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The present invention relates to an audio system configured to remotely reproduce an ultrasonic signal without interference either alteration in a reliable, efficient and versatile way.

Although this invention is mainly oriented towards the remotely reproduction of ultrasonic signal produced by partial discharges, PDs, occurring into electrical apparatus, in particular of electric power plant for generation, transmission and distribution, it may be applied to ultrasonic signal produced by any other kind of source, such as different industrial plant, in different field of application as for example prevention and protection, therapeutic, military, still remaining within the scope of protection as defined by the attached claims.

An efficient management of plants is determined by two factor connected each other: new techniques for accurately measuring of operating condition of plant ad new management methods. There are several techniques for monitoring power plant, such as insulating oils analysis and hot spots determination, but the most useful one is the detection, the localization and the measurement of the PDs into medium and high voltage plant and in particular into the substations. Recently, both in Europe and in the world, the campaigns for detecting the partial discharges are remarkably increased, especially because they have been considered as low cost actions to improve reliability and performance of electricity grids. Unfortunately, there are still many operators who are reluctant to adopt such techniques and wait for the failure condition and then provide for the restoration.

A partial discharge is an electric breakdown, or spark, which damages a small part of the insulation existing between two conductive electrodes or between a conductive electrode and the earth. The partial discharge can occur everywhere in the insulating system, where the electric field intensity exceeds the intrinsic resistance of the insulating system. The partial discharge can occur in the vacuoles inside the solid layer of the insulator, on the surface of the insulator due to the action of pollutants or to geometrical irregularities, inside air bubbles in liquid insulator or around an electrode. There are several causes of insulation failure leading to the discharge activity, including initial design and manufacturing defects, incorrect component installation, faulty materials, mechanical failures and even vandalism. Also if well designed and installed, the plants tend to present discharge activity due to aging and use over time. Environmental conditions as temperature, humidity, atmospheric pressure, vibrations and various mechanical stresses also play a decisive role. When they occur, partial discharges always tend to increase. The deterioration process can propagate and develop until the insulation is not able to withstand the intensity of the electric field, resulting in flash phenomena. The final failure of medium and high voltage plants is often sudden and catastrophic. The best case is that of the plant shutdown caused, for example, by the untimely intervention of the protections. The worst case is that of an explosive release of energy that causes serious harm, injury and, in some cases, the death of an operator. Therefore, the capability to detect and measure partial discharges is an important factor for the good management of the plant, because it allows identifying a potential failure before it actually happens and leads to serious consequences for the operational safety and economy of the plant itself, increasing the efficiency, reliability and safety of the plant with lower running costs. Fault prevention saves costs for the interventions, thus making available resources for the development of new techniques of detection and measurement, guaranteeing even more respect for the surrounding environment.

There are different techniques of PD detection, such as the measurement of the apparent charge (PD currents), the detection of Transient Earth Voltage, TEV, the detection of the emitted electromagnetic field, and the detection of emitted ultrasounds.

Several prior art documents, such as for example US2003214307A1, US2005012507A1, US2014270205A1, and US2016161543, disclose systems and methods for detecting PDs in which the PD detection devices are located near the electrical elements being inspected, optionally provided with microprocessors which can process and send information remotely. These solutions involve high installation and processing costs which increase when the number of elements to be inspected increases, such as distribution lines.

Currently, inspections on parts of a plant that are difficult to access, such as air lines and transformer rooms, are commonly performed by a pair of operators who must go near the plant, get as close as possible to the supports, make an optical detection by a pair of binoculars, perform a thermographic detection by a thermal camera, perform a detection of the ultrasounds emitted by partial discharges by a suitable instrument equipped with an acoustic sensor. All this is performed from ground, therefore the top of some plants, even placed on poles, is not properly inspectable, like the roof of a cabin or the base of insulators placed on top of a transformer. This inspection is completely dependent on the accessibility of the system and is limited to only one point of view, that is, from the ground.

A Remotely Piloted Aircraft, APR, provides the possibility to observe the details of the plant from perspectives that are not possible from the ground and eliminates the problem of accessibility with regard to optical and thermographic detection, but not with regard to ultrasonic detection. In fact, the reliability of the result of this measurement relies on the experience of the operator who performs the measurement and interprets the obtained results, since the detection of the ultrasound signal emitted by PD is considerably complex when carried out in an environment that is not specifically shielded and numerous difficulties occur due to the high presence of noise that interfere and overlap with the signal to be detected. Generally, ultrasonic signals emitted by PD and detected by an acoustic sensor are transformed into numerical decibel values and into acoustic signals that the operator directly listens through suitable headphones.

It is an object of this invention to overcome the disadvantages described above, allowing to detect ultrasonic signals emitted by partial discharges possibly present on parts of industrial plants that are barely reachable, in a reliable and economical way.

It is specific subject-matter of the present invention an audio system to remotely reproduce an ultrasonic signal, including a local unit for detecting and transmitting the ultrasonic signal, and a remote unit for receiving the signal transmitted by said local unit and reproducing the same that it is shifted to acoustic frequencies, the local unit including a microphone transducer for acquiring the ultrasonic signal and a high impedance input and low output impedance buffer for receiving the ultrasonic signal sent by the microphone transducer and an analog RF video transmitter receiving the ultrasonic signal adapted in impedance and amplitude from the buffer and transmitting it, the remote unit including an analog RF video receiver for acquiring the ultrasonic signal transmitted by the analog video transmitter, a transducer for receiving the signal from the analog RF video receiver and reproducing the same that it is shifted to acoustic frequencies.

According to another aspect of the invention, said buffer may be configured to have an adjustable gain for exploiting the whole dynamic range of the analog RF video transmitter without saturating the same and for keeping an high signal-to-noise ratio.

According to a further aspect of the invention, said buffer may have a bandwidth larger than the ultrasonic signal, optionally larger than 20kHz -60 kHz.

According to an additional aspect of the invention, said transducer of the remote unit may comprise a first ultrasonic transducer configured to transmit the signal from the analog video RF receiver and a second ultrasonic transducer configured to capture said signal transmitted by the first ultrasonic transducer. According to another aspect of the invention, said first ultrasonic transducer has a pass-band included in the pass-band of the second ultrasonic transducer.

According to a further aspect of the invention, said second ultrasonic transducer may be equal to the microphone transducer of the local unit.

According to an additional aspect of the invention, said remote unit may include headphones for letting an operator listen to the ultrasonic signal shifted to acoustic frequency.

According to another aspect of the invention, said analog video transmitter and/or said analog video receiver may be respectively an audio/video transmitter and/or receiver of which only the video channel is used.

According to a further aspect of the invention, said local unit may be configured to be mounted on a movable apparatus such as a land vehicle, a drone, a robot, a surface vessel, an underwater vehicle.

According to an additional aspect of the invention, said movable apparatus is an autonomously or remotely piloted one.

The advantages offered by the audio system according to the invention with respect to the prior art solutions are numerous and significant.

The local and remote units, that modulate and demodulate an ultrasonic signal and route it through a radio frequency signal with a bandwidth compatible with that required by the ultrasonic signal itself, allow to make an audio system suitable for being used in all those circumstances in which it is not possible using a cable for connecting an acoustic sensor to a reading instrument.

It is possible to locate the acoustic sensor near the parts of a plant to be inspected, regardless of the position of the operator conducting the inspection, which may stay remote from the plant. This makes it possible to effectively and easily inspect a plant independently of its accessibility to an operator, in an efficient and economical way. In this way, it is possible to make inspections of the electrical distribution networks more efficient, preventing line breakdowns and greatly reducing the high running costs.

The audio system can be advantageously used to detect the presence of partial discharges in environments inaccessible to humans or dangerous, such as those at high temperatures and/or in the presence of medium or high voltage, reducing the risk of injuries and thus increasing safety.

A further advantage due to the absence of cables between the acoustic sensor and the reading instrument is that of allowing the use of the audio system in airborne, aquatic and terrestrial systems with remote control, in various fields of application, both military and civil.

The present invention will now be described, by way of illustration, but not by way of limitation, according to its preferred embodiments, with particular reference to the Figures of the accompanying drawings, in which:

Figure 1 shows a diagram of a preferred embodiment of the audio system according to the invention; and

Figure 2 shows the system of Figure 1 in different using configurations.

In the Figures, identical reference numbers will be used for similar elements.

Figure 1 shows a preferred embodiment of an audio system 100 according to the present invention which comprises a local unit 10 configured to detect an ultrasonic signal from a source, generally comprised between 20KZ and 60kHz, and transmit it to a remote unit 20 which is configured to receive the signal from the local unit 10 and reproduce it so that it can be analysed by an operator 30 (as sketched in Figure 2).

The local unit 10 of the audio system 100 includes a microphone transducer 1 for acquiring an ultrasonic signal within an ultrasonic spectrum and sending the acquired ultrasonic signal to a buffer 2 amplifier/adapter of impedance with adjustable gain, high input impedance and low output impedance, which adapts impedance and amplitude of the ultrasonic signal to be sent to a analog video RF (radiofrequency) transmitter 3 that transmits the ultrasonic signal. The buffer 2, advantageously having a bandwidth higher than that of the ultrasonic signal, is configured to have an adjustable gain to exploit the full dynamic range of the analog video RF transmitter 3 without saturating it (i.e. clipping it) and keeping the signal-to-noise ratio high. With such a configuration, it is clear that the acquired ultrasonic signal, adapted in impedance and amplitude by the buffer 2, is transmitted by the analog video RF transmitter 3 to an analog video RF receiver 4 without any compression or modification of the signal, keeping its signal-to- noise ratio unchanged at the remote unit 20. The remote unit 20 includes an analog video RF receiver 4 for acquiring the ultrasonic signal transmitted by the analog video transmitter 3 of the local unit and sending it to a transducer 5 configured for reproducing the ultrasonic signal shifted to acoustic frequencies completing an ultrasonic virtualization process. Relating to the ultrasonic virtualization, we mean the transformation of an original ultrasonic signal into an electrical signal and its transformation from electrical signal to an acoustic signal shifted in frequency with respect to the original ultrasonic signal. The transducer 5 of the preferred embodiment comprises a first ultrasonic transducer 7 configured to receive a signal from the analog video RF receiver 4 and transmit it and a second ultrasonic transducer 8 configured to receive said signal transmitted by the first ultrasonic transducer 7. Advantageously the first ultrasonic transducer 7 has a bandwidth included in the pass band of the second ultrasonic transducer 8. In the preferred embodiment, the second ultrasonic transducer 8 has a bandwidth with the same band centre of the pass band of the first ultrasonic transducer 7 but with a greater width, optionally the first and second transducer 7, 8 have a bandwidth at -6dB with a 40 kHz band centre and a width equal to 2 KHz and 2.5 kHz respectively. In a further embodiment of the present invention, the second ultrasonic transducer 8 is the same as the microphone transducer 1 of the local unit 10. The remote unit 20 also includes headphones 6 allowing an operator to listen the ultrasonic signal (as shown schematically in Figure 2) shifted to acoustic frequencies, at the output of the transducer 5. Advantageously, the analog video transmitter 3 and/or the analog video receiver 4 may be respectively an audio/video transmitter and receiver of which only the video channel is used.

According to a variation of the present invention, the audio system also comprises a processing device (not shown in the Figures), connectable at the output of the transducer 5, and configured for visual reproduction of the signal shifted to acoustic frequencies with respect to the original ultrasonic signal, and/or for its quantitative processing according to methods known to those skilled in the art. This processing device can be connected to the transducer 5 in parallel or in series with the headphones 6, that is, in the latter case, it can be connected between the output of the transducer s and an input of the headphones 6.

As sketched in Figure 2, the local unit 10 is configured to be mounted on a mobile apparatus such as a land vehicle 41 (possibly unmanned, i.e. autonomous or remote piloted), a drone 42 (i.e., an autonomous or remote piloted aircraft), a robot 43, a surface vessel 44 (possibly unmanned, i.e. autonomous or remote piloted), or a submarine vehicle 45 (possibly unmanned, i.e. autonomous or remote piloted). In such applications, the local unit 10 is mobile, while the remote unit 20 can be advantageously stationary.