DE102009037058B3 - Method for contactless determination of local power and flow direction in telephone line or line combination in integrated network, involves immediately/centrally comparing phase determined by magnetic field measurement and reference phase - Google Patents

Abstract

The method involves deriving a power flow direction from a relation of a phase of measured magnetic fields to a voltage phase as a network phase or a reference phase of an integrated network. The network phase is measured directly in central locations. The network phase is estimated by averaging of the measured phase of the magnetic fields at points within the integrated network adjacent to the line or the line combination. A phase determined by magnetic field measurement and the reference phase are immediately or delayed locally or centrally compared over a global time reference.

Description

introduction

In Times of the free electricity market it becomes for the market participants always more important, as comprehensive as possible and especially independent overview of the To have market. An important aspect is knowing exactly how the services flow in a network, without the information of the To be dependent on utilities.

State of the art

As a state of the art was the European patent EP 1297347 B1 determined. It simultaneously measures the electrical and magnetic fields, converts both values into current and voltage, and thus determines the transmitted active and apparent power.

Problematic in this method, the measurement of the electric field, in particular when it against a local reference potential (in this case potential Earth) is measured. The electric field component is through the Environment strongly influenced, because in this measurement all only slightly conductive objects go in the environment. The magnetic field, on the other hand, only becomes significantly influenced by ferromagnetic substances, with which in measurements in the field not, or only with negligible Quantities must be calculated.

In the publication WO / 2008/143520 A1 For example, as with the present application, only the magnetic field is measured but it attempts to determine the phase jumps of that signal when changing the power flow direction.

Problematic In this method is that the phase shift of the magnetic field no sudden Event is, but by the inertia of the components of the network slowly. The detection of such an event is technically extremely complex to to solve, especially since it has in its appearance a short-term frequency change very similar is.

Further this document describes the use of a bandpass filter, which should separate the signal to be measured from the noise. That too throws great in practice Problems on. Such filters tend to be at their resonant frequency and circle quality dependent from Z. B. temperature and aging, which is the phase of the influenced by them going signal. The change of the phase is thus dependent on the current properties of the filter and the current network frequency. A safe separation of the different interference from the useful signal is technical much more elaborate as in the procedure we have presented.

In the generic document WO / 2008/031029 A2 the magnetic field is measured with the aid of several coils and from this data the position of the individual conductors as well as the current flowing through them are calculated. This data is then used to determine the relative utilization of the line. A determination of the power flow direction is not described therein.

waived one with the conventional one Method on one of the two field components, the direction, into which the power flows in principle no longer be determined.

Around It is necessary to determine the active power on an AC line the current through the line, the voltage difference that the consumer learns and the power factor, which is the phase shift between Current and voltage expresses. The voltage as well as the power factor can in practice as largely be accepted constantly and with empirical values or calibration measurements approximated become. In addition, can one also the estimate of the power factor using the phase information.

Where: P = UI cosφ

The means that the transferred Active power P proportional to the current I, the voltage U and the power factor is cosφ.

The Current flow I can we just over determine the magnetic field. This will be explained in more detail below.

The The direction in which the power flows can be determined by the relative direction of Current and voltage are determined. Our procedure determines this direction from a new method for determining the phase difference. (See details below)

Determination of current flow from the magnetic field

Consider we first here once the opposite case. Which magnetic fields arise at one given current flow?

First, we need to model our transmission line. We can regard these as a current density distribution. Since the pipe and its surroundings can be considered approximately straight, we limit ourselves to looking at a cutting plane through our system. The wires correspond to an area with a complex, usually location-dependent, current density vector field: J → (x, y)

The integral over the wire cross-section A gives the current flow I through this conductor.

As common in power engineering, we consider all electrotechnical quantities as complex pointers on the grid frequency. The angle of the size gives the phase angle of the Exchange size.

According to Amperes law in differential form: redB → = μ 0 J →

Are defined one still has a number of sensors with a given directivity, so receives you have a system of equations. Each equation stands for the signal, which depends on the respective one Sensor was received.

In In a three-wire system, the currents flowing through the three conductors are always in a tight complex relationship to each other. So the current flow through such a system can therefore be described by a variable.

We thus have at n independent live Systems n variables and need thus at least n equations in order to find solutions. Has if one more equations, one can additionally introduce error terms, which can be minimized. This achieves a higher one Accuracy, because you can estimate the errors and deduct.

The Number of systems leaves simply by counting the wires to estimate the lead. In a three-conductor system, as is common in Europe, for example, one counts simply the number of wires and divide this number by 3. For other systems, analogously similar Procedures are applied.

Determination of the magnetic field

magnetic fields can be determined with a variety of sensors such as coils or Hall sensors. These sensors measure either the magnetic field strength or the magnetic flux density, in practice, both values over a constant factor are interconnected.

The Sensors typically emit a signal that is either proportional is to the magnetic field in one direction or proportional to it time derivative.

task

One alternative method of measuring and monitoring power generation and transfer should Of course, the disadvantages of existing methods are not have, namely the measurement of the electric field.

Also it makes sense to collect the measured values at centers can, then bundled around them pass.

The inventive method in detail

Inventive base for the further steps of the new procedure presented here is the circumstance that only the magnetic field is measured at the actual measuring point is and its relative phase to determine the direction the power flow and / or the power factor from the comparison is determined with a centrally derived reference signal.

At the measuring point are one or more components of the magnetic field, measured. Is on the line only one circuit, so can already with a sensor, as well as a conversion factor of the current flow up This line will be determined. From this current flow can then be, assuming that the voltage and the power factor are approximate are time-invariant, determine the performance as already described above becomes. In some cases, the power factor is also time-varying in certain cases Limits (no jump between inductive and capacitive load), so this can also be determined by the present method. In a system with multiple circuits ("line combination") goes nor the position of the individual conductors in relation to the measuring device of the resulting magnetic field in the measurement, and it exists thus a linear system of equations, which the values of the sensors (in the same number as circuits in the line combination are present) in the performance of the individual circuits.

If you blurs It is also possible to use the (then more sensitive) sensor for the Magnetic field at a greater distance to place, so the distances between the lines and the resulting influence on the magnetic field at the sensor decreases with increasing distance to the sensor becomes.

Determining the direction of power flow

To determine the direction of current flow, it is now important to know which Pha senlage the current has to voltage. For this purpose, our method uses a network phase obtained at central locations. This phase can either be obtained simply via the socket, determined by means of a kind of "tuning" from the measured values, or obtained from an external source.

Around the phase position of the reference phase with a phase position on site check the measuring point and to vote Calibration measurements are made to make the process more reliable do. Likewise, the - actually known tension be checked at the measuring location with calibration measurements the process more reliable close.

The Alternative process steps will be explained in more detail in the next section. mixed forms can increase the accuracy. A basic requirement is that all measuring points and the Central units are located within the same interconnected network. Normally remain the temporarily time-invariant phase positions of all measuring points phase-locked to the mains phase. Changes the power flow direction of one Line, the phase of the corresponding measuring points jumps by 180 Degree. Smaller fluctuations can of changes of the power factor.

A illustrative embodiment This procedure can be found in the section "Practical Implementation Examples".

Determination of the network phase

in the Case of the extraction by outlet you can see the voltage at one or determine several phases and determine the network phase from this. Conveniently, this is done for example by determining the zero crossings. This Process can of course take place behind any largely phase-locked arrangement, for example, behind a transformer. Likewise, the process on the by a local consumers caused current flow to be applied.

Around To avoid incorrect measurements, it makes sense to use a narrow-band filter to use which only the area around the grid frequency lets through.

Becomes the network phase over determines a kind of "vote", so one considers the differences between all phases, as well as one from them determined mean. Now changes in one or more Lines the power flow direction, so jumps their phase 180 degrees. Of course, this phase jump must be in averaging considered become. On the other hand lets in the overall view, the flow direction or its change for each single measuring point very easy to determine.

The Averaging could For example, be carried out with a modulo method at the number space to a certain extent was bent to a cyclic number circle. If you count here from 179 degrees upwards, so you end up at 0 degrees. This method is then designed that it is blind to you Phase turns of 180 degrees.

of course is it also possible the grid frequency, and thus the phase, from external sources to get. For example, different network operators publish this data about the Internet. This data could to be included in the evaluation, or at least help the quality of the extracted phase data to judge.

Cold junction of the phases

Of the Comparison of the phase of the measured values and the mains phase can now either at the measuring location itself or at central data collection points. In both cases it is necessary to have a time-dependent phase information transferred to. This information can, along with information about the Amplitude of a signal, over a temporary or permanent connection, as well as message-based Procedure exchanged. This can of course be electronic, wired or by radio, optically or even acoustically.

Phase comparison using a reference signal

Next the complete transmission The signal can also only the time and phase difference to one available at all points virtual reference. This reference can be from widely available signals, such as signals from navigation systems (GPS, Gallileo, Glonas, etc), time signal transmitters (eg DCF77) or synchronous Communication systems (eg DVB-T) are derived. Also, one can sufficiently accurate clock over Single events like lightning strikes or significant changes in network frequency can be synchronized. The Comparison result can be data-saving as phase or time deviation stored and transmitted at reference times.

For example could to run 2 clocks, one runs based on the mains frequency of about 50 Hz and counts thus the cycles. The other counts Cycles of a reference signal. The difference is then determined regularly from both signals and transmits them.

there It should be noted that switching events such as direction or load changes sufficiently well resolved become. If necessary, you can Switching events are also determined at the reference junction.

transmission the measured values

The transfer the measured values can be transmitted continuously or in packets via electronic, optical or mechanical processes take place, which are conducted or wirelessly, as well as publicly or be private. The transfer can be discrete or continuous value and time discrete or continuous occur.

Further processing

In one or more bodies can the data of the measuring instruments collected and further processed at the measuring locations. There you can Data for plausibility checked and measuring errors are detected and eliminated. This can be methods used in graph theory.

Tampering and theft detection

There the meter usually on publicly available, rather remotely located, it makes sense to manipulations and theft.

Yes according to concrete construction, the measuring device at the measuring point a receiver for a position determination system contain. Many such receivers offer very precise time information as a by-product, which are needed in the above methods. You can over example, for example send the current position with the measured values, or also when crossing one certain limit to trigger an alarm.

In addition, can with the help of several sensors with different directional sensitivity a certain protection against tampering can be achieved, since one through the additional Directional information can decide if an external field is plausible is, or indicates a manipulation. This information can then also transmitted to the central offices become.

Advantages of the method over the State of the art

in the Unlike previous methods, this method uses no Measurement of the electric field and is therefore less expensive and moreover potentially less susceptible to interference.

Practical Implementation Examples

A simple embodiment of the method is a device which Contains transmitter, which, as soon as they get power, a voltage-dependent signal send out.

These Transmitters, for example via half-wave rectifiers, powered by in-field coils. The signal then carries the information about strength and temporal phase of the magnetic field, as it is from the half-waves the rectified AC voltage results.

you could now several of these transmitters to one line or adjacent lines place and at a receiver located at some distance the Reduce signals to a lower frequency range. That here could be generated signal you then, for example, over send an isochronous telephone line to the central points, where it can be reconstructed and evaluated.

you receives then at the headquarters several phase-prone signals, from which the power as well as the power flow direction of the individual lines can derive.

A Another advantageous embodiment of the method is a device which 2 watches and a memory and transmission device contains. Clock A is from an external clock, such as a time signal transmitter synchronizes and delivers the reference time also available in other locations a.

Clock B is synchronized with the network and thus shows the number of Vibrations. It supplies the local network time b at the measuring point. This time depends on the current phase shift.

Clock A now determines regular intervals, in which stores the value of both clocks, as well as the strength of the magnetic field become.

These values can now be transmitted individually or in bundles to the control centers. The central unit now has a similar device, which does not measure the magnetic field, but a signal permanently coupled to the mains frequency, but at the same time as possible with the device at the measuring point. By means of the simultaneously recorded network times b1 and b2 of the B clocks, one can determine a time difference dB = b1-b2. This difference now depends mainly on the times of the 0-point of the two clocks. The difference should always be bleached without change of power. If a change in the power factor takes place, then it shows in small deviations. A change of approximately half a period indicates a change in the current flow direction. This is easy to determine. Optionally, a cyclic time scale can be used for numerical reasons to keep the numbers to be transmitted small.

Claims (4)

Method for the contactless determination of the local power and its direction of flow in a line or line combination in a network by measuring a magnetic field caused by a line or line combination in magnitude and phase near a local measuring point and from the magnetic field via the line or Conductor combination is determined flowing power, characterized in that its power flow direction is derived from a relation of the phase of the measured magnetic field to the voltage phase as network phase or reference phase of the interconnected network and that the network phase is measured directly at one or more central locations or that as a grid phase of the suppliers be made publicly available data or that the network phase by averaging the measured at many points within the interconnected network in each case in the vicinity of the line or line combination of the phase of this line or line is caused to be compared locally or centrally with respect to the phase comparison at the measuring location of interest via the phase determined by magnetic field measurement and the reference phase via a time reference. Method according to one of the preceding claims characterized characterized in that the time reference by time signal transmitters, navigation systems, broadcast signals or individual events and is done directly or indirectly, by local clocks sufficiently accurately synchronized by the time reference become. Method according to claim 1 or 2, characterized that the phase comparison directly between the local phase and the distant reference phase takes place after being over time-synchronous communication channels were brought to the same place. Method according to one of the preceding claims characterized marked that at the estimate the network phase by averaging the in many places within the Network in each case nearby the line or line combination measured phase of this Conduction caused magnetic field to avoid errors due to of individual phase jumps a cyclic number space is used.