WO2021058088A1

WO2021058088A1 - Fluid-level measuring in instrument transformers

Info

Publication number: WO2021058088A1
Application number: PCT/EP2019/075685
Authority: WO
Inventors: Fabrizio Negri; Dario SANTINELLI
Original assignee: Siemens Energy Global GmbH & Co. KG
Priority date: 2019-09-24
Filing date: 2019-09-24
Publication date: 2021-04-01

Abstract

The present invention relates to an instrument transformer (1) for high current and/or high voltage conversion and a method for fluid-level measurements within the instrument transformer (1), comprising a housing and at least an active part, which is electrically insulated by a fluid (10) within the housing. At least one sensor (13) is comprised and measures the fluid-level, particularly oil and/or ester level within the housing.

Description

Fluid-Level Measuring in Instrument Transformers

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

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.

The housing comprises for example a head housing with measuring assembly, arranged on a columnar insulator, standing straight upwards on a base. The housing is filled with oil, covering the measuring assembly and electrically isolating it from the housing. On top of the housing a bellow cover for example with oil level indicator and with burst disc is arranged, for manually metering the oil level and dissipation of critical excess pressure within the housing.

During high current and/or high voltage conversion, and by environmental respectively weather changes, the fluid like oil within the housing can change its volume, particularly expand or contract. The volume change is induced for example by waste heat from current-carrying conductors within the instrument transformer, particularly at high currents, and/or by temperature changes in the environment of the instrument transformer. Higher temperatures increase the volume of the fluid and low temperatures decrease the volume. To enable for example expansion and contraction of oil within the housing, space upwards of oil is filled by gas like air. At very high temperature increases, excess pressure can lead to an explosion of the instrument transformer. To prevent the instrument transformer from explosion, to prevent injuries of personal near the instrument transformer and to enable dissipation of excess pressure in a predefined direction, a burst disc is arranged on top of the instrument transformer.

At a critical pressure respectively when pressure exceeds a critical value, for example induced by temperature increase within the instrument transformer and/or expansion of insulation oil, the burst disc breaks respectively bursts, and fluids like oil and gas can dissipate from the housing of the instrument transformer, reducing the pressure to a value below a critical value. An explosion of other parts than the burst disc is prevented, particularly of parts like isolator, base and/or head housing, preventing staff to be hurt and enabling an easy reconstruction of the instrument transformer for example by changing the burst disc.

A further problem of fluid filled instrument transformers, for example filled with oil and/or esters, is leakage. Fluids can be environmental harmful, and a leakage can lead to destruction of the instrument transformer. If parts at high voltage like the measuring assembly within the housing are not particularly fully covered by oil, a measuring can be inaccurate, and parts of the instrument transformer can be damaged or staff can be harmed by high voltage. A detection of leakage manually using an optical oil level indicator, for instance a window with level lines to be seen outside of the housing, requires regular service inspections and is cost and labor-intensive.

An object of the present invention is to overcome the problems described above. Especially an object of the present invention is to reduce costs, reduce manual inspections and increase reliability and life time of the instrument transformer. A further object is to enable a particularly fully automatic measuring and monitoring of fluid levels within the housing of the instrument transformer, particularly the oil and/or ester level, with oil and ester covering high voltage parts within the housing.

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 voltage conversion according to the present invention comprises a housing and at least an active part, which is electrically insulated by a fluid within the housing.

At least one sensor is comprised for fluid-level measurements.

The at least one sensor enables a measuring and monitoring of fluid levels within the housing of the instrument transformer, particularly the oil and/or ester level, particularly with oil and ester covering high voltage parts within the housing. A measuring of fluid-levels with at least one sensor can be fully automatic, reducing costs, reducing the need of manual inspections and enabling an increase in inspection intervals, and increasing reliability and life time of the instrument transformer.

The fluid can be or can comprise oil and/or ester. Oil and ester or combinations of oil and esters provide a fluid with high respectively good electrical insulation properties, filling particularly completely free space between parts of the instrument transformer, particularly parts like current conducting wires at high voltage and/or the measuring assembly and parts like isolator, base and/or head housing. A good electrical isolation between parts of the instrument transformer at high voltage respectively high electrical potential and parts at lower electrical potential is possible, by filling in fluids like oil and/or esters in- between, within the housing.

The oil can be or can comprise transformer oil, mineral oil and/or a synthetic oil, and/or the ester can be or can comprise vegetable esters. These materials provide good electrical isolation properties at a reasonable price.

At least one sensor can be or can comprise a hydro-static pressure sensor. For example, the sensor can be arranged at the bottom part of the instrument transformer, within the housing, enabling an easy and cost effective wiring for connecting the sensor with data processing, data storage, data displaying and/or data transmitting units. The at least one hydro-static pressure sensor can detect and/or monitor fluid leakages, which particularly involve a reduction of fluid-level.

The at least one sensor can be or can comprises a laser-level transmitter. A laser-level transmitter comprises for example a laser and an optical detector, detecting reflected or inflected laser light at the interface between liquid fluids, for example oil and/or esters, and a gas, for example air.

The fluid-level of the liquid can be deduced from an intensity and/or angle value of a reflected or inflected laser beam. This permits the detection and/or monitoring of fluid-levels, detection of fluid leakage, and/or expansion or compression of insulating fluids, with the danger of explosions or the danger of fluid-levels below a critical value, not particularly complete covering parts of the instrument transformer in the housing at high voltage and/or measuring devices like coils, introducing errors in the measuring. The advantages are as described before.

The at least one sensor can be or can comprises a mechanical sensor, particularly a mechanical sensor generating a well- defined tone respectively sound during fluid level changes or by reaching a pre-defined fluid level. The advantages are as described before for laser-level transmitters, but no electrical connection for mechanical sensors is necessary. This allows an easy and cost effective arrangement without the need for wiring even in the upper part of the instrument transformer, near high voltage parts. Data processing, data storage, data displaying and/or data transmitting units can easily be affected or damaged by high voltage, so in most instrument transformers these kind of units is arranged in the bottom part of the instrument transformer, for example in control boxes at the base or at the lower part of the isolator. A connection of electrical sensors with these units by wire can lead to problems, if sensors are near high voltage parts and the units are at the low potential side. This can lead to arcs, damage or destruction of units and the danger of electric shocks of staff. A sound for transmitting data enables a wireless transmission.

Mechanical sensors can be or can comprise sensors with floaters additional or alternative to sound generating sensors, with advantages as described before.

The at least one sensor can be or can comprise an electrical sensor, particularly an electrical sensor generating a signal during fluid level changes or by reaching a pre-defined fluid level. An example for an electrical sensor is an electrical resistant bar or stripe, reaching from an area of low fluid level to an area of high fluid level, changing the resistance between two electrical contacts depending on the fluid level. Combinations of electrical and mechanical sensors are possible, increasing the reliability of fluid level measurements and flexibility to adjust to electrical and dimensional properties within the housing of the instrument transformer. Electrical sensors are reliable, at low price available, and with a need of little space arrangeable within an instrument transformer, and signals are easy to detect and easy to process particularly electronically.

The at least one sensor can be arranged within the bottom part of the instrument transformer, particularly in a base and/or lower part of an isolator. Alternatively or additionally, sensors can be arranged within a head of the instrument transformer, particularly in a bellow cover of the instrument transformer. Depending on the kind of sensor and wiring needs, as described before, the sensor is arranged in the lower or upper part of the instrument transformer.

The fluid within the housing can be filling the head housing and/or the isolator and/or the base, particularly filling space between the housing and active parts, particularly the measuring assembly and the housing. A good filling of free space within the housing results in a good isolation of parts at high voltage respectively potential from parts of low potential. Thereby high reliability, lasting, safe performance with correct measurements can be reached with the instrument transformer according to the present invention.

The at least one sensor can be comprised for automatic fluid- level measurements and an oil level indicator can be comprised for manual fluid-level measurements and/or control. A combination of both increases reliability, reducing costs and maintenance efforts for the instrument transformer, and allowing control and test of accuracy of the sensor performance.

A method for an instrument transformer, particularly for an instrument transformer as described before, comprises that the instrument transformer is able to perform high current and/or high voltage conversion, and a fluid-level measurement of electrically insulating fluid within a housing of the instrument transformer, comprising at least an active part, is performed by at least one sensor.

The at least one sensor can be used to measure the fluid- level of the electrically insulating fluid, particularly liquid, particularly oil and/or ester, electrically, optically and/or mechanically.

The at least one sensor can emit an optical, an acoustic and/or an electrical signal particularly when a predefined fluid-level is reached and/or the fluid is falling below a predefined fluid-level.

The at least one sensor can emit continuously or periodically an optical, an acoustic and/or an electrical signal, particularly dependent on and/or in relation to the fluid- level.

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 an illustrated embodiment shown in the accompanying drawing, in which:

FIG. 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 a fluid like transformer oil 10, and with a sensor 13 to measure the fluid-level within the housing.

An instrument transformer 1 for high current and/or high voltage conversion is shown in section view in the only FIG. The instrument transformer 1 comprises a housing and at least an active part, which is electrically insulated by an isolation fluid 10. In the embodiment of the only FIG. an active part of the instrument transformer 1 includes a measuring assembly 11 with for example windings arranged around an electric conductor, which are wrapped for example by paper. The windings are 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 instrument transformer 1 comprises a head 2, an isolator 3 and a base 4. The head 2 comprises a head housing 12 with high voltage terminals 8, and a bellow cover 6, for example with bust disc. The active part, particularly the measuring assembly 11, is located within the housing of the instrument transformer 1. An oil level indicator 7 for manual metering the oil level is arranged at the head 2, particularly at the bellow cover 6. The isolator 3 is particularly composed of a hollow cylindrical body with fins outside. 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 base 4 is for example in form of a cast- iron pedestal, with terminal boxes 5 for particularly control units, data processing, monitoring, and transmission devices.

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, with the 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 are 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. The whole active part or parts of the active part, for example coils, are wrapped by kraft paper and the housing is filled by a fluid like oil, to electrically insulate active parts. Oil impregnates the kraft paper, improves isolation properties and fills free space within the housing. An oil level is above the active part, for example filling the head housing nearly complete, with air on top of the oil filling. An optical oil level indicator 7 arranged on the upper end of the head housing 12 enables staff to manually detect the filling amount with fluids like oil and to inspect the condition of the instrument transformer 1. The oil is for example transformer oil 10, comprising mineral and/or synthetic oil, and/or esters. Alternatively, esters can be used as insulation fluid.

Sensor 13 is located in the housing of the instrument transformer 1 to measure a fluid-level, particularly oil- level, automatically. Sensor 13 is for example located at or near to the oil level indicator 7 or in the bottom of the instrument transformer 1, particularly at the bottom of the columnar isolator 3 or the base 4, not shown in the only FIG. Sensor 13 is for example an hydro-static pressure sensor, a laser-level transmitter, a mechanical sensor and/or an electrical sensor. In normal operation, the fluid level of the instrument transformer is nearly constant. If there is a leakage, fluid like oil spills out of the housing of the instrument transformer 1, and fluid-level of oil drops. A drop of fluid-level is measurable with sensor 13.

Temperature increases, for example by high heat generation during operation, particularly by a short circuit-current, change a fluid-level due to expansion of fluids like oil, or increase the pressure within the housing. Since oil and gas have different thermal expansion coefficients, a fluid level within the housing will change even in fluid tight housings. An increase of fluid-level is measurable with sensor 13.

For monitoring proper conditions and work of the instrument transformer 1 without changes of fluid-level, sensor 13 is able to measure a constant fluid-level. At changes, a signal can alarm staff to inspect the state of the instrument transformer 1 or trigger automatic reactions, like switching off current. Particularly at reaching critical values, sensor 13 is able to measure critical fluid-levels and release a signal. For example, a reaction is possible before an explosion, bursting of the burst disc, and/or dropping of Fluid out of the instrument transformer 1 occurs.

An acoustic, for example mechanical sensor 13, particularly above a normal fluid-level, is able to give an acoustic signal if fluid is reaching the sensor 13. A sensor 13 below a normal fluid-level is able to give an acoustic signal at dropping of fluid-level below the sensor 13 location. The same applies to electrical sensors 13, whereby for example resistive sensors 13 are able to measure fluid-level changes continuously over a wide range of fluid levels, and not only at certain positions. Optical sensors 13, for example laser- level transmitters, are able to detect an interface between liquid and gas, and to determine the fluid-level from the position of the interface. The laser-level transmitters are located above and/or below the interface. Hydro-static pressure sensors, particularly at the bottom of the instrument transformer 1, are able to detect pressure changes during changes of the fluid-level. Further examples of sensors are mechanical sensors 13, for example in form of a floater.

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. Sensor 13 is able to measure a fluid-level and to transfer the information via wire or wireless, for example by light signal, sound and/or radiocommunication. Measured data are processed for example by sensor 13 itself, or transferred, stored, processed and/or displayed by data-transfer-, storage-, processing-, and displaying-devices . Energy for operation of sensor 13 can be provided by wire or wireless, or sensor 13 is an energy-self harvesting-sensor .

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 fluid-level sensor

Claims

Patent 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 a fluid (10) within the housing, characterized in that at least one sensor (13) is comprised for fluid-level measurements.

2. Instrument transformer (1) according to claim 1, characterized in that the fluid (10) is or comprises oil and/or ester.

3. Instrument transformer (1) according to claim 2, characterized in that the oil is or comprises transformer oil, mineral oil and/or a synthetic oil, and/or the ester is or comprises vegetable esters.

4. Instrument transformer (1) according to any one of the claims 1 to 3, characterized in that the at least one sensor (13) is or comprises a hydro-static pressure sensor.

5. Instrument transformer (1) according to any one of the claims 1 to 3, characterized in that the at least one sensor (13) is or comprises a laser-level transmitter.

6. Instrument transformer (1) according to any one of the claims 1 to 3, characterized in that the at least one sensor (13) is or comprises a mechanical sensor, particularly a mechanical sensor generating a well-defined tone during fluid level changes or by reaching a pre-defined fluid level.

7. Instrument transformer (1) according to any one of the claims 1 to 3, characterized in that the at least one sensor (13) is or comprises an electrical sensor, particularly an electrical sensor generating a signal during fluid level changes or by reaching a pre-defined fluid level.

8. Instrument transformer (1) according to any one of the claims 1 to 7, characterized in that the at least one sensor (13) is arranged within the bottom part of the instrument transformer (1), particularly in a base (4) and/or lower part of an isolator (3).

9. Instrument transformer (1) according to any one of the claims 1 to 7, characterized in that the at least one sensor (13) is arranged within a head (2) of the instrument transformer (1), particularly in a bellow cover (6) of the instrument transformer (1).

10. Instrument transformer (1) according to any one of the claims 1 to 9, characterized in that the fluid (10) within the housing is filling the head housing (12) and/or the isolator (3) and/or the base (4), particularly filling space between the housing and active parts, particularly the measuring assembly (11) and the housing.

11. Instrument transformer (1) according to any one of the claims 1 to 10, characterized in that the at least one sensor (13) is comprised for automatic fluid-level measurements and an oil level indicator is comprised for manual fluid-level measurements and/or control.

12. Method for an instrument transformer (1), particularly for an instrument transformer (1) according to any one of the preceding claims, characterized in that the instrument transformer (1) is able to perform high current and/or high voltage conversion, and a fluid-level measurement of electrically insulating fluid (10) within a housing of the instrument transformer (1), comprising at least an active part, is performed by at least one sensor (13).

13. Method according to claim 12, characterized in that the at least one sensor (13) is measuring the fluid-level of the electrically insulating fluid (10), particularly liquid, particularly oil and/or ester, electrically, optically and/or mechanically.

14. Method according to any one of the claims 12 or 13, characterized in that the at least one sensor (13) emits an optical, an acoustic and/or an electrical signal particularly when a predefined fluid-level is reached and/or the fluid is falling below a predefined fluid-level.

15. Method according to any one of the claims 12 to 14, characterized in that the at least one sensor (13) emits continuously or periodically an optical, an acoustic and/or an electrical signal, particularly dependent on and/or in relation to the fluid-level.