Instrument transformer and method to isolate parts

The present invention relates to an instrument transformer and a method, for high current and/or high voltage conver sion, comprising a housing and at least an active part, which is electrically insulated by an isolation material.

Oil insulated instrument respectively measurement transform ers are for example known from US 5 391 835 A. The instrument transformers are used to measure high currents and/or voltag es, particularly in the range up to some hundred Ampere and/or up to 1200 kV. An instrument transformer comprises a housing and at least an active part, which includes a measur ing assembly. The measuring assembly comprises for example windings arranged around an electric conductor, which can be used to measure a current in the conductor by magnetic induc tion in the windings. The active part is electrically insu lated by an isolation material from the housing of the in strument transformer. The whole measuring assembly or parts of the measuring assembly are wrapped by kraft paper sheets and the housing is filled by oil, to electrically insulate active parts.

An insulation of the measuring assembly by kraft paper, par ticularly paper tape respectively paper sheets, is carried out by manually taping the measuring assembly. A manual tap ing procedure takes much time, is expensive due to manpower costs and suffers from human errors. Due to complex shapes of parts of the measuring assembly, an automation of taping pro cedures is difficult and expensive.

An object of the present invention is to overcome the prob lems described above. Especially an object of the present in vention is to describe a method to insulate parts of an in strument transformer and an instrument transformer with elec- trically insulated parts, with an easy to produce and cost- effective insulation.

The above objects are achieved by an instrument transformer for high current and/or high voltage conversion according to claim 1 and/or by a method for an instrument transformer, particularly for an instrument transformer described above, according to claim 12.

An instrument transformer for high current and/or high volt age conversion according to the present invention comprises a housing and at least an active part, which is electrically insulated by an isolation material. The isolation material comprises or is a paste and/or pulp.

A paste and/or pulp is easy to handle, especially easy to fill in a housing for example by a machine. The use of isola tion material being or at least comprising a paste and/or pulp enables an automation of production, saves costs and is easy to perform, with no or little fault probability. There is no manual taping procedure needed to isolate the measuring assembly, where taping cannot be fully automated, is costly, time consuming and not easy to perform. The human contribu tion during a manufacturing process can be reduced, introduc ing automated respectively fully automated filling processes, leading to cost, time and fault reductions.

The paste and/or pulp can comprise a solvent with solved par ticles, particularly powder of more than 80 % wt . partly and/or fully dissolved in less than 20 % wt . solvent. A rela tively high share of particles and small share of solvent re sults in good electrical properties, that is a good isolation property, by keeping the paste and/or pulp good manageable during production, particularly during filling in a housing for example by a machine, reducing manufacturing time and costs . The paste and/or pulp can comprise particles with a size in the range of micro- and/or nano-meter, partly and/or fully dissolved in solvent. This small size gives good dissolution properties and results in a good handling with advantages as described before. A high fill factor is possible, with little amount of space between particles, easy to be produced of for example paper material and/or cellulose, easy to fill into a housing, particularly fully automated.

The particles can be in spherical form, and/or particles can be in fibrous form. Both forms enable a high surface to vol ume ratio with advantages as described before. Spherical par ticles are easy to produce, with low cost and easy to handle. Fibrous particles give additional stability and are especial ly used in the paper industry, with special properties after a drying process like good linkage of particles and direc tional properties.

Paste and/or pulp can comprise paper material, and/or cellu lose, and/or silicon. Paper material, cellulose and/or sili con are good isolation materials, especially at high voltages up to 1200 kV, are environment friendly, cost-effective and easy to handle. Particles of paper material, cellulose, and/or silicon can be easy handled fully automated and are easy to produce in specific sizes.

Paste and/or pulp can comprise as solvent at least one ionic liquid, particularly l-butyl-3-methylimidazolium chloride

[C4mim]Cl, N-methylmorpholine oxide (NMMO) , N,N- dimethylacetamide/lithium chloride (DMAc/LiCl), 1 , 3-dimethyl-

2-imidazolidinone/lithium chloride (DMI/LiCl), N,N- dimethylformamide/nitrous tetroxide (DMF/N204), dimethyl sul foxide (DMSO) /tetrabutyl-ammonium fluoride (TBAF) , imidazolium phosphates and/or phosphonates , particularly [C2mim] (MeO)2PC>2, [C2mim] - (MeO) MeP0 ₂ , and [C2mim] (MeO)HPC>2, l-butyl-3- methylimidazolium acetate [C4mim]OAc, l-ethyl-3- methylimidazolium acetate [C2mim]OAc, 1- (3, 6, 9-trioxadecyl ) -

3-ethylimidazolium acetate [Me (OEt ) 3-Et-Im] OAc, and/or molten salt hydrates, particularly LiClCy · 3¾0 and/or LiSCN-2H ₂ 0. These liquids are able to solve or partly or fully dissolve particles, particularly paper material, and/or cellulose, and/or silicon, with advantages as described before.

Paste and/or pulp comprises as insulating fluid oil, particu larly mineral oil and/or synthetic oil, and/or ester, partic ularly vegetable esters. Oil as insulating fluid as part of the paste and/or pulp is a good isolation material, especial ly at high voltages up to 1200 kV.

The portion of solvent in the paste and/or pulp can be re duced and/or exchanged by insulating fluid. The insulating properties in the paste and/or pulp can be increased by re ducing and/or exchanging solvent by insulating fluid.

The paste and/or pulp can be in form of or comprise a gel.

Gel is easy to handle, good to produce and allows an automat ed respectively fully automated filling process, leading to cost, time and fault reductions.

The isolation material with paste and/or pulp can be arranged in the housing, particularly the head housing and/or isolator and/or base, particularly arranged between the housing and active parts, particularly the measuring assembly and the housing. Free space can be filled easy, automatically and cost effective particularly completely with a paste and/or pulp, resulting in a good electrical isolation of parts and/or between parts of the instrument transformer, especial ly at high voltages up to 1200 kV.

The isolation material with paste and/or pulp can fill in, particularly can completely fill in space between the hous ing, particularly the head housing and/or isolator and/or base, and active parts, particularly the measuring assembly, with advantages as described before. A method for an instrument transformer, particularly for an instrument transformer as described before, comprises that a housing of the instrument transformer is filled with paste and/or pulp, particularly with paste and/or pulp comprising paper material and/or cellulose, solved in a solvent, partic ularly at least one ionic liquid.

The portion of solvent in the paste and/or pulp can be re duced and/or solvent in the paste and/or pulp can be ex changed by an insulating fluid, particularly oil, particular ly mineral oil and/or synthetic oil, and/or ester, particu larly vegetable esters.

Isolation material, particularly paste and/or pulp, can be filled into the instrument transformer housing, particularly after degassing.

Isolation material, particularly paste and/or pulp, in the housing of the instrument transformer can electrically insu late active parts of the instrument transformer, particularly the measuring assembly, from the housing of the instrument transformer .

The advantages in connection with the described method for an instrument transformer according to the present invention are similar to the previously, in connection with the instrument transformer for high current and/or high voltage conversion described advantages.

The present invention is further described hereinafter with reference to illustrated embodiments shown in the accompany ing drawings, in which:

FIG. 1 illustrates an instrument transformer 1 for high current and/or high voltage conversion in section view, comprising a housing and at least an active part, which is electrically insulated by an isola tion material 9, and FIG. 2 illustrates in section view the head 2 of instru ment transformer 1 of FIG. 1 according to the state of the art, and

FIG. 3 illustrates in section view the head 2 of an in

strument transformer 1 according to the present in vention, with paste and/or pulp 14 as insulation material for the active part.

In FIG. 1 is in section view an instrument transformer 1 for high current and/or high voltage conversion shown. The in strument transformer 1 comprises a housing and at least an active part, which is electrically insulated by an isolation material 9. In the embodiment of FIG. 1 an active part of the instrument transformer 1 includes a measuring assembly 11 with for example windings arranged around an electric conduc tor. The windings can be used to measure a current in the conductor by magnetic induction in the windings. Further ac tive parts are for example control electrodes and/or a dis charge pipe.

The active part, particularly the measuring assembly 11, is located within the housing of the instrument transformer 1. The instrument transformer 1 for example comprises a head 2, an isolator 3 and a base 4, which are particularly assembled by a head housing 12 with bellow cover 6, including an oil level indicator 7, by an isolator 3 particularly composed of a hollow cylindrical body and by a base 4 for example in form of a cast-iron pedestal. The isolator 3 is for example a ce ramic, silicon and/or composite hollow body with plate fins at the outer sheath to increase leakage current length.

The isolator 3 is for example columnar with two ends of the column, arranged with the base 4 on one end and the head 2 on the other end. The head 2 is on top of the upstanding colum nar isolator 3, comprising high voltage terminals 8 to elec trically connect the instrument transformer 1 with high volt- age lines, electrical generators and/or electrical consumers, to measure current/voltage of electrical high voltage lines and/or devices. A measuring assembly 11 as active part within the housing of the instrument transformer 1 measures current and/or voltage in between the high voltage terminals 8.

Transferred via active parts as for example a discharge pipe and/or VT primary, secondary windings and VT core, measuring results can be recorded and/or read from meters within termi nal boxes 5 particularly arranged at the base 4.

The active part is electrically insulated by an isolation ma terial from the housing of the instrument transformer. In the state of the art kraft paper sheets are used as isolation ma terial. The whole active part or parts of the active part are wrapped by kraft paper and the housing is filled by oil, to electrically insulate active parts. Oil impregnates the kraft paper and improves isolation properties. The active part is covered by kraft paper in form of isolator tape respectively sheets wrapped around the active part, which absorbs oil. The oil is for example transformer oil 10, comprising mineral oil .

Wrapping or taping of active parts with kraft paper sheets is manually done, leading to an expensive and time-consuming production process. Due to complex shapes of active parts like the measuring assembly 11, an automation of taping pro cedures is difficult and expensive. Handmade taping is fault- prone and needs high accuracy. Faults can lead to short cur rents and complete failure of the instrument transformer 1, particularly irreversible damage of the instrument transform er 1.

In FIG. 2 the head 2 of the instrument transformer 1 of FIG.

1 is shown in section view. Kraft paper in form of insulator tape 13 is wrapped around the measuring assembly 11 resulting in an isolator shell around the active part, which is impreg nated by oil, particularly transformer oil 10 filled in the housing of the instrument transformer 1. Space between the housing and the active part with kraft paper wrapped, is filled up with oil after assembling. The housing of the in strument transformer 1 is airtight, except an excess pressure outlet. High currents during operation of the instrument transformer produce waste heat, increasing the temperature of oil and leading to high pressure within the instrument trans former 1. Excess pressure and/or oil can dissipate via the excess pressure outlet in an upward direction, to prevent de struction and/or explosion of the instrument transformer 1 and/or injuries of service workforce.

As described above, wrapping active parts of the instrument transformer 1 with isolator tape respectively sheets of kraft paper is time and cost intensive, and fault-prone. In the state of the art wrapping is done handmade, an automation is difficult. Wrapping of active parts before assembling the in strument transformer 1 leads to free space between wrapped parts and the housing, which is filled by oil. Space in be tween active parts like the measuring assembly 11 and the housing, particularly the head housing 12, cannot be effec tively used for isolation by kraft paper, since production tolerances and an assembling of instrument transformer parts lead to free space to be filled by oil.

In FIG. 3 the head 2 of an instrument transformer 1 according to the present invention is shown in section view, with paste and/or pulp 14 as insulation material for the active part.

The instrument transformer 1 in FIG. 3 is as for FIG. 1 and FIG. 2 described, except the wrapping of active parts with kraft paper in form of isolator tape 13. Instead free space between the housing and active parts is filled by paste and/or pulp 14 of isolation material, particularly comprising a solvent with solved particles, particularly powder of more than 80 % wt . partly and/or fully dissolved in less than 20 % wt . solvent. Particles comprise for example paper material, and/or cellulose, and/or silicon, and are for example in spherical form, and/or particles are for example in fibrous form, particularly with a size in the range of micro- and/or nano-meter, partly and/or fully dissolved in solvent.

The solvent comprises for example at least one ionic liquid, particularly l-butyl-3-methylimidazolium chloride [C4mim]Cl, N-methylmorpholine oxide (NMMO) , N,N- dimethylacetamide/lithium chloride (DMAc/LiCl), 1 , 3-dimethyl-

2-imidazolidinone/lithium chloride (DMI/LiCl), N,N- dimethylformamide/nitrous tetroxide (DMF/N204), dimethyl sul foxide (DMSO) /tetrabutyl-ammonium fluoride (TBAF) , imidazolium phosphates and/or phosphonates , particularly [C2mim] (MeO)2PC>2, [C2mim] - (MeO) MeP0 ₂ , and [C2mim] (MeO)HPC>2, l-butyl-3- methylimidazolium acetate [C4mim]OAc, l-ethyl-3- methylimidazolium acetate [C2mim]OAc, 1- (3, 6, 9-trioxadecyl ) -

3-ethylimidazolium acetate [Me (OEt ) 3-Et-Im] OAc, and/or molten salt hydrates, particularly LiClCy · 3¾0 and/or LiSCN-2H ₂ 0.

The particles 14 are composed of or comprise paper material, and/or cellulose, and/or silicon. These materials show good dielectric properties, particularly good electrical isolation properties. To improve the isolation properties, paste and/or pulp 14 comprises as insulating fluid oil 10, particularly mineral oil and/or synthetic oil, and/or ester, particularly vegetable esters. Alternatively, the fluid comprises a gas, for example synthetic air and/or SF ₆ . The portion of solvent in the paste and/or pulp 14 is reduced and/or exchanged by insulating fluid for a further increase in electrical isola tion. Paste and/or pulp 14 can be in form of or comprise a gel, for easy handling during production.

Particles in the paste and/or pulp 14 are for example in spherical form and/or in fibrous form. The described form al lows a high fill factor and a high surface to volume ratio of particles, for example at least two times, particularly at least ten times higher than for the same material in form of sheets. It can further allow a good solution and/or dissolu tion, resulting in a paste and/or pulp easy to fill in and/or handle, particularly in gel form. A high surface to volume ratio improves impregnation with for example oil and increas es with a high fill factor isolation properties.

Paste and/or pulp 14 is filled into the housing for example through a paste/pulp filler inlet 15. The filling process can be fully automated, saving time, cost and reducing faults in the isolation of active parts of the instrument transformer 1. A portion of solvent in the paste and/or pulp 14 is re duced and/or solvent in the paste and/or pulp 14 is exchanged by an insulating fluid, particularly oil 10, particularly mineral oil and/or synthetic oil, and/or ester, particularly vegetable esters, before or after filling into the housing. After filling into the housing can allow to change properties of the paste/pulp, reducing its viscosity and handling prop erties but increasing the isolation properties. Alternatively or additional reduction of solvent in the paste and/or pulp 14 done before filling paste/pulp into the housing, can in crease handling and/or filling properties of the paste/pulp and/or make the exchange process easier. With time a

paste/pulp can coagulate, consolidate and/or solidify, or stay fluidic. The isolation material made of, respectively comprising paste/pulp 14, particularly solved particles in solvent and/or oil, results in a good electrical isolation of active parts towards the housing of the instrument transform er 1.

The above described embodiments of the present invention can be used also in combination and combined with embodiments known from the state of the art. For example, the instrument transformer 1 can be a current transformer, an inductive voltage transformer, a capacitive voltage transformer, a com bined current and voltage transformer, a power voltage trans former, and/or an optical current transformer. Active parts can be located in a head housing 2, in an isolator 3 and/or in a base 4. A measuring assembly 11 is for example in the head housing 2 arranged. Alternative instrument transformer designs comprise an isolator 3 and a base 4 without a head housing, for example with measuring assembly 11 arranged in the base 4.

Paste/pulp 14 of isolation material comprises paper material, and/or cellulose, and/or silicon or combinations of these ma terials. Alternative isolator materials in form of particles can be used too, particularly oil solvable materials like plastics and/or porous materials like zeolite, and/or materi als like silicon oxide. Paste/pulp 14 can be of spherical form, porous and/or fibrous. An impregnation of particles 14 for example with oil or an exchange of oil and solvent can be done before filling the paste/pulp 14 into the instrument transformer 1 or after filling the paste/pulp 14 into the in strument transformer 1. The insulating fluid can be or can comprise oil, particularly mineral oil and/or a synthetic oil, and/or ester, particularly vegetable esters, or gas, for example clean air and/or SF ₆ . Paste/pulp 14 can be degassed.

The isolation material with paste/pulp 14 can be arranged in the housing, particularly the head housing 12 and/or isolator 3 and/or base 4. The isolation material can consist of paste/pulp 14. Alternatively, the isolation material can con sist of and/or comprise paste/pulp 14 and paper sheets in combination, particularly kraft paper sheets. The isolation material can be arranged between the housing and active parts, particularly the measuring assembly 11 and the hous ing, to electrically isolate parts from each other. The iso lation material consisting of paste/pulp 14 can be arranged in the head housing 12 and/or isolation material consisting of paper sheets can be arranged in the isolator 3. In an al ternative arrangement, the isolation material consisting of paste/pulp 14 can be arranged in the isolator 3 and/or isola tion material consisting of paper sheets can be arranged in the head housing 12. In the isolator 3 all free space can be filled with isolation material or only parts, particularly field electrodes and/or electrical conductors, particularly in tube form, are filled and or wrapped and/or coated with isolation material. In the head housing 12 all free space can be filled with isolation material.

List of Reference Characters

1 instrument transformer

2 head

3 isolator

4 base

5 terminal box

6 bellow cover

7 oil level indicator

8 high voltage terminals

9 high voltage insulation

10 transformer oil

11 measuring assembly, particularly secondary core/windings 12 head housing

13 isolator tape, kraft paper

14 paste/pulp

15 paste/pulp filler inlet