A partial discharge detection apparatus and method

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SPANISH OFFICE OF

PATENTS AND TRADEMARKS

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© Publication number: 2 733 744 © Int. CI .:

G01R 12/31 (2006.01)

TRANSLATION OF EUROPEAN PATENT

T3 @ Date of submission and number of the international application: 14.06.2012 PCT / EP2012 / 061274 (8?) Date and number of international publication: 19.12.2013 WO13185820 (96) Date of submission and number of the European application: 14.06. 2012 E 12730847 (6) (97) Date and publication number of the European concession: 03.04.2019 EP 2861999 © Title: Partial discharge detection device and procedure

<td>© Date of publication and mention in BOPI of the</td><td>@ Headlines:</td>

<td>Patent translation: 02.12.2019</td><td>PRYSMIAN SPA (100.0%) Via Chiese, 6 20126 Milano, IT</td>

<td></td><td>@ Inventor / es:</td>

<td></td><td>CANDELA, ROBERTO; DI STEFANO, ANTONIO; FISCELLI, GIUSEPPE and GIACONIA, GIUSEPPE COSTANTINO</td>

<td></td><td>© Agent / Representative:</td>

<td></td><td>CARPINTERO LÓPEZ, Mario</td>

ES 2 733 744 T3

Notice: Within nine months from the date of publication in the European Patent Bulletin, of the mention of granting the European patent, any person may object to the European Patent Office to the granted patent. The opposition must be in writing and be motivated; It will only be considered as formulated once payment of the opposition fee has been made (art. 99.1 of the

Convention on the Granting of European Patents).

ES 2 733 744 T3

DESCRIPTION

Device and partial discharge detection procedure

Background

Technical field

The present invention relates to partial discharge detection techniques. The detection of partial discharges is particularly used to detect and measure partial discharges in electrical components and appliances, such as: medium or high voltage cables, cable connections, overhead line insulators, medium and high voltage distribution box boxes, High and extra high voltage cables that use GIS (Gas Insulated Switches).

Description of the related technique

The term partial discharges is intended to indicate an unwanted recombination of electrical charges that occur in the dielectric material (insulator) of electrical components, when the latter have defects of various types, which eventually leads to dielectric destruction. Here, a pulse current is generated in portions of dielectric material and causes an electromagnetic wave to propagate through the power or ground wires of the relevant electrical system, and radiate through the various surrounding means (dielectric material , metals, air, etc.).

WO-A-2009-150627 describes, among other things, a small-sized, fully isolated and self-powered partial discharge detection device, which allows measurements to be made with maximum safety without the need for direct connection to the system under exam. The device comprises a broadband antenna adapted to act as an electric field sensor and includes a first flat conductor (i.e. a base plane) that cooperates with a second conductor whose profile converges towards the first flat conductor at a point or one line, said second conductor is smaller by approximately two orders of magnitude than the field wavelength to be detected, so that the broadband antenna does not resonate in a band of approximately 0.1 MHz to approximately 100 MHz. For example, the second conductor has the shape of a hollow sphere. An electronic broadband amplifier can be used to adjust the antenna impedance and amplify the captured signals for the detection of weak signals. The broadband amplifier has a minimum band that falls in a range of about 0.5 MHz to 60 MHz. Out-of-band filtering is done using first-order or second-order filters that have a cutoff frequency of a few tens of MHz.

The applicant has noted that a considerable amount of ambient noise is also received when performing a wireless and contactless detection; this noise can be louder than the small impulse signals generated in an electrical component by partial discharge, which reduces the accuracy of the detection procedure.

Document US7183774 discloses a partial discharge detection method in an electrical apparatus that employs a UHF antenna placed in the apparatus receptacle. The procedure consists in analyzing the spectrum of the electromagnetic signal captured by the antenna and identifying in the spectrum one or more frequencies of interest. To identify the frequency of interest, the spectrum of the signal received by the antenna is compared with a reference spectrum. The procedure includes a stage in which the difference in amplitude between the two spectra is calculated for the maximum peak values ​​and for the average values ​​of the two spectra available at each frequency.

JP-A-07-027814 describes an insulation monitoring device for electrical energy equipment that monitors the isolated state of electrical equipment when monitoring corona discharge generation. The device consists of a corona detection antenna that detects the electromagnetic waves generated when the corona discharge occurs in the power equipment, a noise detection antenna that detects external noise waves. In addition, the device is also provided with a signal processing circuit to eliminate the noise signals contained in the signal for corona detection. The processing circuit consists of two amplifiers and a differential amplifier.

Brief summary of the invention.

The Applicant has noted that the technique described in JP-A-07-027814 does not guarantee satisfactory noise cancellation. The applicant has addressed the problem of designing a partial discharge detection apparatus that employs an antenna to capture partial discharge signals that allows the detection of partial discharge pulses having an amplitude comparable to the amplitude of the noise signals received in the same antenna.

The applicant found that two antennas placed (in remote or near positions) such that one antenna shows a respective effective area smaller than the effective area of ​​the other antenna for supposed incoming directions of partial discharge signals could provide satisfactory values ​​of the signal ratio

ES 2 733 744 T3 at S / N noise. In particular, the antenna signal oriented towards the supposed partial discharge source is subtracted from the second antenna signal.

Document US2008 / 0288189 discloses a system for identifying an electric arc event in an electrical distribution equipment comprising a first antenna for detecting radio frequency signals having the characteristic of radio frequency arc and a second antenna for detecting radio frequency signals with characteristics of radio frequency noise. The system disclosed by the aforementioned document includes a signal processor to extract the radio frequency characteristic of the detected signals. The document “Optimization of a sensor for Onsite Detection of Partial Discharges in Power Transformers by the UHF Method”, J. Lopez-Roldan et al., IEEE transactions on dielectrics and electrical insulation, Vol. 15, No. 6. one December 2008, pages 1634-1639, describes the tests of a group of selected antennas carried out in a power transformer that simulates the broadband signals generated by the partial discharge.

According to a first aspect, the present invention relates to a partial discharge detection apparatus comprising:

a first antenna configured to receive electromagnetic signals associated at least partially with partial discharges of an electrical object and to generate a first electrical signal; the first antenna having a first effective reception area for the first reception addresses;

a second antenna configured to receive electromagnetic noise signals and to generate a second electrical signal; the first and second antennas being arranged to make the second antenna have a second effective reception area for said first reception addresses smaller than said first effective reception area; and a first processing module configured to receive said first and second electrical signals and to generate an electrical signal difference that represents the difference between the first electrical signal and the second electrical signal.

Advantageously, at least one of the first antenna and the second antenna is a directional antenna. Preferably, both the first and second antenna are directional antennas.

Advantageously, the first and second antenna are placed in a shared support structure. The shared support structure may be a portion of one of the first or second antenna.

Preferably, in the apparatus of the invention, the first antenna has a third effective area for second receiving addresses, different from said first receiving addresses; and the second antenna has a fourth effective area for the second receiving directions, said fourth effective area being equal to or larger than the third effective area. In this way, the second antenna is more sensitive to noise than the first antenna.

Preferably, in the apparatus of the invention, the first antenna is arranged, for example, on a support structure, so that it has at least 90% of the power received in a first radiation pattern included in a first half-space ; and the second antenna is arranged, for example, in the same support structure, to have at least 90% of the power received in a second radiation pattern included in a second half space opposite the first half-space with respect to a plane of reference that separates the first semi-space from the second semi-space.

More preferably, the first antenna is arranged, for example, in a support structure, to show the maximum values ​​of the respective reception gain for the incoming addresses that are in the first half-space, and the second antenna is arranged, for example, structured and mounted on the same support structure, to show the maximum values ​​of the respective reception gain for the additional input addresses found in the first half-space.

In the event that both the first and second antenna are directional and have substantially non-overlapping reception diagrams, the first antenna preferably includes a first antenna conductor and a flat conductor configured to operate as a base plane for the first antenna conductor. .

Preferably the first antenna has a spherical shape.

Preferably, the second antenna is a patch or loop antenna.

In an embodiment of the present invention, the shared support structure of the apparatus of the invention comprises a flat part that includes: a first side on which the first antenna conductor is mounted and a second side opposite the first side on which said Second antenna conductor is mounted.

Preferably, the support structure comprises a printed circuit board that includes the first processing module.

ES 2 733 744 T3

Preferably, the printed circuit board comprises electrical terminals connected to the first antenna and the second antenna, and a support element that mechanically connects the first antenna conductor to the printed circuit board.

Preferably, the first processing module of the apparatus of the invention comprises a difference module configured to generate said electrical difference signal. The difference module can be selected from an active electronic component, a voltage transformer or a voltage transformer with central socket.

In the presence of a difference module, the first antenna is structured to detect by means of capacitive coupling an electrical synchronization signal that represents the trend of the electrical voltage supplied to the electrical object.

Advantageously, the apparatus of the invention further includes a synchronization module configured to amplify said electrical synchronization signal and provide an amplified electrical synchronization signal.

In a preferred embodiment, said first processing module further comprises a first high-pass filtering module connected to the first antenna, and a second high-pass filtering module connected to the second antenna, the first and second modules being configured. high pass filtering to decouple the electrical synchronization signal from said first and second electrical signals.

In the event that the difference module is an active electronic component, said active electronic component comprises an operational amplifier in a negative feedback configuration without inversion. The operational amplifier advantageously comprises a non-inverting terminal configured to receive said first electrical signal; an inverter terminal configured to receive said second electrical signal; and an output terminal configured to provide the electrical signal difference that represents the difference between the first electrical signal and the second electrical signal.

In another embodiment of the invention, the apparatus further includes an acquisition and analysis device comprising: a digital to analog converter structured to produce from the electrical signal difference a plurality of corresponding samples; an acquisition activation module to select acquisition samples of said plurality of samples; a memory configured to store the selected acquisition samples; a structured processor to generate command signals that will be sent to the acquisition activation module and to memory.

Preferably, the measurement module is structured to receive the amplified synchronization electrical signal from a synchronization module and to provide electrical parameters to the processor.

The acquisition and analysis device preferably further includes a structured transceiver module for sending / receiving data / command to / from an external processor module.

In a preferred embodiment, the apparatus of the invention has the first antenna configured to receive signals that have a frequency included in the range of 0.1 MHz to 100 MHz and the second antenna configured to receive signals that have a frequency included in the range from 0.1 MHz to 100 MHz.

In another aspect, the present invention relates to a partial discharge detection method, comprising:

place a first directional antenna to have a first effective reception area for the first reception addresses;

receiving at least partially associated electromagnetic signals from the first antenna with partial discharges of an electric object;

generate by the first antenna a first electrical signal corresponding to the electromagnetic signals received;

placing a second directional antenna to have a second effective reception area for said first reception addresses smaller than said first effective reception area;

receive electromagnetic noise signals on the second antenna;

generate by the second antenna a second electrical signal corresponding to said received electromagnetic noise signals;

processing said first and second electrical signals to produce a difference electrical signal that represents a difference between the first electrical signal and the second electrical signal.

In the present description and the claims, "directional antenna" means an antenna that radiates or receives electromagnetic waves more effectively in some directions than in others. In particular, as

ES 2 733 744 T3 "directional antenna" means an antenna with a Front / rear ratio greater than 0 dB, preferably greater than 1 dB. The Front / Rear parameter, expressed in decibels, is the ratio between the gain parameter associated with the main lobe of the radiation pattern and the gain parameter associated with the opposite lobe of the radiation pattern. The gain parameter of an antenna is the ratio of the power produced by the antenna from a far-field source on the axis of the antenna beam to the power produced by an isotropic antenna without hypothetical losses, which is equally sensitive to signals. of all addresses.

In the present description and the claims, with reference to the antenna, as "signal reception address" or "signal input address" refers to the direction from which the signals are supposed to come.

In the present description and the claims, "effective area" of an antenna is understood as a measure of how effective an antenna is when receiving the power of electromagnetic waves in each input direction. The effective area of ​​an antenna depends on another parameter that characterizes the behavior of the antenna, which is the directivity of the antenna. In the present description, the terms "effective area" and "directivity" will be used as alternative parameters that characterize the ability to receive energy from the particular input direction of an antenna.

Brief description of the drawings

Other features and advantages will be more apparent from the following description of a preferred embodiment and its alternatives given by way of example with reference to the accompanying drawings in which:

Figure 1 shows an embodiment of a partial discharge acquisition system comprising a first antenna, a second antenna and a difference module;

Figure 2 schematically shows an active electronic component usable by said difference module;

Figure 3 schematically shows a primary voltage transformer with central socket that can be used by said difference module;

Figure 4 shows a first radiation diagram of the first antenna and a second radiation diagram of the second antenna;

Figure 5 is an embodiment of the difference module employing an operational amplifier;

Figure 6 shows an embodiment of a synchronization module included in said partial discharge acquisition system;

Figure 7 shows an embodiment of the acquisition and analysis device included in said partial discharge acquisition system;

Figures 8A and 8B show two different views of a particular embodiment of said partial discharge acquisition system;

Figure 9 shows the experimental results obtained with the partial discharge acquisition system of Figures 8A and 8B.

Detailed description

Figure 1 shows an electric object 100 and a partial discharge acquisition system 500 comprising a partial discharge detection apparatus 400 and an optional acquisition and analysis device 300.

The electric object 100 can be any type of component, device, apparatus or system that can produce electromagnetic pulses of partial discharge and is, for example, a medium or high voltage cable, a cable joint, an overhead line insulator, a medium and high voltage distribution box box, a high and extra high voltage cable that uses GIS (Gas Insulated Switches), an electric motor or generator or a medium or high voltage transformer.

The partial discharge acquisition system 500 is an electronic device that can be used to detect, measure and / or analyze partial discharges generated by electrical sources such as electrical object 100. In particular, the partial discharge acquisition system 500 may be portable and is included in a case not shown in the figures.

The partial discharge acquisition system 500 is configured to be placed near the electric object 100 to receive, in a wireless and contactless mode, electromagnetic discharge signals Sd corresponding to the partial discharge pulses emitted by the electric object 100. It is also noted that the electromagnetic Sn noise signals that could disturb the detection of the electromagnetic signals

ES 2 733 744 T3 corresponding to the partial discharge pulses may be present in the area in which the partial discharge acquisition system 500 is used.

The discharge signals Sd to be detected may be pulses of electromagnetic waves having frequencies included in the range of 0.1 MHz to 100 MHz. Sn noise signals normally have frequencies included in the same range of 0.1 MHz to 100 MHz .

The partial discharge detection apparatus 400 (hereinafter also referred to as "detection apparatus", for reasons of conciseness) comprises a first antenna 1 and a second antenna 2 that can be mounted, for example, on a shared support structure 3 , according to a first embodiment of the invention. The first antenna 1 is configured to receive the Sd discharge signals, but can also receive unwanted electromagnetic Sn noise signals.

In greater detail, with reference to a first set of radiation input directions, the first antenna 1 is structured to show a first effective area Aeff-i having a first Aeff1-dr1 value or values. In particular, the first set of incoming addresses corresponds to the incoming addresses of the download signals Sd.

The second antenna 2 is configured to receive the electromagnetic noise signals Sn present in the area in which the partial discharge acquisition system 500 is used. In some cases, the second antenna 2 may also receive discharge signals Sd. However, the second antenna 2 is structured to show a second effective area Aeff2 which, for said first set of incoming radiation directions, has a second value or Aeff2-dr1 values ​​that is smaller than said first Aeff1_dri value of the first antenna one:

Aeff1-dr1> Aeff2-dr1 (1)

In particular, the first Aeff1-dr1 value is at least ten times the second Aeff2-dr1 value.

The ratio (1) for the first set of incoming radiation directions means that the first antenna 1 is more sensitive to the discharge signals Sd than the second antenna 2.

With reference to a second set of incoming radiation directions, the first antenna 1 shows a first effective area Aeff-ι that has a third value or Aeff1-dr2 values ​​and the second antenna 2 shows a second effective area Aeff2 that has a fourth value or Aeff2-dr2 values. In particular, the second set of incoming addresses corresponds to the incoming addresses of the electromagnetic noise signals Sn.

According to a particular embodiment, the partial discharge detection apparatus 400 is configured so that the following relationship is valid for the first and second antenna 1 and 2, with reference to the second set of incoming addresses:

Aeff2-r2 Aeff1-dr2 (2)

According to the relation (2), the fourth value / s Aeff2-dr2 is equal to or greater than the third value / s Aeff1-dr2. In particular, the fourth Aeff2-dr2 value is at least ten times the third Aeff1-dr2 value / s.

The ratio (2) for the second set of incoming radiation directions means that the second antenna 2 is equal to or more sensitive to the electromagnetic noise signals Sn than to the first antenna 1.

According to a first example, the first antenna 1 and / or the second antenna 2 are directional antennas.

Particularly, the first antenna 1 and the second antenna 2 show different three-dimensional radiation patterns. Particularly, the partial discharge detection apparatus 400 is designed such that the first antenna 1 can provide a sensitive and precise detection of the discharge signal Sd, whereby the first antenna 1 is designed to obtain that the first effective area Aeff-ι show a higher value for the first set of incoming addresses.

In addition, the partial discharge detection apparatus 400 is designed in such a way that the second antenna 2 can provide the detection of the noise signals Sn, whereby the second antenna 2 is designed to obtain that the second effective area Aeff2 shows the higher value for the second set of incoming addresses.

Preferably, the first antenna 1 has a directivity having a Front / rear parameter between 3 and 30 dB; more preferably, the Front / rear parameter is between 6 dB and 10 dB. The second antenna 2 has a directivity that has a Front / rear parameter greater than the Front / rear parameter of the first antenna 1 and, preferably, between 10 and 30 dB; more preferably, the Front / rear parameter of the second antenna 2 is between 11 and 20 dB.

As an example, the first antenna 1 can be one of the following antennas: small patch antenna, loop antenna, dipole and ultra-wideband antenna. A particular spherical antenna that can be used as the first antenna 1 will be described below.

ES 2 733 744 T3

The second antenna 2 can be, for example, a patch antenna, a loop antenna, a dipole, an ultra-wide band antenna or a spherical antenna analogous to the first antenna 1. According to the first embodiment represented in FIG. 1, the partial discharge detection apparatus 400 further comprises a difference module 600 having a first input terminal 4 connected, by means of a first conductive line 5, to a first terminal 6 output of the first antenna 1 and a second input terminal 7 connected, by means of a second conductive line 8, to a second output terminal 9 of the second antenna 2.

In addition, the first antenna 1 is configured to receive the discharge signals Sd and the unwanted noise signal Sn and convert them into a first received electrical signal Sn (for example, an electrical current) available on the first conductive line 5. The second antenna 2 is configured to receive the noise signal Sn and also a part of the discharge signals Sd and convert them into a second electrical signal Sin2 received (for example, an additional electrical current) available on the second conductive line 8.

Figure 4 shows, as an example, a first radiation diagram RD1 of the first antenna 1 and a second radiation diagram RD2 of the second antenna 2, such as when the first antenna and the second antenna 2 are positioned to operate for detection. In particular, Figure 4 shows a vertical section of a first radiation pattern of the first antenna 1 and another vertical section of a second radiation pattern of the second antenna 2. A vertical section is a section between a vertical plane, as an example, a plane perpendicular to the ground surface and the respective pattern. As is clear to the person skilled in the art, the radiation pattern of an antenna is substantially identical to the reception pattern of the same antenna. According to the example shown in Figure 4, the first RD1 diagram is substantially in a first semi-space, while the second RD2 diagram is substantially in the opposite semi-space, with respect to a reference plane, by example, parallel to a soil surface.

In particular, the first radiation pattern of the first antenna 1 and the second radiation pattern of the second antenna 2 do not substantially overlap each other, and particularly, the first antenna 1 shows the maximum values ​​of the reception gain for the directions incoming that are in the first semi-space (to be oriented towards the expected partial discharge source). The second antenna 1 shows the maximum values ​​of the reception gain for the incoming addresses that are in the second half-space that is opposite the first half-space.

Preferably, the first antenna 1 is arranged on the support structure 3 to have at least 90% of the power received from the first radiation pattern included in the first half-space, and the second antenna 2 is arranged on the structure 3 of support to have at least 90% of the power received from the second radiation pattern included in a second half-space opposite the first half-space. As an example, the first antenna 1 and the second antenna 2 show a Front / rear parameter of 20 dB and, in particular, are oriented in different and preferably opposite directions.

The difference of the module 600 of Figure 1 is configured to generate a difference Sout output signal that represents a difference between the first electrical signal Sn received and the second electrical signal Sin2 received. The difference module 600 is provided with a third output terminal 10 for the difference output signal Sout.

According to an example shown in Figure 2, the difference module 600 may comprise an active electronic device, such as an operational amplifier 11 or other type of discrete electronic active component, adapted to generate the difference output signal Sout. A particular embodiment of the difference module 600 employing the operational amplifier 11 will be described below.

According to another example shown in Fig. 3, the difference module 600 may comprise a passive electronic device, such as an electric transformer 11, adapted to generate the output signal Sout difference. The electric transformer 12 is a high frequency transformer. According to the example shown in Figure 3, the high frequency transformer 12, which is in a configuration with a central outlet, includes a first winding 13 having two end terminals adapted to receive respectively the first received electrical signal Snn1 and the second electrical Sin2 signal received and a central terminal 15 connected to an electrical grounding terminal GND. A second winding 14 of the high frequency transformer 12 is mutually coupled with the first winding 13 and is provided with a difference signal terminal 40 for the difference output signal Sout and a grounding terminal GND connected to the power supply. electric ground

In accordance with the embodiment shown in Figure 1, the partial discharge detection apparatus 400 may also be provided with a synchronization module 200 that is configured to receive a first electrical synchronization signal Ssyn1 at a third input terminal 16 and provide to a fourth output terminal 17 a second electrical synchronization signal Ssyn2. The first electrical synchronization signal Ssyn1 represents the behavior of the AC electrical voltage (alternating current) supplied to the electrical object 100 under test and can be obtained, in accordance with one embodiment, by a wireless and contactless detection performed by the first antenna 1 of an electromagnetic supply Ssup signal generated by the electrical voltage that passes through the electrical object 100. According to this embodiment, the third input terminal 16 is connected to the first connection line 5 to receive the first received electrical signal Sn, which also includes the first electrical synchronization signal Ssyn1 and, in particular, the first antenna 1 is designed to function as a sensor

ES 2 733 744 T3 capacitive coupling to detect the first electrical Ssyni signal synchronizing the electromagnetic supply Ssup signal. In this case, the first antenna 1 is designed to offer a suitable capacitive coupling with the AC electric voltage (Alternating Current) that feeds the electric object 100, showing, as an example, a suitable coupling surface.

According to another embodiment, the first electrical synchronization signal Ssyn1 can be detected by a synchronization sensor 18 connectable to the third input terminal 16, such as an additional antenna for wireless and contactless detection, or another type of sensor to be placed. in contact with the electric object 100 or with another electrical component that operates at the same electrical voltage supplied to the electric object 100.

With reference to the difference module 600, according to another embodiment, it can also be structured to properly handle the first received electrical signal Sn and the second received electrical signal Sin2, so that it can also comprise a high-pass filtering module and a Optional equalization module placed before operational amplifier 11 or electrical transformer 12.

Figure 5 refers to an example of the difference module 600 in the case in which the operational amplifier 11 is used. The difference module 600 comprises a first high-pass filtering module 19 having a respective input connected to the first input terminal 4. As an example, the first high pass filter module 19 may include a first capacitor C1 connected in series with a first resistor R1. An output of the high pass filter module 19 is connected to a first optional equalization module 20 which is also connected to a non-inverting terminal "+" of the operational amplifier 11 through a first node 25. The first node 25 is connected to a third resistor R3 that is also connected to the GND grounding terminal.

The difference of the module 600 of Figure 5 also comprises a second high-pass filter module 21 having a respective input connected to the second input terminal 7. As an example, the second high-pass filter module 21 may include a second capacitor C2 connected in series with a second resistor R2. The first and second high pass filter modules 19 and 21 are structured to decouple the first electrical synchronization signal Ssyn1, at a lower frequency, from the first and second electrical signals Snn1 and Sin2, respectively.

An output of the second high-pass filter module 21 is connected to a second optional equalization module 22 which is also connected to an inverting terminal "-" of the operational amplifier 11 through a second node 26. The operational amplifier 11 is provided with: a first supply terminal 32 for a supply voltage VI, a second supply terminal 33 connected to a grounding terminal GND and the fifth output terminal 24 for the differential output signal Sout , which can be a Vout output voltage. The fifth output terminal 24 is connected to the third output terminal 10 by an output resistor Rout.

The output voltage Vout is given by the difference in voltages applied to the non-inverting terminal "+" and to the inverting terminal "-" multiplied by a gain factor Aop of the operational amplifier 11. Particularly, the operational amplifier 11 is configured to show a bandwidth that includes at least the bandwidth of the first antenna 1, such as an example, a bandwidth ranging from 0.1 MHz to 100 MHz. The operational amplifier 11 may include one or more differential amplifiers, each performed by means of pairs of transistors in differential configuration. A plurality of amplification steps may be included in the operational amplifier 11 to achieve a desired amplifier gain. The first resistor R1, the second resistor R2 and the feedback resistor Rf show values ​​of the respective resistors that can be chosen to design the gain factor Aop of the operational amplifier 11 and to match the impedances of the first antenna 1 and the second antenna 2, respectively.

Furthermore, according to a particular embodiment, the operational amplifier 11 is in the non-inverting negative feedback configuration and a feedback resistance Rf is connected between the fifth output terminal 24 and the second node 26 connected in turn to the inverter terminal " - ” The negative feedback configuration allows predictable behavior of the difference module 600 to be obtained. The first equalizer 20 and the second equalizer 21 can be used to compensate for a possible difference in the frequency responses of the first antenna 1 and the second antenna 2.

In operation, the first antenna 1 is used simultaneously with the second antenna 2. The first antenna 1 collects, according to its effective area diagram, the discharge signal Sd, the contribution of the noise signal Sn and the electromagnetic signal Ssup supply and generates the first electrical signal Sn received. The second antenna 2 collects, according to the respective effective area diagram, the noise signal Sn and part of the discharge signal Sd and generates the second electrical signal Sin2 received. The second antenna 2 can also pick up the electromagnetic power Ssup signal.

The first electrical signal S1n1 received and the second electrical signal Sin2 received are sent to the difference module 600. With reference, for example, to the embodiment of Figure 5, the first electrical signal S1n1 received and the second electrical signal Sin2 received are filtered respectively by the first high-pass filtering module 19 and the second filtering module 21 High pass. The optional first and second equalization modules 20 and 22

ES 2 733 744 T3 act on the first electrical signal S¡ni received and the second electrical signal S¡n2 received to equalize the frequency response difference of the first and second antennas 1 and 2 and obtain a first input signal Si and a second signal S2.

It is noted that thanks to the conditions described above on the effective areas of the first antenna 1 and the second antenna 2, the first input signal S1 carries a contribution of discharge signal Sd greater than the contribution of discharge signal Sd carried by the second input signal S2 substantially representing the contribution of noise Sn.

The first input signal S1 is fed to the non-inverting terminal "+" and the second input signal S2 is fed to the inverting terminal "-" of the operational amplifier 11. The operational amplifier 11 makes a difference between the first input signal S1 and the second input signal S2 generating the different output signal Sout in which the noise contribution is substantially reduced or eliminated. The operational amplifier 11 allows subtracting the noise contribution present in the second input signal S2 from the first input signal S1.

Figure 6 shows an embodiment of the synchronization module 200 comprising an amplifier module 27, such as a high gain buffer amplifier, having an input connected to the third input terminal 16 and a sixth output terminal 28 connected to a module 29 low pass filter. The high gain buffer amplifier 27 is also provided with a third supply terminal 30 for the supply voltage VI and a fourth supply terminal 31 connected to the grounding terminal GND. As an example, the high gain buffer amplifier 27 is a voltage amplifier and has a gain greater than 100. In addition, the high gain buffer amplifier 27 shows an input-output impedance> 1 MOhm and can have a total bandwidth of less than 1 kHz. The low pass filter module 29 includes, as an example, a fourth resistor R4 connected between the sixth output terminal 28 and a third node 34 and a third capacitor C3 connected between the third node 28 and the grounding terminal gNd. The third node 34 is connected to the fourth output terminal 17.

The acquisition and analysis device 300 may be included in a housing that also contains the partial discharge detection apparatus 400 or may be included in a separate housing. Figure 7 schematically shows an embodiment of the acquisition and analysis device 300 comprising an optional programmable broadband amplifier 71 (PGA) having an input connected to the third output terminal 10 of the difference module 600 and a respective output connected to a 72 analog to digital converter. The acquisition and analysis device 300 also includes a control module 73, such as a programmable field gate array (FPGA) that is structured to control the programmable broadband amplifier 71 and receive data from the analog to digital converter 72 (ADC) . The programmable broadband amplifier 71 can be programmed to impart a compensation value and an amplification gain value to the output signal Sout by means of the compensation signal Sf and a gain signal S_Qa provided by the control module 73, producing a Saout amplified output signal.

The programmable broadband amplifier 71 allows, for example, a continuous gain variation ranging from about -5 dB to +40 dB. The analog-to-digital converter 72 is structured to be synchronized by a clock signal CK generated by the control module 73 and generate converted DTA data to be sent to the control module 73. The analog-to-digital converter is, for example, capable of converting 250 mega-samplers per second with a resolution of 8 bits. This sampling frequency allows to acquire the difference of electrical Sout signal with a time resolution of 4 ns. It is observed that most of the partial discharge pulses are usually longer than 0.5 ps, the acquisition and analysis device 300 allows to acquire the pulse waveform and represent it with a number of samples between 100 and 200.

In particular, the control module 73 includes a processing unit (PU) 74, such as a microprocessor, and a memory 75 (M), such as a RAM (random access memory). More particularly, memory 75 may be a circular buffer. The processing unit 74 is connected to: a timing module 77 (TM) and a logic synchronization module 76 (SINL) configured to receive the second electrical synchronization signal Ssyn2. The logic synchronization module 76 is structured to measure the phase of the second electrical synchronization signal Ssyn2 and transfer this measured value to the processing unit 74.

In addition, an input / output port 77 allows the output Comm commands generated by the processing unit 74 to be transferred to the programmable broadband amplifier 71 in the form of the Soft compensation signal and the gain signal Sga. The control module 73 is also provided with an activation module 78 (TRLM) and an address generation module 79 (ADD-GEN) configured to generate the addresses necessary to write new data into memory 75 and read the stored data. in memory 75, under the control of the processing unit 74.

The activation module 78 is configured to activate the memorization of samples of the Saout amplified output signal that comes out of the programmable broadband amplifier 71 only for selected values ​​of the Saout amplified output signal, for example, only for positive pulses or negatives that have amplitude (that is, an absolute value) greater than a threshold level. The logic activation module 78 may be a logic module comprising one or more analog comparators for comparing the values ​​of the samples provided by the analog to digital converter with one or more thresholds.

ES 2 733 744 T3

In addition, the control module 73 comprises a host interface module (INTF) 80 that allows data transfer to a transceiver 81 (TR), as an example of a US / Ethernet transceiver, which is configured to exchange data / commands with another processor 82 (as an example, external to the acquisition system 500) via a BD or wireless cable connection line. The external processor is configured to perform the processing and analysis of the received data, which allows, for example, the representation of the discharge pulse behavior on a monitor or the memorization for further processing and consultation.

The control module 73 can also be provided with an extraction module 83 (for example, a CO-P coprocessor) connected to the processing unit 74 that is configured to perform the extraction, in particular, real-time extraction of the characteristics of the data store pulse in memory 79. Examples of possible pulse characteristics extracted by the coprocessor are: peak value and polarity, phase, energy, duration and approximate estimation of Weibull parameters.

In the operation of the control module 73, the acquisition is initiated and the processing unit 74 generates a signal that activates the activation module 78 that produces an activation signal that allows the storage of the selected samples, reading the phase angle of Saout amplified output signal samples with respect to the second synchronization signal Ssyn2. The collected data can be sent to the external processor 82.

The partial discharge acquisition system 500 may also include one or more batteries to supply electrical voltage to the modules described above.

Figures 8A and 8B show two different views of a preferred embodiment of the partial discharge acquisition system 500 made by the applicant and comprising particular embodiments of the first antenna 1, the second antenna 2 and the support structure 3. In more detail, the first antenna 1 is a directional antenna and, in particular, is a non-resonant broadband antenna comprising a first antenna conductor 90 and a flat conductor 91 that acts as a base plane. The first antenna conductor 90 is electrically insulated from the flat conductor 91 and the poles of the first antenna 1 operate. Particularly, the first antenna conductor 90 is spherical in shape and includes a hollow sphere in an electrically conductive material such as, for example, a metal or polymer material. The first spherical antenna conductor 90 shows, as an example, a diameter between 3 and 30 cm, preferably between 5 and 20 cm.

The first antenna conductor 90 is supported by an insulated support 93 that is fixed in the support structure 3 which, according to the example, is a printed circuit board (PCB) that includes electronic circuits corresponding to the difference module 600, the synchronization module 200 and the acquisition and analysis device 300. The base plane 91 is placed on a first side of the support structure 3 that faces the antenna conductor and is implemented as a metallic laminate.

According to the example made, the second antenna 2 comprises a respective base plane, which can be the same base plane 91 of the first antenna 1, and a second antenna conductor 94. Second antenna conductor 94 is an electrically small antenna, designed to obtain electrical characteristics similar to those of the first antenna conductor 90 and not be resonant in the band of interest. In particular, the second antenna conductor 94 may be a small dipole, loop or spiral antenna. In the embodiment represented in Figures 9A and 9B, the second antenna conductor 94 is a patch antenna made on a second side of the support structure 3 opposite the first side. According to one example, patch antenna 94 is realized as a copper area covering between 14 and 12 of the support structure 3 that also acts as a printed circuit board, when using a 1.6 mm FR4 laminate thick to make the printed circuit board 3. This provides electrical characteristics similar to those of the first antenna conductor 90. The printed circuit board 3 is provided with electrical terminals on both sides to contact the first antenna conductor 90 and the second antenna conductor 94.

The embodiment shown in Figures 8A and 8B allows a very compact and robust implementation, ensures an appropriate complementary radiation pattern and does not affect the frequency response of the first conductor antenna 90, so it does not distort the partial discharge Sd pulses received Due to the presence of the base plane, the radiation pattern of the first and second antenna 1 and 2 is directional as shown in Figure 4, so it extends to opposite semi-spaces. This provides exposure and sensitivity for the partial Sd discharge signal and for the Sn ambient noise of the first antenna 1 and the second antenna 2, respectively, which show good yields.

In accordance with further embodiments, the first antenna conductor 90 may also have another two-dimensional or three-dimensional shape, such as a flat shape, for example: triangle shape, cusp shape or disk shape. The first antenna conductor 90 may be analogous to the antenna described in patent application WO-A2009-150627.

Figure 9 shows the result of a test performed with a partial discharge acquisition system 500 implemented in accordance with the embodiment described with reference to Figures 8A and 8B. The experimental configuration used a simulated partial discharge source, performed with an arbitrary waveform generator AFG3102 from Tektronix, configured to generate a regular pattern of pulse signals (period 1 us,

ES 2 733 744 T3 rise / fall time 10/20 ns), connected to a 10 cm long dipole antenna. The first antenna 1 used for this experiment included a first spherical shaped antenna conductor 90, with a diameter of 7 cm.

The partial discharge acquisition system 500 was placed approximately 20 cm from the simulated PD source, the first antenna 1 pointing towards it. The test was performed in a very noisy environment due to the presence of switching converters and motors.

A Tektronix DSO3034 digital oscilloscope (four channels, 350 MHz bandwidth) was connected to the first output terminal 6 and the second output terminal 9 of each of the first and second antennas and the third output terminal 10 to receive the signal Sdiff electric difference.

The three resulting waveforms are shown in Figure 9: the upper Wn waveform is the output of the second antenna 2, the central Wpd waveform is the output of the first antenna 1, the lower Wd waveform is the output of the partial discharge acquisition system 500. It can be seen that both the first and second antennas 1 and 2 receive strong bursts of noise (more than 200 mVpp), considerably larger than the received PD pulses. As expected, the PD pulses are not visible in the waveform Wn received from the second antenna 2 (upper waveform) due to its directivity, while they can be recognized in the first waveform Wpd of the antenna, relatively hidden by noise. It can be seen that noise bursts are detected in the same way by both antennas. As can be seen, the difference waveform Wd taken at the output of the partial discharge acquisition system 500 instead has a much improved signal / noise ratio, in fact, the PD pulses are clearly visible and the noise is very attenuated ( observe the vertical scale of 20 mV).

With reference to a further embodiment of the partial discharge detection system 500, the first antenna 1 and / or the second antenna 2 can be external to a portable case that includes the partial discharge detection apparatus 400 and respectively connected to the module 600 of it differs by the first connection line 5 and the second connection line 9 which are corresponding electrical cables. According to this embodiment, at least one of the first antenna 1 and the second antenna 2 are directional antennas.

Preferably, the first antenna 1 is housed in the case comprising the partial discharge detection apparatus 400 as shown in Figure 1, while the second antenna 2 is external to the partial discharge detection apparatus 400 and can be moved to orient adequately. According to this preferred embodiment, the second antenna 2 is a directional antenna having, as an example, the second radiation diagram RD2 shown in Figure 4.

According to this preferred embodiment, the partial discharge detection apparatus 400 is positioned to orient the first antenna 1 towards the electric object 100 to receive the partial Sd discharge signal, thus showing a first effective reception area for the input addresses. of the partial Sd discharge signal. The second mobile antenna 1 is oriented to receive the electromagnetic noise signal Sn and to show a second effective reception area for the input addresses of the partial discharge signal Sd, which is smaller than said first effective reception area. The first antenna 1 is oriented to be more sensitive to the partial discharge signal Sd than the second antenna 2. The second antenna 2 is oriented to be more sensitive to the electromagnetic noise signal Sn than the first antenna 1. The possibility of moving the second antenna 2 makes it possible to reduce the amount of power of the partial Sd discharge signal received by the second antenna 2 compared to the amount of power of the partial Sd discharge signal received by the first antenna 1. The processing of the electrical signals generated by the first antenna 1 and the second antenna 2 is analogous to that described above with reference to the partial discharge detection apparatus 400 of Figure 1.

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