Autocalibration procedure for a voltage measuring system in overhead line indicators

Abstract

Method for determining a correlation between potentials of the overhead line conductors (11, 12, 13) of a multi-phase overhead line system and respective sensor voltages and their phase shifts, wherein a sensor voltage is the potential difference between the potential of an overhead line conductor and the potential of a measuring sensor (2a) arranged at a predefined distance from the respective overhead line conductor, comprising the method steps - measuring the sensor voltage for each overhead line conductor (11, 12, 13) of the overhead line system, and - transmitting the measured sensor voltage of each overhead line conductor (11, 12, 13) to a central evaluation point, and - Determining the phase difference between the overhead line conductor voltage and the sensor voltage of the middle overhead line conductor, and - Determining the correlation between the potentials of the overhead line conductors (11, 12, 13) and the sensor voltages based on the measured sensor voltages and between the potentials of the overhead line conductors (11, 12, 13) and the phase shifts between the sensor voltages and the overhead line conductor potentials.

Description

The invention relates to a method and a correspondingly set-up device for automatically calibrating galvanically decoupled voltage field sensors for overhead line indicators.Sensors for determining voltages on overhead lines for voltages of more than 400 V up to several hundred kV are known from the prior art. Conventional high and maximum voltage sensors use, for example, ohmic or capacitive voltage dividers or inductive or optical converters. Ohmic or capacitive voltage dividers have the disadvantage, however, that they must be galvanically connected to the reference potential, i.e. typically to the ground potential. Inductive or optical converters have the disadvantage that they are comparatively complex and thus expensive.Voltage sensor concepts for overhead line indicators are also known, which have to be calibrated before the first productive use. For calibration, however, the geometry of the overhead line arrangement is to be specified for this purpose, that is to say the height of the ladder ropes above the ground, the distances of the ladder ropes to one another and the ladder radii and how the ladder ropes are arranged to one another.US 2012 / 0 046 799 A1 describes a device for observing and measuring electrical and mechanical parameters of a power line.US 2011 / 0074 436 A1 describes a method and a system and a computer program product for identifying false positive indications of high impedance errors in high voltage lines and a distribution network, wherein the waveform of the voltage and current curve is evaluated.Therefore, there is a need for an improved overhead indicator system that requires less effort to calibrate the voltage measurement. In the following, such a system is described with reference to the schematic figures. Figure shows FIG. 1 shows overhead line indicators with measurement pickup 2 aon an overhead line conductor cable; FIG. 2 is a schematic illustration of a overhead line indicator; FIG. 3 shows a schematic illustration of a measurement pickup in the E-field of a overhead line conductor cable; FIG. 4 shows an overhead line system with 3 overhead line indicators; FIG. 5 shows further geometries of conductor cable arrangements; FIG. 6 shows methods for determining the correlation in the form of a correlation matrix K.Conventional overhead indicators typically include a means for monitoring current through an overhead line to detect and signal fault conditions such as an overcurrent in the event of a short or ground fault. A so-called overhead line indicator is typically a device for determining the current through an overhead line which is suspended in a small housing to a conductor cable of an overhead line system. Modern overhead line indicators may also be configured to measure the tension of an overhead line cable and accordingly indicate whether an overhead line is live or free of tension. Such a overhead line indicator can thus also detect a ground fault, in particular in compensated networks in which the detection of ground faults is difficult without information about the conductor cable tension.The relationship between the field strength of an electric field around a conductor cable, for example, and the scalar potential field is known asGiven a field strength in the region around a single conductor cable, the potential of a measuring transducer which is arranged at a distance from the conductor cable can thus be determined and measured via a high-impedance or high-impedance resistor. The measuring sensor can be rod-shaped or designed as a plate or ring-shaped and arranged outside the housing of the overhead line indicator or as a correspondingly shaped surface on a printed circuit board.The E-fields of overhead lines of a power supply network can be considered quasi-stationary because of the low frequencies of 50 Hz-60 Hz. The entire field of an arrangement of a plurality of overhead conductors results as superposition of the fields of the individual conductors. With knowledge of the high-voltage potentials of the conductors, the electric fields of a conductor arrangement can thus be determined. Conversely, with knowledge of the electric fields, the potentials of the conductors of a conductor arrangement can be determined. The potential of a floating measuring sensor can likewise be determined, which is arranged on a conductor cable of a overhead line arrangement, as explained in more detail below.Accordingly, the field strength of, for example, an arrangement of three (high-voltage) conductors correlates with the potentials of the conductors according to the equation wherein φ L1 to φ L3 are the potentials of the conductor ropes L 1 to L 3, U Sensor1 to U Sensor3 are sensor voltages of the voltage sensors Sensor 1 to Sensor 3, which are each arranged at a predefined distance from one of the conductor ropes L 1-L 3, and is not a correlation matrix.The sensor voltages U Sensor1 to U Sensor3 are measured by sensors which are each arranged in the immediate vicinity of a overhead line cable. In this case, the sensor voltage U Sensor is the difference of the potential of the measuring transducer arranged at a distance from a conductor cable from the potential of the (high-voltage) conductor.FIG. 1 schematically shows a overhead line indicator 2 which is arranged in the immediate vicinity of a conductor cable 1. A overhead line indicator 2 preferably hangs on an overhead line cable 1.As shown schematically in FIG. 2, a overhead line indicator comprises a measurement pickup 2 a, wherein the overhead line indicator 2 is configured such that the measurement pickup 2 ais preferably arranged parallel to the overhead line 1 during operation. The measuring sensor 2 aof the overhead line indicator 2 is connected to the conductor cable 1 via a high-impedance or high-impedance measuring resistor 2 band accordingly ideally has a floating potential.In addition to a measuring sensor 2 a, a overhead line indicator 2 comprises a sensor 2 cto determine a sensor voltage U Sensor, which is the potential difference between the potential of the measuring sensor 2 aand the respective conductor cable 1. In one embodiment, this sensor voltage is determined by a sensing device via the high-impedance connection, for example via a measuring resistor 2 b, between the measuring sensor 2 aand the conductor cable 2.FIG. 3 shows the arrangement of such a measuring transducer 2 ain the E-field of a conductor cable 1. φ HS therein denotes the potential of the (high-voltage) conductor cable, φ Sensor the potential of the measuring transducer 2 aand U Sensor the determined voltage between the measuring transducer 2 aand the respective conductor cable 1, to which the measuring transducer of the overhead line indicator is connected via the high-impedance connection.Preferably, the sensor 2 cof a respective overhead line indicator 2 determines the voltage U Sensor as a digital value, i.e. the sensor samples the voltage and provides a corresponding value of a sensor voltage together with the point in time of the sampling for transmission and for further processing. The overhead line indicator 2 has a device 2c for scanning, digitizing and processing which is necessary for this purpose and is known per se.The overhead line indicator system comprises, for each stranded wire 1, an overhead line indicator 2 described above. This processing point receives the sensor voltages determined by the respective overhead line indicators and is configured to process the sensor voltages and to transmit determined results to further points, for example to a control room of an energy supply network. The central processing point can be set up in one of the overhead line indicators, so that the latter has a function as master.FIG. 4 shows an arrangement of three conductor ropes 1 1, 12 and 1 3 on a power mast 3. On each of the conductor ropes a respective overhead line indicator 2 is arranged, here corresponding to the conductor ropes denoted as 2 1, 22 and 2 3 wherein the overhead line indicator 2 2 here is configured as master. The communication module 2 dis preferably a device for wireless communication and connects a respective voltage indicator to the master, preferably by means of a wireless transmission method such as a Bluetooth connection. In FIG. 4, such a or corresponding radio connection 4 between the overhead line indicators 2 is schematically represented by the radio waves. Furthermore, a overhead line indicator is preferably set up and configured for communication with a further location, for example via a mobile radio network having a control point in the energy supply network, which is not drawn in the figures.The system described here by way of example comprises three live conductors 1 1, 12 and 1 3. A respective overhead line indicator with a voltage sensor is attached to each live conductor. The overhead indicators are communicatively coupled to one another such that they can transmit and receive data and, more particularly, transmit sensed sensor voltages and associated sampling times. One of the overhead line indicators, here the overhead line indicator arranged on the middle overhead line, serves as a so-called master with regard to the communication and the evaluation of the determined sensor voltages. The two other voltage indicators are accordingly configured as slaves, so that they supply the ascertained sensor voltages to the overhead line indicator configured as master.The overhead line indicators are each configured and configured such that they synchronously ascertain the respective sensor voltage, i.e. at the same time. The two overhead line indicators configured as slaves communicate their respective measurement voltage values ascertained at a point in time and the sampling point in time with the overhead line indicator configured as master.During normal operation, the master may determine the potentials of the system's conductive ropes based on the correlation matrix K and the measured sensor voltages, see equation (2) above. For this purpose, however, the correlation between the sensor voltages and the conductor cable potentials is to be determined first in the form of a correlation matrix K.After conversion of equation (2), K is obtained for the correlation matrixThe correlation matrix [K] can thus be determined on the basis of the determined sensor voltages, i.e. U Sensor1, U Sensor2 and U Sensor3, and the potentials of the conductor ropes. Thus, when starting up such a system with a plurality of overhead line indicators, the correlation matrix can be determined as soon as the sensor voltages and the potentials of the conductor cables are present at a point in time.The master of the tension indicators is furthermore provided and configured to calculate the correlation matrix [K] from transmitted sensor voltages and the conductor cable potentials. For this purpose, the master has a digital signal processor and memory and is configured and configured to determine the correlation matrix for [K] from the data.FIG. 5 shows arrangements a-e of three typical medium voltage overhead lines 1 1, 12 and 1 3, which are each arranged on a mast by means of insulators 5. The mast is located on the ground, so that the mounting height of the overhead lines corresponds to the distance from the ground potential.In the arrangement a, all three overhead lines 1 1, 12 and 1 3 are arranged next to one another in a common horizontal plane, wherein the spacing of the two outer overhead lines 1 1 and 1 3 to the central overhead line 1 2 is the same. The fields of the overhead conductors 1 1 and 1 3 cause an increase in the voltage amplitude in the central overhead conductor 1 2. Due to the symmetry of the conductor arrangement and assuming the same conductor cable tension amplitudes, the fields of the conductor cables 1 1 and 1 3 do not cause any phase shift at the location of the conductor cable 1 2 and likewise at the location of the measuring sensor of a overhead line indicator arranged on the conductor cable 1 2 (not shown in the figure). The voltage detected by the overhead line indicator disposed on the center overhead line cable 1 2 U Sensor2 is therefore in phase with the voltage of the center conductor cable 1 2. However, for the sensor voltages of the two outer conductors 1 1 and 1 3 a phase shift by 5° to 6° was determined at typical conductor spacings.Although all three conductors are likewise arranged in a common horizontal plane in the conductor cable arrangement b, the effect of the fields of the two outer conductors 1 1 and 1 3 is not cancelled out at the location of the conductor cable 1 2 or at the location of the measuring sensor of a overhead line indicator arranged on this conductor cable, since the distance of the middle conductor 1 2 to the two outer conductors 1 1 and 1 3 is not the same. Accordingly, a sensor voltage that detects a overhead line indicator hanging from the center conductor cable 1 2 is out of phase with the voltage of the center conductor cable 1 2.The arrangement shown schematically in c schematically shows an arrangement of three overhead conductors in a triangle, wherein the conductors are arranged at different heights above the earth, and wherein two conductor cables are arranged vertically one above the other. Also in this arrangement, the electric fields of the conductors 1 1 and 1 3 do not cancel each other out at the location of the conductor 1 2 or at the location of a overhead indicator attached to the conductor. A determined sensor voltage of a overhead line indicator attached to the conductor 1 2 is phase shifted by 1.46° with respect to the voltage of the conductor 1 2. for example.Arrangement d shows an arrangement of three conductors 1 1 to 1 3. arranged one above the other on an imaginary vertical axis. Although the two outer conductors 1 1 and 1 3 are arranged at the same distance from the middle conductor 1 2 the fields of the two outer conductors do not balance at the location of the middle conductor line and also not at the location of a overhead line indicator attached to the middle conductor line because the three conductors are arranged at different distances from the earth. The sensor voltage determined by a overhead line indicator arranged in 2 on the middle conductor cable 1 is thus phase shifted with respect to the voltage of the middle conductor cable.Likewise, for the arrangement of conductors in the triangle shown in e, each sensor voltage determined by a corresponding overhead line indicator is also phase shifted with respect to the respective conductor cable voltage.For the various arrangements a to e, the phase difference between the potential of the central conductor and the sensor voltage of a overhead line indicator Δφ L2 / sensor2 attached thereto was calculated by means of a simulation and actually measured.The deviations determined for the phase difference Δφ L2 / Sensor2 between the tension of the middle conductor cable 1 2 and the sensor tension of a overhead line indicator arranged on this cable can be determined with a good approximation using the following equation: wherein φ 21 and φ 23 the phase differences between the sensor voltages of the two outer conductors 1 corrected by 120° in each case are 1, 13 to the middle conductor 1 2.It has been found that, with the exception of the vertical arrangement shown in arrangement d, in which the phase differences after applying formula (4) are about 1°, all other conductor cable arrangements have significantly smaller deviations.The phase differences φ 21 and φ 23 can be determined in a known manner from the sensor voltages, so that the phase difference Δφ L2 / Sensor2 can also be calculated in a simple manner. With this relationship between the determined sensor voltages and the conductor cable voltage of the middle conductor, the correlation between the sensor voltages and conductor cable voltages can be determined.FIG. 6 schematically shows such a method for determining the correlation matrix [K].The correlation matrix [K] can be determined in any device which is configured for this purpose and has a suitable memory and a digital signal processor for storing the values and results. In a preferred embodiment, an overhead line indicator according to the invention, preferably the master 2 2 has a corresponding device for storing the digital data and for carrying out the determination of the correlation matrix [K].At the beginning of the method, the central evaluation point, i.e. the master of the overhead line indicators 2 2, is provided with the information as to which overhead line indicator is arranged on the central conductor. In one embodiment, this information may be input to the system by an operator.The method begins with the determination of the sensor voltages U Sensor1 to U Sensor3, see step 6.1. In this case, the sensor 2 cof a overhead line indicator according to the invention detects the voltage U Sensor over at least one full period, with the result that the sampled values of the sensor voltages U Sensor1 to U Sensor3 each also detect a zero crossing. The values U Sensor determined are acquired together with the point in time of the determination, i.e. with the point in time of the scanning, wherein the times of the sensors 2 cof the overhead line indicators are synchronized in time. The values for U Sensor are preferably determined at a clock rate of at least 1 kHz.Subsequently, the overhead line indicators 2 1, 22 and 2 3 transmit the determined sensor voltages, i.e. the sampling values and the associated points in time of the sampling, to the central evaluation point, see method step 6.2. If the central evaluation point is one of the overhead line indicators of the system and thus the master, the satellites transmit their respectively sampled sensor voltage values and the sampling times to the master.The central evaluation point then determines, see step 6.3, the phase difference of the sensor voltage U Sensor2 of the middle conductor to the voltage or the potential of the middle conductor 2 2 for the time of the zero crossing of the sensor voltage. For the conductor arrangements shown a and e, it is known that the phase difference is zero, i.e. the measured sensor voltage of the middle conductor is in phase with the cable voltage of the middle conductor. For the arrangements b and c, the phase difference between sensor voltage and conductor cable voltage can be determined by means of the above-mentioned equation (4).The rated voltage of the conductor ropes will be estimated in a further step, see method step 6.4, on the basis of the level of the sensor voltage of the middle conductor. Since the sensor voltage of a overhead line indicator depends essentially on the field strength of the E field around the conductor, as shown above, and the E field at the location of the measuring sensor depends on the voltage of the conductor cable and the distance of the measuring sensor from the conductor cable, the nominal voltage of the conductor can be estimated on the basis of the determined maximum sensor voltage and the known distance of the measuring sensor from the conductor cable. In one embodiment, therefore, the level of the rated voltage is determined based on the sensor voltage, a table and fixed limit values. If, for example, a sensor voltage exceeds a predefined limit value, the rated voltage of the conductor cable is determined on the basis of a table, since the rated voltages typically assume discrete values.The phase profile of the conductor cable tension of the middle conductor cable 1 2 with respect to the sensor tension of the middle conductor is thus known, and the amplitude of the rated voltage of the conductor cable is also known.For the further steps of the method, it is assumed that the phases of the two other conductor voltages are ideally 120° out of phase with the tension of the middle conductor and the amplitude corresponds to that of the tension of the middle conductor cable.The master is thus familiar with the sensor voltages U Sensor1 to U Sensor3 and all three conductor cable voltages at the time t=T0, that is to say at the time of the zero crossing of the sensor voltage U Sensor2 so that the correlation between the conductor cable voltages and the sensor voltages can be determined in the form of a correlation matrix [K] on the basis of the equation (3).The system of the plurality of overhead line indicators 2 1, 22 and 2 3 is thus calibrated for the time of the determination of the sensor voltages, i.e. the correlation between the sensor voltages and the conductor cable voltages is determined.Thus, from the time of calibration of the overhead line system, the voltages and phases of the overhead conductors can be determined based on the determined correlation between the sensor voltages and the conductor cable potentials, i.e. the correlation matrix [K], so that the overhead line system can be monitored.List of reference characters1 Overhead line conductor cable 2 Overhead line indicator with measuring pickup 2a, measuring resistor 2b, device 2c for scanning, digitizing and processing voltage values and communication module 2d 3 Power mast 4 Communication connection 5 Isolator 6 Method for determining the correlation

Claims

Method for determining a correlation between potentials of the overhead line conductor ropes (11, 12, 13) of a polyphase overhead line system and respective sensor voltages and their phase shifts, wherein a sensor voltage is the potential difference between the potential of an overhead line conductor rope and the potential of a measuring pickup (2a) arranged at a predefined distance from the respective overhead line conductor rope, comprising the method steps - measuring the sensor voltage for each overhead line conductor rope (11, 12, 13) of the overhead line system, and - transmitting the measured sensor voltage of each overhead line conductor rope (11, 12, 13) to a central evaluation point, and - determining the phase difference between the overhead line conductor rope voltage and the sensor voltage of the central overhead line conductor rope, and - determining the correlation between the potentials of the overhead line conductor ropes (11, 12, 13), 13) and the sensor voltages based on the measured sensor voltages and between the potentials of the overhead line conductors (11, 12, 13) and the phase shifts between the sensor voltages and the overhead line conductors potentials.Method according to claim 1, wherein for an arrangement of three live and arrayed in a common horizontal plane, of which the two outer overhead conductor ropes are evenly spaced from the middle overhead conductor rope, a phase shift between the sensor voltage and the potential of the middle overhead conductor is assumed to be 0°.Method according to claim 1, wherein for an arrangement of three live, evenly spaced overhead line conductor ropes (11, 12, 13), two of which are arranged in a common horizontal plane, a phase shift between the sensor voltage and the potential of the middle overhead line conductor is assumed to be 0°.Method according to claim 2, with the further method step: determining a phase difference (Δφ L2 / Sensor2) between the sensor voltage and the overhead line conductor cable voltage of the middle overhead line conductor (2 2) according to the equation Δ φ L 2 / sensor 2 = 1 3 ⋅ ( φ 21 + φ 23), wherein φ 21 and φ 23 are the phase differences between the sensor voltages of the two outer overhead line conductors (1 1, 13) to the middle overhead line conductor (1 2) if at least two overhead line conductor cables are arranged at a horizontal distance from one another.Method according to claim 2, comprising the further method step: determining a phase difference (Δφ L2 / Sensor2) between the sensor voltage and the overhead line cable voltage of the middle overhead line conductor (2 2) based on the difference of the phases of the sensor voltage of the sensor on the middle overhead line conductor cable (1 2) to the sensor voltages of the two outer overhead line conductor cables (1 1, 13),Method according to one of the preceding claims, wherein a sensor voltage is sampled at a sampling rate of at least 1 kHz,The method of any preceding claim, wherein providing sensing voltages of a overhead line conductor cable comprises wirelessly transmitting the sensing voltages and associated sampling times.The method of claim 6, wherein the determining of the correlation is performed in a clear indicator (2).The method of any preceding claim, wherein the determined sample of a sensor voltage is communicated from a first overhead indicator to another overhead indicator.The method of claim 9, wherein the determined sample of a sensor voltage is communicated along with the time of the sampling.Overhead line indicator system for determining a correlation between potentials of the overhead line conductor ropes (11, 12, 13) of an overhead line (1) having three live overhead line conductors, the system comprising: for each of the live overhead line conductor ropes (11, 12, 13), a respective measurement pickup (2a) which is arranged at a predefined distance from the respective overhead line conductor rope and is connected to the overhead line conductor rope via a high-resistance measurement resistor (2b), and for each of the live overhead line conductor ropes (11, 12, 13), a measurement device (2c) which determines the voltage dropping via the high-resistance measurement resistor (2b), and a device for determining the correlation between the potentials of a respective overhead line conductor rope (11, 12, 12, 13) and the sensor voltages based on the voltages dropped across the high-resistance measuring resistor (2b) according to the method according to claim 1.Overhead line indicator system according to claim 11, wherein an overhead line indicator (2) comprises a measuring transducer (2a) of electrically conductive material arranged parallel to the respective overhead line conductor cable (1).Overhead line indicator system according to Claim 12, wherein the measurement pickup (2a) is configured annularly or rod-shaped or as a planar plate.

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