WO2001016593A1

WO2001016593A1 - Method for detecting and determining the origin of undissolved gases in liquid-filled high voltage systems and devices for carrying out said method

Info

Publication number: WO2001016593A1
Application number: PCT/EP1999/006293
Authority: WO
Inventors: Eckhard BRÄSEL
Original assignee: Braesel Eckhard
Priority date: 1998-07-25
Filing date: 1999-08-28
Publication date: 2001-03-08
Also published as: DE19833601C1

Abstract

The invention relates to a method for detecting and determining the origin of undissolved gases in liquid-filled high voltage systems and to devices for carrying out this method. The novel method is characterised in that the liquid flows in a set sequence from a gas collecting part (15) which is situated in the area of the rising pipeline (14) to the expansion vessel of the high voltage system, and which is filled with liquid during normal operation, into a measuring device (1), where a reversible equilibrium gas phase is formed in relation to the gases that are dissolved in the liquid. This equilibrium gas phase is monitored by sensors. Those gases which remain undissolved partially or completely displace the liquid in the gas collection part (15) and enter the same measuring device (1), where they characteristically alter the partial pressures of the equilibrium gas phase. The latter are detected and represented in the form of time functions of sensors in a control and evaluation unit (12), in such a way that the time functions of sensors (9) for the pressure and for selected gases, individually or together, in addition to the monitoring of gases dissolved in the liquid, enable the undissolved gases to be identified with approximative representation of volume and rate and allow their origin to be determined. The invention also relates to a measuring device (1) with a gas-permeable, liquid-resistant membrane (5) and another measuring device with an equilibrium gas obtained by a gaseous exchange with the liquid.

Description

Method for determining and determining the origin of undissolved gases in high-voltage systems filled with liquid and devices for carrying out the method

The invention relates to a method for determining undissolved gases before the gas collection relay responds in high-voltage systems filled with liquid, and for determining the origin of the gas volume accumulated in each case, which serves in particular for early error detection and avoidance of consequential errors. The invention also relates to a device for performing the method.

In high-voltage systems filled with liquid, especially in the case of transformers filled with mineral oil, gas collection relays have the task of collecting rising, undissolved gas and signaling that an adjustable limit value has been reached. Free gas is on the one hand a danger to the dielectric strength of the insulation system and on the other hand it is an information carrier about the cause of its formation. After signaling the relay gas, it is important for the availability of the high-voltage systems to quickly determine by means of a gas analysis whether faulty gases have arisen due to abnormal loading of the insulation system or whether air has entered the high-voltage system. Because of the rarity of such events, in practice the analysis is carried out manually. The analysis is evaluated according to IEC 599 "Mineral Oil-impregnated electrical equipment in service-interpretation of dissolved and free gases analysis" by the equilibrium criterion, which requires comparison with an analysis of the gases dissolved in the oil from an oil sample taken at the same time. The contents of the fault gases dissolved in the oil are converted to the composition of a fictitious equilibrium gas and compared with the relay gas composition. It is natural law that higher fault gas contents in the relay gas prove its origin from a fault point in the high-voltage device filled with liquid. Disadvantages of this procedure based on full laboratory analyzes are:

High analysis and time expenditure. - The fictitious equilibrium gas is analytically subject to the error of the device used for gas extraction from the oil as well as the gas solubility coefficient and its temperature dependence for the calculation. Regardless of this unsatisfactory situation, the operators of large transformers, in addition to the online analysis of gases dissolved in the oil, require that the presence of undissolved gases be more sensitive than indicated by the gas relay and that an analysis should be carried out as automatically as possible (DVG recommendations of the network companies for monitoring systems on large transformers, Heidelberg , March 1998).

Solutions are known which can partially meet the requirements. According to DE 4136639 AI, undissolved gas volumes from 0.1 ml can be detected. The time course of the further gas accumulation can be determined and the gas periodically fed to an analyzer. For this purpose, the mechanical Buchholz relay (gas collection relay) is followed by a gas collection vessel with a capacity detector or replaced by it. The disadvantages of this solution are:

The gas analysis is carried out separately from the gas detection.

There is therefore the problem of the gas supply line, which leads to loss of sensitivity and reliability. There is also an expense for an analyzer that is rarely used. - For the physically based evaluation of the relay gas according to the equilibrium criterion, analyzes of the gases dissolved in the oil are required. Since these have to be provided by separate devices, there is an analogous influence of errors in the laboratory procedure already described.

For online analyzes of gases dissolved in oil, devices are known which use the nozzles provided for oil sampling. Either membrane-covered sensors are attached directly to these or lines are led to vacuum extraction devices that are coupled to analyzers. In practice, solutions are used that allow gas to pass from the oil into a gas storage space equipped with sensors via membrane materials (DD 238116 AI, DE 4413197 AI, US 3866460, US 4058373). Deviating from this, a solution is described in which an equilibrium gas phase is created for analysis by periodic contact between gas and oil (DD 226651 AI).

Furthermore, solutions are known that only the accumulation of the relay gas by means of a thermistor (DE 2455252 AI) and only the analysis of the signaled relay gas (H. Schliesing; Ein new method for rapid analysis of Buchholz gases from transformers; Elektrizitätswirtschaft 77, 1978, H 19, S. 676-8) enable.

The object of the invention is to install and operate a measuring device on the liquid-filled high-voltage devices in such a way that, on the basis of the monitoring of gases dissolved in the liquid, the detection of undissolved gases with the direct metrological test of the physical balance between dissolved and undissolved Gases for determining the origin of the undissolved gases connects and replaces known, technical solutions that previously allow separate monitoring of gases dissolved in the liquid, the detection of undissolved gases and the analysis of undissolved gases.

According to the invention the object is solved by the features of claims 1, 4 and 8. Advantageous refinements result from the subclaims.

For the successful implementation of the invention it is important that in one and the same measuring device the changes in the measured variable pressure and the measured variable concentration of a gas or several selected gases are displayed together with an equilibrium gas phase of the gases dissolved in the liquid by penetrating undissolved gases and from their characteristic The development and determination of the origin of the undissolved gases takes place over time. The invention will be explained in more detail below on the basis of exemplary embodiments. The concentration sensor for one gas or for several selected gases is preferably selected together without measuring gas consumption, e.g. B. Thermal conductivity measurement and hydrogen measurement using a palladium membrane (by pressure or thermal conductivity detection) are suitable. The associated drawings show in:

Fig. 1, the measuring device according to the invention as a continuously working variant on

Gas collecting nozzle connected, Fig. 2, the measuring device as a continuously working variant as part of the cover of a

3, the measuring device is connected to the gas collecting nozzle as a periodically operating variant. Embodiment 1 with reference to FIG. 1

Essentially, the continuously operating measuring device 1 consists of a metallic cylinder jacket 2, which can be screwed at the bottom, a connecting piece 16, which seals to the cylinder jacket 2 with a web 17, and has a screwable sensor block 8 at the top. A valve element 7 is guided approximately in the middle from the cylinder jacket 2, above the bore of which is the highest point of a specially supported, replaceable, oil-resistant and only gas-permeable membrane insert 5 which is inclined in the cylinder jacket 2. The membrane insert 5 sits on the web of the thicker wall of the separating space 3 and is held in an oil-tight manner from above with a screwable washer 6. This is a gas room

4 created between the cylinder jacket 2, the sensor block 8 and the membrane 5, gas being able to pass through the latter on both sides. The sensor block 8 contains the contact areas of the sensors for pressure 9 and the thermal conductivity 10 facing the gas space 4. The measuring device 1 also includes a control and evaluation unit 12 to which the sensor block 8 as well as one inserted into the cylinder jacket 2 below the valve element 7 are connected via a cable Temperature sensor 11 and a pressure sensor 13 installed outside for detecting the atmospheric pressure are connected.

The cylinder jacket 2 can, for. B. have a diameter of 40 mm. The volume of the gas space 4 behind the membrane insert 5 can be 20 ml and the separation space 3 can be 50 ml. The membrane material can e.g. B. 25 μm PTFE film.

For use in an oil transformer, the measuring device 1 is screwed via the connecting piece 16 into a gas collecting piece 15, which can represent a T-connection flange adapter, until it is sealed on the web 18. The adapter is located in the riser 14 from the boiler to the expansion tank of the transformer.

Via the valve element 7, the separating space below the membrane insert 5 is completely filled with oil from the riser 14. The valve element 7, which has a capillary bore as usual, is then closed. All sensors are switched on via the control and evaluation unit 12, which can be installed at a suitable point on the transformer via a correspondingly long cable connection. The oil below the membrane insert

5 is convectively involved in the exchange with the boiler oil via the riser. It is a surprising finding that the gas contents in the boiler oil approximately match those in the oil in the riser 14. Therefore, the sensors in the measuring device 1 indicate the following state after a short adaptation time: - pressure sensor 9

Sum of the equilibrium partial pressures of the gases dissolved in the oil at the temperature T

- Thermal conductivity detector 10

Thermal conductivity of the equilibrium state in the gas space 4

- Temperature sensor 11 temperature T in the separation room 3

If undissolved gases occur in the boiler oil, they reach the measuring device 1 unhindered via the riser 14 and accumulate in the separation chamber 3. At the highest point near the capillary bore of the valve element 7, the undissolved gases below the membrane begin to partially, completely or beyond to displace the oil into the gas collecting nozzle 15. The speed can fluctuate within wide limits. The accumulation can either stagnate in the event of missing or interrupted subsequent deliveries of undissolved gases or decrease until it is completely dissolved. These visually perceptible time profiles of the accumulated gas volume in the oil below the membrane are determined by the component-specific gas exchange between the undissolved, the dissolved in the oil and the gases in the gas space 4.

If the sensor functions pressure 9 and thermal conductivity 10 in the gas space 4 before the accumulation of undissolved gases are equilibrium indicators for gases dissolved in the oil, characteristic changes occur with the beginning accumulation of undissolved gases. The time profiles are recorded and stored in the control and evaluation unit 12. Their values are mainly influenced by:

- Entry rate of undissolved gases into the riser 14, composition of the undissolved gases, gas content and convection intensity of the oil.

By optimally designing the measuring device parameters (membrane material and thickness, geometry gas space 4 and separation space 3), a maximum analysis of the time profiles can be achieved. The following relationships are used: Detection of undissolved gases:

- Pressure rise via sensor 9, maximum of the rise and the time course allow the volume and the accumulation rate to be determined.

Origin determination for thermal conductivity measurement:

- Recording the time course until the maximum is exceeded, if the maximum is higher than for the gases dissolved in the oil, the origin is "fault gas", otherwise "air entry".

The temperature in the separating chamber 3 is continuously detected via the sensor 11 in order to register the load state of the transformer, which is important for diagnoses. The control and evaluation unit 12 continuously forms a quotient from the measuring pressure sensor 9 and the pressure sensor 13 and displays it as the degree of gas saturation of the oil. This allows prophylactic detection of gas as a result of oversaturation or the cause to be shown after it has occurred.

If a selectively hydrogen-measuring sensor is selected as sensor 10, the hydrogen dissolved in the oil is continuously measured. It is only when undissolved gases accumulate below the membrane insert 5 that the physical balance, which is then more important, is carried out analogously to the procedure with the thermal conductivity detector. If the undissolved gases have dissolved again or a venting has taken place via the valve element 7, the hydrogen dissolved in the oil is measured again, which, by means of comparisons with limit values, permits condition monitoring outside the occurrence of undissolved gases. For this purpose, the sensor display 10 must be temperature normalized using the temperature display 11.

Furthermore, the ongoing measurement of the hydrogen dissolved in the oil allows the rate of increase of the hydrogen to be determined, which, in conjunction with the degree of gas saturation, permits forecasts to be made of undissolved gases as a result of a fault in the active part of the transformer. The sensor 10 can also represent a differential measurement of the thermal conductivity with limited sample gas consumption. Since only the carbon dioxide of the fault gas components of interest has a lower thermal conductivity than air, a separation, e.g. B. chemically, a concentration-proportional thermal conductivity for the remaining universal proportion of fault gas and thus practically suitable for diagnosis according to the hydrogen. If the frequencies and gas volumes of the carbon dioxide separations the membrane permeability can be adapted, a practically usable measuring cycle can be obtained. The differential signal of thermal conductivity, which is proportional to carbon dioxide, can also be used to diagnose solid insulation. If the transformers have a gas collecting relay, the measuring device 1 described with the gas collecting nozzle 15 can in principle be located in the riser in front of the gas collecting relay. After undissolved gases have filled measuring device 1, the other undissolved gases enter the gas collection relay. In practice, this should be taken into account in that the signal setting value of the gas collection relay is reduced by the volume of the measuring device 1. A disadvantage is that the undissolved gases which trigger the signaling in the gas collecting relay itself are not used for determining the origin.

This disadvantage can be eliminated by coupling the measuring device 1 directly to the gas collection relay.

Embodiment 2 with reference to FIG. 2

The measuring device 1 described in embodiment 1 is detachably mounted on the gas collecting relay 19 via its connecting piece 16 instead of the cover. As the only addition to the measuring device 1, the signal line 21 is additionally routed to the control and evaluation unit 12. Here too, the signal setting value of the gas collection relay should be reduced by the volume of the measuring device 1.

In this combination, the measuring device 1 operates analogously to that described in exemplary embodiment 1. The undissolved gases reach the measuring device 1 via the gas collecting relay 19. When the upper float 20 of the gas collecting relay 19 reaches the signal value, this is registered in the control and evaluation unit 12 via the signal line 21. The rapid mixing of the undissolved gases between the measuring device 1 and the gas space in the gas collecting relay 19, which together represent the relay gas, ensures that the time course of the sensor functions includes the determination of the origin of the relay gas in the diagnosis. All other variants are analogous to embodiment 1. Embodiment 3 with reference to FIG. 3

The periodically operating measuring device 22 consists essentially of a cylindrical separating chamber 23, which is connected to a gas chamber 24 located above, which also represents a cylinder, and an oil collection vessel 25. In the separating chamber 23, an oil line 26 leads to the upper part The switching valve 27 is equipped and has a diameter such that undissolved gases can also be transported vertically downwards by means of oil, and in the lower part via an switching valve 28 an oil line 29. From the head of the gas space 24, a connecting line 31, into which a switching valve 32 is installed at the highest point, with a gas pump 33, a switching valve 34, and a septum stub 35, under which the line is expanded a certain section, leads down into the separating space 23 Both the separating space 23 has a nozzle bottom 36 below the oil line 29 and the gas space 24 has the nozzle bottom 37 below the oil line 38 running to the oil collecting vessel 25, which has a switching valve 39. The gas space 24 has an oil level sensor 40 above the entry point of the oil line 38 in the cylinder wall. The same sensors 41, 42 are located offset in height in the oil collecting vessel 25, from the bottom of which a connecting line 43 with an oil pump 44 leads to the expansion vessel 45 of the transformer, sensor 42 projecting above the oil level sensor 40 in terms of height. The oil line 26 represents the inlet from the transformer and attaches to the gas collecting nozzle 46 located in the riser to the expansion vessel with a connecting nozzle 47 via a valve element 48. A sensor for the pressure 49 and a sensor for the thermal conductivity 50 are screwably inserted into the head of the gas space 24, both of which are secured by splash guards located underneath. A temperature sensor 51 is inserted in the center of the cylinder wall of the separating space 23.

A further switching valve 52 is installed in the connecting line 31 at the level of the switching valve 30. All switching valves and sensors are connected via lines to the control and evaluation unit 53, to which a pressure sensor 54 is connected from the surroundings of the transformer. For use on an oil transformer, the measuring device 1, which is located in a housing, is installed at a suitable point on the transformer. The oil line 26 leads up to the gas collecting nozzle 46, which is located in the riser, in the presence of a gas collecting relay in front of it, and is screwed into it by means of a connecting nozzle 47. The measuring device 22 must be filled before starting. For this purpose, the valve element 48 is opened once by hand. The "fill" key is pressed in the control and evaluation unit 53, as a result of which all the switching valves are opened. The oil entering the separating chamber 23 from the oil line 26 fills it slowly as well as the lines 29, 31 and 38 up to the level of the oil level sensor 40 in the gas chamber 24, upon reaching which all the switching valves close, with the exception of the switching valve 30, which is somewhat used for post-ventilation closes with a time delay. Before the "Start" button is pressed, the oil change time for the separation chamber 23, the duration of an exchange process and the number of exchange processes until the result of the formation of gases dissolved in the oil must be entered. This information must be determined once according to the design features of the measuring device 22 and its installation. Furthermore, the cycle of the result formation of gases dissolved in the oil must be specified. Once this information has been entered, it starts. The switching valves 27 and 28 open until the oil change time, which allows at least a double oil change in the separation chamber 23, has expired. Then the switching valve 28 closes, the switching valve 27 closes a little later with a time delay. The first exchange process then begins when the switching valve 30 opens and the pressure sensor 49 is checked. If the display remains unchanged, the switching valves 34 and 32 also open and the gas pump 33 switches on. The air in the gas space 24 and in the connecting line 31 is now moved by the oil from atmospheric pressure via the nozzle bases 36 and 37. During the specified duration of the exchange process, an isothermal partial pressure equilibrium is established with the gases dissolved in the oil, which changes the initial contents in the oil and in the gas space. After the time has elapsed, the gas pump 33 switches off and, after a settling time, the switching valves. The sensor values for pressure and thermal conductivity are registered in relation to time. The other exchange processes are repeated analogously, the respective partial pressure equilibrium constantly approaching that of the gases dissolved in the oil of the transformer. After the specified number of exchange processes has been reached, the partial pressure equilibrium is practically reached and all sensor displays are registered and the results of gases dissolved in the oil are displayed. For all next cycles of the formation of results of gases dissolved in the oil, the number of exchange processes is lower than after pressing the start button, since the gas chamber does not contain atmospheric air, but the last equilibrium gas. Before a new cycle begins, the oil level sensor 40 checks the oil level, which is readjusted automatically if necessary by opening the switching valve 39 via the oil line 38.

After each cycle, 35 gas samples can be taken through the septum nozzle. For this purpose, the switching valves 27 and 52 open, which creates a slight excess pressure. The gas samples can be taken manually or automatically.

If undissolved gases get into the riser, they collect in the connecting piece 47; with larger quantities, they also displace the oil from the gas collecting pipe 46. The next time the oil is changed in the separation chamber 23, the undissolved gases are transferred to the oil pipe 26 in the latter. For this purpose, the switching valves 27 and 28 open and switch valve 27 closes a little later with a time delay, which creates an overpressure in the undissolved gases in the separating chamber 23, which corresponds to the static pressure of the oil column between the oil collecting tank 25 and the oil level expansion tank 45 of the transformer. The switching valve 30 now opens and a pressure rise is registered via the control of the pressure sensor 49. At the same time, the sensor for thermal conductivity 50 is registered until the maximum value is reached. These and the stored pressure and thermal conductivity values of gases dissolved in the oil are used to determine and determine the origin of undissolved gases.

Statement:

Pressure increase via sensor 49, the amount of the increase allows the volume to be determined. The accumulation rate results from the passage of time on the basis of further exchange processes.

Origin determination for thermal conductivity measurement:

- Recording the time course until the maximum is exceeded, if the maximum is higher than in the last exchange process, the origin is "fault gas", otherwise

"Air entry".

After the maximum thermal conductivity has been exceeded, the switching valves 28, 32 and 39 open until the oil level has reached the oil level sensor 40. Then the switching valves close again. Then a new cycle of the formation of results of gases dissolved in the oil begins analogously. If the upper oil level sensor 41 is reached in the oil collecting vessel 25, switches automatically the oil pump 44 and pumps the oil until the lower oil level sensor 42 is reached via the oil line 43 into the expansion vessel 45 of the transformer. The variation of the sensors and the evaluation options are possible analogously to embodiment 1. If the transformers have a gas collecting relay, the measuring device 22 described can in principle be mounted via its connecting piece 47 instead of the cover onto the gas collecting relay analogously to exemplary embodiment 2.

In a further embodiment of the invention, the arrangement of a sensor 56 for checking for undissolved gases in the gas collecting nozzle 46 means that after signaling by the sensor 56, the measuring cycle can also be initiated operatively.

Claims

claims

1. A method for determining and determining the origin of undissolved gases in liquid-filled high-voltage systems with a riser and an expansion vessel based on the monitoring of gases dissolved in the liquid, characterized in that from one in the area of the riser (14) to the expansion vessel of the high-voltage system arranged, in normal operation liquid-filled gas collecting nozzle (15, 46), the liquid flows in a certain sequence into a measuring device (1, 22), where a reversible equilibrium gas phase forms with the gases dissolved in the liquid and these are measured by sensors (9, 10, 49, 50) for the pressure and for the concentration of a gas or a plurality of selected gases is monitored together, that undissolved gases partially or completely displace the liquid in the gas collecting nozzle (15, 46), these get into the measuring device (1, 22), where the partial pressures the equilibrium gas phase chara change cteristically and time functions of the sensor measured values are recorded, evaluated and displayed by a control and evaluation unit (12, 53) and that the time functions of the sensors additionally permit an approximate volume and rate display of undissolved gases.

2. The method according to claim 1, characterized in that via the time function of a temperature sensor (11, 51) in the measuring device (1, 22) both the result normalization of gases dissolved in the liquid and a determination of the load condition of the high-voltage system.

3. The method according to claim 1, characterized in that the gas saturation level of the liquid is determined via the ratio of the time functions of the pressure sensor (9, 49) in the equilibrium gas phase and a pressure sensor (13, 54) measuring in the vicinity of the high-voltage system.

4.Device for determining and determining the origin of undissolved gases in liquid-filled high-voltage systems with a riser and an expansion vessel for continuously carrying out the method according to claim 1, characterized by a measuring device (15) connected to a gas collecting nozzle (15) arranged in the region of the riser to the expansion vessel of the high-voltage system ( 1) that from a separating space (3) in connection with the gas collecting nozzle (15), in which there is a temperature sensor (11), a gas space (4) downstream of the separating space (3), in which there are sensors (9, 10) for pressure and for the concentration of a gas or several selected gases and there is a liquid-resistant and gas-permeable membrane insert (5) installed at an incline between the two spaces mentioned and that the measuring device (1) is connected to a control and evaluation unit (12), to which also a pressure sensor (13) from the surroundings of the high-voltage system is connected.

5. The device according to claim 4, characterized in that the sensor (10) for the concentration is a thermal conductivity sensor and that a differential measurement of the thermal conductivity before and after a carbon dioxide separation can be carried out with it.

6. The device according to claim 4, characterized in that the measuring device (1) has a cylinder jacket (2) which has a cylindrical connecting piece (16) screwable below and a screwable sensor block (8) above and contains a valve element (7) approximately in the middle , above the bore of which is the highest point of a specially supported, exchangeable, liquid-resistant and only gas-permeable membrane insert (5) built into the cylinder jacket (2), which is inclined downward from a web of the thicker inner wall of the lower cylinder jacket part, which faces inwards, and towards is held liquid-tight at the top by a screwable washer (6).

7. The device according to claim 4, characterized in that the measuring device (1) is coupled to a mechanical gas collecting relay (19) in such a way that the connecting piece (16) of the measuring device (1) forms the cover of the gas collecting relay (19), the Signal line (21) is also connected to the control and evaluation unit (12).

8.Device for determining and determining the origin of undissolved gases in liquid-filled high-voltage systems with a riser and an expansion vessel for periodically carrying out the method according to claim 1, characterized by a measuring device (46) connected to a gas collecting nozzle (46) arranged in the region of the riser to the expansion vessel of the high-voltage system ( 22), which consists of a separating space (23) connected to the gas collecting nozzle (46), in which there is a temperature sensor (51), a gas space (24) downstream of the separating space (23), in which there are sensors (49, 50 ) for pressure and for the concentration of a gas or several selected gases, devices (25, 29, 38) to ensure cyclical liquid renewal until the partial pressure equilibrium is reached and devices for creating a gas cycle from the gas space (24) to the separation space ( 23) exists and that the Me ßeinrichtung (22) is connected to a control and evaluation unit (53), to which a pressure sensor (54) from the environment of the high-voltage system is connected.

9. The device according to claim 8, characterized in that the sensor (50) for the concentration is a thermal conductivity sensor and that with it a differential measurement of the thermal conductivity before and after a carbon dioxide separation can be carried out.

10. The device according to claim 8, characterized in that the measuring device (22) is coupled to a mechanical gas collection relay directly in such a way that the connecting piece (47) forms the cover of the gas collection relay, the signal line additionally to the control and evaluation unit (53 ) is switched.