly in the surrounding extinguishing agent, generally quartz sand, is embedded. This arrangement results an almost homogeneous cylindrical surface, which is only with very high electrical Stress (high voltage or very small distances) tends to partial discharges. Of the Quartz sand also has a balancing effect on the surface field strength due to the high dielectric constant the fuse element. Experience has shown that this partial protection area is open the high current side, in usual, compact arrangements in the transformer under oil up to Operating voltages of 24 kV are not critical with regard to partial discharges.

In the area of the cold fuse or on the low current side with the fuse element made of tin in On the other hand, silicone tubes occur due to the causes mentioned above, that you want to avoid. Appropriate countermeasures are the aim of the present Invention.

With a single-zone fuse, you have an insulating one on the inner surface Coating applied a field-controlling layer to limit partial discharges, which covers the entire security, including its entrances and exits. Because of the Bridging the entire fuse, this inner conductive layer must be high-resistance and from Resistance can be defined very precisely. When the fuse is switched off, it must field-controlling layer namely be sufficiently insulating; on the other hand with the fuse intact be sufficiently conductive to provide good shielding. The resistance of this relative high-resistance layer must therefore be set very precisely and is accordingly complicated to apply.

The object of the invention is to provide a multi-range protection of the type mentioned create, in which at least one of the low-current partial fuses free of partial discharge is, in particular the dielectric strength and the mechanical design be improved.

This object is achieved according to the invention in that a metallic screen in Area of the low-current fuse element and the connection point to the next higher-current fuse element, preferably partially overlapping, on the outside of the insulating covering is attached. Unlike the known one described last Dual area fuse, in which the entire fuse with the precisely set high-resistance conductor layer was bridged, the metallic shield is sufficient according to the invention, which is preferably made of copper or brass, above the low-current side Fusible conductor, but then only extends into the area of the connection point to the next higher current fuse element and ends there. So you don't need one Produce and apply a conductor layer with a high, precisely set resistance.

While in the known case the field-controlling layer is preferably a semiconducting one Material can be used, while simplifying production and use according to the Invention of the screen to be metallic. If you compare the multi-range fuse with the known two-range fuse, in which the low-current fuse element made of tin and the high-current fuse element consists of silver, then the expert would under Attention to the teaching of the invention, the entire tin melt conductor on the outside provide the insulating sheath with the metallic shield and this shield area too Extend via the connection point to the silver fuse element. Serves in relation to tin Silver to safeguard higher currents. For a multi-area security, the extension should of the metallic shield beyond the area of the low-current fuse element Reach a short distance to the neighboring fuse element on the higher current side. Including This high-current fuse element can be a small part of the connection point be overlapped, but the metallic shield does not extend from the low-current side to the high current cap. With a multi-range fuse with tin for the low current side and silver for the high current side has been shown to be such a metallic one Screen according to the above characteristics, the arrangement is sufficiently resistant to partial discharge makes. The solution according to the invention for avoiding partial discharges in the area of the low-current fuse element is easier because the shield does not need to be semiconducting and not to be high-impedance, because it does not need the entire insulating sheath bridge. The metallic screen only needs in the area described low-current fuse element and the connection point to be provided.

It is particularly advantageous if, according to the invention, the metallic screen is firmly attached to the low-current side cap is connected. Aside from a cheap mechanical The strength of the new multi-range safeguard if this measure is taken into account metallic shield can also be electrically connected to the low-current side cap. The soldering creates a reliable connection and good electrical contact.

It is also advantageous according to the invention if the screen in the form of a metallic coating applied to the outer surface of the insulating covering and is preferably connected to the low-current side cap. As an insulating covering you can preferably use a porcelain tube, the outer surface of which is through Metallization can be provided with the coating described. Such on a Porcelain tube on the outside easy to apply metallization can with the low-current side Be connected cap (safety cap), from this to the high current side and completely cover the partial fuse in question, for example the low-current side Fuse element; in the case of the example above, the tin fuse. Especially This solution is cost-saving for multi-zone fuses, the caps of which are insulated Wrapping, i.e. are soldered onto the porcelain tube. For this, the porcelain tube is in the area metallize the caps, for example in the arc spraying process. In a simple way can the metallization on one side of the porcelain tube, for example on the low current side End, according to the length of the partial fuse, for example the low-current fuse, be extended in the direction of the high-current connection. This can be done in the same work step during production and requires only slightly more Working time and material costs. In the case of tin as a low-current fuse element whose area, i.e. the area around this fuse element, free of partial discharge. Especially such a multi-range fuse works well for relatively low voltages, for example up to 12 or 15 or even 17 kV.

It is also advantageous according to the invention if the screen is in the form of a metallic one Coating is applied to the outer surface of the insulating sheath and preferably an electrical interruption compared to the low-current cap having. The metallization to be applied to the insulating sheath can be compared to low-current side cap be insulated. The electrical interruption mentioned is between the metallic coating on the one hand and the low-current side cap or associated solder layer on the other hand. This interruption can be caused, for example, by a ring or another axially 5 to 10 mm wide, non-metallized area over the Scope of a porcelain tube can be achieved. Such an insulating area can be produced, by putting an adhesive tape around the corresponding place before metallizing the pipe the tube is wrapped and removed after metallizing. You get with it The advantage of a potential-free arrangement of the screen, which also withstands the dielectric strength small diameter significantly increased, as follows in connection with a similar another embodiment is explained in more detail.

In a further advantageous embodiment of the invention, the screen is a solid tube with a metallic surface, which is supported on the low-current side cap and is coaxial extends outside at a distance around the insulating sheath. In this embodiment instead of direct metallization on the surface of the insulating sheath separate screen tube placed, which has at least on its surface metal. This again ensures the conditions described above, according to which Area around the low-current fuse element is made partially discharge-free. On the other hand is another advantage of the separate shield tube with the larger diameter Dielectric strength of the multi-range fuse increased. Through the separate shield tube the dielectric strength of the new multi-range fuse after the low-current fuse element compared to the first-mentioned solution with the metal layer on the insulating sheath can be significantly enlarged. After the melting of the Fusible conductor, the recurring voltage can isolate the inner insulation gap between the end of the undamaged fuse element (e.g. silver) on the higher current side and the opposite one low-current side cap no longer in the form of a sliding discharge bridge. This solidifies the switching path, which affects the function of the entire multi-range security improved.

The reason for such sliding discharges is the particularly good capacitive coupling between the inner surface of the insulating jacket and the outer metallized counter electrode. The small wall thickness of a porcelain tube as an insulating covering of, for example, 3 - 6 mm, in conjunction with the high dielectric constant (ε _r = 6), gives favorable conditions for the formation of sliding discharges. A reduction in the area-related capacitance between the inner wall of the insulating covering (that is to say the inner wall of a porcelain tube) and the shielding electrode reduces the sliding discharge resistance of such an arrangement. These disadvantages are avoided by using the separate shield tube, ie the sliding discharge threshold voltage and thus the electrical strength of the inner switching path are significantly increased. If, for example, a shield tube with a 10 mm larger diameter than that of the insulating sheath (diameter of the porcelain tube) is used, the dielectric strength can be increased to 30 kV or 35 kV. It is of course also possible to make the diameter of the shield tube 20 mm larger than that of the insulating sheath. However, if the diameter of the shield tube increases, the overall structure will lose its compactness. The diameter size is therefore limited under these conditions. If, in a preferred example, the diameter increase of the shielding tube is chosen between 10 and 12 mm compared to the insulating sheath, then such a shielding electrode could increase the dielectric strength of the switching path after switching off the low-current fuse element by about 50% compared to an embodiment without a shielding tube. In this case, the shield tube is always firmly connected to the cap. The shield tube can be a metal tube, for example. The metal tube is firmly coupled and electrically connected to the low-current side cap and projects from there separately and without contact with the surface of the insulating sheath by the distance described above parallel to this sheath in the direction of the nearest higher-current side fuse element. It is advantageous here if the increase in diameter of the separate shielding tube compared to the sheathing is in the range between 3 and 20 mm, preferably in the range between 5 and 15 mm and very preferably 5 mm.

It is advantageous if, according to the invention, the screen tube with the metallic surface on a sleeve attached to the low-current end of the insulating sheath Insulating material is attached. With frictional engagement you can, for example, by clamping the Push the insulating sleeve on the outside of the low-current cap and press it on fasten. In this way, the shield tube rigidly keeps the distance to the insulating sheath also on the higher current end, where the shield tube ends freely. The shield tube exists preferably made of brass or copper. You can also use any other metal use if the conductivity of the surface is guaranteed on the outside.

By using the insulating sleeve you have a technically optimized solution achieved, at which on the one hand the discussed diameter increase was kept to a minimum on the other hand, the dielectric strength of the inner switching path is increased to the maximum becomes. The particular advantage of this embodiment is that it is preferred cylindrical shield electrode is attached isolated from the low-current side cap. This normally undesired, potential-free arrangement in high-voltage arrangements the shield electrode proves itself in an excellent manner by the inventive Measures as particularly suitable, the cold fuse with the low-current fuse element to make it partially free of discharge and yet maintain a high dielectric strength. In normal The operating state is the capacitive coupling of the shield electrode to the fusible conductor potential sufficient to provide extensive electrical shielding of the interior. After switching off the low-current fuse element, the shield electrode takes on Potential, which is however between the potential of the two end caps. That potential is not fixed, however, but depends on the degree of capacitive coupling to the Cap or to the fuse element of the intact partial fuse. Form at the end due to the high local electric field strength, partial arcing to the inner surface of the insulating covering (of the porcelain tube), then the capacitive improves Coupling to the potential of this partial fuse. The potential of the shield electrode will increase approach the potential of the undamaged fuse element and thus the driving voltage reduce the discharge. In addition, the field strength at the end of the undamaged safety part clearly by the presence of the outer screen reduced and thus increases the threshold voltage for partial discharges.

While in the first described embodiments, the strength of the switching path after switching off the low-current fuse element only when the diameter increases was increased by about 50% from 10 to 12 mm, this is achieved in practice with the potential-free shield electrode with a diameter increase of only about 5 mm the insulating covering (porcelain tube).

It is particularly advantageous if, according to the invention, the screen tube from an outside metallized insulating material. For example, you can use the plastic shield tube form and metallize outside. You can even piece the shield tube with the sleeve design. Then you do not need to stock them as a separate part during assembly hold and attach with special operations. In the case of a plastic also the fit of the shield tube on the cap easier to reach. The one-piece The design of the sleeve and the shield tube allows the assembly and use to be mechanical get easier.

Due to the potential-free attachment of the shield tube on the casing, only a small one Diameter increase compared to the cladding is required, and yet a high one Dielectric strength of 40 kV and above reached.

The invention discussed above proposes measures by which at different Applications more or less simply a partially discharge-free section of the low current side multi-range security is guaranteed. Additional measures ensure a good one Dielectric strength and a simple mechanical design, although the low-current side Incremental fuses can still be designed without partial discharge.

Figur 1

den Längsschnitt durch eine Zweibereichssicherung gemäß einer ersten Ausführungsform mit einem Niederstrom-Schmelzleiter auf der Basis Zinn auf der linken Hälfte und einem Hochstrom-Schmelzleiter auf der Basis Silber im rechten Bereich,

Figur 2

eine teilweise im Längsschnitt genommene Ansicht des Zinnschmelzleiters der Figur 1,

Figur 3

eine ähnliche Schnittansicht wie Figur 1, wobei hier jedoch eine zweite Ausführungsform mit einem Schirmrohr aus Metall dargestellt ist,

Figur 4

eine Querschnittsansicht durch die Zinnteilsicherung gemäß der Linie IV-IV der Figur 6 ist,

Figur 5

eine ähnliche Querschnittsansicht, hier aber auf die gegenüberliegende Seite geblickt und mit dem Hochstrom-Schmelzleiter Silber gemäß der Schnittlinie V-V der Figur 1, und

Figur 6

die Längsschnittansicht einer weiteren anderen Ausführungsform, bei welcher die Muffe zwischen der niederstromseitigen Kappe und dem Schirmrohr weggelassen ist und das Schirmrohr ein Kunststoffrohr mit metallischer Außenbeschichtung ist.

Further advantages, features and possible applications of the present invention result from the following description of preferred embodiments in conjunction with the attached drawings. Show it:

Figure 1

the longitudinal section through a two-zone fuse according to a first embodiment with a low current fuse element based on tin on the left half and a high current fuse element based on silver in the right area,

Figure 2

2 shows a view of the molten tin conductor of FIG. 1, partially in longitudinal section,

Figure 3

2 shows a sectional view similar to FIG. 1, but here showing a second embodiment with a metal shield tube,

Figure 4

FIG. 6 is a cross-sectional view through the tin part fuse according to line IV-IV of FIG. 6,

Figure 5

a similar cross-sectional view, but here looking at the opposite side and with the high-current fusible conductor silver according to the section line VV of Figure 1, and

Figure 6

the longitudinal sectional view of a further other embodiment, in which the sleeve between the low-current-side cap and the shield tube is omitted and the shield tube is a plastic tube with a metallic outer coating.

In all embodiments there is a star-shaped cross section in the center Support body (Figures 4 and 5), which is hollow on the inside. It's made of ceramics, preferably steatite ceramics. It is important that it is a high temperature resistant Material must act. The support body 1 extends almost over the entire length of the Multi-range fuse and is graduated with a smaller radius on the left and a larger radius on the right side, both formed as one piece. The diameter of the support body in the left area is for example 25 mm, while the right one Part has a diameter of 35 mm. The diameter dimension is about diametrical opposite outer edges measured. While the support body with a total of 1 is designated, the part arranged on the left in FIGS. 1, 3 and 6 bears the reference number 1a and corresponding to the part shown on the right in the figures, the reference number 1b.

On the left part 1a of the support body 1 with the smaller diameter is a total fuse element designated 2a with low melting point and for low current wound, which is why the reference number 2a denotes the low-current fuse element is. Accordingly, on the right is a pair of high-current fuse links 2b on the right or high current side part 1b of the insulating body 1 is wound. The fusible conductors 2a and 2b are in the middle on a connector strip 3 made of copper and also with each other electrically and mechanically connected. This also applies if the high-current fuse element that is used for Example preferably consists of silver, in the form of two thinner wires that are parallel run, wound up. Both wires of the fuse element 2b are then on the connecting strap 3 attached by soldering or welding. This makes the series connection of the two Fusible conductor 2a and 2b given.

The low-current fuse element 2a is shown in more detail in FIG. A ladder core 4 extends in the center from one end of the fuse element 2a to the other and is over a distance to form an annular air gap 5 from a silicone tube 6 surrounded, which in turn is coated on the outside with a glass fabric 7, around a reinforcement to be provided for increasing the compressive strength. The conductor core 4 is off in this example Tin. At the ends, the fusible conductor 2a carries an adhesive tape 8, which is an assembly aid represents so that the glass fabric 7 does not dissolve after the cut at the end. To the left, i.e. the low-current end is a connecting lug with the fuse element 2a 9 connected, which is threaded through a connecting disk 10 and held in this. This connecting disc is used to center the support body 1 and is on the outside of a cap welded on. The weld is not shown in the drawings. One differentiates on the left side in the drawings between the low-current side cap 11a and opposite at the other end of the multi-range fuse of the high current cap 11b.

On the two end faces of the caps 11a and 11b there is a clamped cover 12 centrally soldered a nut 13, which has an internal thread, so that an electrical connection after outside is made possible.

While at the low-current end the terminal lug 9 on the metal disc 10th by welding electrically on the low-current side cap 11a electrically and mechanically is connected, at the opposite end on the high current side one is made of a single piece Sheet metal stamped and formed by angling the connecting plate 14 on the support body 1b attached. An angled short flag 15 serves to protect against rotation Support body 1. Via the long flags 16, the connection with the right, i.e. of the high-current side cap 11b created.

Coaxial to the support body 1 and at a distance from it is an insulating sheath 17 appropriate. In the embodiments shown here, this is done by a porcelain tube educated. The annular interior 18 is filled with quartz sand in a manner not shown.

Is located on both ends of the insulating sheath 17, also in the case of a porcelain tube a solder layer 19 is applied externally by means of metallization, over which also the respective cap 11a or 11b is attached to the casing 17.

An important feature of the invention in the embodiment of FIG. 1 consists of a metallic screen 20, which consists of copper or brass and in the form of a metallic Coating 20a directly on the outer surface of the insulating sheath 17 is applied. This metallic coating 20a is also in direct electrical and mechanical connection with the low-current cap 11a, namely via the solder layer 19. This metallic coating 20a in the embodiment of FIG. 1 represents a thin one Metal layer, which by metallizing the porcelain tube, i.e. the casing 17, can be formed. It was mentioned that the envelope 17 outside in the area anyway Caps 11a, 11b is metallized. Now you can start producing the metallic coating 20a the area of this metallization on the low-current side of the solder layer 19 to the right up to the connecting band 3 and even a little way beyond this be expanded. The first 5 to 20 and especially the first 10 mm from the level of Support body 1 with the large diameter to the right to the high current end also still covered by the metallic coating 20a, i.e. which in relation to Tin fuse 2a higher current fuse 2b is made of the metallic coating 20a (also quite generally overlapped by the metallic screen 20). That is not free The end of the metallic screen 20 ends in the area of the low-current cap 11a or the solder layer 19 there, and the opposite end of the metallic screen 20 ends well in front of the high current cap 11b. In other words, the metallic one covers Screen 20 essentially not the high-current fuse element 2b. Just a small part of about 5 - 20% of the length of the high-current part 1b of the support body 1 is from the Screen 20 overlaps or covers. This measure is sufficient to cover the area around the to make low-current fuse element 2a (tin) partially discharge-free. The dielectric strength is up to 10, 12 and sometimes even 15 kV. The potential of the metallic Coating 20a according to FIG. 1 is the same as that of the cap 11a and the low-current side Solder layer 19. The operation is generally high voltage; after switching off and melting down the fusible conductor 2a, usually around earth potential.

The embodiment of Figure 3 differs from that of Figure 1 in that the metallic coating 20a is replaced by a metallic tube 20b. This is in the Area of the low-current side cap 11a via an annular sleeve 21, a kind Intermediate piece or socket. This sleeve 21 is on the outside via the cap 11a attached and sits firmly pressed on by clamping and frictional connection. Thereby the metallic tube 20 is rigid and precise with a constant distance to the center of the entire backup held. This metallic or screen tube 20b is preferably made of Made of brass or copper. If the sleeve 21 is also made of metal, it has metallic tube 20b the potential of the low-current side cap 11a.

In another conceivable embodiment of a mechanical structure as in FIG. 3 however, the sleeve 21 can also be made from an insulating material. Then that's metallic Shielding tube 20b potential-free, since there is no shield 11a on the low-current side electrical connection more.

Such an embodiment can still be improved by having the shield tube 20c and the sleeve 21 made of an insulating plastic and designed in one piece. This embodiment is shown in FIG. 6.

The shield tube designated here with 20c is made of plastic, but carries one on the outside Metal layer 20d. Their potential is free and without any connection to the cap 11a

Reference list

1

Support body

1a

part of the supporting body on the low-current side

1b

part of the support body on the high current side

2a

low-current part of the fuse element (tin)

2 B

part of the fuse element on the high current side (silver)

3rd

Connecting strap

4th

Ladder soul

5

annular air gap

6

Silicone hose

7

Glass fabric

8th

duct tape

9

Connection lug

10th

Connecting washer

11a

low current side cap

11b

high current side cap

12th

cover

13

mother

14

Terminal block

15

short flag

16

long flag

17th

insulating covering

18th

annular interior

19th

Solder layer

20th

metallic shade

20a

metallic coating

20b

metallic pipe

20c

Shield tube with metallic outer surface

20d

Metal layer

21

ring-shaped sleeve

Claims (7)

Multi-area fuse for an electrical connecting line, in particular a cable line between a transformer and a switchgear, with at least two partial fuses which are covered in an insulating sheath (17) and each have at least one fuse element (2a, 2b) wound on a support body (1a, 1b), whereby the multi-range fuse is closed at both its low-current side and at its high-current side end with a cap (11a, 11b), characterized in that a metallic shield (20) in the area of the low-current fuse element (2a) and the connection point (3) to the the next higher-current fuse element (2b), preferably partially overlapping it, is attached to the outside of the insulating sheath (17). Multi-range fuse according to claim 1, characterized in that the metallic Screen (20, 20a) is firmly connected to the low-current side cap (11a). Multi-range fuse according to claim 1 or 2, characterized in that the Screen (20) in the form of a metallic coating (20a) on the outer Surface of the insulating sheath (17) applied and preferably with the low-current side cap (11a) is connected. Multi-range fuse according to claim 1 or 2, characterized in that the Screen (20) in the form of a metallic coating (20a) on the outer Surface of the insulating sheath (17) is applied and preferably an electrical interruption opposite the low-current-side cap (11a) having. Multi-range fuse according to claim 1 or 2, characterized in that the Screen (20, 20b) a solid tube (20b; 20c) with a metallic surface (20d) which is supported on the low-current side cap (11a) and coaxially on the outside extends at a distance around the insulating sheath (17). Multi-range protection according to claim 1 or 5, characterized in that the Shield tube (20b; 20c) with the metallic surface (20d) on one on the low current side End of the insulating sheath (17) attached sleeve (21) Insulating material is attached. Multi-range fuse according to claim 1, 5 or 6, characterized in that the Shield tube (20c) consists of an externally metallized (20d) insulating material.

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