Yan-Bo Wang

Localization of multiple partial discharge sources in air-insulated substation using probability-based algorithm

Ultra-high-frequency (UHF) sensing technique has been introduced to detect and localize partial discharge (PD) sources in air-insulated substation (AIS). This paper presents a probability-based algorithm to localize multiple PD sources which may occur simultaneously in different power equipment. Assuming that the time difference of arrival (TDOA) between all pairs of antennas in a array are normally distributed, the probability density function (PDF) of PD source coordinates can be obtained by substituting the linearized form of time difference equations into PDFs of TDOAs. When large number of PD signals are recorded, the joint PDF (JPDF) can be calculated from the product of PDF of each TDOA. Then the PD coordinates to be solved are regarded as with highest probability, and can be solved by taking the derivative of JPDF. In the case of multiple PD sources, mixed UHF signals are separated by clustering the TDOA vectors with K Means clustering method. PD experiments are performed to test the presented algorithm, and the localization accuracy of proposed algorithm is compared with other typical methods such as Newton-Raphson, Particle Swarm Optimization and plane intersection method. The results indicate that the probability-based localization algorithm reasonably integrates the TDOAs of continuous signal sequence, which can effectively reduce the influence of TDOA estimation errors and improve the localization accuracy.

UHF antenna configuration optimization for partial discharge source localization in air-insulated substation

Ultra-high-frequency (UHF) method has been applied to detect and localize partial discharge (PD) in air-insulated substation (AIS). The localization accuracy is closely dependent on the configuration of antenna array. This paper presents a PD localization error simulation method. Assuming that the estimated time difference of arrival (TDOA) error is normally distributed, the mean value and standard derivation of localization error for numerous positions in AIS are calculated with a Monte Carlo method. Then the localization error of square, Y shape, triangle and diamond arrays are compared, and the factors influence the localization error are analyzed. Since the optimal orientation is easily to be recognized and with minor distance error, the diamond array is more suitable for PD localization in AIS. Experiments are conducted for square and diamond arrays to calculate the localization error, and confirm the effectiveness of proposed simulation method.

Study of dielectric response characteristics for thermal aging of XLPE cable insulation

In urban power grids, the proportion of cross-linked polyethylene (XLPE) power cable continues to increase. Judging the insulation condition of XLPE cable precisely is of great significance. In this paper, a number of cable samples are thermally accelerated aged at different temperatures and during various periods. Polarization/depolarization current (PDC) and frequency-domain dielectric spectroscopy (FDS) tests are performed on these samples. Based on the results of PDC and FDS, combining with Debye model and dielectric theory, we analyzed their dielectric response characteristics and acquired some characteristic parameters representing the aging degree of XLPE insulation. From the aspect of PDC measurement, at a certain temperature, with the aging time increases, the attenuation time of depolarization current rises correspondingly and becomes slower to reach the steady state. Whats more, an aging factors A could be calculated which rises with the aging time. As for the FDS test, with the aging time increases at one temperature, the curve of dissipation factor tanδ moves upward; curves of complex permittivity real component have a tendency of moving right. The results are alike when observing samples at different aging temperatures. With the increase of aging time and aging temperature, the pyrolysis reaction and oxidizing reaction will become more drastic. As a result, there will be more boundary between sphaero-crystal and amorphous region. Some polar oxides could also be created. These changes can produce more interfacial polarization and space charges which could make the dielectric relaxation phenomenon more obvious.

Detection and localization of partial discharge in Air-Insulated Substations using UHF antenna array

UHF-based partial discharge (PD) early warning technique has been tried to monitor and localize PD activities in the whole Air-Insulated Substation (AIS). This paper presents a PD detection and localization system based on this method. This system is composed of four-antenna array (double-cone structure), signal conditioning unit (wide band filter, low-noise amplifier and band-stop filter) and high-speed acquisition unit The main sources of background noise are analyzed and corresponding rejection methods are developed to reduce their effect The probability-based localization algorithm which comprehensively consider the time differences of multiple signals are proposed to estimate the position of PD source. The developed system is applied to PD detection and location in substations, and the on-site results prove the effectiveness of the system.

Insulation status diagnosis of XLPE cable based on polarization and depolarization current (PDC)

Cross-linked polyethylene (XLPE) insulation cable is widely used in distribution power system, so it is important to reasonably estimate cable insulation status. Cable insulation is mainly affected by high temperature and water tree. Therefore, in this paper, we use PDC method to evaluate cable insulation, which is non-destructive due to its low voltage. In order to find out the relationship between PDC curve and aging status, we put 5 single-core cable samples in oven and set aging temperature as 14°C. Then, we divide these samples into different aging time (new, 10 days, 20 days, 30 days, 40 days) and measure the PDC curve. The result shows that with the increase of aging time, the PDC curve decreases quicker and the absolute value of steady current becomes higher. PDC will be a very practical way to judge cable insulation in the future.

Research on conversion of polarization/depolarization current and frequency domain spectroscopy for XLPE cable

Cross-linked polyethylene (XLPE) insulation cable is the main type of cable in use now. Its main insulation is aging with the increasing of service years. Two methods are used to diagnose the condition of the cable insulation-polarization/depolarization current (PDC) and frequency domain spectroscopy (FDS). The PDC is a time domain method, while the FDS is frequency domain. In this paper, we put forward a method to get the dissipation factor curve of FDS under low frequency by carrying out the PDC experiment. This method is based on three R-C series branches extended Debye model. In this model each branch stands for a type of polarization process. Firstly, The measurement of cable samples aged for different days is carried out to get the PDC and dissipation factor curves. Then, the PDC curves are fitted with a third-order exponential decay function, and the parameters of the extended Debye model are calculated. Comparing the calculated dissipation factor curves with the measured, we find that they agree very well with each other under low frequency range. By this way, we can reduce the measuring time.