FI95328C - Transformers surge protection - Google Patents

Abstract

An overvoltage protection system for a transformer, designed to conduct a surge which has strayed into an electric line to earth, said transformer comprising a frame (1) and, mounted on top of it, feedthrough insulator (2), to which the electricity from the line conductors (3) flows via downleads (4), overvoltage protection being formed by a spark gap (7) provided between protective horns (5, 6) mounted in connection with the feedthrough insulator (2). The overvoltage protection system comprises a by-pass rail (8) extending substantially horizontally from the top end of the feedthrough insulator (2), the downlead (4) from the disconnector above being passed to one end of this rail, a downward directed first protective horn attached to the end of the by-pass rail (8) and forming an essentially straight extension to the downlead, and a second protective horn (6) mounted on the transformer frame (1) and placed below the first protective horn (5), said second protective horn (6) being connected from the transformer frame to earth by means of a separate earth conductor (10).

Description

1 95328

TRANSFORMER OVERVOLTAGE PROTECTION

The invention relates to overvoltage protection of a transformer, in particular a distribution transformer, as defined in the preamble of claim 1 '.

It is known that during a thunderstorm, the voltage difference between the earth and the cloud increases large. In most cases, the cloud is prepared to be more positive than the ground, i.e. the eruption occurs more often from the cloud to the ground than vice versa.

10 However, the surge protectors used also work in lightning strikes from the ground to the cloud.

The following is known about the lightning-induced surge and its behavior. According to Kirchhoff's and Ohm's law, the surge wave is partially branched, ie 15 several routes are discharged into the ground and from there the most can be reached, ie where the resistivity of the medium is as small as possible. When a surge travels at a speed of about 1/3 light at a direct line to a sharp bend in the conductor, the surge is not able to follow the conductor of 20 earth, but an explosion (arc, Korona) occurs in the bend, after which the discharge has to find a new path inducing nearby metals and lie. In addition, the surge behaves unpredictably. For example, while 25 lightning may have jumped miles from cloud to ground, it may also jump a few meters from one of its various structures to another with a transformer.

The surge wave is best tamed and the transformer is shielded by providing a path that is advantageous to the surge wave for the surge wave and a tip spacing to be installed in the right place, where the lower tip forms a strong ground potential electrode. When the overvoltage is discharged in the tip gap, an arc is created and an earth fault occurs. To turn off the arc, the automatic-35 relays cut off the power to the mains for about a second. A power failure is called a quick reconnect (Pjk).

95328 2

The prior art has not been taken into account with sufficient precision in the prior art currently in use. Mistakes are made in small details, causing the flash to even entice 5 to damage the transformer. The most common damages in known transformer designs are: burning of the transformer winding, sooting and cracking of the oil-filled bushing, and rupture of the outer casing of the oil-filled transformer by arc melting 10 or cracking of the outer casing by internal explosion bulging. In other words, the problem with the prior art is that the surge wave cannot be safely and reliably guided past the transformer and its various parts, but the surge wave can often damage the various parts of the transformer.

The object of the invention is to eliminate the above-mentioned drawbacks. In particular, it is an object of the invention to provide a new type of transformer overvoltage protection which effectively prevents the surge wave from entering the various structures of the transformer 20 and directs the surge wave without facing the transformer to the ground.

With regard to the features characteristic of the invention, reference is made to the claims.

According to the invention, the surge protection of the distribution transformer comprises a transformer bushing insulator. a bypass rail extending substantially horizontally from the upper end, to the other end of which a mustache coming from above a separator is connected. In addition, a downwardly directed first horn 30 is attached to this same end of the bypass rail, forming a substantially straight extension to the mustache. In addition, a second protective horn is located on the transformer body, which is located below the first protective horn and is connected to ground by a ground conductor separate from the transformer body. Similarly, like the first shield horn and the mustache, the second shield horn and the ground wire departing therefrom form a substantially straight, downward conductor connection with no significant bends or curves in which the surge wave would not be able to follow the conductor.

Thus, in the structure according to the invention described above, it is essential that the surge wave towards the transformer 5 is guided along the entire structure of the transformer along substantially straight and only evenly curved or circular paths so that the surge wave, regardless of its magnitude, can follow conductors without significant arcs and bends. of course, the arc created in the spark gap.

Preferably, the second protective horn is attached to a support rail resting on the transformer body. In this case, the corresponding second shields of the different phases can all be attached to a common, same support rail, in which case the earth conductors can be connected as a common earth conductor by conductors running from the shield horn and the support rail.

The advantage of the overvoltage protection 20 according to the invention compared to the prior art is that the surge wave can be safely controlled past the entire structure of the transformer, so that the transformer is not damaged by the surge wave, but after quick reconnection the transformer is always fully operational.

♦ In the following, the invention will be described in detail with reference to the accompanying drawings, in which Fig. 1 shows a surge protection of a distribution transformer according to the prior art, Fig. 2 shows another solution according to the prior art and Fig. 3 shows a surge protection according to the invention.

Figure 1 shows a typical transformer built to the end of the 1970s, where lightning protection is implemented in the air gap 7 formed by the protective horns 5 and 6 mounted on the transformer bushing insulator 2. The lower protective horn 6 is ground potential through the transformer body 1 and the upper protective horn 5 is (usually 20kV). There is oil inside the transformer, as well as oil inside the bushing insulator 2 and a conductor along which electricity is introduced into the windings inside the transformer. Suo-5 and the horns are in the right place for protection, but in the wrong position.

When the lightning strikes the line 3 and the traveling wave, i.e. the surge wave, travels towards the transformer, the first explosion tapahtuu takes place in the terminal holder 17 (the straight conductor 3 10 ends). From the terminal holder, the wire usually leaves at an angle of 90 degrees upwards. This is the wrong direction for lightning, as it seeks the shortest path to the ground. In explosion A, the surge wave branches up and down directly into the sj connection line, i.e. to the mustache 4. The second rä-15 cooling B takes place on the basis of the observed traces in the bend at the upper end of the harrier rail. This can cause some of the plunge to continue into the transformer windings, damaging them (explosion C). The second part of the surge wave jumps from point B of the explosion, as is often observed on the basis of melt traces, through protective horns 5 and 6 to the transformer body 1, which is earthed to 18 ground. If the protective horn 6 has been poorly attached to the transformer cover from its attachment point (oxidized, paint in between), an explosion D will occur at the poor connection point and the resulting arc will burn a hole in the transformer cover.

The flammable transformer oil then leaks into nature, almost invariably causing a fire in the transformer and the environment. The outer sheath, i.e. the body 1, of a transformer filled with transformer oil 30 should not be used as part of the earth conductor. The weakness of this method of protection has been the electrical disturbances caused by animals in the tip gap 7. As a result, the tip gap 7 must have been unnecessarily long, even if there was a need to increase the overvoltage protection by shortening the tip gap 7.

A common installation error in the situation of Fig. 1 is that the mustache 4 supplying electricity is introduced 95328 5 directly from above into the straps of the bushing insulator 2. The mustache 4 does not hook from the side. In this case, the explosion B takes place right at the upper or lower end of the grommet 2 (explosion C) as a result of the insulator going into 5 pieces. In addition to the situation in Figure 1, the explosion B creates a third discharge path for the surge wave, in which a light arc sootes the outer surface of the grommet 2 and burns a hole in the transformer cover at the base of the grommet 2.

In addition, a type of transformer according to Fig. 2 is known, in which the surge protection horns 20 and 21 are raised to the highest level, even above the conductor 22. The air gap 23 (spark gap) is then horizontal. It thus does not take into account the fact that 15 lightning strikes from the cloud towards the earth. In addition, upon arrival at the first detonation point A, the propagation wave caused by the lightning strike may continue an almost linear downward motion through the mustache 24 to the transformer 25. The surge wave in the conductor 22 the tidal wave has already traveled a long way down the mustache 24. This downward "suction" 25 could be reduced by removing the ground 26 from the transformer housing, but other more important reasons prevent it from being removed. When the protective horns are installed at the highest point of the transformer, the grounding acts as an excellent lightning arrester for direct lightning strikes, but the surge and travel wave discharged through the grounding conductor 30 In this case, the protective horns are in the wrong place and in the wrong position for the transformer.

Figure 3 shows an overvoltage protection of a converter according to the invention, which eliminates the above-mentioned problems. It is important for the close protection of the transformer, 95328 6, that the protective horns 5 and 6 are installed in the vicinity of the bushing insulator 2. What is new is that the Viik-4 coming from above is brought as straight as possible from the upper end of the bushing insulator 2 to the end of the substantially horizontal bypass rail 8, which also has a substantially straight and downwardly extending horn horn 5. A protective cover 12 around the bypass rail 8 prevents animals access to electronic metal parts. Likewise, what is new and inventive is that the ground conductor 10 exits directly from the support rail 11 below the spark horn 6 as a substantially direct extension thereof, whereby no explosion points are formed on the surge wave. Thus, the easily damaged transformer body 1 is not used as a surge path. With the bypass rail 8 and the support rail 15, the spark gap 7 can be adjusted sufficiently far horizontally from the bushing insulator 2. In this case, the arc 2 possibly in the tip gap 5-6 cannot soot the bushing.

Protective horns 5 and 6 can be curved. In this case, the upper horn 5 of the 20 can form a triangle when viewed from the side, the function of which is to derail e.g. the twigs from the tips. The protective horns 5 and 6 can also be of other shapes, e.g. sharp tip electrodes.

The bypass rail 8 is mounted slightly inclined and 25 downwards and outwards at an oblique position. In this case, the rainwater • flows outwards and it is more difficult for the surge wave to move in the direction of the through-crossing 2.

The application of Figure 3 also includes a previously known protective snout 13, 30 mounted in the air gap 7, the function of which is to prevent animals (mostly birds and squirrels) from settling between the protective horns 5 and 6 to cause an earth fault (pjk). The orsi is plate-shaped and gently sloping outwards. When the arc ignites from the protective horn 5 towards the horn 6, it collides with a plate-35-like, downwardly oblique orifice 13. On the collision, the arc is crushed and ejected away from the bushing insulator 2 due to the position of the orifice 2, a · K & il BlftAl 1.1 1: «t * _« 9532 soot insulator. This crushing also causes the resulting arc to break quickly, leaving no quick reconnection (pjk). The plate-like stem also prevents the animals from approaching the tips 5 and 6 from the lateral direction 5 at the same time, so that the arc caused by the animals does not come. For this reason, the shape of the ore makes it possible to shorten the tip gap 7, whereby the overvoltage protection of the transformer is improved.

The plate-like stem (bird spike) shown can also be installed elsewhere than in the transformer bushing insulator, e.g. a separator, shown here.

In addition, the overvoltage protection of Fig. 2 includes a protective member 16 connected to the ground conductor 15 of the body of the disconnector 9, which extends above the conductor 3 and the disconnector 9 15. This bypass arrangement directs direct lightning strikes from above past transformer structures directly to the ground.

The above-mentioned overvoltage protection according to the invention thus effectively controls the surge wave caused by the lightning 20, which is strayed into the electrical parts, past the transformer without damaging it. At the same time, short power outages are significantly reduced.

The invention has been described in detail above with the aid of the accompanying drawings, in which various embodiments of the invention are possible within the scope of the inventive idea defined by the claims.

Claims (10)

95328 8 1. Surge protection of a transformer for conducting a stray wave to the electrical conductor to the ground, the transformer 5 comprising a body (1) and bushings (2) on it, to which electrical conductors (3) pass through mustaches (4), the surge protection being provided by 5,6), characterized in that the overvoltage protection comprises - a bypass rail (8) extending substantially horizontally from the upper end of the bushing (2), to the end of which a mustache (4) runs from the top of the separator (9); a first protective horn (5) which is a substantially straight extension for the mustache, and - a second protective horn (6) resting on the transformer body (1) below the first protective horn (5) connected to the ground by a separate earth conductor (10) from the 20 transformer body. Surge protection according to Claim 1, characterized in that the second protection horn (6) is fastened to a support rail (11) which rests on the transformer body (1). . Surge protection according to Claim 2, characterized in that the second protective horns (6) of the various phases are fastened to a common support rail (11). Surge protection according to Claim 3, characterized in that the earth conductors (10) run separately downwards from the second protective horns (6) and merge in a circular shape into a lower common earth conductor. Surge protection according to one of Claims 1 to 4, characterized in that the bypass rail (8) gently guides the bushing (2) 9 95328 downwards from the upper end, preventing rainwater from flowing over the bushing. Surge protection according to one of Claims 1 to 5, characterized in that the bypass rail (8) has an insulator (12) to prevent animals from entering the electrical metal parts. Surge protection according to one of Claims 1 to 6, characterized in that the spark gap (7) between the protective horns (5, 6) comprises a substantially horizontal and plate-shaped protective trough (13) resting on the bushing (2). Surge protection according to Claim 7, characterized in that the plate-shaped shield (13) must extend downwards from the bushing insulator (2), pointing away from the bushing insulator coming from above. Surge protection according to one of Claims 1 to 8, characterized in that the transformer body (1) is earthed by a separate earth conductor (14). Surge protection according to one of Claims 1 to 9, characterized in that a protective element (16) extending above the conductor (3) and the separator (9) is connected to the earth conductor (15) of the separator (9) body to direct direct lightning strikes from above directly to the transformer structures. X ♦ «95328 10 1. Transformers with a voltage to the mains of the transformer (5), with a single voltage to the transformer (3) (4), in which case the cross-linking means are used (7), in which case the contactors of the genome-10 are isolated (5, 6); (8), the shaft is not shown in Figure 15 (4), up to a maximum of 9 (4), - that the shunting unit is a cross-section of the power supply (5), andra skydds-20 Horn (6) at the side of the side of the transformer (5) genomen en frän transformatorns stomme separat jord nigsledning (10) account jorden. 2. A transverse embodiment according to claim 1, which comprises a transverse arrangement, the hornet (6) being provided with a transformer stem (1) as a stem (11). 3. A transverse embodiment according to claim 2, which can be used as a tool (6) and in the same embodiment 30 (11). , 4. The translation of claim 3, which is incorporated herein by reference in its entirety (10), may be used as a result of the use of the same method (6). 5. Reference to a patent according to claims 1 to 4, to which reference is made, Fig. 95328 11 Shuntskenan (8) Lutar svagt nerät frän genomförings-isolatorns (2) Övre ända förhindrande att regnvatten * Rinner pä genomföringsisator. 6. A transverse arrangement according to claims 1-5, paragraphs 1-5, according to which a shunt (8) is provided with an insulating (12) for a first-time connection of an electric metal connection. 7 <. The transverse isolates are shown in claims 1 to 6, and the transverse insulators (7) are provided with a transverse isolator (5, 6) according to the genomic isolation isolator (2). 8. A transverse embodiment according to claim 7, which is defined in the preamble of claim 15, (13) further comprising a genomic isolating device (2). 9. A transverse view according to claims 1 to 8, comprising 20 transforming stations (1) and having separate separation means (14). 10. The transverse conditions of the invention are set out in claims 1-9, which are incorporated into the provisions of this Regulation (9) by means of a number of provisions (15) which apply to the reference number (3) and * * * of the reference number. (16) For the purpose of implementing this Directive, the design of the trans-formator construction is not appropriate. «• I k