A DEVICE FOR MEASUREMENT OF THE TEMPERATURE AT POWER LINES

Abstract: A meter device for the detection of measurement test results at an object, e.g. the temperature at a cable (3) of a high-voltage power line, at which a probe (1) arranged at the object transmits data to a receiving gauging station (4). When such meter devices are used at power lines (2) transmitting very high-voltage current, e.g. 400 or 800 kV, interference problems occur due to difficulty controlled fields of force, leaks, corona-effects, etc..., which make conventional transmission of data, radio transmission or inductive transmission impossible. A reliable data transmission is therefore according to the invention achieved by the fact that the probe (1) is arranged to transmit data during short transmitting periods (t) which are located in connection with the zero passage of the current transmitted in the cable (3) of the power line.

Description: ADEVICEFORMEASUREMENTOFTHETEMPERATUREATPOWERLINES The present invention refers to a meter device adapted fo detecting of measurment test results at an object, preferabl the temperature of the cables at a high-voltage power line whereby a probe, which is arranged at the object, transmit measurment test results to a receiving gauging station. BACKGROUND OF THE INVENTION AND THE STATE OF THE ART Today large amounts of energy is transmitted from electricit producers, such as water power stations, nuclear power plants, termal power plants and the like by way of extensive net o powe lines to the consumers. To build and expand the powe line extensive investments is needed why it is desirable to use existing plants optimally. The primary factor which limits the loading capacity of a power line is the temperature in the cable. It is therefore important that some theoretical calculated limit values not will be exceeded. To calculate these limit values one for the purpose designed calculating method is used in which consideration must be taken to a number of parameters such as velocity of the wind, the ambient temperature, the solar radiation, emission factors and so on. All these parameters must, of understandable reasons, be roughly estimated at the calculations why it also is very hard to decide how well the theoretical calculated line temperature will " correspond to the real one. It is most likely, that one in reality lies considerably under the temperature, the limit value, which could be accepted in the cable. Because of the uncertainty in the calculations and that one must secure large marginals to the limit value the power lines cannot be optimally used. If for example the cable temperature could be increased from 50 degrees C to 60 degrees C the load on the line could be increased with 25 percent. Hereby is realized the importance of being as near as possible to the limit value. It is therefore also important that one is teaching how well the calculating methods corresponds to the reality and find the parts on a line where the highest temperature, at a given load , appears . Today one cannot decide if this is in an open place in the forest, on an open meadow, at a -jointing sleeve of the line or at another place. In order to solve these problems, a device which may measure the temperature of the cables of the power lines in the present environment under field service conditions is needed. As easily may be realized, special problems are connected to measurment of the temperature at optional parts along -a high-voltage power line, conventional technique cannot be used. For example, a temperature probe, connected to a cable, cannot be galvanic connected to a gauging station located for example on the ground, as the risk for flash-overs from the cable, which may provide a voltage of up to 400 or 800 kilovolt, is impending. To transmit measurment test results wireless in a conventional inductive way or by means of conventional radio transmitting technique involve insurmountable problems in the form of radio interferences which arise in the neighbourhood of power lines intended for high-voltage. The reason to such interferences is corona-e ects, creeping currents in the insulators, heavy electromagnetic fields and so on. Devices for measurment of temperatures and for wireless transmitting of measurement test results are though earlier known. Such a device is for example shown in the German OS 2129295 which discloses an electronic temperature meter mainly intended for measurment of the temperature in objects, which pass through a long drying oven or the like. Measured temperature is transmitted wireless to a receiving gauging station, located somewhere outside the oven. This device is not appropriate to be used on a cable of a high-voltage power line and cannot at the same time detect a number of parameters such as current flow, ambient temperature and the temperature of the cable. The wireless transmitting is not either adapted to eliminate influence of electromagnetic inter erences in the neighbourhood why the transmitting of the measurement test results will be very uncertain and sensitive to interferences^ The temperature meter device is also provided with batteries which must be changed regularly. THE OBJECT OF THE INVENTION AND ITS MOST IMPORTANT CHARAC TERISTICS The object with the present invention is to provide a mete device by which among other things the temperature of a cabl of a power line and its instantaneous load may be detecte whereby the achieved measurement test results may b transmitted wireless to a gauging station for transcription, storing and/or treatment. Further object is that the mete device should give accurate measurement information, be eas to apply on desired locations along a cable of a power line, be provided with voltage supply from the power line and to be in operation long periods without maintainance . This is achieved thereby that the probe is arranged to transmit measurement test results wireless during short transmitting periods which are located in connection with the zero passage of the current transmitted in the cable of the power line. SHORT DESCRIPTION OF THE DRAWINGS The invention will in the following be described in an embodiment with reference to the enclosed drawings. Fig. 1 shows the invention mounted in its normal operation environment . Fig. 2 shows a view at an angle from below and from the side of one, on a cable of a power line mounted, probe. Fig. 3 shows a cross-section through the probe according to Tig. 2. Fig. A shows an example of an transcript of transmitted measurement test results. Fig. 5 shows a current diagram, wherein the measurement and transmitting periods are marked. Fig. 6 shows a block-diagram of the electronic configuration of the probe. Fig. 7 shows a block diagram of the electronic structure of the receiving gauching station. DESCRIPTION OF EMBODIMENTS In figure 1 is shown a meter device according to the invention whereby a probe 1 is mounted on one of the cables 3 of the high-voltage power line 2. Beneath the probe 1 is a receiving gauging station located and arranged e.g. to receive frequency modulated radio signals from one or more probes 1 during regularly recurrent time periods. The gauging station 4 includes (see also fig. 7) a radio receiver 5 for frequency modulated signals, electronic units 6, 7, 8 for converting of data, a data storing unit and/or a printer 9 and a modem 10 for possible connection to a centrally located computer 11 by way of a telephone line 12 or the like. The measurement test results which is transmitted from the probe 1 refer to, in this embodiment, the instantaneous current flow in the cable 3, the operation temperature of the cable 3 and its ambient temperature. The information is received of the gauching station 4 and is stored, alternatively is written out, by an earlier decided frequency. The result may e.g. be read off in the form of a written table, wherein the ambient temperature is written furthest to the left, the temperature of the cable 3 in the middle and the present load of the cable 3 in the form of current strength, furthest to the right (see fig. 4). Once an hour date and time is written. In figure 2 the probe 1 is shown more in detail, whereby its soft rounded lines are disclosed, which are intended to decrease among other things the corona-ef ects against the neighbourhood. At the potentials which are present the ambient air is easy ionized whereby small discharges, which beams mainly in right angle out from bodies with high-voltage, arise and cause radio frequent and broad band interferences the frequences of which may reach very high in the frequency spectrum. Interferences of this kind change in intensity at different meteorological situations and may together with the interferences from creeping currents be exceptional annoyin for the radio communication, when e.g. moist winds saturate with salt blow from the sea onto the cables and th insulators . Paradoxically, it is at those difficult meteorologica situations as interruptions of the service and break downs occur on the power lines and it is most important to receiv the measurement test results to make it possible to use the net of power lines optimally. Figure 3 show a vertical cross section through the probe 1 in its axial direction. The probe 1 includes a cylindrical casing 13 with thick walls of aluminium and the end parts 14, 15 of which are rounded and preferably designed spherical. The casing 13 is mechanical and galvanical connected to the cable to which the probe is mounted by means of two attachments, 16, 17, each provided with one mainly circular mounting device or brace 18, 19 at the top. At one attachment 16 and the brace 18 is a first current transformer 20 arranged in such a way that it at least partly surround the cable 3 and in the other attachment 17 and brace 19 is partly a monolithic temperature sensor 22 arranged in connection to the cable 3 and partly a second current transformer 21 which at least to a part, surround the cable 3. The first current transformer 20 is arranged to detect the current which flows instantaneously through the cable 3 and the other current transformer 21 discharge, by way of the electromagnetic field which occur around the cable 3 in its loaded condition, electrical power which runs the electronic of the probe 1. In this way the need of batteries or other internal or external energy sources is eliminate . The temperature sensor 22 detects the temperature of the cable 3 and emit a measurement test result to the electronics. The ambient temperature of the cable 3 and the probe 1 is detected by means of a temperature sensor 23 located inside the casing 13 of the probe 1. Thereby, that the probe 1 is located at some distance from the cable 3 and has the casing 13, the surface of which has a design which is similar to the surface of the cable 3 is a temperature value obtained which corresponds to the temperature of the cable 3 in its unloaded condition, i.e. a reference value is achieved which may be equal to the ambient temperature. The electronic in the probe 1 consists mainly of integrated circuits manufactured in CMOS-technique, which means that the electronic is current saving and emits very little heat, which does not influence the measuring of the ambient temperature. The attachments 16, 17 of the probe 1 are, as mentioned, at the top designed circular and each is provided with a centrally located hole 24 the diameter of which is adjusted to the diameter of the cable 3 to which the probe 1 is mounted. To make possible a simple and fast mounting to the cable 3 is a part, a cup 25, of the circular attachment 16, 17, detachable, whereby the bracers 18, 19 easily may be mounted on the cable 3 whereby the cups 25 once more may be mounted in place. At the mounting it is nessesary to "■ squeeze" the cable to make shure that the probe 1 will stay in place and so that the temperature sensor 22 is put in contact to the cable 3. In figure 6 is shown a block diagram of the electronic structure of the probe 1. A first current transformer 20 detects the power fields which surrounds the cable 3 and emits an electrical signal, corresponding to the intensity of the power field, to a first converter 26 and to a zero passage detector 27. The output from the converter 26 is supplied to one of the inputs of a A/D-converter 28. The zero passage detector 27 detects the signal from the current transformer 20 and emits a signal each time the current through the cable 3 is zero. A timer 29 initiates an activity modul 30 regularly, e.g. every two minutes, whereby the measurement test results are detected and transmitted. Alternatively the measurement test results may be detected regularly but the transmitting is executed only when some change has occurred of the detected parameter values. The activity module 30 influences, connects , ✓-"ttU -iJ? in its turn a current supply unit 31 , which convert and stor energy discharged from the cable 3 , and a control logic uni 32. The first temperature sensor 22, located in connection to th cable 3 of the power line and arranged for measurment of th temperature of the cable, . is. in electrical connection to second signal converter 33, the output of which is connecte to the A/D-converter 28. The further temperature sensor 23 located inside the cylindrical casing 13 of the probe 1 fo measurment of the ambient temperature, is connected to a thir signal converter 34, which also is in electrical connection t the A/D-converter 28. The control logic unit 32 controls th A/D-converter 28 in such a way that the analogue signals fro the current transformer 20 and the first and the secon temperature sensor 22, 23 is consecutively is connected an converted to digital signals which are fed to a UART-unit. I the UART-unit the parallel input signals are converted t serial output signals, which are fed to the FM-transmitter 36. The measurement test results are detected and transmitted, consecutively, during short measurement and transmittin periods, by way of one for the purpose arranged slot-antenna 37, with one on a carrier frequency superpost signal. In figure 5 is shown schematically a curve chart of the transmitted current through the cable 3. The power field around the cable increases in proportion to this current as well as the interferences which influence on among other things the radio communication. In an area (shaded) just before and after the passage through the zero level the interferences are as low as possible. The interferences are naturally also connected to the instantaneous voltage of the cable 3 which not always is in exact phase with the current. The size of the phase di ference, between the voltage and the current, is still neglectable small in these matters where many different consumers are loaded the power line. The probe 1 is therefore arranged to detect zero passage of the current and by means of among other things a timer 38 calculate a measurement and transmitting period (t) the beginning of which lies approximately 60 degrees 6 before the zero passage and which ends approximately 60 degrees after the zero passage. During this period, which accordingly lies symetrically around zero, the electronics of the probe 1 is activated by among other things the zero passage detector 27 in such a way that the detecting of e.g. the parameters current flow, cable temperature and ambient temperature, and the transmitting of these measurement test results to the gauging station 4, is executed. The transmitting velocity may e.g. be 2400 baud, which gives 4 ms/byte. It is also very important, as may be clear from above, that the electronics may provide measurement, treatment of the measurement test results and transmitting of the measurement test results during the short periods when the current in the cable 3 of the power line is low and consequently discharges, flash-overs and the like, which cause radio-frequent interferences , are at minimum. By the meter device according to the invention, by which among other things the primary parameter, the temperature of the cable, is supervised, may the existing power lines be used optimally. This is important especially when high loads occur instantaneously and at extreme operation condition, such as for instans at local breakdowns when some line breaks because of for instance "line-rush", flasch-overs or the like. Further expansion of the power lines may, by means of this invention, be displaced in time which may delay costly investments. The invention is naturally not limited to the above disclosed embodiment but a number of alternatively embodiments are possible within the scope of the claims. Thus it is possible that the detecting and storing of the measurement test results is carried out continuesly but is transmitted to the gauging station only during limited transmitting periods.

Claims: C L A I M S 1. A meter device for the detection of measurement tes results at an object. e.g. the line temperature at high-voltage power line, at which a probe arranged at th object transmits data to a receiving gauging station, c h a r a c t e r i z e d i n, that the probe ( 1 ) is arranged to transmit data wireles during short transmitting periods (t) which are located i connection with the zero passage of the current transmitted in the cable (3) of the power line. 2. A meter device according to claim 1 , c h a r a c t e r i z e d i n, that the transmitting periods (t) start not more than 60 degrees before the zero passage of the current transmitted in the cable (3) of the power line and ends not later than 60 degrees after said zero passage. 3. A meter device according to claim 1 or 2 , c h a r a c t e r i z e d i n, that the probe { 1 } is arranged to detect the line temperature of the cable (3) of the power line, the ambient temperature and the current transmitted in the cable. 4. A meter device according to any of the preceding claims, c h a r a c t e r i z e d i n, that a current transformer (21) is arranged to discharge electric energy from the cable (3) for driving the electronics in the probe ( 1 ) .

Inventors: ARNFJORDEN JAN, ARNFJORDEN, JAN
Applicants: INTAB
Application year: 1983
Main classification: G08C25
IPC codes: G01K1, G01R15