Abstract
The time measurement efficiency of the partial discharge (PD) relies on the signal-to-noise ratio (SNR) and gain of the high-frequency current transformer (HFCT) sensor. However, the PD's time measurement efficiency decreases with the noise coupled to the HFCT in onsite measurements. To overcome that setback, this paper proposes one pre-processing, through modelling and simulation, considering the physical effects, features of the electrical circuit and coil construction parameters of the HFCT. The main goal is to reach reasonable high SNR under the strong influence of background noises. This investigation aims to validate the hypothesis of improvement or deterioration of the HFCT signal response through a transfer function optimization. This research effort's contributions are threefold: 1. Generation of PD pulse signal and noise addition; 2. HFCT modelling, simulation, and frequency response analysis; and 3. Models performance evaluation and validation of hypothesis. In conclusion, the pre-processing approach stands out as a means to robustify and provide freedom to the electric utility, making up for an eventual need to redefine the physical and geometrical parameters of the HFCT sensor under specific background noise for maintenance tests purpose. According to a cyber-physical system framework, experiments corroborate the project's goals to contribute to the PD pattern monitoring in onsite measurements and incorporate robustness to signals with low SNRs.
Highlights
The dielectric material degradation in electrical systems is generally associated with the partial discharges (PD) [1], unleashed within voids, and cracks in conductor–dielectric interfaces in solid insulation systems, in the case of liquid dielectrics or corona, in gaseous [2]
− q − n diagram (Fig. 2a.); 2. resolved time data, i.e. q − t waveform – where q is the load magnitude and t the analysis interval, or V − t – where V represents the voltage over time t; 3. signal data that are neither resolved phase nor resolved time, e.g. the q − V diagram – magnitude variation of discharge pulse by test voltage amplitude or the Pulse Sequence Analysis (PSA) diagram – in that data related to PD pulses should be saved as a sequence [3]
Where RL is the terminal load resistance, ri is the internal radius, ro is the external radius, r is the sensor radius, rc is the radius of the core, N is the number of turns of the sensor coil, Ac is the cross-sectional area, lm is the path of the magnetic flux ( c), I(t) is the current of the secondary circuit and Vo(t) is the output voltage of the circuit, i.e., the high-frequency current transformer (HFCT) sensor output signal
Summary
The dielectric material degradation in electrical systems is generally associated with the partial discharges (PD) [1], unleashed within voids, and cracks in conductor–dielectric interfaces in solid insulation systems (bubbles), in the case of liquid dielectrics or corona, in gaseous [2]. In step 3, HFCT models were created based on the variation of constructive and electrical parameters and subsequent evaluation of TFs (Transfer Functions) performance [12]. The main goal of statistical operators is to evaluate the sensor response performance regarding the similarity and prediction quality. It is done by comparing the output “pre-processed” signal from the sensor and the exact input signal (in this paper, PD pulse) [12,13,17,18].
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