Ghulam Murtaza Hashmi

Modeling and experimental verification of on-line PD detection in MV covered-conductor overhead networks

The falling trees on covered-conductor (CC) overhead distribution lines produce partial discharges (PDs). The measurements have been taken in the laboratory and PD signal characteristics under various circumstances have been described. In this paper, an on-line single-phase PD monitoring system using Rogowski coil is simulated in EMTP-ATP. The simulation results are compared with those obtained from the laboratory measurements. The proposed model can be used to estimate the length of the practical CC lines at which PDs due to falling trees can be detected and localized; thus, deciding the number and positioning of the sensors over a particular length of the CC lines. The different noise sources have been described that cause interference with low level PD signals, which is a major challenge for on-line/on-site condition monitoring. The design aspects of the wireless sensor for this specific application are also discussed. Automatic detection of falling trees will reduce visual inspection work after storms and it will improve reliability and safety of the CC distribution system.

Multi-end correlation-based PD location technique for medium voltage covered-conductor lines

In Finland, overhead covered conductors (CC) are commonly used in the medium voltage (MV) networks because the distribution loads in rural areas are not heavy and are widely distributed in the forested terrain. Such parts of the network are exposed to leaning trees and therefore partial discharging into the overhead CC frequently occurs. In this paper, a multi-end correlation-based technique for locating partial discharge (PD) sources on CC lines is presented. The theory of maximum correlation factor is used in order to find the time differences between signal arrivals at three synchronized-measuring points. This helps to solve the problem of varying parameters of the CC line that can change the propagation velocity and the problem of identifying the arrival times of the corresponding PD pulses at different measuring points. The algorithm is developed and tested using a simulated study and experimentally verified using an alternating current (ac) energized system. The Electromagnetic Transient Program-Alternative Transient Program (EMTP-ATP) is used to implement and analyze a PD monitoring system. The Discrete Wavelet Transform (DWT) is used to de-noise PD signals measured from a Rogowski coil utilized as a high frequency transducer. The noise model is added to the simulated-power network signals and then a DWT-based de-noising process is carried out. The proposed algorithm performance is evaluated by extracting the high frequency features using a windowed-standard deviation. The simulated and experimental evaluations prove that accurate PD source location can be achieved using the proposed algorithm technique.

Covered-Conductor Overhead Distribution Line Modeling and Experimental Verification for Determining its Line Characteristics

In this paper, theoretical model of the covered-conductor (CC) overhead distribution line is presented and the frequency-dependent distributed transmission line (TL) parameters, wave propagation characteristics, and characteristic impedance are calculated. The derived wave propagation characteristics are compared with those obtained from the time domain reflectometry (TDR) measurements to validate the theoretical model of the CC line. The TDR measuring system is also simulated in EMTP/ATP as real time verification. An accurate determination of the TL characteristics for practical CC lines can be used as a design aid for the modeling of partial discharge (PD) measuring system in EMTP/ATP; thus deciding the optimal locations of the sensors in getting reliable PD detection results due to falling trees on the lines.

Comparing Wave Propagation Characteristics of MV XLPE Cable and Covered-Conductor Overhead Line using Time Domain Reflectometry Technique

In this paper, the wave propagation characteristics of single-phase medium voltage (MV) cross-linked polyethylene (XLPE) cable are determined using time domain reflectometry (TDR) measurement technique. TDR delivers the complex propagation constant (attenuation and phase constants) of lossy cable transmission line as a function of frequency. The frequency-dependent propagation velocity is also determined from the TDR measurements through the parameters extraction procedure. The TDR measurement results for MV XLPE cable and covered-conductor (CC) overhead line are compared and it is proved that CC line has lower attenuation and higher propagation velocity than power cable. The measurement results can be used to localize the discontinuities in XLPE power cables and for PD detection to monitor falling trees on the MV CC overhead lines.

On-line PD measuring system modeling and experimental verification for covered-conductor overhead distribution lines

In this paper, EMTP/ATP simulation environment is used to model on-line single-phase partial discharge (PD) measuring system using Rogowski coil for the monitoring of falling trees on the covered-conductor (CC) overhead distribution lines. The CC is modeled as a distributed parameters line and Rogowski coil is modeled based on its equivalent circuit as a saturable current transformer having linear magnetizing characteristics. The simulation results are compared with those obtained from the laboratory measurements. The model can be used to estimate the length of the CC line at which PDs due to falling trees can be detected; thus, deciding the number and positioning of the sensors over a particular length of the CC overhead distribution line.