Hasan, Md Mahamudul (2020) Modelling and Evaluation of SWER Channel for PLC-based Protection Scheme Applications. PhD thesis, Victoria University.

Abstract

After the disastrous “Black Saturday" bushfires of 2009, bushfire mitigation efforts for preventing power line faults has become one of the most intriguing research topics for the Australian industry. This thesis presents narrowband channel modelling efforts supported by experimental analysis of key fundamental concepts in developing a novel Power Line Communication (PLC)-based protection scheme for rural Single Wire Earth Return (SWER) networks. A SWER line often breaks and makes contact with vegetation when hit by a falling tree, starting fires. The proposed protection scheme relies on transmitters at various ends of the network continually transmitting to a receiver at the substation end. If the line breaks, then there will be a loss of transmission indicating a potential line breakage. Irrespective of the application, accurate channel modelling is critical in studying how the SWER channel would perform as a potential communication channel for PLC signal transmission and assessment of the channel’s performance with regards to key questions on the attenuation, signal-to-noise ratio, and reliability. This thesis therefore presents narrowband modelling procedure and analysis of an exemplary SWER distribution network as a potential PLC communication channel. The protection scheme is to be implemented over this channel. The research presented focuses on the channel modelling and network coupling aspects of the work, rather than the design of the protection scheme itself. Narrowband network modelling includes High-Frequency (HF) modelling of overhead conductors, transformers, and a capacitive coupling circuit. Three different types of SWER conductors have been tested and modelled to justify the model. Line modelling was undertaken based on the mathematical modelling of overhead conductors using a lossy line model with frequency-dependent characteristic such as the characteristic impedance, line resistance and radiation. Another key contribution is the introduction of a modelling method that relied on s-parameter measurements of network elements such as transformers and coupling circuits and their integration into the narrowband model. This was used particularly in the modelling of transformers by measuring, recording, and integrating real data from these network elements. One-port winding impedance measurements and two-port s-parameter data have been integrated into the model significantly reducing the effort required in the modelling of transformers evading a time-intensive discrete modelling process. High Frequency (HF) modelling of an entire end-to-end network has enabled simulation of the overhead network to predict PLC signal tone strengths for a number of cases including the de-energised and grid connected network scenarios. The technique has been used for an evaluation of the profile of transmitted and received signals under different conditions. The proposed narrowband model has been verified by comparing with measurements from field injection tests. PLC propagation field tests were successfully undertaken with the logistic support from the industrial partner, which included network access, site acquisition and other in-house support during the test dates. Results show high accuracy between the actual measurements and the model predicted signal strengths with a mean error rate of 2.27 dB and 3.10 dB across the frequency band for the de-energised and grid connected cases respectively. The network model has also been used to analyse the impacts of parameters such as network size, pole height, and loading effect on the PLC propagation with findings expected to inform the development of the proposed protection scheme. Development of a High Voltage (HV) coupling circuit is one of the biggest challenges in HV-PLC applications. In this work, a HV coupling capacitor based L-C impedance matching circuit has been designed, built and tailored for the proposed SWER PLC protection application. Impedance characterization of the power line integrated HV-coupling capacitor was a real challenge, which has been addressed in this thesis and a simplified method demonstrated for its modelling. This frequency dependent impedance measurement technique could be used to categorize the impedance characteristics of other HV-coupling capacitor-based PLC applications. The designed coupling circuit shows promising performance, with only around -4 dB insertion loss for evaluated 50 kHz to 150 kHz band. The thesis has been divided into seven chapters. Chapter 1 introduces the motivation behind the work, key objectives and the methodology employed. Chapter 2 covers an up-to-date literature review. Chapter 3 comprises the design, evaluation and performance analysis of the proposed HV capacitive coupling matching circuit. Chapter 4 presents impedance modelling of a various SWER conductors with mathematical detailing. Chapter 5 discusses a novel hardware in loop approach for modelling HF SWER transformers. Chapter 6 represents the entire end-to-end network model, its simulation studies, and comparison of simulation results against measurements from field propagation tests. Chapter 7 includes the conclusion by summarizing all significant key findings with hints on potential future works.

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