WO2014024060A1

WO2014024060A1 - Device for monitoring an activity of partial discharges which occurs in an electrical apparatus

Info

Publication number: WO2014024060A1
Application number: PCT/IB2013/055693
Authority: WO
Inventors: Gian Carlo Montanari
Original assignee: TECHIMP Tech SRL
Current assignee: TECHIMP Tech SRL
Priority date: 2012-08-06
Filing date: 2013-07-11
Publication date: 2014-02-13
Anticipated expiration: 2015-02-06
Also published as: ITBO20120435A1

Description

DEVICE FOR MONITORING AN ACTIVITY OF PARTIAL DISCHARGES WHICH OCCURS IN AN ELECTRICAL APPARATUS

Technical field

This invention relates to a device for monitoring an activity of partial discharges which occurs in an electrical apparatus. Background art

It should be noted that a partial discharge (PD) is an electric discharge limited to a portion of the insulation of an electrical system and does not therefore cause immediate failure of the system but causes its gradual degradation. By their very nature, therefore, partial discharges are substantially limited in extent to a defect in the insulating system.

Thus, the technical field of this invention is that of devices for detecting and processing the electrical signals generated by partial discharges, aimed at providing a diagnostic indication on the insulation of an electrical apparatus (typically subjected to medium or high voltage, or in any case subject to an activity of partial discharges), to be able to plan maintenance and support activities on the apparatus itself (for example, an electrical cable or an electricity generator, or a transformer).

A major problem of these devices is the reliability of the data measured, for the purpose of the diagnostic evaluation.

In effect, the devices of this type lead to the risk of generating false alarms or, vice versa, of not being able to signal a critical situation regarding the insulation.

This problem affects, for example, instruments which, for each pulse detected, substantially measure an amplitude value (linked, for example, to the peak amplitude, or to the pulse energy), without taking into due account the form of the pulse wave.

On the other hand, a storage of the entire wave form of all the pulses measured would result in considerable difficulties, due to the enormous quantity of data to be stored, and the inconvenience of having to process these pulses during a post-processing step following the measurement and storage.

A solution to these problems is provided by the technology described in patent documents WO2007/144789 and WO201 1 /1 10984A1 in the name of the same Applicant as this invention.

It is noted that devices are known from patent documents US2012/029718A1 and WO02/08771 A1 , for use as online monitoring of electrical quantities; however, said devices are unsuited for detection and subsequent analysis of PD pulses.

Disclosure of the invention

In light of this, this invention constitutes an application and an improvement of that technology, aimed, in particular, at providing a monitoring device; the term "monitoring device" means a device designed to be installed in-situ, that is, on the electrical apparatus being measured, to be able to operate continuously, on-line (that is, during the normal activities of the apparatus), in a completely autonomous manner (standalone), that is, without the presence of any operator.

The aim of this invention is, therefore, to provide a device for monitoring an activity of partial discharges which occurs in an electrical apparatus, that is particularly reliable and efficient.

More specifically, the aim of this invention is to provide a device for monitoring an activity of partial discharges which occurs in an electrical apparatus, which is able to provide an indication for diagnostic purposes in a completely autonomous manner with respect to the intervention of an operator.

A further aim of this invention is to provide a device for monitoring an activity of partial discharges which occurs in an electrical apparatus, which is easy to install. These aims are fully achieved by the device according to the invention as characterised in the appended claims.

In particular, the monitoring device according to this invention comprises:

- a sensor having a ring of ferromagnetic material which can be coupled to a conductor of the electrical apparatus so as to enclose it, designed for measuring electrical pulses generated by the partial discharges and generating an analogue signal representing the entire wave form of the pulses;

- a box-shaped body integral with the sensor for forming with it a single body;

- an electronic card contained in the box-shaped body, connected to the sensor for receiving the analogue signal from the sensor and designed for processing substantially in real time the wave form of the pulses of the signal extracting the value of at least one predetermined parameter relative to the pulses;

- an output stage connected to the electronic card and set up to perform a signalling to the outside as a function of the values extracted for the at least one predetermined parameter.

It should be noted that the term "processing substantially in real time" means a processing which does not need the storage of data in a memory.

In particular, as regards the expressions "(substantially) in real time" and "storage memory" the following should be noted.

The expression "substantially in real time of data" means that, within a flow of data (for example, from an input to an output), data is processed without the processing substantially causing a stoppage of the data flow. For example, the fact of placing the data in a memory (potentially for an indefinite period of time), to be able to recover it at any time and process it, constitutes an interruption of the flow of data, and, therefore, a storage. The expression "storage memory" means a memory designed to (that is, from the hardware point of view, a memory managed in such a way as to) hold data for a potentially undefined period of time, to be able to successively recover it (at any time) and process it. In light of this, it should be noted that a mass storage memory, such as, for example, the hard drive of a computer, is typically a storage memory, whilst a RAM can, depending on how it is managed, constitute a storage memory (as described above), or, alternatively, constitute a buffer (temporary memory), that is, a means for slowing down the flow of data (in a certain point of the path which the data travels along from the input to the output), without, however, interrupting it. Thus, the term "processing in real time" means that the processing occurs during the passage of data from an input to an output in a substantially continuous flow, this being able to provide a slowing down of the data flow, by a temporary accumulation of the data in a substantially volatile memory.

It should also be noted that the sensor is preferably a measurement transformer.

Preferably, the sensor is a sensor for high frequencies, for example in the range [100 kHz - 100 MHz].

Preferably, the sensor defines a passband of at least 500 kHz - 20 MHz and more preferably of 1 MHz - 10 MHz.

Thus, the device according to this invention is an autonomous device, that is, standalone. In effect, the device, once it is installed, does not need the presence of any operator and performs the relative function of monitoring the activity of partial discharges and signalling of alarm messages in a fully autonomous and automatic way.

In this light, preferably, the output stage comprises interfacing means for sending an alarm signal outside the device.

For instance, said interfacing means may comprise an acoustic or visual alarm element (such as a siren or a light which can be turned on and off) or a digital alarm element, driven by the processor for sending at output a digital predetermined alarm signal, through a connection which links the device to a remote control station; said connection may be though a cable or wireless, depending on the application.

In any case, the output stage comprises signaling means for transmitting an alert signal outside the device; said signaling means are connected to the processor; the processor is programmed to activate the signaling means automatically as a function of an on line (and preferably) real time processing of the PD data acquired by the device itself (according to the solution described in the present document).

Moreover, the device is compact, as it integrates the sensor and the hardware designed for processing the signal measured by the sensor, for the purpose of obtaining an assessment parameter on the basis of which to generate the alarm signal.

Thus, the device has a particularly reduced size; in effect, it can be easily handled and transported by hand and it has a size which is identical to that of the measurement TAs available on the market.

Preferably, the electronic card of the device (that is, the processing means of the device, which could also comprise a suitably programmed DSP device or other electronic means) is programmed for performing predetermined operations in a time sequence.

It should be noted that the device is also designed for storing (preferably in a memory inside the device) the data measured, that is, the data processed starting from the signal detected by the sensor.

In light of this, the electronic card of the device (that is, the processing means of the device) is preferably programmed for managing the data stored in an automatic (and intelligent) way.

This, advantageously, renders the device autonomous and efficient for a very long, potentially indefinite, period of time.

In particular, preferably, the electronic card (that is, the processing means of the device) is programmed for performing, at predetermined time intervals, a statistical processing of at least a sub-set of the stored data, comprising at least the data most recently stored, in order to derive an assessment parameter and to command the output stage to perform or not the signalling, as a function of the assessment parameter derived from the at least one data sub-set.

Preferably, the electronic card (that is, the processing means of the device) is programmed for storing in the memory a succession of data packets; each data packet comprising the values of the at least one parameter extracted by the pulses measured in a corresponding acquisition period; in light of this, the electronic card is programmed for performing a succession of acquisitions at predetermined time intervals. Moreover, the electronic card is programmed for performing, periodically, a statistical processing of the last data packet stored, for deriving an assessment parameter and commanding the output stage to perform or not the signalling, as a function of the last data packet stored.

It should also be noted that, preferably, the electronic card is programmed for performing a statistical processing of a plurality of data packets stored, for deriving a trend assessment parameter, as a function of a comparison of the data packets themselves, and commanding the output stage to perform or not the signalling, as a function of the trend data packet.

Brief description of drawings

These and other features of the invention will become more apparent from the following description of a preferred, non-limiting embodiment of it, with reference to the accompanying drawings, in which:

- Figure 1 is a perspective view of a device according to this invention;

- Figure 2 is an open top view of the device of Figure 1 ;

- Figure 3 is an open side view of the device of Figure 1 ;

- Figure 4 is a perspective view of the device of Figure 1 in an alternative embodiment;

- Figure 5 is an open top view of the device of Figure 4;

- Figure 6 is an open side view of the device of Figure 4. Detailed description of preferred embodiments of the invention

The numeral 1 in the drawings denotes a device according to this invention.

The device 1 is a device for monitoring an activity of partial discharges which occurs in an electrical apparatus.

The device 1 comprises a sensor 2; the sensor 2 is integrated in the device 1 .

The sensor 2 has a ring 3 of ferromagnetic material.

The ring 3 can be coupled to a conductor of the electrical apparatus to be monitored, so as to enclose it; for example, the ring 3 can be coupled to an earth connection cable of an electric machine, or to a portion of the braid of a cable screen (merely by way of providing some practical examples).

It should also be noted that, in a variant embodiment not illustrated, the ring 3 has a portion movably coupled to the rest of the ring, in such a way that the ring can be opened and closed.

This allows the ring 1 to be coupled to the apparatus with particular ease, even without the need to put the apparatus out of service.

The sensor 2 is designed for measuring electrical pulses (in particular the electrical pulses generated by the partial discharges) and generating an analogue signal representing the entire wave form of the pulses.

The device 1 also comprises a box-shaped body 4 integral with the sensor for forming with it a single body.

The box-shaped body 4 constitutes a protective casing, that is, an outer case of the device 1 .

Preferably, the box-shaped body 4 defines a through hole and an annular housing wherein the ring 3 of the sensor 2 is positioned.

In that way, preferably, the box-shaped body 4 also encloses the sensor 2.

This makes the device 1 particularly robust mechanically, even with respect to any infiltration of humidity.

Moreover, the device 1 comprises an electronic card 5, that is, hardware designed to receive and process the signal measured by the sensor 2. The electronic card 5 is contained in the box-shaped body 4.

The electronic card 5 is connected to the sensor 2 for receiving the analogue signal.

In light of this, the electronic card 5 defines an input stage (of the device 1 ) designed for receiving the analogue signal and generating a digital signal representing the entire wave form of the pulses.

It should be noted that the analogue signal (and, therefore, also the corresponding digital signal) represents a sequence (that is, a succession) of pulses; in effect, the partial discharges (and the pulses generated from them and propagating through the monitoring equipment) follow one another and repeat over time, giving life to a so-called "activity of partial discharges".

Moreover, the electronic card is designed for processing substantially in real time the wave form of the pulses of the signal; in particular, the electronic card 5 is designed for extracting substantially in real time from the digital signal the value of at least one predetermined parameter relative to the pulses.

Moreover, the device 1 comprises an output stage, connected to the electronic card 5 and set up to perform a signalling to the outside as a function of the values extracted for the at least one predetermined parameter.

It should be noted that the fact that the extraction of the values of the at least one parameter relative to the wave form of the pulses is performed (substantially) in real time is important as it allows the accumulation of large quantities of data to be prevented; in effect, this allows a selected set of data, which is considerably reduced in terms of quantity of data, but particularly significant for the purpose of a diagnostic assessment of the apparatus being monitored, to be derived from the digital signal (which contains a large quantity of data, comprising all the samples of the pulses measured). In light of this, the electronic card 5 (that is, the processing means of the device 1 ) is designed for extracting substantially in real time at least one of the following parameters:

- a parameter representing the amplitude of the pulses;

- a parameter representing the wave form of the pulses;

- a parameter representing the time interval between the instant of measuring a pulse and the instant of measuring the previous pulse (as part of the sequence of pulses representing the analogue signal and the digital signal).

The parameter representing the amplitude of the pulses comprises, for example, a measurement of the peak or of the energy associated with the signal representing the pulse.

The parameter representing the time interval between the instant of measuring a pulse and the instant of measuring the previous pulse is particularly indicative of the intensity of the discharge activity and of the type of discharge activity (which is correlated, as is known, to the type of defect of the insulation system in which the discharge activity occurs). The parameter representing the form of the pulses is particular indicative of the transfer function associated with the path followed by the pulses from the discharge site to the sensors (which constitutes a measurement site); therefore, this parameter allows pulses generated by different discharge sources, and discharge pulses rather than pulses due to disturbances or noise, to be distinguished and separated.

Preferably, the electronic card 5 is designed for extracting (substantially in real time):

- a first shape parameter (T), correlated with the duration of the pulses; and

- a second shape parameter (W), correlated with the frequency content of the pulses.

The first shape parameter (T), known as "Equivalent duration", consists preferably of the standard deviation of the partial discharge pulse processed in the time domain (but alternative formulae can be used).

The second shape parameter (W), known as "Equivalent bandwidth", consists preferably of the standard deviation of the partial discharge pulse processed in the frequency domain (but alternative formulae can be used). Preferably, the device 1 also comprises a battery connected to the electronic card 5 for powering it, for allowing operation of the device 1 even with a power failure.

The output stage comprises a signal connector 6, for an output transmission of the signalling data (however, it is also envisaged that the interfacing means are also wireless).

Preferably, the device 1 comprises a power supply connector 7, for connecting the device 1 to an electric power supply.

The power supply connector 7 also constitutes the signal connector 6 (this solution is illustrated in the example of Figures 1 -3).

Alternatively, there is a signal connector 6 separate from the power supply connector 7 (this solution is illustrated in the example of Figures 4-6).

In this case, the signal connector 6 is preferably of the RJ45 type.

Preferably, the output stage comprises a relay (not illustrated, since it is of a known type), connected to the electronic card 5 for setting up as a function of the assessment parameter.

It should be noted that the output stage is also defined by the electronic card 5 itself.

Preferably, the electronic card 5 (that is, the processing means of the device 1 ) is designed for processing a power supply current (received from the device 1 through the power supply cable 7) for extracting a a synchronism signal.

This synchronism signal represents the trend of an electronic field applied to the electrical apparatus during monitoring; this is useful when the apparatus is powered with alternating current.

In light of this, preferably, the electronic card 5 is designed for extracting a phase parameter from the synchronism signal (substantially in real time) for each of the pulses measured.

The phase parameter represents a position of an instant of measurement of the pulse relative to a period of variation ([0-360 degrees] sexagesimal) of the electrical field applied to the apparatus.

Preferably, the electronic card 5 is programmed for processing the at least one predetermined parameter extracted for one or more pulses and deriving an assessment parameter.

In effect, the values derived for the at least one parameter extracted in real time constitute a data set.

The electronic card 5 (that is, the processing means of the device 1 ) is designed for processing this data (for deriving the assessment parameter), for example by means of statistical analysis.

The processing of the data set is preferably performed after having stored the data set in a memory 8 (that is, in post-processing).

In light of this, it should be noted that the electronic card 5 is programmed for storing in the memory 8 the data comprising the values of the at least one extracted parameter (in real time) for the pulses measured.

Preferably, the electronic card 5 is programmed for performing, at predetermined time intervals, a statistical processing of at least a sub-set of the stored data, in order to derive an assessment parameter and to command the output stage to perform or not the signalling, as a function of the assessment parameter derived from the at least one data sub-set. The assessment parameter typically comprises a combination of the parameters extracted in real time, according to a predetermined algorithm (which can be set as a function of the diagnostics criteria which vary with the variation in the type of apparatus being monitored).

Preferably, the data sub-set comprises the data most recently stored, according to a predetermined criteria; this criteria is preferably based on a predetermined time interval (for example, the last week) or on a predetermined number of pulses measured (for example, the last 1 ,000,000 pulses). Preferably, the electronic card 5 is programmed for storing in the memory 8 a succession of data packets comprising the values of the at least one extracted parameter for the pulses measured in a corresponding succession of predetermined acquisition intervals.

For example, the electronic card 5 is programmed for performing an acquisition of a preset duration (or of a preset number of pulses) at a preset time rate (for example, every hour or every day).

This determines a succession of data packets, one for every acquisition. In light of this, preferably, the electronic card 5 is programmed for performing, periodically, a statistical processing of the last data packet stored, for deriving the assessment parameter and commanding the output stage to perform or not the signalling, as a function of the last data packet stored.

Moreover, it should be noted that the electronic card 5 is also programmed for performing a processing (statistical) of a plurality of data packets stored, for deriving a trend assessment parameter, as a function of a comparison of the data packets themselves.

Moreover, the electronic card 5 is programmed for commanding the output stage to perform or not the signalling, as a function (also) of the last data packet stored.

In this case, the signalling (that is, the decision whether or not to perform the signalling) is determined by the device 1 not only on the basis of the most recent data, but also as a function of a history of the data acquired (considering, therefore, a longer length of monitoring time), performing an assessment of the trend over time of one or more quantities correlated with the activity of the partial discharges (and thus with the status of the electrical insulation of the apparatus).

The signalling can be of the simple, binary type, determined, for example, by the open or closed status of the relay.

This allows for the signalling that it is necessary for an operator to intervene for inspecting or at least analysing further the apparatus or part of the apparatus monitored by the device 1 .

A signal of this type can be generated by setting a threshold for the assessment parameter.

This configuration favours the constructional simplicity of the device 1 . However, the signalling also comprises a more complex information, generated by the processing means defined by the electronic card 5.

Moreover, it should be noted that, preferably, the device 1 is designed to receive a setting or control signal to allow an operator to modify the settings remotely or to remotely perform processing on the data contained in the device 1 .

In light of this, the output stage of the device 1 comprises interfacing means 9, designed for transmitting output data from the device.

Preferably, the interfacing means are designed for receiving data from the outside.

For example, the interfacing means comprise a card and hardware compatible with ATEX standards.

Claims

1 . Device (1 ) for monitoring an activity of partial electrical discharges which occurs in an electrical apparatus, comprising:

- a sensor (2) having a ring (3) of ferromagnetic material which can be coupled to a conductor of the electrical apparatus so as to enclose it, designed for measuring electrical pulses generated by the partial electrical discharges and generating an analogue signal representing the entire wave form of the pulses;

- a box-shaped body (4) integral with the sensor (2) for forming with it a single body;

- an electronic card (5) contained in the box-shaped body (4), connected to the sensor (2) for receiving the analogue signal from the sensor and designed for processing substantially in real time the wave form of the pulses of said signal, for extracting the value of at least one predetermined parameter relative to the pulses;

2. The device according to claim 1 , wherein the electronic card (5) is designed for extracting substantially in real time at least one of the following parameters:

- a parameter representing the amplitude of the pulses;

- a parameter representing the wave form of the pulses;

- a parameter representing the time interval between the instant of measuring a pulse and the instant of measuring the previous pulse, the analogue signal representing a sequence of pulses.

3. The device according to claim 2, wherein the electronic card (5) is designed for extracting substantially in real time:

- a first shape parameter (T), correlated with the duration of the pulses; and - a second shape parameter (W), correlated with the frequency content of the pulses.

4. The device according to any one of the preceding claims, wherein the electronic card (5) is programmed for processing the at least one predetermined parameter extracted for one or more pulses and deriving an assessment parameter.

the output stage comprises a relay, connected to the electronic card (5) for setting up as a function of the assessment parameter.

5. The device according to any one of the preceding claims, wherein the electronic card (5) is programmed for storing in a memory (8) data comprising the values of the at least one extracted parameter for the pulses measured.

6. The device according to claim 5, wherein the electronic card (5) is programmed for performing, at predetermined time intervals, a statistical processing of at least a sub-set of the stored data, comprising at least the data most recently stored, in order to derive an assessment parameter and to command the output stage to perform or not the signalling, as a function of the assessment parameter derived from the at least one data sub-set.

7. The device according to claim 5 or 6, wherein the electronic card (5) is programmed for storing in the memory (8) a succession of data packets comprising the values of the at least one extracted parameter for the pulses measured in a corresponding succession of predetermined acquisition intervals and wherein the electronic card (5) is programmed for performing, periodically, a statistical processing of the last data packet stored, for deriving an assessment parameter and commanding the output stage to perform or not the signalling, as a function of the last data packet stored.

8. The device according to claim 7, wherein the electronic card (5) is programmed for performing a statistical processing of a plurality of data packets stored, for deriving a trend assessment parameter, as a function of a comparison of the data packets themselves, and commanding the output stage to perform or not the signalling, as a function of the trend data packet.

9. The device according to any one of the preceding claims, wherein the device (1 ) can be transported and handled by hand.

10. The device according to any one of the preceding claims, wherein the ring (3) has a portion movably coupled to the rest of the ring, in such a way that the ring can be opened and closed.

1 1 . The device according to any one of the preceding claims, comprising a connector (7) for connecting the device to an electric power supply, wherein the electronic card (5) is designed for processing a power supply current for extracting a a synchronism signal representing an electric field applied to the electrical apparatus during the monitoring.

12. The device according to claim 1 1 , wherein the electronic card (5) is designed for extracting substantially in real time from the synchronism signal, for each of the pulses measured, a phase parameter representing a position of an instant of measuring the pulse in relation to a period of variation of the electric field applied to the apparatus.