WO2001004645A1

WO2001004645A1 - Directional high-voltage detector

Info

Publication number: WO2001004645A1
Application number: PCT/DK2000/000376
Authority: WO
Inventors: Oluf Peter Kaad Johansen
Original assignee: Jomitek Aps
Priority date: 1999-07-12
Filing date: 2000-07-07
Publication date: 2001-01-18
Also published as: AU5806000A

Abstract

Directional high-voltage detector for a high-voltage conductor comprising at least one voltage-measuring circuit for measuring the voltage in said conductor, at least one current-measuring circuit for measuring the current in said conductor and means for determining the energy flow in the conductor on the basis of the measurements made by said voltage-measuring circuit and said current-measuring circuit.

Description

DIRECTIONAL HIGH-VOLTAGE DETECTOR

Field of the invention

The invention relates to a directional high-voltage detector according to the preamble of claims 1 and 12, an apparatus for measuring on a high-voltage conductor according to the preamble of claim 14, an apparatus for measuring on a conductor according to the preamble of claim 15, a high-voltage fault detector according to the preamble of claim 17 and method for determining the direction of an energy flow in a high-voltage conductor according to the preamble of claims 18 and 20.

Background of the invention

A high-voltage distribution or transmission system normally comprises numerous conductors directly or indirectly connecting a number of electrical energy generators and electrical energy consumers. The conductors in the distribution system can be in the form of overhead power lines and underground power cables or combinations thereof. The electrical energy generators will normally be power plants such as nuclear, water or coal burning electrical power plants but also wind turbine plants and similar kinds of plants are possible.

The energy consumers may be all kinds of electrical energy consumers in society such as electrical machinery in factories, electrical light in offices and electrical heating apparatuses in private households etc. Other kinds of electrical energy consumers are hospitals where e.g. life support machines are driven by electrical energy and airports where traffic system computers are also driven by electrical energy.

The dependency by a society on a reliable electrical power supply, and especially a reliable distribution or transmission system, is indisputable and even shorter interruptions of the supply can have a significant economic effects on society and also result m loss of human lives .

The transmission and distribution system is particularly vulnerable to different kind of faults due to its size. In order to detect and locate faults in a fast and reliable way, it is necessary to be able to monitor the system continuously.

So far, monitoring has been performed by detectors shattered along the transmission and distribution system, with communication links to a monitoring center. The detectors normally read the voltage or current in the system on the basis of different kinds of measuring methods such as inductive or capacitive methods. Combinations of inductive and capacitive detectors measuring both voltage and current are also known.

The detectors report any detection of significant cnanges m the voltage or current indicating that a fault has occurred m the transmission and distribution system. A major problem is, however, that they lack the capability of indicating where the fault has occurred. At the same time, known detectors are voluminous and heavy in addition to being quite expensive. Especially detectors using measuring methods including transformers or Rukowski coils will suffer from these drawbacks.

Summary of the invention

When, as stated in claim 1, a directional high-voltage detector for a high-voltage conductor comprising at least one voltage-measuring circuit for measuring voltage in said conductor, at least one current-measuring circuit for measuring current in said conductor and means for deriving the energy flow in the conductor on the basis of measurements by said voltage-measuring circuit and said current-measuring circuit, it is possible not only to detect a fault in the conductor but also to indicate in which direction it has occurred from the detector.

This is an important advantage over prior art because it makes it possible to locate faults in the conductor in a quick manner and thereby restore the transmission and distribution system to its normal functional way at a sooner point.

When, as stated in claim 2, the voltage-measuring circuit comprises at least one capacitive detector forming a capacitive coupling with the conductor, it is possible to measure high-voltage without creating a physical connection between the conductor and the measuring circuit. This is very important due to the high-voltage level being measured. When, as stated in claim 3, the capacitive detector comprises a plate covering a section of the conductor partially or totally, it is possible to create a capacitive coupling which is easy to design and adapt to different kinds of conductors or voltage values. The size of the plate may easily be changed as may the distance between the plate and the conductor.

When, as stated in claim 4, the edges or corners of the plate are bent away from the conductor, it is possible to raise the breakdown voltage for the capacitive detector by increasing the distance from the plate to the conductor in places most likely exposed to a breakdown.

When, as stated in claim 5, the dielectric material between the plate and the conductor is silicone, which covers the surface of said detector partially or totally, it is possible to create a capacitor with an accurately defined dielectric constant.

When, as stated in claim 6, the silicone layer serves as an isolation layer between the high-voltage potentials in said detector and the exterior, it is possible to protect e.g. human beings from the danger of life-threatening electric shock.

The silicone also protects the circuits of the detector from humidity and aggressive gasses.

When, as stated in claim 7, at least one capacitor is connected serially to the capacitive coupling and a reference potential respectively, it is possible to create a purely capacitive voltage divider. Thereby, the output voltage from the divider will be without phase displacement which makes any adjustments to the measured voltage or current values of the calculation superfluous while also making it possible to detect very low voltage levels.

The measured value will moreover be a real-time image of the conductor voltage value and polarity.

When, as stated in claim 8, the reference potential is the ground-symmetrical potential of at least one conductor, it is possible to measure the current proportionately to a fixed reference, ensuring a high degree in the accuracy of measurement.

When, as stated in claim 9, the current-measuring circuit comprises at least one detector for measuring of the magnetic field generated by the current in the conductor, it is possible to measure the current without any physical connection between the conductor and the measuring circuit.

The measured value will also be a real-time image of the value and polarity of the current in the conductor.

When, as stated in claim 10, the magnetic field detector comprises two hall elements, it is possible to cancel out an interference field by adding the two detected values to the interference field. The first hall element will detect the interference field in one direction and the second hall element will detect the interference field in the opposite direction. Hereby, it is possible to e.g. cancel out a magnetic field from a conductor placed in proximity to a conductor equipped with a directional high-voltage detector which must not affect the actual reading of the detector.

When, as stated in claim 11, the supply lines for the magnetic field detectors and the calculation circuit comprise shields against magnetic fields, it is possible to avoid reading errors. The measured voltage is only a few milivolts and occurs in a very powerful electromagnetic field only a few milimeters from the high voltage in the conductor. This may easily result in reading errors as the slightest and seemingly insignificant capacitive coupling between the various components/supply lines and the conductor results in reading errors of the current due to the capacitive coupling of the conductor voltage. Furthermore, the electromagnetic fields from other conductors may also create reading errors .

When, as stated in claim 12, a directional high-voltage detector for a high-voltage conductor comprising at least one voltage-measuring circuit for measuring a voltage in said conductor by means of at least one capacitive detector, at least one current-measuring circuit for measuring current in said conductor by means of at least one magnetic field detector and means for deriving the energy flow in the conductor on the basis of measurement by said voltage-measuring circuit and said current- measuring circuit, it is possible to determine the energy flow in the conductor in an advantageous manner. When, as stated m claim 13, said means determine the energy flow direction on the basis of the polarity of the current and voltage between two preceding zero-crossings of voltage, it is possible to determine the direction of the energy flow m a fast and reliable way. Especially since the measured voltage and current values are realtime images of the conductor voltage and current in value and polarity.

When, as stated in claim 14, an apparatus for measuring on a high-voltage conductor comprising at least one voltage-measuring circuit for measuring voltage in said conductor by means of at least one capacitive detector, at least one current-measuring circuit for measuring current m said conductor by means of a magnetic field detector and means for determining the energy flow m the conductor on the basis of measurements by said voltage- measuring circuit and said current-measuring circuit, it is possible to determine the direction of an energy flow m a high-voltage conductor.

When, as stated m claim 15, an apparatus for measuring on a conductor comprising at least one voltage-measuring circuit for measuring voltage m said conductor by means of at least one capacitive detector, at least one current-measuring circuit for measuring current in said conductor by means of at least one magnetic field detector and means for determining the energy flow m the conductor on the basis of measurements by said voltage- measuring circuit and said current-measuring circuit, it is possible to determine the direction of an energy flow in a conductor. When, as stated in claim 16, the magnetic field detector comprises at least one magnetic-resistant detector it is possible to measure a small current intensity in an advantageous manner.

When, as stated in claim 17, a high-voltage fault detector for a high-voltage conductor, said detector comprising means to determine the direction of an energy flow in said conductor, it is possible not only to detect a fault in the high-voltage conductor but also to determine in which direction it has occurred from the detector .

Drawings

The invention will be described below with reference to the drawings in which

fig. 1 illustrates a transmission and distribution system provided with a directional high-voltage detector according to the invention, fig. la illustrates part of a transmission and distribution system in detail, fig. 2 illustrates the basic elements in a directional high-voltage detector, fig. 3 illustrates a preferred embodiment of a directional high-voltage detector according to the invention, fig. 4 illustrates the preferred embodiment of a directional high-voltage detector seen from another angle, fig. 5 illustrates a representation of voltage and current values, fig. 6 illustrates a fraction of the representation centered around a zero-crossing of the voltage.

Detailed description

Referring to fig. 1, a transmission and distribution system 2 is shown consisting of overhead power lines or underground power cables, connecting one or more energy producers 1 with energy consumers or loads enabling a transfer of electrical energy. The transfer of electrical energy will normally be high-voltage, and especially AC voltage, to ensure a minimum of energy loss during the transport through the transmission and distribution system. Also, the voltage will normally be a 3-phased voltage, i.e. the power lines or cables consist of at least 3 conductors .

The lines or cables of the transmission and distribution system are of considerable length which makes it vulnerable to faults of different kinds. A short-circuit 6 in the system may occur as a result of e.g. animal attacks, landslides and construction machinery working in the wrong places. Deterioration of the cable isolation can be another reason for a short-circuit. In order to determine the location of the fault, a number of directional detectors 5 are placed along the conductors of the transmission and distribution system. On the basis of voltage and current measurements, the detectors will be able to determine the direction of the energy flow in the conductor. When a fault occurs, the directional detectors will point to the location of the fault to which energy is flowing. Referring to fig. la, a possible fault situation in a transmission and distribution system is illustrated. The transmission and distribution system includes a high- voltage cable or line Hv and a number of high-voltage transformers Tr which have each been connected to one or more loads 4 on the low-voltage side. In this fault situation, a short-circuit 6 has occurred on the high- voltage side of a transformer Tr. The detectors 5 placed along the high-voltage cable or line all point to the location of the short-circuit towards which energy is lowing .

Referring to fig. 2, a directional high-voltage detector 5 is displayed together with a conductor 10 in a transmission and distribution system 2. The directional detector comprises a voltage-measuring circuit with a capacitive detector 11 and a current-measuring circuit with one or more magnetic field detectors 14. The capacitive detector 11 forms a voltage divider together with a capacitor 12. The capacitor 12 is also connected to a reference point 13 which may be chosen as the symmetrical point of origin of e.g. a 3-phase cable, which equals the ground potential.

The divided measured voltage value and the measured current value are fed to a calculation circuit 17 which calculates the directional value of the energy flow in the conductor on the basis of these values.

Referring to fig. 3, a preferred embodiment of the directional detector is illustrated. The capacitive measurement of voltage is carried out by a capacitive coupling between a metal panel 20 and the conductor 10. The metal panel 20 is curved so that it resembles the shape of the conductor 10 and is in close proximity which ensures high capacitance in the capacitive coupling. The metal panel 20 is preferably rectangular in shape with an area between 4 to 6 cm² of metal panel mounted a few millimeters over the conductor 10. Other shapes and sizes of the metal panel 20 are naturally also possible.

The current-measuring circuit comprises one or more magnetic field detectors 14 for detection of the magnetic field generated by the current flow in the conductor 10. The magnetic field detector 14 is preferably a hall element 15, 16 placed in close proximity to the conductor. The hall element provides a voltage level proportionate to the current in the conductor.

To avoid or minimise interference from external magnetic fields, it is preferable to use double hall elements instead of single hall elements. This will cancel out interference fields because the first hall element will detect the interference fields in one direction and the second hall element will detect the interference fields in the opposite direction resulting in a measured value of nil. Examples of external magnetic fields are the Earth' s magnetic field and magnetic fields from conductors or components placed close to the detector.

The detected values are led to the calculation circuit 17 placed in a circuit board 23. To avoid any magnetic fields generating voltage in the supply lines 22 for the magnetic field detectors 14, the lines are surrounded by shields 21 connected to a ground potential. The shields 21 also protect the circuit board 23 containing the calculation circuit 17.

The isolation of the entire detector in relation to high- voltage is obtained by embedding the entire circuit in silicone rubber. At the same time, the silicone is used as a dielectric between the metal panel and the conductor. The voltage providing cable and the ground cable from the construction are led through an isolating silicone tube into the silicone-protected circuit. Thus, the construction becomes protected from an electrical point of view.

The cables will normally be shielded to avoid any generation of interfering magnetic fields in close proximity to the detectors.

The calculation circuit 17 generates information concerning the energy direction either through an optic fiber to e.g. a control center or on a display 18 comprising e.g. a couple of light-emitting diodes (LEDs) indicating an energy flow in one direction or the other.

The voltage often falls out in case of short-circuiting. This is the reason why the calculation circuit 17 simulates the voltage in 1 or 2 seconds subsequent to the detection of a fault in the conductor. In this manner, it is still possible to compare the polarity of the recorded short-circuit current with the polarity of the voltage. The direction of the short-circuit current is determined by the calculation circuit 17 within the first two periods after a current increase above a certain trigger level . The energy supply takes place from an external voltage source. This voltage source must provide a DC voltage of 9 to 12 volts m such a manner that the DC-ground is galvanically separated from the ground potential. The circuit also requires voltage n the short-circuit situation where the voltage supply from the short- circuited net cannot be expected. This is the reason why the external voltage supply must feature a back-up battery. With the protected construction of the measuring unit, it is possible to replace the battery (approx. every 10 years) without interrupting the high voltage.

Referring to fig. 5, the calculation circuit samples the signals a number of times per period, presently set at 20 times per period. The exact current I and voltage U, i.e. value and polarity, are read at each sampling. Due to the frequent samplings, it is possible to determine quite accurately when the zero-crossing (phase change) of the voltage takes place. Once the voltage polarity has been determined, it is possible to determine the sample numbers of a period to provide a comparison of the polarities of the current and the voltage.

In a preferred embodiment of the invention, the relative direction of the energy is determined by a simple mathematical multiplication of the polarities of the current and the voltage at a given point m time between the zero-crossings.

The detector will determine the direction of the energy flow when a high current level above a certain limit is detected. The polarity of the current is measured and subsequently compared with the polarity of the voltage (whether actually measured or simulated) and the energy direction is determined. One or more of the zero-crossings of the voltage or current can be simulated as well as measured.

Referring to fig. 6, the algorithm is designed m such a manner that once the voltage is above the positive noise limit, it is checked whether a zero-crossing has taken place immediately before that. If the preceding voltage

(from the preceding sampling) is below a positive noise limit, a closer examination is made. If the voltage is below the negative noise limit 4/20 periods earlier (4 samples ago), a zero-crossing has taken place.

The sample number for the exact zero-crossing point m time must now be somewhere between the current sample X and the 4/20 previously made sample X-4. If the value of the sample X-3 is below the negative noise limit, the zero-crossing is at X-l or X-2. Of the two samples, the sample closest to zero is chosen irrespective of the noise limit. If the value for X-3 is above the negative noise limit, X-2 is chosen as the zero-crossing value.

Despite the above-mentioned algorithm, there is still a minimal risk of the determination of the zero-crossing being incorrect m a noise-filled reading environment. This is the reason why the algorithm has a built-in phase-locked loop circuit so that two succeeding zero- crossing points may not deviate more than certain period (e.g. 4/20) from each other during their respective periods . With this algorithm, it is possible to make an accurate determination of the zero-crossing point in time irrespective of the noise level m the measuring system.

It is understood that the algorithm is capable of determining the zero-crossing at a negative to positive voltage crossing (illustrated m fig. 6) as well as a positive to negative crossing.

Those skilled m the art will appreciate that the present invention is not limited to the detection of an energy flow direction in the event of a fault on a high-voltage transmission and distribution system. Detection and indication of an energy flow direction in a normal working state is also possible as well as indication of an energy flow direction on other high-voltage systems involving an energy flow m a conductor.

Also a directional detector for low-voltage systems is possible, such as a portable detector for household cabling, making it possible to trace defects m the cabling causing a current which is higher than in a normal working state. The current and voltage detectors may preferably be of different types than the ones described above. Especially because of the low-current values, magnetic-resistant detectors may replace the hall elements m an advantageous manner. The method of measuring voltage with a capacitive detector may also advantageously be replaced by methods involving direct contact to the conductor. List

1. Generator

2. Transmission or distribution system consisting of underground cables or overhead lines

3. Electric consumers or loads

4. Directional indicators

5. Directional detectors

6. Electrical fault e.g. a short-circuit 10. Conductor

11. Capacitive detector

12. Capacitor

13. Reference potential e.g. ground potential

14. Electromagnetic field detector 15. First electromagnetic field detector element

16. Second electromagnetic field detector element

17. Calculating circuit

18. Directional indicator 20. Metal panel 21. Shield for electromagnetic field

22. Supply lines to the electromagnetic field detectors

23. Circuit board containing the calculation circuit

30. X-axis in degrees (°)

31. Y-axis in absolute values (U/U and I/I) 32. Noise level

U. Voltage I . Current Tr. Transformer Hv. High-voltage cable or line X, X-l, .... Samples of the X-axis

Claims

Patent Claims

1. Directional high-voltage detector for a high- voltage conductor (10) comprising

• at least one voltage-measuring circuit for measuring voltage m said conductor (10),

• at least one current-measuring circuit for measuring current m said conductor (10)

• and means for determining the energy flow n the conductor (10) on the basis of measurements made by said voltage-measuring circuit and said current- measuring circuit.

2. Directional high-voltage detector according to claim

1, cha r a ct e r i s e d i n that the voltage- measuring circuit comprises at least one capacitive detector (11) which forms a capacitive coupling with the conductor ( 10) .

3. Directional high-voltage detector according to claim

2, ch a ra ct e r i s e d i n that the capacitive detector (11) comprises a metal plate (20) covering a section of the conductor (10) partially or totally.

4. Directional high-voltage detector according to claim 3, ch a ra ct e r i s e d i n that the edges or corners of the plate are bent away from the conductor (10).

5. Directional high-voltage detector according to claim 1, c h a r a ct e r i s e d i n that the dielectric material between the metal plate (20) and the conductor

(10^ is silicone covering the surface of said detector partially or totally.

6. Directional high-voltage detector according to claim 5, cha r a ct e r i s ed in that the silicone layer serves as an isolation layer between the high-voltage potentials in said detector and the exterior, respectively .

7. Directional high-voltage detector according to claim 1, ch a r a ct e r i s e d i n that at least one capacitor (12) is connected serially to the capacitive coupling (11) and a reference potential (13), respectively.

8. Directional high-voltage detector according to claim 7, c h a r a ct e r i s ed i n that the reference potential (13) is the ground potential of at least one conductor .

9. Directional high-voltage detector according to claim 1, ch a r a ct e r i s ed i n that the current- measuring circuit comprises at least one detector (14) for measuring the magnetic field generated by the current in the conductor (10) .

10. Directional high-voltage detector according to claim 1, cha r a ct e r i s e d i n that the magnetic field detector (14) comprises two hall elements (15, 16).

11. Directional high-voltage detector according to claim 1, c h a r a ct e r i s e d i n that the supply lines for the magnetic field detector (15, 16) and the calculation circuit (17) comprise shields (21) against magnetic fields.

12. Directional high-voltage detector for a high- voltage conductor comprising

• at least one voltage-measuring circuit for measuring voltage in said conductor (10) by means of at least one capacitive detector (11),

• at least one current-measuring circuit for measuring current m said conductor (10) by means of at least one magnetic field detector (14, 15, 16),

• and means (17) for determining the energy flow in the conductor (10) on the basis of measurements by said voltage-measuring circuit and said current-measuring circuit .

13. Directional high-voltage detector according to claim 12, cha r a ct e r i s e d i n that said means (17) determine the energy flow direction on the basis of the polarities of the current and voltage between two preceding zero-crossings of the voltage.

14. Apparatus for measuring on a high-voltage conductor (10) comprising • at least one voltage-measuring circuit for measuring voltage in said conductor (10) by means of at least one capacitive detector (11),

• at least one current-measuring circuit for measuring current m said conductor (10) by means of at least one magnetic field detector (14, 15, 16)

• and means for determining the energy flow in the conductor (10) on the basis of measurements by said voltage-measuring circuit and said current-measuring circuit .

15. Apparatus for measuring on a conductor (10) comprising

• at least one current-measuring circuit for measuring current in said conductor (10) by means of at least one magnetic field detector (14, 15, 16)

16. Apparatus for measuring on a conductor (10) according to claim 15, cha r a ct e r i s ed in that the magnetic field detector (14) comprises at least one magnetic-resistant detector (15, 16).

17. High-voltage fault detector for a high-voltage conductor (10) wherein said detector comprises means for determining the direction of an energy flow in said conductor ( 10 ) .

18. Method for determining the direction of an energy flow n a high-voltage conductor wherein at least one voltage-measuring circuit measures voltage n said conductor by means of at least one capacitive detector, at least one current-measuring circuit measures current in said conductor by means of a magnetic field detector and a calculation circuit calculating a direction value derived from the measured voltage and current.

19. Method for determining the direction of an energy flow m a high-voltage conductor according to claim 18, cha r a ct e r i s e d i n that the calculation circuit calculates the direction value on the basis of the polarities of the current and the voltage between two preceding zero-crossings of the voltage.

20. Method for determining the direction of an energy flow n a high-voltage conductor wherein at least one current-measuring circuit measures current, at least one voltage-measuring circuit measures voltage, where a calculation circuit divides said voltage into a number of samples within a period of time and where said calculation circuit compares the first voltage sample value numerically larger than a constant value with the immediately preceding values to determine the sample value closest to zero voltage.

21. Method for determining the direction of the energy flow in a high-voltage conductor according to claim 20, ch a r a ct e r i s e d i n that the calculation circuit calculates the direction value on the basis of the polarities of the current and voltage between two preceding zero-crossings of the voltage.

22. Method for determining the direction of the energy flow m a high-voltage conductor according to claim 21, c h a r a c t e r i s e d i n that the constant value exceeds the noise level.