Life Prediction of Gas Filling in Electrical Switchgear

Abstract

The present invention discloses a method for predicting the life of a gas filling (2) of an electrical switchgear (1), wherein at different time points t1 and t2, at a predetermined temperature T p The invention relates to a method for measuring pressure values ​​p1 and p2 in a system of the electrical switching device (1) containing the gas filling (2). The life of the gas filling (2) is calculated based on a pressure difference Δp between the pressure values ​​p1 and p2. Alternatively, the pressure values ​​p1 and p2 may be measured at temperatures T1 and T2 within a predetermined temperature range at different time points t1 and t2.

Description

Technical Field

[0001] The present invention relates to a method for predicting the life of a gas filling of an electrical switching device. Background Art

[0002] Initially, a system of electrical switching devices can be filled with an insulating gas that forms the gas filling of the electrical switching device. For example, the insulating gas can consist of or contain sulfur hexafluoride (SF6). Over time, the gas filling can leak from the system, so that the insulation performance can degrade. In order to ensure minimum insulation performance, for example for switching devices arranged in the gas filling system, a minimum pressure value of the gas filling can be defined. As soon as the pressure of the gas filling drops below this minimum pressure value, the operation of the electrical switching device can become dangerous. This is why it is recommended to stop the operation of the electrical switching device in such a situation. Unfortunately, this situation can occur unexpectedly and lead to undesirable downtimes of the electrical switching device. Summary of the Invention

[0003] Therefore, an object of the present invention is to provide a method for predicting the life of a gas filling of an electrical switching device. In particular, unplanned downtimes of the electrical switching device should be avoided.

[0004] The object of the present invention is achieved by a method for predicting the life of a gas filling of an electrical switching device, the method comprising the following steps:

[0005] a) At a first time point t1, at a predetermined temperature T p A first pressure value p1 is measured in a system of an electrical switching device containing a gas filling, and at a second time point t2 at the same predetermined temperature T p Measuring a second pressure value p2 in a system of electrical switching devices containing a gas filling, or

[0006] b) measuring a first pressure value p1 in the system of the electrical switching device containing a gas filling at a first temperature T1 within a predetermined temperature range at a first point in time t1, and measuring a second pressure value p2 in the system of the electrical switching device containing a gas filling at a second temperature T2 within the same predetermined temperature range at a second point in time t2,

[0007] - calculating the pressure difference Δp between the first pressure value p1 and the second pressure value p2, and

[0008] - Calculating the life of the gas charge based on the pressure difference Δp.

[0009] In this way, unplanned downtime of the electrical switching apparatus may be avoided, and maintenance of the electrical switching apparatus may be better planned.

[0010] In order to avoid rapid temperature changes of the gas filling that may be caused by switching operations of the switching devices arranged in the gas filling system, it is recommended to keep the temperature of the gas filling at the same predetermined temperature T p The pressure value is measured at a temperature below, or at least within, a predetermined temperature range. Specifically, during the opening of the switch contacts of such switching devices, the switching arc can rapidly heat the gas charge and cause a spike in the gas charge pressure p and temperature T curve. Tests and research have revealed a time difference between the peak in pressure p and the peak in temperature T. Therefore, to account for the effect of temperature T on pressure p, the following gas equation is used:

[0011] p·V gas =R·T

[0012] where R is the gas constant of the gas filling and V gas is the volume of the gas filling, which may lead to invalid lifetime predictions in unfavorable cases, in particular, when pressure p and temperature T are measured during such transition phases as when the switching device is turned off. However, this does not necessarily mean that only at the predetermined temperature T p Instead of measuring pressure values ​​under different conditions or over a temperature range, the pressure p can be measured continuously and the appropriate value can be picked up from the data stream for use in the lifetime prediction calculation.

[0013] Specifically, the total life of the gas filling LT total This can be calculated using the following formula:

[0014]

[0015]

[0016]

[0017] Wherein p1 is a first pressure value, p2 is a second pressure value, Δp is a pressure difference between the second pressure value p2 and the first pressure value p1, t1 is a first time point and t2 is a second time point, Δt is a time difference between the second time point t2 and the first time point t1, Δp ptu is the nominal pressure drop per time unit (e.g. per year), LT nominal is the nominal life of the gas packing, p low is the minimum pressure of the gas filling and p high It is the maximum pressure value of the gas filling.

[0018] Minimum pressure value p of gas filling low A minimum insulation level is ensured. Below this value, operation of the electrical switching device may become dangerous. Maximum pressure value p of the gas filling high Normally the initial pressure when the system is filled. Nominal life of gas packing LT nominalis the expected life of the gas packing, for example 30 years. Nominal pressure drop per time unit Δp ptu Corresponding to this nominal life LT nominal and the maximum pressure value p high With the minimum pressure value p low The difference between.

[0019] Remaining life of gas filling LT remain This can be calculated using the following formula:

[0020]

[0021] In another embodiment, the total life of the gas packing LT total This can be calculated using the following formula:

[0022]

[0023] Where p1 is the first pressure value, p2 is the second pressure value, p low is the minimum pressure of the gas filling, p high is the maximum pressure value of the gas filling, Δp is the pressure difference between the second pressure value p2 and the first pressure value p1, t1 is the first time point, t2 is the second time point, and Δt is the time difference between the second time point t2 and the first time point t1.

[0024] In addition, the remaining life of the gas packing LT remain This can be calculated using the following formula:

[0025]

[0026] Where p1 is the first pressure value, p2 is the second pressure value, p low is the minimum pressure value of the gas filling, Δp is the pressure difference between the second pressure value p2 and the first pressure value p1, t1 is the first time point and t2 is the second time point, and Δt is the time difference between the second time point t2 and the first time point t1.

[0027] In an advantageous embodiment, the first pressure value p1 in the aforementioned formula can be obtained by using the following formula: 1corr Instead and with reference temperature T ref As a reference and / or second pressure value p2 can be obtained by p 2corr Instead and with reference temperature T ref For reference:

[0028]

[0029]

[0030] Where T1 is the first temperature, T2 is the second temperature, V gas is the volume of the gas filling, R is the gas constant of the gas filling, p 1corr is the first correction pressure value and p 2corr is the second corrected pressure value. By these means, when the temperature range for pressure measurement is limited, the pressures p1 and p2 can be determined more accurately. Preferably, the reference temperature T ref within the stated temperature range.

[0031] Preferably, the first pressure value p1 and / or the second pressure value p2 is calculated based on a volume change of a capacitor with an elastomer as a dielectric material between two electrodes of the capacitor.

[0032] In detail, the deformation of an elastic body or dielectric material based on the pressure change Δp can cause a proportional volume change ΔV of the initial volume V0 at the initial pressure. The proportionality factor is usually denoted as B, and the formula for the pressure change Δp is written as:

[0033]

[0034] The volume change can be calculated based on the change in capacitance of the capacitive pressure sensor. Assuming the capacitor is spherical, the capacitance C can be calculated using the following formula:

[0035]

[0036] where r o is the radius of the external flexible electrode, r i is the radius of the inner (rigid) electrode, ε0 is the absolute permittivity or absolute dielectric constant, and ε r is the relative permittivity or relative dielectric constant. Based on the known radius r of the inner (rigid) electrode i and the radius r of the external flexible electrode o , at the initial pressure and the actual pressure, the volume change ΔV and, therefore, the pressure change Δp can be easily calculated. Of course, capacitive pressure sensors of other shapes (eg cylindrical) also work.

[0037] Preferably, if the first pressure value p1 or the second pressure value p2 drops below the minimum pressure value p low , an alarm is output. For example, the alarm can be output via a signal light and / or a wireless interface to inform the responsible personnel. In this way, an abnormal pressure drop can be identified.

[0038] Advantageously, the predetermined temperature T p Or the predetermined temperature range is selected according to IEC standard IEC 62271-100 / 200 or the nominal temperature operating range of the electrical switching device. In this way, an appropriate predetermined temperature T can be selected.p or temperature range. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] The present invention will now be described in more detail hereinafter with reference to specific embodiments, to which however the invention is not limited.

[0040] Figure 1 shows a schematic diagram of an electrical switching device, and

[0041] Figure 2 A more detailed embodiment of the evaluation unit is shown. DETAILED DESCRIPTION

[0042] In general, identical or similar components are denoted by identical / similar names and reference numerals. The features disclosed in this specification apply to components having identical / similar names and reference numerals. Indications of orientation and relative positions relate to the associated drawings, and indications of orientation and / or relative positions must therefore be modified accordingly in the different drawings, as appropriate.

[0043] Figure 1 A schematic diagram of an electrical switching device 1 is shown, which comprises a gas filling 2 in a gas tank 3 within a housing 4 of the electrical switching device 1. The gas filling 2 has a pressure p and a volume V gas and temperature T.

[0044] In a gas tank 3, an electrical switching device 1 includes a capacitive pressure sensor 5 having an outer electrode 6, an inner electrode 7, a dielectric material 8 located therebetween, and a base 9. The dielectric material 8 may be composed of or include an elastomer. The pressure p of the gas filling 2 can be calculated based on the volume change of the capacitor formed by the electrodes 5 and 6 and the dielectric material 8.

[0045] Furthermore, a temperature sensor 10 is arranged on the base 9. The capacitive pressure sensor 5 and the temperature sensor 10 are connected to an evaluation unit 11a, which includes a processor 12, a memory 13, and a wireless interface 14. Furthermore, a signal lamp 15 is connected to the evaluation unit 11a. Finally, the electrical switching device 1 includes an exemplary switching device 16 arranged in the gas filling 2.

[0046] It should be noted that the gas tank 3 may be part of a larger system filled with the gas filling 2. For example, the system may include additional chambers, pipes, etc. Therefore, the pressure sensor 5 and / or the temperature sensor 10 are not necessarily arranged in the gas tank 3, but may be arranged at another location within the system filled with the insulating gas.

[0047] The function of the electrical switching device 1 is now described as follows:

[0048] Initially, the system and therefore the gas tank 3 are filled with an insulating gas forming the gas filling 2 of the electrical switching device 1. For example, the insulating gas may consist of or contain sulfur hexafluoride (SF6). Over time, the gas filling 2 may leak from the system, in particular from the gas tank 3, so that the insulation performance may degrade. In order to ensure a minimum insulation performance, for example for the switching device 16 and other devices (as the case may be), a minimum pressure value p of the gas filling 2 may be defined. low Once the pressure p of the gas filling 2 drops below the minimum pressure value p low , the operation of the electrical switching device 1 may become dangerous. This is why it is recommended to stop the operation of the electrical switching device 1 in this case.

[0049] In order to avoid unexpected downtime of the electrical switching device 1, the life of the gas filling 2 is predicted according to the following method, which includes the following steps:

[0050] a) At a first time point t1, at a predetermined temperature T p A first pressure value p1 is measured in a system of an electrical switching device 1 containing a gas filling 2 and a second pressure value p1 is measured at a second time point t2 at the same predetermined temperature T p measuring a second pressure value p2 in a system of an electrical switching device 1 containing a gas filling 2, or

[0051] b) measuring a first pressure value p1 in the system of the electrical switching device 1 containing the gas filling 2 at a first temperature T1 within a predetermined temperature range at a first point in time t1, and measuring a second pressure value p2 in the system of the electrical switching device 1 containing the gas filling 2 at a second temperature T2 within the same predetermined temperature range at a second point in time t2,

[0052] - calculating the pressure difference Δp between the first pressure value p1 and the second pressure value p2, and

[0053] - Calculating the life of the gas charge 2 based on the pressure difference Δp.

[0054] Specifically, the total life of the gas filling LT total This can be calculated using the following formula:

[0055]

[0056]

[0057]

[0058] Wherein p1 is a first pressure value, p2 is a second pressure value, Δp is a pressure difference between the second pressure value p2 and the first pressure value p1, t1 is a first time point and t2 is a second time point, Δt is a time difference between the second time point t2 and the first time point t1, Δp ptu is the nominal pressure drop per time unit (e.g. per year), LT nominal is the nominal life of the gas charge 2, p low is the minimum pressure value of the gas filling 2 and p high is the maximum pressure value of gas filling 2.

[0059] As already mentioned, p low The minimum pressure value of the gas filling 2 is higher than the minimum pressure value, which can ensure the safe operation of the electrical switching device 1. The maximum pressure value of the gas filling 2 is p high Normally the initial pressure when the system or tank 3 is filled. Nominal life LT of the gas packing 2 nominal is the expected life of the gas packing 2, for example 30 years. Nominal pressure drop per time unit Δp ptu Nominal life LT corresponding to gas filling 2 nominal and the maximum pressure value p of gas filling 2 high With the minimum pressure value p low The difference between.

[0060] Remaining life LT of gas filler 2 remain This can be calculated using the following formula:

[0061]

[0062] In detail, in this embodiment, the pressure p of the gas filling 2 is measured by means of the pressure sensor 5 by measuring the capacitance formed by the electrodes 6 and 7. In order to avoid rapid temperature changes of the gas filling 2 that may be caused by the switching operation of the switching device 16, it is recommended to p The pressure value is measured at a temperature below, or at least within, a predetermined temperature range. Specifically, during the opening of the switching contacts of the switching device 16, the switching arc can rapidly heat the gas charge 2 and cause a spike in the graph of the pressure p and temperature T of the gas charge 2. Tests and studies have revealed that there is a time difference between the peak in pressure p and the peak in temperature T. To account for the influence of temperature T on pressure p, the following gas equation is used:

[0063] p·V gas =R·T

[0064] Where R is the gas constant of the gas filling, which may lead to invalidation of the lifetime prediction in unfavorable cases, in particular in the case of pressure p and temperature T measurements during such transition phases as closing the switching device 16. However, this does not necessarily mean that only at a predetermined temperature T p Instead of measuring pressure values ​​under different conditions or over a temperature range, the pressure p can be measured continuously and the appropriate value can be picked up from the data stream for use in the lifetime prediction calculation.

[0065] Therefore, in detail, the processor 12 of the evaluation unit 11a can continuously (i.e., at predetermined time intervals) measure the pressure p using the pressure sensor 5 and continuously measure the temperature T using the temperature sensor 10, and store the pressure and temperature values ​​in the memory 13. In order to calculate the life of the gas charge 2, the measured values ​​can be read from the memory 13 and used for the above calculation. Alternatively, the processor 12 can monitor the temperature T using the temperature sensor 10 and measure the pressure p at a suitable temperature.

[0066] Predetermined temperature T p Or the predetermined temperature range may be selected according to IEC standard IEC 62271-100 / 200 or the nominal temperature operating range of the electrical switching device 1. In this way, an appropriate predetermined temperature T may be selected. p or temperature range.

[0067] In a preferred embodiment, if the first pressure value p1 or the second pressure value p2 drops below the minimum pressure value p low , an alarm is output. For example, the alarm can be output via a signal light 15 and / or a wireless interface 14 to inform the responsible personnel. In this way, an abnormal pressure drop can be identified.

[0068] In another embodiment, the total life LT of the gas packing 2 total This can be calculated using the following formula:

[0069]

[0070] And the remaining life LT of the gas filling 2 remain This can be calculated using the following formula:

[0071]

[0072] In all embodiments, the first pressure value p1 in the above formula can be obtained by using the following formula: 1corr Instead and with reference temperature T ref As a reference and / or second pressure value p2 can be obtained by p 2corr Instead and with reference temperature Tref For reference:

[0073]

[0074]

[0075] where p 1corr is the first correction pressure value and p 2corr is the second corrected pressure value. By these means, when the temperature range for pressure measurement is limited, the pressure can be determined more accurately. Preferably, the reference temperature T ref within the stated temperature range.

[0076] Generally, the pressure p of the gas filling 2 can be calculated based on the volume change of the capacitor formed by electrodes 6 and 7 and dielectric material 8, as previously described. Specifically, the deformation of the elastomer or dielectric material 8 based on the pressure change Δp causes a proportional volume change ΔV of the initial volume V0 at the initial pressure. The proportionality factor is generally denoted as B, and the formula for the pressure change Δp is written as:

[0077]

[0078] The volume change ΔV can be easily calculated based on the change in capacitance of the capacitive pressure sensor 5. Assuming the capacitor is spherical, the capacitance C can be calculated by using the following formula:

[0079]

[0080] where r o is the radius of the external flexible electrode 6, r i is the radius of the inner (rigid) electrode 7, ε0 is the absolute permittivity or absolute dielectric constant, and ε r is the relative permittivity or relative dielectric constant. Based on the known radius r of the inner (rigid) electrode 7 i and the radius r of the external flexible electrode 6 o , at the initial pressure and the actual pressure, the volume change ΔV and, therefore, the pressure change Δp can be easily calculated.

[0081] Figure 2 Finally, a more detailed embodiment of the evaluation unit 11b is shown, except that Figure 1In addition to the evaluation unit 11 a, the system also includes a signal injector 17, a signal conditioner 18, a signal amplifier 19, and a capacitor 20. The signal injector 17 is provided to apply a signal to the capacitor 20 and the capacitive pressure sensor 5 connected in series. The signal conditioner 18 is provided to generate a pressure signal based on the voltage across the capacitor 20 and based on the signal of the temperature sensor 10. Finally, the signal amplifier 19 amplifies the signal from the signal conditioner 18 and outputs its signal to the processor 12.

[0082] It should be noted that the present invention is not limited to the embodiments disclosed above, but a combination of different variants is possible. In practice, the electrical switching device 1 and the evaluation units 11a, 11b may have more or fewer components than shown in the figures. Furthermore, the present description may include the subject matter of further independent inventions.

[0083] It should also be noted that the term "comprising" does not exclude other elements, and the use of the article "a" or "an" does not exclude a plurality. Elements described in connection with different embodiments may also be combined. It should also be noted that the reference signs in the claims should not be construed as limiting the scope of the claims.

[0084] List of Figure Numbers

[0085] 1 Electrical switchgear

[0086] 2 Gas filling

[0087] 3 gas tanks

[0088] 4. Housing

[0089] 5. Pressure sensor

[0090] 6 External electrodes

[0091] 7 Internal electrodes

[0092] 8 Dielectric Materials

[0093] 9 base

[0094] 10 Temperature sensor

[0095] 11a, 11b Assessment Units

[0096] 12 processors

[0097] 13 Memory

[0098] 14 Wireless Interface

[0099] 15 signal lights

[0100] 16 Switching devices

[0101] 17 Signal Injector

[0102] 18 Signal Conditioner

[0103] 19 Signal Amplifier

[0104] 20 capacitors

[0105] p pressure

[0106] T temperature

[0107] V gas Volume of gas filling

Claims

1. A method for predicting the life of a gas filling (2) of an electrical switching device (1), said method comprising the following steps: a) At a first time point t1, at a predetermined temperature T p A first pressure value p1 is measured in the system of the electrical switching device (1) containing the gas filling (2) and at a second time point t2 at the same predetermined temperature T p measuring a second pressure value p2 in the system of the electrical switching device (1) containing the gas filling (2), or b) measuring a first pressure value p1 in the system of the electrical switching device (1) containing the gas filling (2) at a first temperature T1 within a predetermined temperature range at a first time point t1, and measuring a second pressure value p2 in the system of the electrical switching device (1) containing the gas filling (2) at a second temperature T2 within the same predetermined temperature range at a second time point t2, - calculating the pressure difference ∆p between the first pressure value p1 and the second pressure value p2, and Characterized in that the method further comprises the following steps: - calculating the total life of the gas charge (2) based on the pressure difference ∆p, wherein the first pressure value p1 and / or the second pressure value p2 is calculated based on the volume change of a capacitor with an elastomer as dielectric material (8) between the two electrodes (6, 7) of the capacitor, and - the total life of the gas packing LT total Use the following formula to calculate: where p low is the predetermined minimum pressure value of the gas filling (2), p high is the initial pressure value of the gas filling (2), and ∆t is the time difference between the second time point t2 and the first time point t1.

2. The method according to claim 1, wherein: where ∆p ptu is the nominal voltage drop per time unit, LT nominal is the nominal life of the gas filler (2).

3. The method according to claim 1, characterized in that The remaining life LT of the gas filler (2) remain Calculated by using the following formula: Where p1 is the first pressure value, p2 is the second pressure value, p low is the predetermined minimum pressure value of the gas filling (2), ∆p is the pressure difference between the second pressure value p2 and the first pressure value p1, t1 is the first time point and t2 is the second time point, and ∆t is the time difference between the second time point t2 and the first time point t1.

4. The method according to any one of claims 1 to 3, characterized in that By using the following formula, the first pressure value p1 is given by p 1corr Instead and with reference temperature T ref As a reference and / or the second pressure value p2 is p 2corr Instead and with reference temperature T ref For reference: Where T1 is the first temperature, T2 is the second temperature, V gas is the volume of the gas filling (2), R is the gas constant of the gas filling (2), p 1corr is the first correction pressure value and p 2corr is the second correction pressure value.

5. The method according to any one of claims 1 to 3, characterized in that If the first pressure value p1 or the second pressure value p2 drops below the predetermined minimum pressure value p of the gas filling (2) low , then output an alarm.

6. A system for predicting the life of a gas filling (2) of an electrical switching device (1), the system comprising: i. A pressure sensor (5) for measuring a pressure value in a system of the electrical switching device (1), the pressure sensor (5) comprising a capacitor with an elastomer as a dielectric material (8) between two electrodes (6, 7) of the capacitor, ii. a temperature sensor (10) for measuring a temperature value in a system of the electrical switching device (1), iii. an evaluation unit (11a), comprising a processor (12) and a memory (13), the pressure sensor (5) and the temperature sensor (10) being connected to the evaluation unit (11a), The system is configured to perform the following steps: a) A predetermined temperature T is measured at a first time point t1 using the temperature sensor (10) p The first pressure value p1 in the system of the electrical switching device (1) containing the gas filling (2) is measured using the pressure sensor (5) and at a second time point t2 at the same predetermined temperature T measured using the temperature sensor (10) p measuring a second pressure value p2 in the system of the electrical switching device (1) containing the gas filling (2) using the pressure sensor (5), or b) measuring a first pressure value p1 in the system of the electrical switching device (1) containing the gas filling (2) using the pressure sensor (5) at a first temperature T1 measured using the temperature sensor (10) within a predetermined temperature range at a first time point t1, and measuring a second pressure value p2 in the system of the electrical switching device (1) containing the gas filling (2) using the pressure sensor (5) at a second temperature T2 measured using the temperature sensor (10) within the same predetermined temperature range at a second time point t2, - calculating the pressure difference ∆p between the first pressure value p1 and the second pressure value p2, and -characterized in thatthe system is further configured to perform the following steps: - calculating the total life of the gas charge (2) based on the pressure difference ∆p, wherein the first pressure value p1 and / or the second pressure value p2 is calculated based on the volume change of a capacitor with an elastomer as dielectric material (8) between the two electrodes (6, 7) of the capacitor, and The total life of the gas packing LT total Use the following formula to calculate: where p low is the predetermined minimum pressure value of the gas filling (2), p high is the initial pressure value of the gas filling (2), and ∆t is the time difference between the second time point t2 and the first time point t1.

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