Nowadays, electrical power supply systems represent highly complex networks for distribution of electrical power, which often have a large number of power feeds and outgoers. In addition to supply reliability, that is to say ensuring that a sufficient amount of electrical power is available for every power consumer at all times, the quality of the electrical power that is supplied (referred to in the following text as the “electrical power quality” or “power quality”) also plays a critical role. The electrical power quality in the power supply system can be defined, for example, using so-called power quality characteristic variables such as the frequency, voltage and voltage harmonics or current harmonics, distortion factors, flicker, voltage imbalances and powers. Highly sensitive electrical devices nowadays demand an electrical power supply in the form of a sinusoidal wave which is as pure as possible and is at a standard frequency and has a standard amplitude. Standards such as EN 50160 or IEC 61000 therefore specify upper and lower limit values within which these power quality characteristic variables of a power supply system must lie.
To allow statements to be made about the electrical power quality, power quality field devices which record measured values of the respective power quality characteristic variables are provided at various measurement points in the electrical power supply system. The recorded measured values can normally be stored, for archiving, in power quality field devices. The stored measured values are transmitted at regular intervals to other data processing facilities, for example to central evaluation computers, which carry out an evaluation, in order to evaluate the measured values to determine whether limit values have been exceeded at specific times. Time-dependent profiles of the power quality characteristic variables can therefore be produced in the central evaluation computer, and compliance with the limit values can be checked and verified.
Since the data memory modules incorporated in the power quality field devices cannot be chosen to be indefinitely large, for cost reasons, the stored measured values must be transmitted to the central evaluation computer relatively frequently. If the stored measured values are not transmitted at the right time, then either no more new measured values can be stored, because the data memory is completely full, or old measured values will be overwritten by more recent ones (so-called “ring memory operation”). In order to increase the time intervals between two transmission processes in this case, it would therefore be necessary to provide a correspondingly larger data memory in the power quality field device.
The invention is based on the object of specifying a method for monitoring the electrical power quality in an electrical power supply system, a power quality device and a power quality system, thus allowing the electrical power quality to be monitored with comparatively little effort.
With regard to the method, this object is achieved by a method for monitoring the electrical power quality in an electrical power supply system, in which the following steps are carried out:
The major advantage of the method according to the invention is that the power quality field device itself carries out a first assessment of the state of the electrical power quality of the electrical power supply system such that it is no longer necessary to store all the detected measured values in a data memory in the power quality field device for subsequent evaluation and, instead, an event signal is produced only if at least one of the threshold values, of which the power quality field device is aware, is or are infringed. This makes it possible to considerably reduce the required memory capacity and costs associated with it for the power quality field device.
One advantageous development of the method according to the invention provides that the event signal is used to control an optical signaling device of the power quality field device. This allows a threshold value infringement to be indicated directly on the power quality field device. In this case, by way of example, the indicating device may be a light-emitting diode, which indicates only the presence of a threshold value infringement, or a screen (for example an LCD) which indicates additional information relating to the threshold value that has been infringed.
A further advantageous embodiment of the method according to the invention provides that the event signal causes a control device for the power quality field device to produce a data message, with the data message including at least one data record which indicates the infringed threshold value. This generates an alarm message, so to speak, in the form of the data message which indicates information about the infringed threshold value to the operator of the electrical power supply system. In addition, further information, for example an identification (for example a serial number) of the power quality field device, can be included in the data message in order that the operator can clearly associate the threshold value infringement with one specific power quality field device and therefore with a specific measurement point in the electrical power supply system.
In this context, it is also considered to be advantageous for the data message to additionally include a data record which indicates the first and/or the second measurement time. This allows the threshold value infringement to be clearly associated with a time.
Furthermore, in this context, it is advantageous for the data message to additionally include information about whether the infringed threshold value has been infringed by overshooting it or undershooting it. This makes it possible, so to speak, to indicate a direction of the threshold value infringement.
Furthermore, in this context, provision may be made for the data message to additionally include the first and/or the second measured value. This allows an even more comprehensive evaluation of the threshold value infringement to be carried out since the extent by which the threshold value has been overshot or undershot can also be determined on the basis of the measured values.
In this context, it may also be advantageous to provide for the data message to be stored in a non-volatile data memory in the power quality field device and/or to be transmitted to a data processing facility which is superordinate to the power quality field device. This allows the operator to access the data message either directly on transmission of the data message by means of the superordinate data processing facility or, if the data message is stored in the power quality field device, by reading the non-volatile data memory. Even if the data message is stored in the power quality field device, this results in a considerable reduction in the amount of memory space required, in comparison to the storage of all the measured values.
A further advantageous embodiment of the method according to the invention provides that the event signal causes a control device for the power quality field device to store the first measured value and/or the second measured value in a non-volatile data memory in the power quality field device. In this case, therefore, only those two measured values between which a threshold value infringement has occurred are stored. This means that considerably fewer measured values are stored in the non-volatile data memory than in the case of continuous data storage, as a result of which its capacity is sufficient for a considerably longer measurement time period.
According to an advantageous development of the method according to the invention, provision is made, in addition to the measured values, for the first and/or the second measurement time to be also stored in the non-volatile data memory. This means that it is clearly possible to determine during the evaluation of the stored measured values the time at which a threshold value infringement occurred.
A further advantageous embodiment of the method according to the invention provides that the power quality field device (50) records a time clock of a device-internal timer and uses this time clock to determine the measurement time of the respective measured value. This allows a so-called time stamp to be allocated to each measured value, in a simple manner.
However, it is regarded as particularly advantageous if the power quality field device records an external time clock and determines the measurement time of the respective measured value on the basis of this external time clock. The privision of an external time clock, that is to say a time clock which is produced outside the field device (for example a GPS time signal), allows the measured values from a plurality of power quality field devices to be compared with one another even better, since each power quality field device is synchronized in time to the other power quality field devices. Each measured value is therefore associated with a measurement time which is determined exclusively by the external time clock and also has absolute validity in the other power quality field devices.
A further advantageous embodiment of the method according to the invention also provides that in addition to measured values of the first power quality characteristic variable, measured values of at least one further power quality characteristic variable are also detected, and a further event signal is produced when two measured values, with one following the other directly in time, of the at least one further power quality characteristic variable are located on different sides of at least one further threshold value. This allows a complete analysis of the relevant power quality characteristic variables to be carried out by a power quality field device.
Finally, it is also considered to be advantageous with regard to the method according to the invention for the event signal to cause the control device to additionally carry out further power quality functions of the power quality field device. In this case, for example, the event signal can be used to cause the power quality field device to record additional measured values over a defined time period, that is to say to produce a so-called fault plot, on the basis of which the measured value profiles of the power quality characteristic variables can be displayed accurately before and after the threshold value infringement. Such fault plots can either be stored in the non-volatile data memory in the power quality field device or can be transmitted to a superordinate data processing facility. In addition to the creation of fault plots, the event signal can also, for example, be used to trigger an increase in the sampling rate at which the measured values are recorded.
With regard to the power quality field device, the object mentioned above is achieved according to the invention by a power quality field device having a measurement device for detecting measured values, and a control device which is designed such that it compares the detected measured values with at least one predetermined threshold value and produces an event signal when, of two measured values which follow one another directly, one is above the at least one threshold value and one is below the at least one threshold value. This allows the state of the electrical power quality of the electrical power supply system to be assessed at this stage. Furthermore, the amount of data that is to be stored in the non-volatile data memory can be reduced considerably in comparison to continuous data storage since only an event signal is produced.
The power quality field device is advantageously provided with an indicating device (light-emitting diode, screen) which can be activated by the event signal.
One advantageous development of the power quality field device provides that the field device has a communication device which, when the event signal is present, sends a data message, which indicates the infringed threshold value, to a data processing facility which is superordinate to the power quality field device. The immediate transmission of the data message makes it possible to save memory space in the power quality field device.
Furthermore, it is advantageously possible to provide that the power quality field device has a non-volatile data memory in which, when the event signal is present, at least one data record which indicates the infringed threshold value is stored by means of the control device. This development as well allows memory capacity to be saved in the power quality field device in comparison to continuous data storage.
It is advantageously possible to provide that the control device is also designed to carry out functions for protection of components of an electrical power supply system. This relates to a combined power quality field device and protective device. Overall, this allows a smaller number of field devices to be provided for an electrical power supply system than when using separate power quality field devices and protective devices. In addition, in this case, both the power quality functions and the protective functions of the combined field device can access the same measurement inputs, as a result of which a small number of measurement transducers is required.
A further advantageous embodiment of the field device according to the invention provides that the field device has a device-internal timer which is designed to produce a time clock, and the control device is designed to determine the respective measurement time of the individual detected measured values on the basis of this time clock. This allows a time stamp to be allocated to each measured value in a simple manner.
One particularly advantageous embodiment of the power quality field device according to the invention provides, however, that the field device has a receiving device which is designed to receive an external time clock, and the control device is designed to determine the respective measurement time of the individual detected measured values on the basis of the received external time clock. This allows the power quality field device to associate measurement times with the measured values, which measurement times are dependent only on the external time clock and are therefore also valid in other devices which receive the same time clock. In this context, it is advantageously possible to provide for the receiving device to be a GPS receiver.
A plurality of such power quality field devices together with a central data processing facility to which they are connected via a data communication network may form a power quality system.
The invention will be explained in the following text with reference to exemplary embodiments. In this case, in the figures, in detail:
The control device 13 for the power quality field device 10 is also connected to a communication device 15 which, via a communication output 17, sets up a data link between the power quality field device 10 and further devices. Although the communication output is indicated in
The control device 13 is also connected to a timer 18, for example a crystal-controlled internal device clock, which provides the control device with a time pulse by means of which the respective measurement time of the individual measured values recorded by the measurement device 11 can be defined.
The power quality field device 10 represents a field device for monitoring the electrical power quality of components in an electrical power supply system, for example a section of an electrical power transmission line, a busbar or a transformer.
Normally, conventional power quality field devices record measured values of power quality characteristic variables at the individual components and store these continuously in a non-volatile data memory in the conventional electrical power quality field device. Since the non-volatile data memory is designed to store a limited amount of measured values, the measured values stored in it must be read before the memory capacity of the non-volatile data memory is exceeded. A reading process such as this can be carried out either directly at the power quality field device by transmission of the measured values to a transportable data memory, which is temporarily connected to the electrical power quality field device, for example a floppy disk or a USB stick. Alternatively, the measured values can also be transmitted from the electrical power quality field device via a data transmission path, which may be either cable-based or wire-free, to another data processing facility, for example a central evaluation computer.
Since the measured values which are of particular interest for evaluation of the behavior of power quality characteristic variables are those with which an infringement of predetermined threshold values has occurred, in the case of the power quality field device 10 illustrated in
In a first step 21, illustrated in
According to a following step 23, the control device 13 checks whether the first measured value M1 recorded in step 21 is below a predetermined threshold value S (M1<S). If this is the case, then, in a further step 24, the second measured value M2 recorded in step 22 is then checked to determine whether it is above the predetermined threshold value S (M2>S). If this is also the case, the control device 13 for the power quality field device 10 produces an event signal ES in a final step 25.
If it is found during the check in step 23 that the first measured value M1 is not below the predetermined threshold value S, that is to say the first measured value M1 is in consequence above the predetermined threshold value, then a check is carried out in a step 26 which now follows this to determine whether the second measured value M2 is below the predetermined threshold value S (M2<S). If this is the case, then, according to step 27, an event signal ES is produced by means of the control device 13 for the power quality field device 10.
If it is found in step 24 that the second measured value M2 is not above the threshold value S (that is to say both measured values M1 and M2 are below the threshold value S), then, according to step 28, no event signal ES is produced. The procedure is the same in the situation in which it is found in step 26 that the second measured value M2 is not below the predetermined threshold value S (that is to say both measured values M1 and M2 are above the threshold value S), and no event signal is produced, according to step 29.
After each run through the process, it is started again at step 21, with the previous second measured value M2 now being treated as the first measured value M1 and a new measured value M2 being detected.
In order to cope with the rare situation in which one of the measured values or even both is or are precisely equal to the threshold value S, a test based on a greater than or equal to/less than or equal to condition (for example M1≦S) can be carried out instead of the greater than/less than condition (for example M1S) in steps 23, 24 and 26.
The event signal ES which is produced by the control device when the measured values M1 and M2 infringe the threshold value can be used, for example, to cause a visual indicating device 19 of the power quality field device 10 to emit a visual signal which indicates the threshold value infringement to the operator of the electrical power supply system. In the simplest case, a lamp or a light-emitting diode may be used as the visual indicating apparatus, although it is also possible to use a screen such as a display (for example an LCD), by means of which it is possible to display even further information (for example the time of the threshold value infringement, identification of the threshold value) relating to the threshold value infringement.
However, the event signal ES can also be used to cause the control device to produce a data message which contains at least an identification of the threshold value which has been overshot. In addition, the data message may include further details, for example relating to an identification of the power quality field device 10 (for example a unique serial number), the time of the threshold value infringement (one or both of the measurement times at which the measured values M1 and M2 were detected), the direction of the threshold value infringement, that is to say whether the threshold value was overshot or undershot, or the individual measured values M1 and/or M2 themselves or itself. The data message produced by the control device 13 may also include a selection of some of said details.
The data message can either be transmitted via the communication device 15 for example to a superordinate data processing facility, or can be stored in the non-volatile data memory 14 in the power quality field device in order to be read from there at a later time.
Finally, the event signal ES can also be used to cause the first measured value M1 and/or the second measured value M2 to be stored in the non-volatile data memory in the power quality field device.
Furthermore, the event signal ES can also initiate a plurality of the abovementioned actions in combination, that is to say for example the production of a data message and the indication of a visual signal directly on the power quality field device.
In summary, it can therefore be stated that, when using the method as shown in
In addition to the first power quality characteristic variable, for example a voltage, further power quality characteristic variables, such as an electrical power and a frequency, can also be recorded at further measurement inputs 12b and 12c of the measurement device 11 of the electrical power quality field device 10 and these are monitored using the method illustrated in
The power quality field device 10 may also be a combined power quality field device and protective device. Electrical protective devices monitor components of an electrical power supply system for compliance with predetermined operating states, for example by measuring current and voltage profiles on the respective component and using so-called protective algorithms to check whether the component is in a permissible operating range or whether a fault, for example a short, has occurred. In the event of a fault, an electrical protective device disconnects the component in the electrical power supply system from that system by opening circuit breakers, thus preventing propagation of the fault to the rest of the electrical power supply system. The integration of functions of an electrical power quality field device and of a protective device in a single field device makes it possible to avoid generally costly provision of separate protective and power quality field devices.
The method described in
In this context, and by way of example,
The illustration in the form of a staircase curve has been chosen because instantaneous values of a power quality characteristic variable are normally not evaluated in power quality field devices, but mean values of this power quality characteristic variable are evaluated, since instantaneous values may be subject to random fluctuations and brief peaks or extreme values may therefore occur. The averaging time period is normally variable and extends, for example, from a few milliseconds up to one or even more minutes or hours. For the purposes of
The graph in
If one considers the measured value profile illustrated in
In this situation, the voltage measured value V1 can be completely deleted, while the voltage measured value V2 must still be retained for a further run of the method described in
In further runs of the method described in
Only when the voltage measured values V7 and V8 are analyzed does the control device 13 find a further threshold value overshoot, to be precise with the voltage profile reentering the permissible range. In this case, an event signal is produced again, and can initiate various actions, as explained above.
In a corresponding manner, the control device 13 for the electrical power quality field device 10 finds an infringement of the lower threshold value S1 between the voltage measured values V9 and V10, as well as between the voltage measured values V10 and V11, as a result of which event signals are also produced in this case.
If one looks at the measured value profile illustrated in
The graph illustrated in
As shown in
As shown in
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/DE2006/000696 | 4/18/2006 | WO | 00 | 10/17/2008 |