CN113993979A

CN113993979A - Inductive device comprising a container with an insulating liquid

Info

Publication number: CN113993979A
Application number: CN202080042047.8A
Authority: CN
Inventors: N·拉文森; J·施斯琳; L·沃尔弗里德森; M·伯格伦德; O·赫乔特斯坦; M·达伦
Original assignee: Hitachi Energy Switzerland AG
Current assignee: Hitachi Energy Co ltd
Priority date: 2019-06-17
Filing date: 2020-06-05
Publication date: 2022-01-28
Anticipated expiration: 2040-06-05
Also published as: CN113993979B; WO2020254125A1; EP3754674B1; EP3754674A1

Abstract

In an inductive device comprising a container (24) with a winding (20) of an inductive component (12) surrounded by a solid insulator (22), the container (24) is filled with an insulating liquid (26) comprising a first main component in the form of a first oil having an effective resistivity higher than the effective resistivity of the solid insulator, and at least one second auxiliary component in the form of a second oil or additive having a lower equilibrium resistivity, resulting in an effective resistivity of the insulating liquid lower than the effective resistivity of the solid insulator, wherein the first oil is a gas-to-liquid oil and the effective resistivity of the solid insulator is higher than the effective resistivity of the insulating insulatorThe effective resistivity of the liquid is 1 to 10 times higher, the first oil has at least 10¹³An equilibrium resistivity of ohm-meters and the insulating liquid has at least 10¹¹Ohm-meters and an equilibrium resistivity of at most half of the equilibrium resistivity value of the first oil.

Description

Inductive device comprising a container with an insulating liquid

Technical Field

The invention relates to an inductive device comprising a container with an inductive means and an insulating liquid.

Background

Inductive devices, such as transformers, are important equipment in a variety of electrical environments. One such environment is a High Voltage Direct Current (HVDC) environment in which the transformer is subjected to a strong DC potential field.

Dielectric insulation in converter transformers typically comprises liquid insulation (such as in the form of mineral oil) and solid insulation (such as cellulose like paper and cardboard). Solutions utilizing alternative liquids, such as synthetic esters, are also contemplated. The solid insulator is then typically impregnated with and surrounded by a liquid.

The resistivity of the oil is an important factor due to the strong DC potential field to which the transformer and its insulation are subjected.

GB 611254 discusses the resistivity of mineral oils to which additives have been added. This document relates more particularly to a capacitor comprising a mineral oil impregnated spacer as dielectric material. According to this document, when the mineral oil contains a small amount of beta naphthol, the capacitor containing the mineral oil exhibits a significant improvement in high-temperature operation stability and in lifetime. The addition of beta naphthol is described as resulting in a significant decrease in the resistivity of the oil. The stabilizing effect of beta naphthol seems to be related to the effect of electrical stress at high temperature on mineral oil.

GB 426135 discloses the manufacture of capacitors wherein the mixture comprises a non-aqueous organic liquid having high resistivity and good dielectric properties; for example tricresyl phosphate, triphenyl phosphate, aryl phosphates, dibutyl phosphate, trichlorobenzene or mineral oil are used together with the paper. The mixture also contains a non-aqueous organic liquid having a relatively low resistivity and being, for example, cresol, phenol, alpha-naphthylamine, beta-naphthol, aniline, acetic acid, dinitrobenzene or furfural.

When mineral oil or ester oil is used as the liquid insulation for use with cellulosic solid insulators, such as cardboard and paper, the resistivity of the oil is much lower than that of impregnated cellulosic materials.

A new type of liquid insulation, the so-called gas-to-liquid (GTL), has recently emerged. This liquid has a very high purity. It is essentially free of sulfur. For various reasons, this type of oil is of interest for use in transformers. However, the resistivity of oil is high due to its purity. The resistivity is significantly higher than that of mineral oil. This changes the ratio between the resistivity of the oil and the cellulose.

Transformers subjected to a strong DC potential field are subject to DC stress. DC stress in impregnated cellulose insulation is typically higher compared to liquids after a DC voltage has been applied for some time. This is advantageous because impregnated cellulose has a higher dielectric withstand capability. Impregnated cellulose is more stressed because it generally has a higher effective resistivity than a liquid. For GTL and GTL impregnated cellulose, the effective resistivity of the liquid is greater than for the impregnated cellulose. This means that the DC electric field is instead shifted into the liquid, which is weaker in dielectricity than impregnated cellulose, and this has a negative effect on the insulation system.

Therefore, there is a need to reduce the stress of such insulating liquids.

Disclosure of Invention

An aspect of the invention relates to an inductive device comprising a container with a winding of an inductive means surrounded by a solid insulator, wherein the container is filled with an insulating liquid comprising a first main component in the form of a first oil having an effective resistivity higher than the effective resistivity of the solid insulator and at least one second auxiliary component in the form of a second oil or additive having a lower equilibrium resistivity, resulting in an effective resistivity of the insulating liquid lower than the effective resistivity of the solid insulator,

wherein the first oil is a gas-to-liquid synthetic oil, the effective resistivity of the solid insulator is 1 to 10 times higher than the effective resistivity of the insulating liquid, and the first oil has a resistivity of at least 10¹³An equilibrium resistivity of ohm-meters and the insulating liquid has at least 10¹¹Ohm-meters and an equilibrium resistivity of at most half the equilibrium resistivity value of the first oil,

wherein the equilibrium resistivity is the resistivity obtained at room temperature when the insulating liquid is subjected to an electric field strength below 0.01kV/mm in a direct potential field or a slowly varying alternating potential field, wherein the variation is a variation of the frequency below 10mHz, and the effective resistivity is the resistivity during steady state operation when the enclosure is subjected to an electric field strength in the range of 1 to 10kV/mm in a direct potential field.

The equilibrium resistivity of the first oil may additionally be higher than 8 x 10¹³Ohm-meters and the equilibrium resistivity of the insulating liquid may be at 10¹¹-4*10¹³In the range of ohm meters. The equilibrium resistivity of the insulating liquid can additionally be lowered so that it is at 10¹¹–2.5*10¹³In the range of ohm meters.

Thus, the equilibrium resistivity of the second component is lower than the equilibrium resistivity of the first major component.

The first oil may be of more than 1 x 10¹⁴A hydrocarbon oil of equilibrium resistivity in ohm-meters.

The additive may be an organic acid, a metal and ammonium salt of an organic acid, a mixture of a metal and ammonium salt of an organic acid, carbon black and an alcohol like phenol or naphthol, such as beta naphthol. The additives may be added in an amount ranging from 0.001 to 1% by weight, advantageously in an amount ranging from 0.01 to 1% by weight, and preferably in an amount ranging from 0.1 to 1% by weight. The remaining part of the insulating liquid may be the first oil.

The second oil may be a mineral oil. It may also be a synthetic oil or a natural ester oil. When the second oil is a mineral oil, it may be added in an amount ranging from 5 to 49% by weight. The mineral oil is advantageously added in an amount ranging from 10 to 49% by weight. Where the second oil is a natural or synthetic ester, the second component may be present in an amount in the range of from 1 to 40% by weight, more preferably in an amount in the range of from 2 to 20% by weight. In both cases, the remaining part of the insulating liquid may be the first oil.

Thus, the effective resistivity of the at least one second auxiliary component is lower than the equilibrium resistivity of the first main component. During steady state operation, the effective resistivity of the solid insulator is 1 to 10 times higher than the effective resistivity of the insulating liquid. In this case, steady state operation may last in the range of at least 10 to 90 minutes, and for example last at least 60 minutes.

As mentioned above, the equilibrium resistivity is obtained at room temperature, which is typically a temperature in the interval of 20 to 25 ℃.

Additionally, the electric field strength may be an electric field strength obtained during steady state operation of the inductive device.

The present invention has many advantages. It reduces the oil stress that the insulating liquid may be subjected to in a strong direct current potential field. The invention also improves the reliability and safety of the inductor arrangement. It also allows the insulating liquid to be tailored to the environment in which it is used.

In general, all terms used in the claims are to be interpreted according to their ordinary meaning in the technical field, unless explicitly defined otherwise herein. All references to "a/an element, device, component, means, step, etc" are to be interpreted openly as referring to at least one instance of the element, device, component, means, step, etc., unless explicitly stated otherwise. The steps of any method disclosed herein do not have to be performed in the exact order disclosed, unless explicitly stated. The use of "first", "second", etc. for different features/components of the present disclosure is intended only to distinguish the features/components from other similar features/components, and not to impart any order or hierarchy to the features/components.

Drawings

Embodiments will be described, by way of example, with reference to the accompanying drawings, in which:

fig. 1 schematically shows two transformers connected to two converters of an HVDC converter station, an

Fig. 2 schematically shows a liquid-filled transformer according to an embodiment of the invention.

Detailed Description

Embodiments will now be described more fully hereinafter with reference to the accompanying drawings, in which certain embodiments are shown. However, many different forms of other embodiments are possible within the scope of the present disclosure. Rather, the following embodiments are provided by way of example so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art. Like numbers refer to like elements throughout.

The present invention relates to an inductive device comprising a tank with a winding of an inductive device, such as a transformer, in which tank an insulating liquid is provided for the winding. However, before discussing this in more detail, the environment of such an inductive device will first be described with reference to fig. 1.

Fig. 1 shows an inductive device 12 in a converter station 10. The inductive device 12 is a first transformer and this first transformer is connected to the Alternating Current (AC) side of the first converter 14. The first converter 14 has a Direct Current (DC) side connected to a first pole P1 of a High Voltage Direct Current (HVDC) system. Thus, the first converter 14 is also an AC/DC converter. There is also a second transformer 16 connected to the AC side of a second AC/DC converter 18 having a DC side connected to a second pole P2 of the HVDC system. Both

converters

14 and 18 are also connected to a grounded neutral line. Here, the first pole P1 may have a high positive potential, while the second pole P2 may have a second low potential. The potential may be in the range of 100 to 1100kV, 300 to 1100kV or 500 to 1100 kV. For example, the first potential P1 may be +800kV and the second potential-800 kV. In a system, there may also be polarity reversal. That is, in the given example, the first pole P1 may change from having a potential of +800kV to having a potential of-800 kV, while the second pole P2 may change from having a potential of-800 kV to having a potential of +800 kV.

The system in fig. 1 is merely an example. It should be realized that the invention is by no means limited to the HVDC system shown or indeed any DC system. The inductive device is also not limited to a transformer. It may be, for example, a reactor. However, the figure shows that an inductive device such as a transformer may experience a high DC electric field strength due to the environment in which it is provided, even though it acts to switch between different AC levels.

Fig. 2 shows an implementation of the inductive means 13 comprising an inductive device in the form of a first transformer 12. The inductive device 13 comprises a housing (e.g. realized as a transformer tank 24) comprising the transformer windings 20 of the transformer and a solid insulation 22, which is typically cellulose-based, such as pressboard and/or paper. A solid insulator typically surrounds the windings 20. The cellulose is also impregnated in an insulating liquid, which may be the below-described insulating liquid or another insulating liquid, such as a mineral oil or an ester. The impregnated cellulose generally has a content of more than 10¹⁴And sometimes also above 10¹⁵Electrical resistivity in ohm-meters. There is also an insulating liquid 26 in the tank 24.

The insulating liquid 26 is based on a first oil, which in various embodiments is a hydrocarbon oil, such as Gas To Liquid (GTL). Such oils may be isoparaffinic oils having a uniform molecular structure and low impurity levels, and may additionally be substantially free of sulfur. As an example, the oil may be Dial S4 ZX-I from Shell. Alternatively, the first oil may be a hydrocracked isoparaffin oil. This type of oil may haveHigher dc field resistivity than solid insulators. The first oil typically has an equilibrium resistivity of at least 10¹³Ohm-rice. It may be higher than 8 x 10¹³Ohm m, and advantageously at 10¹⁴More than ohm meter. The equilibrium resistivity of the first oil is the resistivity when it is subjected to an electric field strength of less than 0.01kV/mm in a direct current or slowly varying alternating current potential field. The variation is typically a variation with a frequency below 10 mHz. The equilibrium resistivity is additionally obtained at room temperature, such as at a temperature in the interval of 20 to 25 ℃.

In many cases it is desirable to use such oils as insulating liquids in inductive devices. One reason may be that the oil is biodegradable. Thus, the use of such oils may be more environmentally friendly than conventional oils.

Also, by placing the transformer near a high potential (such as the potential of the first pole P1 shown in fig. 1), the transformer 12 with the solid insulator 22 liquid insulator 26 will experience a high DC electric field strength.

It is advantageous if the electrical stresses caused by such high DC electric field strengths are borne by a solid insulator.

However, if GTL oil is used as the insulating liquid, this will not normally be the case, since it has a higher resistivity than solid insulators.

Thus, a shift of the electric field into the oil is possible, which has a significantly lower resistance than solid insulators. With oil having a higher resistivity than solid insulators, the oil is stressed and this may lead to breakdown.

Furthermore, when conducting the DC withstand voltage test, it is important that almost all of the stress is accommodated on the solid insulator.

For polarity reversal, it is desirable that the oil resistivity be less than but close to that of the impregnated cellulose. This ensures that some stress remains in the oil before polarity reversal, thereby limiting the stress in the oil directly after polarity reversal, while ensuring that most of the stress is on the cellulose after some time.

To solve this problem, the first oil used in the housing is the first major of the insulating liquidA component, the insulating liquid also receiving at least one second auxiliary component in the form of a second oil and/or additive having a lower equilibrium resistivity than the first oil. The addition of the second auxiliary component thus results in the equilibrium resistivity of the insulating liquid in the housing being reduced in use. According to an aspect of the invention, the second component is added in an amount such that the equilibrium resistivity of the insulating liquid is at least 10¹¹Ohm-meters and at most half of the equilibrium resistivity value of the first oil. When the equilibrium resistivity of the first oil is higher than 8 x 10¹³The equilibrium resistivity of the insulating liquid may be at 10 ohm-meters¹¹To 4 x 10¹³In the range of ohm meters. The insulating liquid may also have an equilibrium resistivity of 10¹¹To 2.5 x 10¹³In the range of ohm meters.

When the second component is a mineral oil, this second component may be added in an amount ranging from 5 to 49% by weight, or more preferably in an amount ranging from 10 to 49% by weight, while the remainder is the first oil. Where the second component is a natural or synthetic ester, the second component may be present in an amount in the range of from 1 to 40% by weight, or more preferably in an amount in the range of from 2 to 20% by weight, with the remainder being the first oil. Where the second component is an additive, it may be added in an amount in the range of 0.001 to 1% by weight, more preferably in an amount in the range of 0.01 to 1% by weight, and preferably in an amount in the range of 0.1 to 1% by weight, with the remainder being the first oil.

By using the second component, the resistivity is thus reduced, and this may be used to improve the performance of the transformer with the first oil based insulating liquid.

Thus, the first liquid may have received some additive or has been mixed with the second oil. Examples of the second oil are mineral oils or synthetic or natural ester oils, wherein the mineral oils may have a paraffinic structure, a naphthenic structure, and/or an aromatic structure. The mineral oil may additionally contain nitrogen, sulphur and/or oxygen. An example of a natural oil is Nytro 10 XN. Natural or synthetic esters may in turn be derived from organic or inorganic acids and comprise at least one o-alkyl substituted hydroxyl group. An example of a synthetic ester is Midel 7131, while an example of a natural ester is FR 3. When the second component is an additive, it may be an additive of the group of organic acids, metal and ammonium salts of organic acids, and mixtures of organic acids and metal and ammonium salts of organic acids. In this case, the salt of the organic acid may be an organic ammonium, such as tetrabutylammonium. The additive may additionally be carbon based (such as carbon black) or comprise an alcohol like phenol or naphthol (such as beta naphthol).

As mentioned above, the equilibrium resistivity is the resistivity at equilibrium at low field strength. However, as mentioned before, inductive devices are typically used at high electric field strengths.

The resistivity of the insulating liquid is believed to have a severe dependence on the field strength and the time during which it is subjected to a particular DC field. The resistivity depends on the amount of ionized molecules (positive and negative ions). This amount depends on the electric field and thus the resistivity of the insulating liquid will have a dependence on the strength of the electric field.

The resistivity may more particularly be considered to be inversely proportional to the sum of the ion mobilities of the positive and negative ions times the ion concentration times the base charge.

It is therefore important that the added second component causes the insulating liquid to have a resistivity that has a relationship with the resistivity of the solid insulator when operating in such a strong field. This type of resistivity is called the effective resistivity and is the resistivity when the inductive device is subjected to an electric field strength in the range of 1 to 10kV/mm in a direct potential field. The effective resistivity may additionally be a resistivity obtained during steady state operation of the inductive device over a set time. This time may be between 10 and 90 minutes and may be, for example, 60 minutes.

Thus, the first oil may have an effective resistivity that is higher than the effective resistivity of the solid insulator. In this case, the second component also has an effective resistivity lower than that of the first main component. In this case, the second component may be added in an amount such that the effective resistivity of the insulating liquid is lower than the effective resistivity of the solid insulator. The second component may additionally be added in an amount such that the effective resistivity of the solid insulator is 1 to 10 times higher than the effective resistivity of the insulating liquid.

In this way it can be seen that in the case of liquids which are smaller in resistance than solids, a resistivity ratio between solid and liquid insulation can be achieved. In this case, the insulating liquid may still retain some electrical stress. This eliminates the risks associated with high resistance oils in inductive devices. It can be seen that the risk of excessive oil stress at DC may be eliminated and the stress at polarity reversal reduced. Thus, the resistivity of the insulating liquid can be adjusted such that the ratio between the resistivity of the solid insulator and the resistivity of the insulating liquid does not become as large as when mineral oil is used as the insulating liquid. Since the amount of the second component can be adjusted, it will be possible to tailor the insulating liquid to the particular environment in which it is to be used. Whereby the insulation design can be optimized.

The present disclosure has been described above primarily with reference to several embodiments. However, as is readily appreciated by a person skilled in the art, other embodiments than the ones disclosed above are equally possible within the scope of the disclosure, as defined by the appended claims.

Claims

1. An inductive device (13) comprising a container (24) with a winding (20) of an inductive means (12) surrounded by a solid insulator (22), the container (24) being filled with an insulating liquid (26) comprising a first main component in the form of a first oil having an effective resistivity higher than the effective resistivity of the solid insulator and at least one second auxiliary component in the form of a second oil or additive having a lower equilibrium resistivity resulting in an effective resistivity of the insulating liquid lower than the effective resistivity of the solid insulator,

wherein the first oil is a gas-to-liquid synthetic oil, the effective resistivity of the solid insulator is 1 to 10 times higher than the effective resistivity of the insulating liquid, and the first oil has an effective resistivity of at least 10¹³Of AmmiBalanced resistivity and the insulating liquid has at least 10¹¹An equilibrium resistivity of at most half of the equilibrium resistivity value of the first oil,

wherein the equilibrium resistivity is the resistivity at room temperature when the insulating liquid is subjected to an electric field strength below 0.01kV/mm in a direct current potential field or a slowly varying alternating current potential field, wherein the variation is a variation of frequency below 10mHz, and the effective resistivity is the resistivity during steady state operation when the enclosure is subjected to an electric field strength in the range of 1 to 10kV/mm in a direct current potential field.

2. An inductive device according to claim 1, wherein the first oil is of more than 1 x 10¹⁴A hydrocarbon oil of equilibrium resistivity in ohm-meters.

3. An inductive device according to claim 2, wherein the equilibrium resistivity of the first oil is higher than 8 x 10¹³Ohm-rice.

4. An inductive device according to any one of the preceding claims, wherein the additive is an additive in the group consisting of organic acids, metal and ammonium salts of organic acids, mixtures of metal and ammonium salts of organic acids, carbon black and alcohols like phenol or naphthol.

5. The inductive device of claim 4, wherein the additive is added in an amount in the range of 0.001% to 1% by weight.

6. The inductive device of claim 4, wherein the additive is added in an amount in the range of 0.01% to 1% by weight.

7. The inductive device of claim 4, wherein the additive is added in an amount in the range of 0.1% to 1% by weight.

8. An inductive device according to any one of the preceding claims, wherein the second oil is mineral oil.

9. The inductive device of claim 8, wherein the mineral oil is added in an amount in the range of 5% to 49% by weight.

10. The inductive device of claim 8, wherein the mineral oil is added in an amount in the range of 10% to 49% by weight.

11. An inductive device according to any one of claims 1 to 7, wherein the second oil is a natural or synthetic ester oil.

12. The inductive device of claim 11, wherein the second component is present in an amount in the range of 1% to 40% by weight.

13. The inductive device of claim 11, wherein the second component is present in an amount in the range of 2% to 20% by weight.

14. An inductive device as claimed in any one of the preceding claims, wherein the insulating liquid has an equilibrium resistivity of 10¹¹To 4 x 10¹³In the range of ohm meters.

15. An inductive device according to any one of claims 1 to 13, wherein the insulating liquid has an equilibrium resistivity of 10¹¹To 2.5 x 10¹³In the range of ohm meters.