HK1127671B - Method for monitoring the electrical energy quality in an electrical energy supply system, power quality field device and power quality system - Google Patents

Description

Method for monitoring the power quality of a power supply network, field device and power quality system

Technical Field

The invention relates to a power quality monitoring method, a power quality field device and a power quality system in a power supply network.

Background

The current electrical supply network is a highly complex network for distributing electrical energy, usually with a large energy feed-in and energy consumption. In addition to the safety of the supply of power, i.e. in order to ensure that a sufficient amount of power is supplied to each energy consumer at each moment in time, the quality of the supplied power (hereinafter referred to as "power quality") plays a critical role. The power quality in the power supply network is determined, for example, by so-called power quality parameters such as frequency, voltage and voltage harmonics or current harmonics, distortion factors, flicker, voltage asymmetry and power. High-sensitivity electrical devices currently require an electrical energy supply in the form of a sine wave as pure as possible with a uniform frequency and amplitude. In standard networks, such as EN50160 or IEC61000, upper and lower limit values are thus specified, within which the characteristic parameters of the electrical energy quality of the electrical power supply system must lie.

In order to be able to represent the power quality, power quality field devices are provided at different measurement locations of the power supply network, which record measured values of individual power quality parameters. In power quality field devices, the recorded measured values can be stored for archiving purposes. In order to evaluate whether the measured values exceed a limit value at a specific point in time, the stored measured values are transmitted at regular intervals to a further data processing device, for example a central evaluation computer, for evaluation. The time-dependent change of the power quality characteristic variable and the maintenance of the limit value can thus be generated in the central evaluation computer.

Since the data storage module embodied in the power quality field device cannot be selected to be arbitrarily large for cost reasons, the transmission of the stored measured values to the central evaluation computer must take place relatively frequently. If the stored measured values cannot be transmitted in a timely manner, either new measured values can no longer be stored or old measured values are overwritten by new measured values, since the data memory is completely full (so-called "ring memory operation"). In order to increase the time interval between two transmission processes, a correspondingly larger data memory must therefore be provided in the power quality field device.

Disclosure of Invention

The object of the present invention is to provide a method, a power quality device and a power quality system for monitoring the power quality of a power supply network, by means of which the monitoring of the power quality can be carried out with relatively little effort.

In terms of method, the above-mentioned object is achieved by a method for monitoring the quality of electrical energy in an electrical power supply system, in which the following steps are carried out:

at a first measurement time, a first measured value of a first power quality characteristic variable is acquired by means of a measuring device of a power quality field device arranged at a measuring location of the power supply network;

a second measurement value of the first power quality characteristic variable is acquired at a second measurement time following the first measurement time by means of a measurement device of the power quality field device;

-comparing the first and second measured values with at least one predefined threshold value, and

-generating an event signal indicating a violation of the at least one threshold value when one of the two measurement values is above the at least one threshold value and one of the two measurement values is below the at least one threshold value.

The method according to the invention has the main advantage that a first evaluation of the power quality state of the power supply network is already carried out by the power quality field device, so that it is not necessary to store all the acquired measured values in a data memory of the power quality field device for a subsequent evaluation, but rather the event signal is generated only when at least one threshold value known for the power quality field device is violated. The required storage capacity and the costs associated therewith can be significantly reduced in the case of power quality field devices.

According to an advantageous development of the method according to the invention, the event signal is used for controlling an optical signaling device of the power quality field device. In this way, a threshold disruption can be displayed directly on the power quality field device (Schwellenwertverletzung). The display device can be, for example, a light-emitting diode which displays only when a threshold destruction occurs, or a display (for example an LCD) which also provides additional information about the destroyed threshold.

According to a further preferred embodiment of the method, the event signal causes a control device of the power quality field device to generate a data message which contains at least one data set which indicates a corrupted threshold value. This generates an alarm in the form of a data message which provides the operator of the power supply network with information about the damaged threshold value. In addition, other information, such as the identification of the power quality field device (e.g., product number), can also be contained in the data message, so that the operator can uniquely associate a threshold violation with a specific power quality field device and thus with a specific measurement location in the power supply network.

In this connection, the data message preferably also contains a data set indicating the first measurement time and/or the second measurement time. The threshold violation can thus be uniquely associated with a time instant.

For this purpose, it is advantageous if the data telegram also contains information about whether the corrupted threshold was corrupted by being exceeded or being undershot. Thereby giving the direction of the threshold violation.

The data message may also contain the first and/or second measured values. A more detailed analysis of the threshold violation is thus also possible, since the degree of exceeding or falling below the threshold value can also be determined by means of the measured values.

For this purpose, the data telegrams are preferably stored in a fixed data memory of the power quality field device and/or transmitted to a higher-level data processing device provided on the power quality field device. The operator can thus access the data telegrams directly by means of the data processing device arranged at the higher level when transmitting the data telegrams or by reading them out of the fixed data memory when storing them in the power quality field device. Storing the data telegrams in the power quality field device requires significantly less storage capacity than storing all the measurements.

According to a further preferred embodiment of the method, the event signal causes the control device of the power quality field device to store the first measured value and/or the second measured value in a fixed data memory of the power quality field device. Only two measured values between which a threshold violation has occurred are stored. In comparison with continuous data storage, significantly fewer measured values are stored in the fixed data memory, so that the memory capacity is sufficient for significantly longer measurement times.

According to a preferred development of the method according to the invention, in addition to the measured values, the first and/or second measurement time are/is also stored in a fixed data memory. In this way, it is possible to uniquely determine, when analyzing the stored measured values, at which point in time a threshold violation has occurred.

According to a further preferred embodiment of the method, the power quality field device (50) collects the clock of a clock generator within the device and determines the measurement time of each measured value on the basis of this clock. Each measured value can therefore be assigned a so-called time stamp in a simple manner.

In a particularly preferred embodiment, the power quality field device can also capture an external clock and determine the measurement time of the respective measured value from this external clock. By providing an external clock, i.e., a clock generated external to the field devices (e.g., a GPS time signal), the measurements of multiple power quality field devices can be better compared to one another because each power quality field device is synchronized in time with the other power quality field devices. Each measured value thus corresponds to only one measurement time determined by the external clock, which is absolutely valid also in other power quality field devices.

Furthermore, in accordance with a further preferred embodiment of the method according to the present invention, in addition to the measured value of the first power quality characteristic variable, a measured value of at least one further power quality characteristic variable is also acquired, and a further event signal is generated if two temporally adjacent measured values of the at least one further power quality characteristic variable lie on different sides of at least one further threshold value. In this way, the power quality field device can be used to carry out a complete evaluation of the relevant power quality characteristic variable.

Finally, according to a preferred embodiment of the method according to the invention, the event signal also causes the control device to carry out further power quality functions of the power quality field device. In this case, the event signal can, for example, cause additional measured values to be recorded over a defined time period of the power quality field device, i.e. a so-called fault record (stoerschibe) is generated, from which the measured value changes of the power quality characteristic variable before and after the threshold value is destroyed can be precisely displayed. Such fault records can be stored in a fixed data memory of the power quality field device or transmitted to a superordinate data processing device. In addition to establishing a fault record, the sampling rate for recording measured values can also be increased, for example, by an event signal.

In the case of a power quality field device, the above-mentioned object is achieved according to the invention by a power quality field device having a measuring device for recording measured values and a control device, which is designed to compare the recorded measured values with at least one predefined threshold value and to generate an event signal if one of the two immediately adjacent measured values exceeds and falls below the at least one threshold value. The state of the electrical energy quality of the electrical supply network has thus already been evaluated. For this purpose, the amount of data stored in the fixed data memory can be significantly reduced compared to continuous data storage, since only event signals are generated.

The power quality field device can preferably be provided with a display device (light-emitting diode, display) which can be activated by an event signal.

In accordance with a preferred development of the power quality field device according to the invention, the communication device is provided which, in the event of an event signal, transmits a data message representing the corrupted threshold value to a data processing device arranged at a higher level of the power quality field device. The immediate transmission of data messages saves storage space in the power quality field device.

For this purpose, the power quality field device preferably has a fixed data memory, in which at least one data set that indicates a corrupted threshold value is stored by means of the control device in the event of an event signal. The storage capacity of the power quality field device is also saved in this extension compared to continuous data storage.

The control device is also preferably designed to perform the function of protecting components of the power supply network. In this case a combination of power quality field devices and protection devices. In general, therefore, fewer field devices for the power supply system can be provided than if separate power quality field devices and protection devices were used. In addition, the power quality function and the protection function of the combined field device can be used in this case for sampling the same measurement input, so that only a small number of measurement transformers are required.

In accordance with a further preferred embodiment of the field device according to the invention, it has a clock generator within the device which is designed to generate a clock, and the control device is designed to determine the measurement time of each acquired measured value on the basis of the clock. A time stamp can thus be assigned to each measured value in a simple manner.

According to a particularly preferred embodiment of the power quality field device according to the invention, the power quality field device has a receiving device for receiving an external clock, and the control device is designed to determine the measurement time of each acquired measurement value as a function of the received external clock. In this way, the power quality field device can associate the measured value with a measurement time that is dependent only on the external clock and therefore also has validity in other devices that receive the same clock. The receiving device is preferably a GPS receiver.

A plurality of such power quality field devices may form a power quality system with a central data processing apparatus to which the power quality field devices are connected via a data communication network.

Drawings

The present invention will be described with reference to examples. For this purpose in the attached drawings:

figure 1 shows a first embodiment of a power quality field device in a schematic block diagram,

figure 2 shows a method flow diagram explaining a method for monitoring the power quality of a power supply grid,

figure 3 shows a first graph of an exemplary variation of the measured values,

figure 4 shows a second graph of a second exemplary variation of the measured values,

FIG. 5 shows a second embodiment of a power quality field device, an

Fig. 6 illustrates a power quality system including a plurality of power quality field devices.

Detailed Description

Fig. 1 shows a power quality field device 10 in a highly schematic manner. The power quality field device 10 has a measuring device 11 with measurement inputs 12a, 12b and 12c for recording measured values. The measuring device 11 of the power quality field device 10 is connected on the output side to a control device 13, and the control device 13 is itself connected on the output side to a fixed data memory 14. A fixed data memory is to be understood here as a data memory which, in contrast to a volatile data memory, for example, is suitable for the continuous storage of data. In this case, it may be a so-called permanent data memory, for example a flash memory or a hard disk, which ensures continuous data storage without external energy supply. However, a fixed data memory is also understood in the context of the present invention to be a volatile data memory which is supplied with electrical energy via an external energy source, so that continuous data storage at least up to the call in the volatile data memory of the energy buffer can be achieved.

For this purpose, the control device 13 of the power quality field device 10 is also connected to a communication device 15, which establishes a data connection between the power quality field device 10 and another device via a communication output 17. Although the communication outputs in fig. 1 are represented as cable-connected data connection sections, wireless data connections, for example via radio or infrared, are also possible instead, via which data can be transmitted to correspondingly designed receiving devices. Furthermore, communication device 15 may also be a device by means of which an external data memory (for example a USB interface or a drive for optical or magnetic data storage media) can be connected to power quality field device 10.

The control device 13 is furthermore connected to a clock generator 18, for example a quartz-controlled internal instrument clock, to which time pulses are supplied, by means of which the measuring times of the measured values recorded by the measuring device 11 can be determined.

Power quality field device 10 represents a field device for monitoring the power quality of a power grid component, such as a section of power transmission wire, a bus bar, or a transformer.

Conventional power quality field devices typically record measured values of a power quality characteristic parameter at various components and store these values continuously into the conventional power quality field device. Since the fixed data memory is used to store a limited number of measured values, the measured values stored therein must be read out before the storage capacity of the fixed data memory is exceeded. Such a readout process may be performed directly on the power quality field device by transferring the measurement values to a removable data storage device, such as a floppy disk or USB stick, temporarily connected to the power quality field device. Alternatively, the measured values can also be transmitted by the power quality field device via a wired or wireless data transmission path to another data processing device, for example a central evaluation computer.

Since the measured values which corrupt the predefined threshold value are of particular interest for analyzing the behavior of the power quality characteristic variable, the method for monitoring the power quality of a power supply grid described below with reference to fig. 2 is carried out in the case of the power quality field device 10 shown in fig. 1.

In a first step 21 shown in fig. 2, a first measured value M of a first power quality parameter is recorded at a measurement input of power quality field device 10, for example at measurement input 12a, by means of measuring device 11₁. The first power quality parameter can be, for example, a voltage detected on a line section of the power supply system. In a subsequent second step 22, a first measured value M of the first power quality parameter is again recorded by means of the measurement input 12a of the measuring device 11₁Second measured value M₂. The two measured values M acquired₁And M₂To the control device 13 of the power quality field device 10.

The control device 13 checks the first measured value M recorded in step 21 according to a subsequent step 23₁Whether it is below a predetermined threshold value S (M)₁<S). If so, in a further step 24 the second measured value M recorded in step 22 is checked₂Whether it is above a predetermined threshold value S (M)₂>S). If this is the case, an event signal ES is generated in a final step 25 by means of control device 13 of power quality field device 10.

If it is determined during the check in step 23, the first measured value M₁Not below a predetermined threshold value S, i.e. a first measured value M₁Above a predetermined threshold value, the second measured value M is checked in a step 26 that follows from now on₂Whether it is below a predetermined threshold value S (M)₂<S). If so, an event signal ES is generated in accordance with step 27 by means of control device 13 of power quality field device 10.

If determined in step 24, the second measured value M₂Not above a predetermined threshold value S (i.e. two measured values M)₁And M₂Both below a pre-given threshold S), no event signal is generated according to step 28. Likewise for the second measured value M determined in accordance with step 26₂Not below a predetermined threshold value S (i.e. two measured values M)₁And M₂Both located above a predetermined threshold S), no event signal is generated according to step 29.

After each run of the method, step 21 is resumed, in which the second measured value M is taken to this point₂From now on as the first measured value M₁And new measured values M are acquired₂。

To prevent the rare case where one or even both of the measured values are exactly at the threshold S, it is possible in steps 23, 24 and 26 not to use a greater/smaller than condition (for example M₁<S) instead of the condition of being equal to or more than/equal to or less than (e.g. M)₁S or less) is checked.

For example, the measured value M of the passage by the control device can be used₁And M₂The event signal ES, which is generated in the event of a threshold violation, causes the optical display 19 of the power quality field device 10 to output an optical signal, which indicates the threshold violation to the operator of the power supply network. In the simplest case, the optical display device can be a lamp or a light-emitting diode, but a display (for example an LCD) can also be used, by means of which further information (for example the time of the threshold value violation, the identification of the threshold value) can also be displayed for the threshold value violation.

The event signal ES can also be used to cause the control device to generate a packetA data message containing an identification of at least one exceeded threshold. In addition, other information is also contained in the data message, such as an identification of the field device 10 with regard to the quality of the electrical energy (for example a unique product number), the time of the threshold disruption (measured value M was recorded)₁And M₂One or two measurement instants) of the threshold value, i.e. whether the threshold value is exceeded or fallen below, or the respective measurement value M₁And/or M₂Itself. A selection of the parts of the information mentioned can also be contained in the data messages generated by the control device 13.

The data telegrams can be transmitted via the communication device 15, for example, to a superordinate data processing device or stored in the fixed data memory 14 of the power quality field device for reading out from it at a later time.

Finally, the event signal ES can also be used to prompt the first measured value M₁And/or a second measured value M₂Stored in a fixed data storage of the power quality field device.

The event signal ES can also cause a combination of a plurality of the aforementioned actions, that is to say for example the generation of a data message and the display of an optical signal directly on the power quality field device.

Overall, with the method according to fig. 2, the event signal is always generated by the control device 13 of the power quality field device 10 only when a threshold value violation actually occurs. The control device 13 of the power quality field device 10 knows that the threshold value is corrupted, based on one of the two measured values lying below the threshold value and one of the two measured values lying above the threshold value. Changes in the measured values are thus stored discontinuously in the power quality field device. That is when the event signal ES is used to prompt the measured value M₁And M₂In the case of storage in the fixed data memory 14 of the power quality field device, considerable storage space is also saved in comparison with continuous measurement value storage, since only event-dependent data storage is performed. In this way, a small amount of data is effectively stored in fixed data memory 14 of power quality field device 10And (6) measuring the values. The measured values stored in the fixed data memory 14 are therefore also only rarely called up from the power quality field device 10.

In addition to the first power quality characteristic variable, for example voltage, further power quality characteristic variables, for example electrical power and frequency, which monitor the threshold value violation of the further threshold values, which respectively correspond to the further power quality characteristic variables, according to the method shown in fig. 2 and lead to the generation of the event signal ES only if the threshold values are exceeded, can also be recorded at the further measurement inputs 12b and 12c of the measuring device 11 of the power quality field device 10. For this purpose, measurement sensors for measuring individual measurement parameters can be provided upstream of the individual measurement inputs 12a to 12 c. However, it is also possible to carry out measurement value preprocessing within the power quality characteristic variable 10, for example to determine further power quality characteristic variables, for example power and frequency, as a function of the measured current and voltage changes, and to transmit them to the measurement value detection device 11 of the power quality field device 10.

Power quality field device 10 may also be a combined power quality field device and protection device. For example, electrical protection devices monitor whether a component of the power supply system maintains a predefined operating state by measuring current and voltage changes at the individual components and checking, according to a so-called protection algorithm, whether the component is in an allowed operating range or whether a fault, for example a short circuit, is present. In the event of a fault, the electrical protection device separates the components of the power supply system by disconnecting the power switch from the power supply system, so that the fault does not continue to the rest of the power supply system. The integration of the functions of the power quality field device and of the protection device into a single field device can avoid the expensive arrangement of a protection device and a power quality field device, which are usually separate.

The method described in fig. 2 is further elucidated below with the aid of the measured value variations shown in fig. 3 and 4.

Fig. 3 shows an example of a voltage measurement V in the form of a step curve in a voltage-time diagram₁To V₁₂Change over time.

The staircase curve is selected to describe because, in general, in power quality field devices, rather than an instantaneous value of a power quality parameter, an average value of the power quality parameter is evaluated, since the instantaneous value may be subject to occasional fluctuations and thus short-term spikes or limit values may occur. The average duration can generally be set and is for example from a few milliseconds to a minute or even minutes or hours. For fig. 3 and 4, the measured values are to be understood as the results of averaging over a corresponding averaging duration (e.g. 10 minutes). As an alternative to this, instead of forming an average value, instantaneous measured values of the power quality characteristic can be recorded for successive measurement instants and the method described in fig. 2 can be carried out using these instantaneous measured values.

In FIG. 3, furthermore, a first threshold S₁And a second threshold value S₂Indicated by a dashed line extending parallel to the time axis. That is, a range is usually specified in the standard network for the power quality parameter, within which the power quality parameter must lie in order to ensure sufficient power supply quality. Upon leaving the range, i.e. below the lower threshold S₁Or exceeds the upper threshold S₂In the case of (2), the power supply quality is regarded as defective.

Considering the variation of the measured values shown in fig. 3, it can be seen that the first voltage measured value V₁And a second voltage measurement value V₂Are all located at the lower threshold S₂And is located above the upper threshold S₁Below. The control device 13 (see fig. 1) carries out the method described in fig. 2 on the two voltage measurement values and knows that at the measurement value V₁And V₂To time t₁Threshold S does not occur₁Or S₂Over-pass of (c). No event signal ES is generated during the method.

In this case, the voltage measurement V can be used₁Discarded completely, and the voltage measurement V₂Must also be reserved for useThe next process of the method described in fig. 2. Control device 13 of power quality field device 10 takes a voltage measurement V from now on₂And V₃The method described in fig. 2 is implemented. The control device 13 knows the voltage measurement V here₂At the upper threshold S₂And the voltage measurement value V₃At the upper threshold S₂Above (d). In other words, at the voltage measurement V₂And the measured value of voltage V₃There occurs an upper threshold S₂Over-pass of (c). This results in the control device 13 of the power quality field device 10 generating the event signal ES. The presence of the event signal ES can, for example, cause the control device to generate a data telegram which indicates a threshold violation and which is transmitted to the superordinate data processing device. In addition, a second voltage measurement value V can be determined₂And/or a third voltage measurement value V₃Stored (if necessary together with the respective measurement time) in the fixed data memory 14 of the power quality field device 10.

Voltage measurement V of the method described in fig. 2₃To V₇In other processes, the control device 13 of the power quality field device 10 does not recognize a threshold crossing, since all voltage measurements V₃To V₇Are all located at the upper threshold S₂Above (d). Therefore, the event signal ES is not generated during these processes of the method.

Until the voltage measurement V is observed₇And V₈The control device 13 recognizes that another threshold value has exceeded and the voltage change again enters the permissible range. In this case, an event signal is generated again, which, as explained above, can trigger different actions.

The control device 13 of the electrical energy quality field device 10 accordingly takes the voltage measurement V₉And V₁₀In between and at the voltage measurement V₁₀And V₁₁To the lower threshold S₁Thereby generating an event signal therein.

When considering the change in the measured values shown in fig. 3, it can be seen that in the case of continuous storage of the measured values, 12 individual voltage measured values (possibly together with their respective measuring times) are to be stored for subsequent analysis. When using the method described in fig. 2, only 4 event signals are generated, which for example lead to the generation of 4 data messages. When taking into account the fact that there is very little threshold disruption in the actual measured value change than the assumed measured value change shown in fig. 3, the amount of data stored is itself significantly reduced when the event signal ES causes the respective voltage measured value to be stored in the fixed data memory 14.

The graph in fig. 4 shows the voltage measurement V as in fig. 3₁To V₁₂In principle similar variations. In fig. 4, another threshold S is also set₃The position of the measured values is checked for this threshold value by the control device 13 of the power quality field device 10. By increasing the number of threshold values in this way, the evaluation of the captured power quality characteristic variable (in which more than two threshold values are specified) can be matched to a predefined criterion, or the resolution of the generated event signals ES can be increased, since the event signals (however, more particularly) are thereby generated more frequently. By introducing a further threshold value in fig. 4, therefore, instead of generating 4 event signals ES (in the case of fig. 3), 6 event signals ES are now generated. When the threshold value S₁To S₃Is exceeded between two successive measurement values, an event signal is always generated.

Fig. 5 illustrates another embodiment of a power quality field device. The power quality field device 50 according to fig. 5 has a similar construction to the power quality field device according to fig. 1, so that corresponding components are denoted by the same reference numerals. The power quality field device 50 according to fig. 5 differs from the power quality field device 10 according to fig. 1 only in the type of clock generator used to determine the measurement times of the individual measured values. The clock generator 52 of the power quality field device 50 shown in fig. 5 has a receiving device 51 which can receive an external clock. Based on the external clock received via the receiving device 51, the clock generator 52 of the control device 13 of the power quality field device 50 provides a time pulse, from which the measurement time of the respective measured value can be precisely determined with respect to the external clock.

The receiving device 51 of the clock generator 52 according to fig. 5 can be, for example, a GPS receiver (global positioning system) which receives a clock transmitted by a GPS satellite 53 installed in an orbit. The clock transmitted by the GPS satellite 53 is a high-precision clock having a frequency of one pulse per second. The control device 13 of the precision clock power quality field device 50 can associate the individual measured values with an accuracy in the microsecond range, for example, to the individual measurement instants. Instead of a GPS receiver receiving signals from GPS satellites, other receivers suitable for receiving signals having clocks generated externally to the power quality field device 50 may also be provided.

Finally, fig. 6 shows a system of a plurality of power quality field devices 61a to 61g arranged on a line section of a power supply network 62, which is only schematically illustrated. The power quality field devices 61a to 61g have a receiving device for receiving a GPS signal of an external clock, for example a GPS satellite 53, in accordance with the representation of fig. 5. In this way, it is possible to operate all clock generators in the power quality field devices 61a to 61g precisely synchronously, and thus to assign the measured values recorded by the power quality field devices 61a to 61g to absolute measurement times which are also valid in the remaining power quality field devices 61a to 61g and thus can be compared with one another. In other words, it is ensured in this way that the measured values recorded in the power quality field device 61b (which are adapted to the measurement time t by the control device of the power quality field device 61 b) are matched to the measurement time t₁) At the same time as another measured value recorded in the power quality field device 61f (this measured value is likewise adapted to the measurement time t by the control device of the power quality field device 61 f)₁). If no external clock is used for all power quality field devices 61a to 61g, no precise indication can be given of the measurement time t of the field device 61b due to the lack of synchronization between the clock generators of the individual power quality field devices 61a to 61g₁And field devices 61ft₁Whether or not they are actually identical. In some cases, however, it may also be sufficient to provide a high-precision clock generator as in the example according to fig. 1 when there is no such high requirement for the synchronization of the measured values of the individual power quality field devices. The power quality system can then also be constructed without an external clock and without a corresponding receiving device.

According to fig. 6, the individual power quality field devices 61a to 61f are connected to one another and to the evaluation computer 64 via communication lines indicated by dashed lines. Via which the contents of the data memories of the individual power quality field devices 61a to 61g can be transmitted to the evaluation computer 64. The communication network may be, for example, an ethernet network, wherein the communication is performed according to the industrial standard IEC 61850. All of the power quality field devices 61a to 61g involved can be determined system-wide by the evaluation computer 64, when a threshold violation has occurred and how often.

Claims (22)

1. A method for monitoring the power quality of an electrical power supply network, wherein the following steps are carried out:

-acquiring a first measured value of a first power quality characteristic variable at a first measurement time by means of a measuring device (11) of a power quality field device (10, 50) arranged at a measurement location of the power supply network;

-acquiring a second measured value of the first power quality characteristic variable by means of a measuring device (11) of the power quality field device at a second measuring time following the first measuring time;

-comparing the first and second measured values with at least one predefined threshold value, and

-generating an event signal indicating a violation of the at least one threshold value when one of the two measurement values is above the at least one threshold value and one of the two measurement values is below the at least one threshold value.

2. The method of claim 1,

-using said event signal for controlling an optical signal device of a power quality field device.

3. The method of claim 1,

the event signal causes the control device of the power quality field device to generate a data message, wherein the data message contains at least one data set which indicates a corrupted threshold value.

4. The method of claim 3,

the data message also contains a data set indicating the first measurement time and/or the second measurement time.

5. The method of claim 3,

-said data message further contains information about whether said corrupted threshold was corrupted by being exceeded or being undershot.

6. The method of claim 3,

-the data message further comprises the first measurement value and/or the second measurement value.

7. The method of claim 3,

the data telegrams are stored in a fixed data memory of the power quality field device and/or transmitted to a higher-level data processing device arranged on the power quality field device.

8. The method according to any of the preceding claims,

-the event signal causes a control device of the power quality field device to store the first and/or second measured value in a fixed data storage (14) of the power quality field device.

9. The method of claim 8,

-storing said first and/or second measurement instants in said fixed data memory (14) in addition to said measurement values.

10. The method of claim 1,

-the power quality field device (50) collects the clock of a clock generator internal to the device and determines the measurement instant of each measurement value from this clock.

11. The method of claim 1,

-the power quality field device (50) collects an external clock and determines the measurement instant of each measurement value from the external clock.

12. The method of claim 1,

in addition to the measured value of the first power quality characteristic variable, measured values of at least one further power quality characteristic variable are also recorded, and a further event signal is generated if two temporally adjacent measured values of the at least one further power quality characteristic variable lie on different sides of at least one further threshold value.

13. The method of claim 1,

-said event signal also causing the control means of the power quality field device to implement other power quality functions of said power quality field device.

14. A power quality field device (10, 50) having:

-a measuring device (11) for acquiring measured values and a control device (13) which is configured to compare the acquired measured values with at least one predefined threshold value and to generate an event signal when one of the two immediately adjacent measured values exceeds and falls below the at least one threshold value.

15. The power quality field device of claim 14,

-having optical signaling means that can be activated by an event signal.

16. The power quality field device of claim 14 or 15,

the data message is transmitted to a data processing device arranged upstream of the power quality field device, in the event of the occurrence of the event signal.

17. The power quality field device of claim 14,

the control device is configured to determine a threshold value for the corruption of the data set, and to store the data set in the data store in the event of the occurrence of the event signal.

18. The power quality field device (10, 50) according to claim 14,

-said control means (13) are also configured for implementing the function of protecting the components of the power supply network.

19. The power quality field device (50) of claim 14,

-having a clock generator internal to the device for generating a clock, and

the control device (13) is designed to determine the measurement time of each acquired measurement value on the basis of the clock.

20. The power quality field device (50) of claim 14,

-having receiving means (51) for receiving an external clock, and

-the control device (13) is configured to determine the measurement instant of each acquired measurement value from the received external clock.

21. The power quality field device (50) of claim 20,

-said receiving means (51) is a GPS receiver.

22. An electrical energy quality system (60) consisting of:

-a plurality of power quality field devices (61a to 61g) according to any of claims 14 to 21, and

-at least one central data processing device (64), to which central data processing device (64) the power quality field devices (61a to 61g) are connected via a data communication network (63).