WO2021058102A1

WO2021058102A1 - Instrument transformer and method of assembling

Info

Publication number: WO2021058102A1
Application number: PCT/EP2019/076023
Authority: WO
Inventors: Fabrizio Negri
Original assignee: Siemens Energy Global GmbH & Co. KG
Priority date: 2019-09-26
Filing date: 2019-09-26
Publication date: 2021-04-01

Abstract

The present invention relates to an instrument transformer (1) for high current and/or high voltage conversion, comprising a housing and at least an active part, which is electrically insulated by an isolation material. The isolation material comprises shells (13). A method for assembling the instrument transformer comprises arranging at least an active part, particularly a measuring assembly (11), within at least one shell (13) and arranging the assembly within a housing of the instrument transformer (1).

Description

INSTRUMENT TRANSFORMER AND METHOD OF ASSEMBLING

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

Oil insulated instrument respectively measurement transformers are for example known from US 5391 835 A. The instrument transformers are used to measure high currents and/or voltages, 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 measuring 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 induction in the windings. The active part is electrically insulated by an isolation material from the housing of the instrument 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, particularly paper tape respectively paper sheets, is carried out by manually taping the measuring assembly. A manual taping 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 procedures is difficult and expensive.

An object of the present invention is to overcome the problems described above. Especially an object of the present invention is to describe a method to insulate parts of an instrument transformer and an instrument transformer with electrically insulated parts, with an easy to produce and cost-effective insulation, particularly produceable with an automated process.

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 assembling an instrument transformer, particularly for assembling an instrument transformer described above, according to claim 10.

An instrument transformer for high current and/or high voltage 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 shells.

Shells are easy and cost effective to produce and to handle, especially easy to assemble with other parts of the instrument transformer. The use of shells enables an automation process for example by using machines to produce shells and to assemble, 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 contribution during a manufacturing process can be reduced, introducing automated respectively fully automated processes, leading to cost, time and fault reductions.

Shells can be in form of at least two half-shells. Two half shells are easy to assemble and to produce for example by extrude and/or stamping processes, and a measuring assembly is easy to arrange in between two half-shells, with advantages as described before.

Shells can comprise or can consist of cardboard, particularly comprising paper material and/or cellulose. These materials are good electrical isolator materials and cost effective, easy to produce and easy to handle, particularly by extrude and/or stamping processes as well as automated production and assembling processes.

Space between shells and housing can partly or complete be filled with transformer oil and/or particles. Free space at interfaces between half-shells can be filled with transformer oil and/or particles. A filling with isolation material like transformer oil and/or particles of space between shells enables fault reduction and makes a closed, electrically isolating shell possible. Without a current and/or voltage leak via a gap between shells, a closed isolation of for example measuring assemblies is possible and no electrical faults are possible via a gap between shells. Alternatively or additional, shells can be pressed together with force, to close gaps.

Shells and/or particles can be impregnated by an insulating fluid and/or embedded in fluid, particularly gas and/or liquid, particularly mineral oil and/or a synthetic oil, and/or ester, particularly vegetable esters. An impregnation by isolating fluid, particularly oil and/or ester, increases the isolation properties of shells and/or particles, with advantages as described before.

Particles can be composed of or comprise paper material, and/or cellulose, and/or silicon. Paper material and/or cellulose are good isolation materials, especially at high voltages up to 1200 kV, are environment friendly, cost- effective and easy to handle as particles. Particles of paper material, silicon and/or cellulose can be easy handled fully automated and are easy to produce in specific sizes. Particle size can be in the range of micro- and/or nano-meter, and/or the isolation material can comprise particles with a size in the range of micro- and/or nano-meter.

This size gives a high fill factor, with little amount of space between particles, can easy be produced of paper material, silicon and/or cellulose, can be easy impregnated by a fluid, and/or is easy to fill into a housing and/or in space between shells, particularly fully automated.

The surface to volume ratio of particles can be higher, particularly at least two times, particularly at least ten times higher than for the same material in form of sheets. A high surface to volume ratio of particles enables a high electrical isolation effect, a good dissolution in fluids and/or impregnation in for example fluids, and a good filling of gaps respectively free space.

Particles can be in spherical form, and/or particles are in fibrous form. Both forms enable a high surface to volume ratio with advantages as described before.

The isolation material is 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. This arrangement enables a good electrical isolation between measuring assembly and housing. The isolation material with shells, and particularly with particles, can fill in, particularly completely fill in space between the housing, particularly the head housing and/or isolator and/or base, and active parts, particularly the measuring assembly. A good electrical isolation of parts of the instrument transformer between each other can be reached.

A method according to the present invention for assembling an instrument transformer, particularly for assembling an instrument transformer as described before, comprises arranging at least an active part, particularly a measuring assembly, within at least one shell, and arranging the assembly within a housing of the instrument transformer.

At least one shell can be assembled of at least two half shells, particularly made out of cardboard, particularly comprising paper material and/or cellulose. Space between shells and housing, particularly the whole housing of the instrument transformer, and/or space at the interface of half-shells, can partly or complete be filled with transformer oil and/or particles, and/or shells and/or particles can be impregnated by an insulating fluid and/or embedded in fluid, particularly mineral oil and/or a synthetic oil, and/or ester, particularly vegetable esters.

Particles can get impregnated by insulating fluid to create a pulp, particularly after degassing, and afterwards the pulp can be filled into the instrument transformer housing.

The at least one shell, particles and/or a paste out of particles, and/or an insulating fluid in the housing of the instrument transformer can electrically insulate 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 assembling an instrument transformer, particularly for assembling an instrument transformer as described before, 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 accompanying 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 isolation material 9, and

FIG. 2 illustrates in section view the head 2 of instrument transformer 1 of FIG. 1 according to the present invention, and FIG. 3 illustrates in angular view a half-shell 14 according to the present invention particularly made of cardboard.

In FIG. 1 is in section view an instrument transformer 1 for high current and/or high voltage conversion shown. The instrument 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 conductor. The windings can be used to measure a current in the conductor by magnetic induction in the windings. Further active parts are for example control electrodes and/or a discharge 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 ceramic, 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 columnar isolator 3, comprising high voltage terminals 8 to electrically connect the instrument transformer 1 with high voltage 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 terminal boxes 5 particularly arranged at the base 4.

The active part is electrically insulated by an isolation material from the housing of the instrument transformer. In the state of the art kraft paper sheets are used as isolation material. 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 wrapped around the active part, which absorbs oil. The oil is for example transformer oil, comprising mineral oil.

Wrapping or taping of active parts with kraft paper tape 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 procedures is difficult and expensive. Handmade taping is fault-prone and needs high accuracy. Faults can lead to short currents and complete failure of the instrument transformer 1, particularly irreversible damage of the instrument transformer 1.

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

1 is shown in section view. In the state of the art kraft paper in form of insulator tape is wrapped around the measuring assembly 11 resulting in an isolator around the active part, which is impregnated by oil, particularly transformer oil filled into 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 instrument transformer 1 is airtight, except an excess pressure outlet, which can be used as filler inlet 15 to fill in for example isolator oil and/or particles. High currents during operation of the instrument transformer produce waste heat, increasing the temperature of oil and leading to high pressure within the instrument transformer 1. Excess pressure and/or oil can dissipate via the excess pressure outlet in an upward direction, to prevent destruction 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 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 instrument transformer 1 leads to free space between wrapped parts and the housing, which is filled by oil. Space in between active parts like the measuring assembly 11 and the housing, particularly the head housing 12, can not be effectively 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.

According to the present invention shells 13, which are precast respectively ready-made, particularly made of cardboard, are used instead of kraft paper taping. This allows an automation process, saving costs and time. Shells 13 can for example be produced of cardboard material, particularly comprising paper material and/or cellulose, particularly by an extruding process in a mold and/or by stamping, and/or 3D printing, or by another shaping process. Ready-made shells 13 are afterwards assembled with the measuring assembly 11, particularly a secondary core and/or windings, and assembled with other parts of the instrument transformer 1, particularly mounted in the head housing 12.

Shells 13 are for example impregnated by oil and/or ester, particularly transformer oil and/or vegetable ester. The impregnation increases isolation properties of shells 13. The impregnation can be performed before assembling or within a housing of the instrument transformer 1 after assembling, for example by filling in isolation fluid through filler inlet 15. Cardboard soaks up and/or through with isolation fluid like for example transformer oil. Free space and space in- between or at interfaces of shells 13 can be filled with isolation fluid 10 particularly comprising isolation particles.

Particles of isolation material, particularly particles in powder form, are able to fill in between interfaces of shells 13, within shells 13 between the measuring assembly 11 and shells 13, and/or between shells 13 and other parts of the instrument transformer 1 like for example the head housing 12. The particle size is for example in the range of micro- and/or nano-meter, and/or the isolation material comprises particles with a size in the range of micro- and/or nano meter.

The particles 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 particles are impregnated by a fluid, particularly mineral oil and/or a synthetic oil, and/or ester, particularly vegetable esters. Alternatively, the fluid comprises a gas, for example synthetic air and/or SF₆. Particles are for example in spherical form, and/or particles are in fibrous form. The described form allows 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 tape. A high surface to volume ratio improves impregnation with for example oil and increases with a high fill factor isolation properties. Small particles fill in well gaps between shells 13.

Fig. 3 shows a half-shell 14 in angular view according to the present invention particularly made of cardboard. A half shell 14 is for example in form of a pan, to meet the form of parts like for example the measuring assembly 11. A shell 13 is assembled by joining or adding two half-shells 14 together, with in-between for example the measuring assembly 11. A recess for particularly electric connections, electrodes and/or other devices or units of the instrument transformer 1, for example to electrically connect the measuring assembly 11, is formed in one or both half-shells 14. In the middle of both half-shells 14 a tube like opening for a current line, with current to be measured by the instrument transformer 1, is formed.

An assembling of the instrument transformer 1 with pre produced respectively ready-made half-shells 14, comprising steps like insertion of measuring assembly 11 into one half shell 14, putting or joining two half-shells 14 together with measuring assembly 11 in-between, arranging assembly within the head housing 12 and assembling further instrument transformer parts, filling the instrument transformer 1 with isolation fluid 10 particularly comprising particles, can be performed automatically, for example by robots, or manually with little effort and costs in short time.

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 combined current and voltage transformer, a power voltage transformer, 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.

Shells 14 and/or particles of isolation material comprise paper material, and/or cellulose, and/or silicon or combinations of these materials. Alternative isolator materials can be used too, particularly plastics and/or porous materials like zeolite, ceramics and/or materials like silicon oxide. A shell 14 can be made of one piece of cardboard or out of different pieces. Particles can be of spherical form, porous and/or fibrous. An impregnation of shells 14 and/or particles for example with oil can be done before assembling or after assembling the instrument 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 SF₆.

The isolation material 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 and/or comprise shells 14 for example produced of cardboard, particles of for example cellulose, paper and/or silicon, and/or isolation fluid like for example transformer oil. Alternatively, the isolation material can consist of and/or comprises shells 14, particles and/or isolation fluid in combination, or one of these alone, and/or in combination with for example kraft paper sheets and/or tape. The isolation material can be arranged between the housing and active parts, particularly the measuring assembly 11 and the housing, to electrically isolate parts from each other. 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 assembled and/or filled and/or wrapped and/or coated with isolation material. In the head housing 12 all free space can be filled with isolation material, particularly shell 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 with particles

11 measuring assembly, particularly secondary core/windings

12 head housing

13 shell

14 cardboard half-shell

15 filler inlet

Claims

1. Instrument transformer (1) for high current and/or high voltage conversion, comprising a housing and at least an active part, which is electrically insulated by an isolation material, characterized in that the isolation material comprises shells (13).

2. Instrument transformer (1) according to claim 1, characterized in that shells (13) are in form of at least two half-shells (14).

3. Instrument transformer (1) according to any one of the claims 1 or 2, characterized in that shells (13) comprise or consist of cardboard, particularly comprising paper material and/or cellulose.

4. Instrument transformer (1) according to any one of the claims 1 to 3, characterized in that space between shells (13) and housing is partly or complete filled with transformer oil and/or particles.

5. Instrument transformer (1) according to any one of the claims 2 to 4, characterized in that free space at interfaces between half-shells (14) is filled with transformer oil and/or particles.

6. Instrument transformer (1) according to any one of the claims 4 or 5, characterized in that shells (13) and/or particles are impregnated by an insulating fluid and/or embedded in fluid, particularly liquid and/or gas, particularly mineral oil and/or a synthetic oil, and/or ester, particularly vegetable esters.

7. Instrument transformer (1) according to any one of the claims 4 to 6, characterized in that particles are composed of or comprise paper material, and/or cellulose, and/or silicon.

8. Instrument transformer (1) according to any one of the claims 4 to 7, characterized in that particle size is in the range of micro- and/or nano-meter, and/or the isolation material comprises particles with a size in the range of micro- and/or nano-meter.

9. Instrument transformer (1) according to any one of the claims 1 to 8, characterized in that the isolation material is arranged in the housing, particularly the head housing (12) and/or isolator (3) and/or base (4), particularly arranged between the housing and active parts, particularly the measuring assembly (11) and the housing.

10. Method for assembling an instrument transformer (1), particularly for assembling an instrument transformer (1) according to any one of the preceding claims, characterized in that assembling comprises arranging at least an active part, particularly a measuring assembly (11), within at least one shell (13) and arranging the assembly within a housing of the instrument transformer (1).

11. Method according to claim 10, characterized in that the at least one shell (13) is assembled of at least two half shells (14) particularly made out of cardboard, particularly comprising paper material and/or cellulose.

12. Method according to claim 11, characterized in that space between shells (13) and housing, particularly the whole housing of the instrument transformer (1), and/or space at the interface of half-shells (14), is partly or complete filled with transformer oil and/or particles, and/or particles and/or shells (13) are impregnated by an insulating fluid and/or embedded in fluid, particularly mineral oil, and/or a synthetic oil, and/or ester, particularly vegetable esters.

13. Method according to claim 12, characterized in that particles get impregnated by insulating fluid to create a pulp, particularly after degassing, and afterwards the pulp is filled into the instrument transformer housing.

14. Method according to any one of the claims 10 to 13, characterized in that the at least one shell (13), and/or particles, and/or a paste out of particles, and/or an insulating fluid in the housing of the instrument transformer (1) electrically insulate active parts of the instrument transformer (1), particularly the measuring assembly (11), from the housing of the instrument transformer (1).