DE10232823B4 - Density monitor for SF6-insulated high or medium voltage systems - Google Patents

Abstract

Density monitor (10) for monitoring the density of the gas present in gas-insulated high or medium voltage systems, for example high-voltage switchgear, converters, pipelines, switching devices or transformers, for example SF ₆ , with an electronic density sensor (14) as a measuring sensor, which has a measuring quartz crystal (16) arranged in the gas (12) and delivers a frequency signal proportional to the density of the gas as the measured value (18), the frequency signal being fed to an input of an electronic evaluation unit (20), characterized in that the evaluation unit (20) has a memory (24) in which the measured values subject to a first conversion function (26) are stored in chronologically successive measured value acquisitions together with the time of the respective measurement as value pairs consisting of density value and time of the measured value acquisition, and that the measured values are stored using a second numerical conversion function i n Pressure values are converted.

Description

The invention relates to a density monitor for monitoring the density of gas in gas-insulated high or medium voltage systems, for example high-voltage switchgear, converters, pipelines, switching devices and transformers, as an insulator, for example SF ₆ , with an electronic density sensor as a measuring sensor, one has measuring oscillating quartz arranged in the gas and delivers a frequency signal proportional to the density of the gas as the measured value, the frequency signal being supplied to an electronic evaluation unit.

A density sensor of the type mentioned is, for example, from the DE 40 04 969 A1 known. These sensors are based on the density-dependent frequency shift of the mechanical resonance of a quartz crystal which is arranged in the gas whose density is to be determined. In particular, this density sensor is used in circuit breakers, converters, pipelines of high-voltage systems in power plants, transformer stations, distribution stations, which are mainly filled with SF ₆ gas, which serves as an electrical insulator and, in particular for circuit breakers, also has the task of extinguishing electrical arcs.

From the DE 199 01 119 A1 A monitoring system for gas-insulated high-voltage switchgear systems is known, in which different maximum permissible gas temperature limit values are also specified in the overcurrent range for different current values. A monitoring device compares the current gas temperature actual value with the maximum permissible gas temperature limit value for the current current value. A shutdown command is given when the actual gas temperature value reaches or exceeds the gas temperature limit.

In general, these gas-insulated high-voltage systems exist the problem that much of the plants one over constant or approximate for many years has a constant leak rate. In some cases, it can also become a there is a sudden increase in the leak rate. In both cases falls short the density of the insulation gas ultimately a first upper Threshold. This threshold is a so-called warning threshold, when it is reached, a control function is not yet triggered. This warning threshold is set or selected such that the High voltage system still complete functioning is when the density of the protective gas reaches this warning threshold.

At the next lower threshold it is a so-called interference threshold. The density of the protective gas of the high-voltage system reaches it Störschwellwert, the high-voltage system or the circuit breaker, Transformer, transducer and the like generally out of order set. For example, a high voltage circuit breaker Stop or turn off commands when the current density of the shielding gas this interference threshold below. In such operating situations, for example the protective function of a circuit breaker for that part of the Network or the one to be protected equipment no longer exist. Possibly. Have to then entire system parts or high-voltage systems are switched off to the part of the plant where the gas density is the interference threshold has fallen below to disconnect from the high-voltage network.

Because a decrease in the density of the protective gas below the interference threshold of the respective high-voltage system part because of the associated inoperability this high-voltage system part can be avoided in any case should, as a rule, already when the gas density meets the warning threshold has fallen below, the high-voltage system part immediately from the Taken network. This is because the leak rate is not known and the situation with regard to their further development is difficult to assess and the need for action is difficult to classify. Then it has to a cause research and in particular restoration of the desired Density of the protective gas is carried out become. These measures are, however, with great technical effort and can also be temporary Blackouts at Lead customers although in the big one Majority of cases in which the gas density of the protective gas is initially only the warning threshold has fallen short of an immediate review, research into causes and Maintenance is not required, but only in a few days or Weeks is, for example, if routine or standard maintenance is required anyway carried out become.

From the DE 196 03 9421 Finally, a data acquisition device for the independent and independent acquisition and storage of electrical quantities is known, such as voltages, currents, frequencies, temperatures, pH values, air humidity, incidence of light, wind speeds, distances and the like. The data are recorded over longer periods of time, a timer being provided so that measured values and times can be stored over longer periods of time by means of a non-volatile memory and called up as required.

The invention is therefore the object based on a density guard of the type mentioned at the outset to the effect that a improved forecast of the occurrence of the accident and an improved Analysis of the causes of faults allows is.

This task is carried out with the density monitor the features mentioned in the characterizing part of the claim 1 solved.

As a result of this measure, it is not only possible to record an instantaneous value of the current gas density of the protective gas of the high-voltage system and to compare it with threshold values, but it is also possible to assess the development over time of the density values of the protective gas over a definable period, since the density values include the measurement times are stored in a memory. For example, if the gas density has fallen below the warning threshold value, the course of the gas density over time can be analyzed over a longer measurement period in the past. If it is determined that there is a linear or steady or slowly changing reduction in the gas density, the point in time at which the interference threshold value is expected to be undershot can be predicted, so that the required maintenance or decommissioning of the high-voltage system can be carried out, for example, when a block stoppage of a power plant or power plant part or a plant part is planned anyway. The invention makes it possible to detect the leak rate depending on the operating state of the switch position (load) and thus to make forecasts for further operation of the system or the device. Another advantage of the density monitor according to the invention is its universal applicability in all SF ₆ systems, switching devices, transformers, piping and transducers, regardless of the respective installation location and the respective installation position and the absence of direct or indirect temperature measurement of the gas to be monitored.

According to a first advantageous embodiment According to the invention, the evaluation unit has a preferably several, in particular three, optionally freely programmable Has setpoint generator, the measured values being compared with the setpoints become and inadmissible Deviations one or more different alarm levels, especially via relays or display devices can be activated. For example with only slight deviations from the target value of the gas density Optical display or a flashing measured value display activated become. If the warning threshold is reached, a first relay can be activated be activated, for example an alarm in a monitoring center triggers. If the interference threshold is undershot another relay can be activated, which on the one hand the affected high-voltage system, for example deactivated with regard to switching operations and on the other hand triggers a warning alarm at a control point.

According to a further embodiment The invention is a first setpoint generator for a warning threshold and a second and third setpoint generator for an interference threshold set or the third interference threshold to exceed the maximum density of the gas set. The last variant with Setting the third interference threshold on exceeding A maximum gas density can be particularly important when monitoring arcing, such as lightning, in gas rooms to adjust.

According to another advantageous embodiment of the invention, the measured values of the density sensor are converted into standardized density values by means of the second conversion function and, if necessary, displayed with a display device of the evaluation unit. The ability to display is another advantage over most prior art density meters. The density sensor works on the principle of preferably two quartz crystals, one quartz crystal being exposed to the gas whose density is to be measured and the other quartz crystal is preferably arranged in a vacuum, but is at the same temperature level as the quartz crystal and to compensate for temperature drifts Vibration frequency of the measuring oscillating quartz serves. The basis of this measuring principle is that when the quartz crystal is rearranged with, for example, SF ₆ molecules of higher density, the quartz crystal vibrates at a higher frequency than the reference quartz crystal, which is exposed to the vacuum. Ultimately, the frequency difference between the measuring crystal and the reference crystal is evaluated, which is a measure of the density of the measuring gas, for example SF ₆ .

The relationship between changes in Output frequency of the density sensor and the density is not linear, can, however, by means of a second conversion function or

Conversion table that may be specific can depend on the specific density sensor used, can be linearized.

According to the invention it is also possible that the Measured values numerically in using a second conversion function preferably standardized pressure values are converted.

This makes it possible for the currently measured density can be compared with the specification on the respective rating plate of the gas compartment. As a reference value for the Temperature is recommended at 20 °, as is usually found on the devices is.

According to the invention, the density pairs ascertained from the measured values by means of the first conversion function and the time of the respective measured value acquisition are stored in the memory as pairs of values. This measure offers the advantage that the temporal course of the measured values or density values can be analyzed retrospectively over a past, in particular longer, period. For example, it can be determined whether the past changes in density of the protective gas are a continuous, temporally continuous process acts or whether the density change occurs in rapid, abrupt or discontinuous jumps. This analysis of the time course of the change in density of the protective gas in the past then determines, for example, the type or the time of the actions to be initiated as soon as the gas density has fallen below the warning threshold value, for example.

It is an advantage after one another advantageous embodiment of the invention that the memory is designed as a ring buffer or shift register and the filed Data after a measurement period that includes a plurality of measurements includes, will be overwritten by new data. This measure is the consideration on the basis that if the currently recorded gas density, for example falls below the warning threshold, it for the actions to be initiated and the timing of which is not required the gas density above the entire period of the past measurements to analyze, but only over a period of time in the area from days to weeks before the warning threshold is undershot lies.

The measurement value storage preferably takes place Gas density in minute or hour intervals, for example every 15 up to 45 minutes or half an hour instead of and is an advantage, for example plant-specific in terms of time adjustable.

Another beneficial Embodiment of the invention provides that the in the memory stored measurement values or density values as well as the measurement times a past Measurement period from several days to months, for example from cover a week to a month or two weeks, with this measurement period can in turn preferably be set on a plant-specific basis should be. So can for example, the measurement period as well as the distance between the measured value acquisition for parts of the system which experience has shown are not very susceptible to changes the leak rate are rather large, while for other parts of the system that fluctuate due to high stress leak rate, these intervals or measuring distances rather set shorter are.

After a particularly advantageous one Embodiment of the invention provides that the Evaluation unit of the recorded and stored time course the measured values or the gas density are subjected to a trend analysis becomes. This can be preferred downstream integration functions or differential functions be provided with which aspects of interest change over time Gas density of the high-voltage system can be filtered out.

A trend analysis can also be advantageous individual operating parameters of the high-voltage system, in particular for example the switching state of a high-voltage switchgear, with be included.

For example, a high voltage circuit breaker equipped with different types of seals, between static and dynamic seals must be distinguished. With regard to the Fault detection in such a high-voltage switchgear is it is important to determine whether the system is on or when switched off shows the leak or whether the leak on a static or a dynamic seal occurs. Taking into account the current one Switching status and the switching position of the high-voltage switchgear in connection with the time when an abnormal density change of the protective gas has occurred, you can use this information usually recognize whether the high voltage circuit breaker is a Leakage on a static or a dynamic seal having. In other words, this means that if a Circuit breaker an impermissible has a high leakage rate and also by means of the density monitor according to the invention knows the time at which this impermissibly high leak rate occurs, by means of the switching report of the circuit breaker afterwards it can be determined which event triggered the leak rate. For example can then be recognized whether the leak is due to a short break has occurred through the circuit breaker at which. the seals the circuit breaker is exposed to high loads, or whether the leak is gradually spreading over you has developed over a long period of time.

The setting and operation of the density monitor arises according to another advantageous embodiment of the invention is particularly simple by using parameters of the evaluation unit, such as Threshold values, measuring rate, measuring period or the like via a Keyboard of the evaluation unit or via an interface connectable PC changed and logged if necessary.

The measurement and data security of the density monitor is further improved in that the evaluation unit has a Microcontroller with assigned memories and the memory battery-buffered or designed as a non-volatile memory are, the microcontroller or the program sequence being preferred monitored by a watchdog function for freedom from interference becomes.

Further advantages and possible applications of the present invention result from the following description of an embodiment based on the drawings.

Show it:

1 an embodiment of a density sensor of the seal monitor as a block diagram,

2 an embodiment of the evaluation unit of the density monitor in the block diagram and

3 the relationship between the frequency measurement value of the density sensor and the density of the sample gas of a special embodiment game of a density sensor.

The in 1 and 2 shown density monitor 10 is preferably used to monitor the density of the gas present in gas-insulated high or medium voltage systems, such as high-voltage switchgear, converters, pipelines, switching devices and transformers, as an insulator. Such high-voltage systems can be high-voltage switchgear, high-voltage converters, high-voltage pipelines. As a gas 12 SF6 is preferred.

The density keeper 10 points accordingly 1 an electronic density sensor 14 as a transmitter. A quartz crystal 16 of the density sensor 14 is in the gas 12 , for example SF ₆ , arranged. Another reference quartz crystal 70 is in a vacuum 72 arranged. Both quartz crystals 16 . 70 are at essentially the same temperature. The quartz crystals 16 . 70 are each on an oscillator 74 . 76 connected, whose output signals to a mixer 78 be directed. In the mixer, the difference is essentially the frequency of the reference quartz crystal 70 and the quartz crystal 16 educated.

This difference frequency becomes a pulse generator 80 fed. In the present embodiment, the signals of the pulse generator 80 using a modulator 82 modulated the power supply so that at the output 88 of the density sensor 14 a reading 18 is tapped. This metric 18 is a frequency signal in the exemplary embodiment, the frequency of which depends on the density of the gas.

The density sensor 14 measures the gas density with an excellent long-term stability, as with the reference quartz crystal 70 in a vacuum 72 possible temperature errors can be compensated for directly. The density sensor 14 is able to measure a density range from 0 to approx. 60 kg per cubic meter over a temperature range from –40 ° C to + 70 ° C.

In 3 is the dependence of density 86 on the frequency 84 at the exit 88 of the density sensor 14 shown. It can be seen that this dependency does not take the form of a straight line passing through the zero point. In this respect, it makes sense to do this in 3 linearize the specified dependency. For example. the formula can be used for this: Density = {√ ((0.231 o F [Hz]) - 2.126) - 0.43 } 2

The exit 88 of the density sensor 14 can go to an entrance 22 the evaluation unit 20 be connected. The evaluation unit 20 includes a memory 24 , in the measured values which may be subject to a conversion function 18 successive measured value acquisitions are stored together with the time of the respective measurement as data.

The evaluation unit also includes 20 preferably several, for example 2 to 4, optionally freely programmable setpoint transmitters 28 . 30 32 . 34 , with the readings 18 compared with the target values and, in the event of an impermissible deviation, one or more, preferably different, alarm levels are activated. These alarm levels of different priority can be via relays 36 . 38 . 40 or a display device 42 activated or controlled. In particular, a first setpoint generator 28 . 30 ; 32 . 34 and a second setpoint device 28 . 30 . 32 . 34 provided, which are each set to a warning threshold and a different interference threshold. The recorded minimum or maximum density values can also be continuously checked or monitored.

Using a microcontroller 50 are the readings 18 via a conversion function 26 or a table numerically converted into density values and possibly with a display device 42 the evaluation unit 20 brought to the display. In the store 24 are the measured values 18 or density values and the time of the measured value acquisition as value pairs. The memory is preferred 24 formed as a ring memory or shift register, the stored data being overwritten by new data after a measurement period which comprises a plurality of measurement value acquisitions.

The measured value is recorded at intervals of minutes to hours, preferably every 15 to 45 minutes, especially every half hour. The measurement value acquisition can preferably be set individually, for example depending on the respective high-voltage system. The one in memory 24 stored measured values 18 or density values and measurement times cover a measurement period of several days to months, in particular 1 week to 1 month, preferably 2 weeks. This period of time can preferably be set individually and specific to the system type.

It is understood that the stored data of the measured values 18 of the density sensor 14 or the density also successively in the memory 24 can be stored, then based on the order in which the measured values are written 18 in the store 24 there is already a time allocation. In this case, it is of course not necessary to store the times of the measured value acquisition in the memory 24 to write, because the time assignment can already be derived from the storage location. For example, storage location no. 1 can have the most recent measured value 18 be written in, so that it can be deduced from this that the measured value in storage space No. 2 was, for example, half an hour ago and that in storage space 336 registered reading is already 7 days old. In this example, it was assumed that successive measurements were taken every half an hour become.

The captured and in memory 24 The time curve of the density of the gas or the measured values that has been stored is advantageously subjected to a trend analysis as soon as the current density of the gas has fallen below a warning threshold value, for example. To do this, are in the microcontroller 50 prefers integration or differential functions or other algorithms with which time changes of interest can be highlighted or filtered out. This trend analysis also takes into account the individual operating parameters of the high-voltage system in the measurement period, their data in the memory 24 are filed. These include, for example, the switching state of a high-voltage switchgear, so that any abnormalities in the density of the protective gas that may occur can be assigned to these switching states or operating parameters.

Parameters of the evaluation unit 20 , such as threshold values, measuring rate, measuring period and the like, can be done using a keyboard 44 on the evaluation unit or via an interface 46 connectable PC 48 or laptop changed and logged if necessary.

In addition to the microcontroller 50 and the memory 24 has the evaluation unit 20 more storage 52 . 54 on, with the memory 24 . 52 . 54 battery-backed or designed as non-volatile memory. During the store 24 The memory is in particular designed as a battery-buffered RAM 52 an Eprom, which contains the complete software that is in the microcontroller 50 is processed. The memory 54 is designed as an E-Eprom and contains programmed parameters that will definitely not remain volatile even if the supply of the density monitor and the battery buffer of the RAM fail. In particular, are in the memory 54 Programming values saved, which the evaluation and processing of the measured values 18 of the density sensor 14 affect. Likewise, in the store 54 also setpoints for the setpoints 28 . 30 . 32 . 34 be filed.

There is also a watchdog function 56 provided with which the microcontroller 50 or the program sequence is monitored for freedom from interference. It should be mentioned that in the evaluation unit 20 also a power supply 58 is provided drivers 60 for the display device 42 , an oscillator 62 as a timer for the microcontroller 50 , an alarm check function 64 as well as signal processing 66 and signal conversion 68 for those at the entrance 22 the evaluation unit 20 Measured values fed in 18 of the density sensor 14 ,

A preferred embodiment of the density monitor 10 comprises three alarm contacts and an optical alarm, the switching points being freely selectable or programmable.

Furthermore, as an interface 46 an RS 232 interface is provided for data analysis. The density keeper 10 can be operated in a wide supply voltage range from 82 to 264 V AC or 36 to 350 V DC and has an LED number display. The measured value memory 24 is battery-buffered. In addition to menu-driven programming, a real-time clock is provided. The density monitor also has a counter for power failure, minimum / maximum value recording and a watchdog function.

With the density monitor 10 the density, for example of the SF6 gas, can be measured and recorded in kilograms / cubic meters directly on site. The internal data memory logs the gas density and the respective time as standard over a period of, for example, a maximum of 7 days, successive measurements preferably being carried out every half an hour. Overall, the last 336 measured density values are stored in the data memory with these settings.

For monitoring gas density fluctuations can three relay switch contacts can be freely programmed.

An additional fourth alarm signals for example as a flashing measured value display from a distance a slight deviation in the required gas density. amendments the device parameters can carried out on site by hand or using a PC or laptop and be printed out.

The entrance 22 of the density monitor 10 works at frequencies in the range of 0.5 KHz to measure gas density. The measured frequency is determined using a fixed formula or

Table converted to the density of the SF ₆ gas in kilograms / cubic meters or can be adjusted accordingly. The measured value is shown on an LED display. At the push of a button, the measured value can be displayed converted to a standardized pressure (for example at 20 ° C) for a period of approx. 2 seconds. The switching points of the relays can be freely adjusted over the entire measuring range. If a switching point is exceeded or undershot, this can also be signaled optically using a flashing LED display.

The device parameters are programmed directly on the evaluation unit 20 using the keyboard 44 or using a PC via the interface 46 performed. All programmed values remain non-volatile even after a power failure. Using the device programming, the sampling rate for the measured value acquisition can be changed, an online display and logging of the measured value memory can be carried out, and a linearization table can also be programmed into the evaluation unit.

The watchdog function 56 is a control function to crash the microcontroller 50 to recognize. For this purpose, an internal counter of the microcontroller 50 counted down completely independently from a certain initial value. When the counter value reaches 000, a program reset is forced and the software is restarted. The software ensures that the counter is periodically reset to its start value in order to prevent the reset in the normal case. If a watchdog reset occurs, the power failure counter is incremented and a new measurement value storage is forcibly carried out. After that, the storage of the measured values and times is continued according to the programmed sampling rate.

10

density Controller

12

gas

14

density sensor

16

Measuring quartz crystal

18

reading

20

evaluation

22

entrance

24

Storage

26

conversion function

28

Setpoint generator

30

Setpoint generator

32

Setpoint generator

34

Setpoint generator

36

relay

38

relay

40

relay

42

display device

44

keyboard

46

interface

48

PC

50

microcontroller

52

Storage

54

Storage

56

Watch-dog function

58

power supply

60

driver

62

oscillator

64

alarm function

66

signal conditioning

68

signal conditioning

70

Reference oscillator crystal

72

vacuum

74

oscillator

76

oscillator

78

mixer

80

pulse generator

82

modulator

84

frequency

86

density

88

output

Claims (12)

Density monitor ( 10 ) to monitor the density of the gas located in gas-insulated high or medium voltage systems, for example high-voltage switchgear, converters, pipelines, switching devices or transformers, for example SF ₆ , with an electronic density sensor ( 14 ) as a measuring sensor that 12 ) arranged quartz crystal ( 16 ) and as a measured value ( 18 ) delivers a frequency signal proportional to the density of the gas, the frequency signal being input to an electronic evaluation unit ( 20 ) is supplied, characterized in that the evaluation unit ( 20 ) a memory ( 24 ) in which a first conversion function ( 26 ) subject to measured values recorded in chronological succession together with the time of the respective measurement as value pairs, consisting of density value and time of the measured value acquisition, and that the measured values are numerically converted into pressure values using a second conversion function. Density monitor according to claim 1, characterized in that the evaluation unit ( 20 ) one, preferably several, in particular two to four, optionally freely programmable setpoint transmitters ( 28 . 30 . 32 . 34 ), with the measured values ( 18 ) compared with the target values and, in the event of impermissible deviations, one or more different alarm levels, especially via relays 36 . 38 . 40 ) or a display device ( 42 ), to be activated. Density monitor according to claim 2, characterized in that a first setpoint generator ( 28 . 30 . 32 . 34 ) to a warning threshold and a second ( 28 . 30 . 32 . 34 ) and, if necessary, the third setpoint generator is set to a different interference threshold value, or a third interference threshold value is set to exceed the maximum density of the gas. Density monitor according to one of the preceding claims, characterized in that the density values with a display device ( 42 ) of the evaluation unit ( 20 ) are displayed. density Controller according to one of the preceding claims, characterized in that the measured values are normalized to using the second conversion function Pressure values are converted. Density monitor according to one of the preceding claims, characterized in that the memory ( 29 ) is designed as a ring memory or shift register and the stored data is overwritten by new data after a measurement time span which comprises a plurality of measurement value acquisitions become. density Controller according to one of the preceding claims, characterized in that the measurement recordings or measurement value storage in minutes to hourly intervals, For example, every 15 to 45 minutes or every half hour and preferred is individually adjustable. Density monitor according to one of the preceding claims, characterized in that the in the memory ( 24 ) stored density values and measuring times cover a measuring period of several days to months, for example one week to one month or two weeks, the measuring period preferably being individually adjustable. density Controller according to one of the preceding claims, characterized in that the recorded time course of the density of the gas of a trend analysis, for example through downstream integration or differential functions, is subjected. density Controller according to claim 9, characterized in that in a trend analysis also the individual operating parameters of the high-voltage system, especially the switching state of a high-voltage switchgear included become. Density monitor according to one of the preceding claims, characterized in that parameters of the evaluation unit ( 20 ), such as threshold values, measuring rate, measuring period or the like, via a keyboard ( 44 ) of the evaluation unit ( 20 ) or via an interface ( 46 ) connectable PC ( 48 ) changed and logged if necessary. Density monitor according to one of the preceding claims, characterized in that the evaluation unit ( 20 ) a microcontroller ( 50 ) with assigned memories ( 24 . 52 . 54 ) and the memory ( 24 . 52 . 54 ) are battery-buffered as non-volatile memories, the microcontroller ( 50 ) or the program flow in the microcontroller ( 50 ) preferably through a watchdog function ( 56 ) is monitored for freedom from interference.