Resumen
[0001] The invention relates to a method specially designed for detecting events associated with partial discharges (PDs) in high voltage cables, comprising the identification of the location and the evaluation of the amplitude and rate of repetition per period of the grid voltage, with the possibility of identifying different sources producing PD signals as a function of the location thereof and recognising the type of defect associated with PDs in the same location, including the measurement of the generated electric signals and the discrimination thereof in relation to the background noise. The invention also relates to a system for carrying out said method, comprising means for discriminating the noise in relation to the transient waveform of the PD, determining the parameters associated therewith, determining the map of sources of PDs along the length of the cable, graphically representing said sources, and identifying the patterns of the sources of PDs separated as a function of the location thereof along the length of the cable.
Reivindicaciones
1. A method for the continuous monitoring of sources of partial discharges (PDs) in high voltage cables during connection to, and operation in the power grid by means of discriminating, locating, measuring, identifying and diagnosing sources of partial discharges (PDs) in high voltage cables, particularly a method which allows detecting partial discharge-type events by measuring the generated electric signals, discriminating them from the background noise, identifying the location of the PDs along the length of the cable, knowing their amplitude and rate of repetition, identifying different sources producing PD signals as a function of the location thereof where they were detected, and recognising the type of defect associated with PDs in the same location, characterised in that it comprises: - synchronously measuring (block 4.1) analogue signals sensed by at least two sensors working in a frequency range comprised between 50 kHz and 20 MHz, and transforming them into their corresponding representative digital signals; - discriminating (block 4.2) within the signal measured in (block 4.1) the instants in which a partial discharge has occurred and, in those instants, separating the electric noise from the measured signal by means of applying the Wavelet transform together with the statistical treatment of the measured signal; - determining (block 4.3) the magnitude for each PD-type signal, obtained from its waveform analysis, as well as from the instant in which the signal appears in relation to the zero-crossing of the applied voltage wave; - determining (block 4.4) a set of representative parameters for each PD-type signal, obtained from the comparative analysis with other PD-type signals sensed by different sensors (parameter of the phase in which the PD is produced, pulse arrival time t<i> and parameter of the distance from the sensor to the location of the source of PD); - repeating (block 4.5) the steps of the previous stages enough times to enable calculating, for each sensor, a representative value of the magnitude of the amplitude and of the rate of repetition of PD pulses, the number of acquisitions considered sufficient for the mentioned calculation of 50 acquisitions of a window being equal to the period of the grid voltage; - determining (block 4.6), from the set of PD-type signals detected by each sensor, the representative value of the magnitude of the amplitude and of the rate of repetition of PD pulses per period of the grid voltage wave associated with the last 50 acquisitions made; - repeating (block 4.7) the preceding stages enough times, of the order of at least 200 times, to enable having a statistically representative sample of acquisitions to apply to subsequent stages; - determining (block 4.8) the location map of PD signals, taking into account the arrival time delay for the PDs coming from contiguous sensors and analysing the coherence of PD-type signals obtained by other sensors, showing the amplitudes of PDs and the mean rate of repetition of the mentioned PD-type signals in the location map; - automatically generating (block 4.9) the pattern of the PD pulses as a function of the phase difference with the applied voltage wave of each of the PD clusters (4.9) in the same location of the cable, and - correlating (block 4.10) each cluster of source of PDs generated in (block 4.9) with defects of the type producing PDs by means of recognising the patterns of the PD signals as a function of the phase difference with the voltage wave applied to the cable through a neural network. 2. The method according to claim 1, characterised in that the mentioned stage associated with the block (4.2) for noise discrimination allows distinguishing signals (2a.1 and 2b.1) with a characteristic transient waveform of a PD from other signals (1.1 and 1.2 of Figure 1) characteristic of superimposed background electric noise. 3. The method according to claim 1, characterised in that the mentioned stage associated with the block (4.4) relative to determining a set of parameters associated with each PD signal detected, allows knowing the phase in which the PD signal originated, and a first estimation of the location of the source of the PD. 4. The method according to claim 1, characterised in that the mentioned stage associated with the block (4.8) relative to determining the map of sources of PDs, allows validating or rejecting PD-type pulses related to the position of the sources of PDs along the length of the cable, and allows knowing, in each location where the presence of sources of PDs, the magnitude of the original PD pulses and their mean rate of repetition are identified as statistical parameters resulting from treating a PD population sample; 5. The method according to claim 1, characterised in that the mentioned stage associated with the block (4.9) provides the graphical representation of the sources of PDs as sub-sets of the PDs positioned in the same region of space along the length of the cable. 6. The method according to claim 1, characterised in that the mentioned stage associated with the block (4.10) provides the identification of patterns of sources of PDs by applying a neural network to the different clusters of separated PDs as a function of the location thereof along the length of the cable. 7. A physical system for carrying out the method according to claims 1 to 6, specially designed for detecting partial discharge-type (PD) signals based on taking simultaneous measurements in all the sensors arranged along the length of a cable and being collected by a central system which allows discriminating the noise in relation to the characteristic transient waveform of a PD, determining the parameters associated with each PD, determining the map of sources of PDs along the length of the cable, graphically representing the sources of PDs as sub-sets of the PDs positioned in the same region of space along the length of the cable, and identifying the patterns of the separated sources of PDs as a function of the location thereof along the length of the cable, characterised in that it comprises the following sub-systems: - control and analysis sub-system (6.1) (CAS), where the signals captured by the digital recorders (6.2.2) are compiled and processed and the stages of the method of claims 2 to 6 are applied; - measurement sub-systems (6.2) (MS), installed at points close to the monitoring positions, where synchronisation pulses are received and retransmitted, partial discharge signals are detected through protection and control equipment, the measured signals are recorded and sent to the control and analysis sub-system (6.1) to be processed, and - a data transmission network (6.3) (DTN), which allows transferring data and commands from the control and analysis sub-system (6.1) to the measurement sub-systems (6.2), distributed along the length of the cable. 8. A numerical tool for the practical application of the methodology of the method,of claims 1 to 6, for the purpose of showing the results of the measurements, analysing them and emitting the diagnosis of the condition of a cable (block 4.11).
