EP2290663B1 - Oil transformer - Google Patents

Description

The invention relates to an oil transformer with transformer tank, wherein at least one oil conservator is connected to the transformer tank via at least one flow channel, wherein at least one enclosed along the flow channel and / or the oil conservator arranged and connected thereto each cavity for the collection of from within the transformer tank and / or the oil expansion vessel released and / or generated gas is provided, wherein the cavity has a closable opening for discharging gas in its upper region.

It is well known that electrical transformers for power distribution networks, for example, with a rated power of 10 MVA to several 100 MVA and, for example, with a nominal voltage of 10 kV to> 400 kV, depending on the embodiment in an oil-filled associated transformer tank are arranged. In particular, transformers in the upper range of the specified rated power band are designed as oil transformers, wherein transformers below the specified rated power band are often designed as dry-type transformers. The oil serves, inter alia, as an electrical insulation medium but also as a cooling medium for dissipating heat generated during the transformer operation loss heat.

The transformer oil increases or decreases in this case depending on the operating oil temperature its volume, so that usually an oil expansion vessel is provided by which such volume fluctuations are compensated. The Ölausdehnungsgefäß is usually located above the transformer tank and connected via a connecting channel with its inner hollow portion. While older embodiments of oil balancing vessels were open at the top, they are now increasingly designed to be closed at the top, in each of which an air-filled membrane is arranged in the interior. Depending on the state of expansion of the oil in the transformer, the membrane is more or less compressed, so that the interior of the transformer tank, the oil balance vessel and the connecting channel connecting them form a closed cavity system, which for example also has an advantageous effect on a reduced risk of contamination of the oil.

In order to be able to discharge gases possibly arising in the oil during the transformer operation, for example due to arcing due to a faulty insulation location, a cavity for collecting gas is usually provided at the topmost point, from which the collected gases, if necessary, via a suitable closure means can be drained to the outside.

So is from the document US 3344380 a control transformer with recessed in the transformer tank tap changer, in which from the load switch container to a Dehngefäß leading oil line a discharge of rising switching gases serving bleed valve is inserted. There is a common expansion space for the boiler oil and the switch oil whose oil level is completed by an inert gas cushion or by an elastic membrane against the outside air provided.

It is also known that in oil transformers for the early detection of faults within the transformer, such as a faulty isolation, regularly oil samples are tapped, which are then an evaluation - for example, in a chromatograph - fed. The transformer oil contains a large number of indication factors which provide information about the condition of the transformer. In the case of faulty insulation between two adjacent turns, for example, arcing phenomena may occur, including gas formation, which in turn lead to entries in the transformer oil, which is known to the person skilled in the art, however.

Usually, a larger part of the tapped oil samples is returned to the oil transformer after analysis so as to counteract a loss or consumption of the oil. This has since been done by feeding the analyzed oil sample in the upwardly open oil balance tank. This also has the advantage that the oil sample can escape over a longer period of gases, which were solved during their analysis in this. These gases do not get into the interior of the transformer tank in this way, but rather degassing takes place in the upwardly open oil conservator.

In fact, an analysis of oil samples, for example in a chromatograph or in a gas chromatograph, usually requires the use of a carrier gas - for example argon - which is then at least partially dissolved in the oil sample during the analysis. The outgassing of the carrier gas from the oil sample is a longer process, which can take several days, wherein an occurrence of a gas such as argon within the transformer tank is to be avoided in any case.

Based on this prior art, it is an object of the invention to provide a transformer with the possibility of returning oil samples. It is also an object of the invention to provide a corresponding method for returning oil samples.

This object is achieved by an oil transformer of the aforementioned type. This is characterized in that in addition to the at least one flow channel further means are provided to introduce a liquid into the enclosed cavity.

By introducing a liquid, in particular an oil sample into the cavity, which is provided for the collection of gas generated during operation, it is ensured that the gas escaping the oil sample over time, especially the carrier gas, which in the analysis of Oil sample was entered into this, over a longer period of time, for example several hours to several days, can escape, without going to the overwhelming extent directly into the transformer tank itself.

The cavity for collecting gas is usually at the highest point, but at least in the upper region of the formed from transformer tank and oil conservator Cavity provided and thus fluidly separated from the transformer tank at least by a flow channel. The returned oil in the cavity so can not get directly into the transformer tank, so that there is usually a sufficient period of time for degassing.

Since this cavity already has a closable opening for discharging gas in its upper region, the gas escaping from the returned oil sample can also be removed from the cavity system without additional effort.

The means for introducing a liquid or an oil sample into the cavity include, if necessary, a device for increasing the pressure, such as a pump or a manual dosing, so as to be able to ensure the return also contrary to the prevailing in the inner cavity system pressure. Advantageously, the return takes place via a closable introduction into the cavity, which can be opened and closed, for example, by a tap or a valve.

In a preferred embodiment of the oil transformer, the means for introducing are provided to initiate the liquid through the already provided for the discharge of gas opening in the at least one cavity. In this way, no further opening through the wall of the cavity is necessary, the return of the oil sample is rather by the already existing for the discharge of gas opening, which is formed for example as a pipe. In the further course of the pipe then a branch point is to be provided, for example, a T-piece, which then lead to a channel for oil return and a channel for discharging gas.

In a particularly preferred variant of the oil transformer, the oil expansion vessel is closed at the top and a compressible membrane is arranged inside the oil expansion vessel, wherein an opening is provided in the upper region of the oil expansion vessel, which opens into a cavity for collecting gas. In such an arrangement, the advantages of the invention are particularly significant, because this is a closed cavity system for Oil, which does not allow easy return of the oil in an open-topped oil conservator.

In a further preferred embodiment of the oil transformer, the at least one cavity for collecting gas is formed by a Buchholz protection relay.

A Buchholz protective relay is a common protection device in oil-cooled transformers which is usually located in the flow channel to the oil conservator. Insulation failure or severe overload of a transformer lead early to a local overheating in the transformer, which causes gas to develop in the oil room of the transformer. The gas bubbles collect in the upper part of the housing of the Buchholz protection relay and displace the oil. In the case of small errors, this causes a float to be pushed down when a sufficient amount of gas has accumulated and a contact closes, which signals an error. For significant and immediate errors such as a sudden overpressure, which causes a strong flow of oil. As a result, a switch is closed with the help of a Stauschiebers, which switches off the transformer immediately and thus protects against further damage. Buchholz protection relays usually have a closable opening for the automatic discharge of collected gas.

A Buchholz protective relay thus has essential components required according to the invention, namely a connection possibility to the inner cavity system with transformer tank and oil conservator, a cavity for collecting gas and a discharge device for collected gas. It is therefore particularly advantageous for use in an oil transformer according to the invention, with only appropriate modifications to the closable opening are necessary. Preferably, such a Buchholz protective relay is mounted in the flow channel between transformer tank and oil conservator and / or but also to the closable opening of a closed-top oil conservator. It is both an arrangement of a single Buchholz protection relay on an oil transformer and the arrangement of several conceivable, in the latter case, only a single of the several Buchholz Protection relay must be provided for the inventive repatriation of oil samples.

In a further embodiment of the oil transformer according to the invention, the opening provided for the discharge of gas is provided with a three-way cock with at least two external terminals, wherein the third terminal is connected to the cavity for collecting gas. A three-way cock is a device to connect a pipe-like port or an opening optionally with one of two further tube-like connections. Due to the simple construction and its robustness, a three-way cock is particularly suitable for selectively connecting the opening from the cavity for collecting air with a supply or discharge opening.

In a further embodiment of the invention, the opening for discharging gas can be closed by a valve means. By such a valve means, for example, both a rotatable faucet-like closure and a for example, magnetic or pneumatically controlled shut-off valve to understand. In particular, a controlled shut-off valve simplifies an automation process.

In a variant of the invention, at least one closable opening for removing oil is provided on the transformer tank. Such an opening is provided for example with a lockable cock or other closure means. Thus, a removal of oil samples from the area of the transformer tank is guaranteed. Preferably, a plurality of such removal points are provided so as to ensure a representative extraction of oil samples even in non-homogeneous oil distribution within the transformer tank.

• Unterbrechen eines durch eine verschließbare Öffnung aus einem Hohlraum zum Sammeln von Gas führenden Luftablasskanals, wobei der Hohlraum seinerseits direkt oder indirekt über einen Verbindungskanal in den Transformatorkessel mündet
• Herstellen eines Verbindungskanals zwischen dem Hohlraum und einer Zuführstelle
• Einführen der Ölprobe in die Zuführstelle und Rückführen des Öls in den Hohlraum durch den zuvor hergestellten Verbindungskanal
• Unterbrechen des zuvor hergestellten Verbindungskanals zwischen dem Hohlraum und der Zuführstelle
• Wiederherstellen des durch eine verschließbare Öffnung aus einem Hohlraum zum Sammeln von Gas führenden Luftablasskanals

The object according to the invention is also achieved by a method for returning an oil sample to an oil transformer according to the invention with the following steps:

• Interrupting a vent passage leading through a closable opening from a cavity for collecting gas, wherein the cavity in turn opens directly or indirectly via a connecting channel in the transformer tank
• Producing a connection channel between the cavity and a feed point
• Introducing the oil sample into the feed point and returning the oil into the cavity through the previously established communication channel
• Breaking the previously established connection channel between the cavity and the feed point
• Restoring the air discharge passageway through a closable opening from a cavity for collecting gas

The achievable advantages correspond to the advantages explained above in the description of the oil transformer according to the invention. It is conceivable both a purely manual process, a partially automated process and a fully automated process.

In a further embodiment of the method according to the invention, the oil sample to be returned is taken from the transformer tank and analyzed at its beginning.

Further advantageous embodiment possibilities can be found in the further dependent claims.

Reference to the embodiments illustrated in the drawings, the invention, further embodiments and other advantages will be described in detail.

Fig. 1:

einen exemplarischen Öltransformator in einer ersten Ausführungsvariante

Fig. 2:

einen exemplarischen Öltransformator in einer zweiten Ausführungsvariante

It shows:

Fig. 1:

an exemplary oil transformer in a first embodiment

Fig. 2:

an exemplary oil transformer in a second embodiment

Fig. 1 shows an exemplary oil transformer in a first embodiment 10, which has both an actual electric transformer 11, so a transformer core with winding, and a transformer tank 12.

The transformer tank 12 is completely filled with an oil filling 13 -shadowed. The oil filling 13 serves both as an isolation medium and as a cooling medium. The transformer 11 is supported on several stand blocks 36, which remove its weight on the base 34.

The oil filling 13 of the oil transformer 10, which has, for example, an expected life of 40 years, has been in the transformer tank 12 for a long time, for example a few years. It therefore also has traces or entries of gassing processes within the transformer 11. Typically, multiple insulators are used within the transformer winding. If, in the case of a local fault - for example, in a local failure of an insulating layer between two adjacent winding conductors - a strong warming occurs, so guest from the affected insulation material, with entries of such degassing are then included in the transformer oil 13.

An analysis of the transformer oil 13 therefore allows conclusions to be drawn about such a creeping fault, ie an error which does not directly and immediately restrict the functionality of the transformer 11, but leads to lasting damage to the transformer 11 in the short or medium term. With a serious immediate fault such as a short circuit, which then leads to a significantly increased short-circuit current, the transformer is taken by appropriate protection devices usual way directly from the network.

In the upper region of the transformer tank 12, a flow channel 16a is branched off, which opens into a first above the transformer tank 12 arranged first Buchholz protection relay 26a. This first Buchholz protective relay 26a has a first enclosed cavity 18a, the upper region of which is provided for collecting gases possibly arising or emerging in the transformer oil 13, the lower region also being filled with transformer oil 13. In the upper left area of the Buchholz protection relay 26a, a first opening 20a is provided, which is provided according to the actual purpose of a Buchholz protection relay only for discharging the collected gases. The opening 20a is closable with a second valve means 25b. Further Details of the Buchholz protective relay, such as a float, are not shown in the drawing, but are nevertheless believed to be present.

Also connected to the first opening 20a of the first Buchholz protective relay 26a is a first valve means 25a, which is preferably only to be opened alternately to the second valve means 25b. If an oil sample is now returned to the oil transformer 10 after the oil analysis, the second valve means 25b must first be closed and then the first valve means 25a opened. In the case of a three-way stopcock, the opening and closing would occur synchronously by the rotation of a stopcock element, with the three-way stopcock then combining both the first 25a and the second 25b valve means.

An oil funnel 24 and a connected to the drain pump 22 together with the first valve means components of the means for the oil return. The return oil to be completely filled for example in the oil funnel 24 and subsequently with the pump 22 in the first enclosed cavity 18 a of first Buchholz protective relay 26a to pump. A pump 24 is advantageous in this case to pump in the oil against the pressure prevailing in the first inner cavity 18a overpressure. But it is also quite a syringe-like manually operated cylinder piston device conceivable to build a required back pressure.

The now pumped into the first inner cavity 18a oil leads to a partial displacement of oil already in the cavity 18a, which then flows according to the path of least resistance predominantly via a second flow channel 16b in an associated with the first Buchholz protection relay 26a oil conservator 14 ,

The recirculated oil contained in the first inner cavity 18a now predominantly - depending on the usually sluggish operational volume fluctuations of the transformer oil 13 - silent and guest over a longer period of time, without the liberated in the course of time gases, such as argon, directly into the Transformer boiler 12 with oil filling 13 arrive. Rather, the released gases are in the upper region of the first cavity 18 a of the first Buchholz protection relay 26a collected over a period of time and when exceeding a certain amount of collected gas automatically - according to the function of a Buchholz protective relay - via the first opening 20a and the second valve means 25b in the direction of the arrow 40.

The oil expansion vessel 14 is closed in its upper region with a closure 28. Apart from the closable openings 20a, 20b, the transformer tank 12, the flow channels 16a, 16b, 16c and the oil conservator 14 form a connected and closed cavity system. To compensate for the operating temperature-related volume fluctuations of the oil volume, a compressible membrane 30 is provided in the interior of the oil expansion vessel 14, which is filled with air, for example. Depending on the volume to be leveled, this membrane 30 is compressed more or less.

In the upper right area of the oil conservator 14, an opening 44 is provided, which opens via a third flow channel 16c in a second Buchholz protection relay 26b. Such a Buchholz protective relay serves primarily to monitor the compressible membrane 30, wherein bursting of this membrane leads to an immediate release of the amount of air contained therein. In such a case, this amount of air passes via the opening 44 and the third flow channel 16c connected thereto into the second inner cavity 18b of the further Buchholz protective relay 26 and, due to the sudden rise, leads to an error triggering there. Of course, it is possible to connect the second Buchholz protection relay 26b directly to the opening 44 of the oil conservator 14, whereby the third flow channel 16c would be infinitesimal short in this case.

The second Buchholz protective relay is provided in its upper region with a second opening 20b, which is closable with a second valve means 25b and via which, if necessary, in the direction of the arrow 40 in the cavity 18b collected gas can be discharged.

Fig. 2 shows an exemplary oil transformer in the second embodiment 50. The second embodiment 50 substantially corresponds to the first embodiment 10, wherein the same reference numerals have been used for identical components.

In the second variant, means, namely a first valve means 25a, a pump 22, and an oil funnel 24 are now provided to allow oil return into the second enclosed cavity 18b of the second Buchholz protection relay 26b. Their operation is analogous to the means described in the first embodiment for the return of oil into the first enclosed cavity 18a of the first Buchholz protective relay 26a. However, these are no longer shown in the second embodiment 50.

LIST OF REFERENCE NUMBERS

10

Exemplary oil transformer in the first embodiment

11

transformer

12

transformer tank

13

oil filling

14

Oil conservator

16a

first flow channel

16b

second flow channel

16c

third flow channel

18a

first enclosed cavity

18b

second enclosed cavity

20a

first closable opening

20b

second closable opening

22

pump

24

oil funnel

25a

first valve means

25b

second valve means

26a

first Buchholz protection relay

26b

second Buchholz protection relay

28

Upper end of the oil conservator

30

compressible membrane

32

Opening for removal of oil

34

footprint

36

stand blocks

38

Return of oil

40

Drain of gas

42

transport container

44

opening

50

Exemplary oil transformer in the second embodiment

Claims (9)

1. Oil-filled transformer (10, 50) comprising a transformer tank (12), wherein at least one oil expansion vessel (14) is connected to the transformer tank (12) by means of at least one flow channel (16a, 16b, 16c), wherein at least one enclosed hollow space (18a, 18b), which is arranged along the flow channel (16a, 16b, 16c) and/or on the oil expansion vessel (14) and is respectively connected to the said oil expansion vessel, is provided for collecting gases which are released and/or produced within the transformer tank (12) and/or the oil expansion vessel (14), wherein the hollow space (18a, 18b) has, in its upper region, a closable opening (20a, 20b) for discharging gas, characterized in that, in addition to the at least one flow channel (16a, 16b, 16c), further means (22, 24, 25a) are provided for conducting a liquid into the enclosed hollow space (18a, 18b).
2. Oil-filled transformer according to Claim 1, characterized in that the means (22, 24, 25a) are provided for conducting the liquid into the at least one hollow space (18a, 18b) through the opening (20a, 20b) which is provided for discharging gas.
3. Oil-filled transformer according to either of Claims 1 and 2, characterized in that the oil expansion vessel (14) is closed (28) at the top, in that a compressible diaphragm (30) is arranged within the oil expansion vessel (14), and in that an opening (44) is provided in the upper region of the said oil expansion vessel, which opening issues into a hollow space (18b) for collecting gas.
4. Oil-filled transformer according to one of the preceding claims, characterized in that the at least one hollow space (18a, 18b) for collecting gas is formed by a Buchholz protective relay (26).
5. Oil-filled transformer according to one of Claims 2 to 4, characterized in that the opening (20a, 20b) which is provided for discharging gas is provided with a 3-way tap having at least two external connections, wherein the first connection is provided for discharging gas (40) and the second connection is provided for supplying the liquid (38).
6. Oil-filled transformer according to one of the preceding claims, characterized in that the opening for discharging gas (20a, 20b) can be closed by a valve means (25b).
7. Oil-filled transformer according to one of the preceding claims, characterized in that at least one opening for removing oil (32) is provided on the transformer tank (12).
8. Method for returning an oil sample to an oil-filled transformer (10) according to Claim 7, comprising the following steps:

   • interrupting an air discharge channel which leads through a closable opening (20a, 20b) out of a hollow space (18a, 18b) for collecting gas, wherein the hollow space (18a, 18b), for its part, issues into the transformer tank (12) directly or indirectly by means of a connecting channel (16a, 16b, 16c)

   • establishing a connecting channel between the hollow space (18a, 18b) and a supply point (24)

   • inserting the oil sample into the supply point (24) and returning the oil to the hollow space (18a, 18b) through the previously produced connecting channel

   • interrupting the previously produced connecting channel between the hollow space (18a, 18b) and the supply point (24)

   • re-establishing the air discharge channel which leads through a closable opening (20a, 20b) out of a hollow space (18a, 18b) for collecting gas.
9. Method according to Claim 8, comprising the following additional steps at the beginning of the method:

   • removing an oil sample from the transformer tank (12)

   • analysing the oil sample.

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