Faculty of Engineering and Built Environment
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Item High impedance fault detection protection scheme for power systems distribution networks(Elsevier BV, 2022) Moloi, Katleho; Davidson, InnocentProtection schemes are used in safe‐guarding and ensuring the reliability of an electrical power network. Developing an effective protection scheme for high impedance fault (HIF) detection remains a challenge in research for protection engineers. The development of an HIF detection scheme has been a subject of interest for many decades and several methods have been proposed to find an optimal solution. The conventional current‐based methods have technical limitations to ef‐ fectively detect and minimize the impact of HIF. This paper presents a protection scheme based on signal processing and machine learning techniques to detect HIF. The scheme employs the discrete wavelet transform (DWT) for signal decomposition and feature extraction and uses the support vec‐ tor machine (SVM) classifier to effectively detect the HIF. In addition, the decision tree (DT) classi‐ fier is implemented to validate the proposed scheme. A practical experiment was conducted to ver‐ ify the efficiency of the method. The classification results obtained from the scheme indicated an accuracy level of 97.6% and 87% for the simulation and experimental setups. Furthermore, we tested the neural network (NN) and decision tree (DT) classifiers to further validate the proposed methodItem Optimization of university campus microgrid for cost reduction: a case study(Trans Tech Publications, Ltd., 2022) Akindeji, Kayode Timothy; Tiako, Remy; Davidson, InnocentThis paper presents an optimization model to minimize the fuel cost and CO2 emision on university campuses using an hybrid power system (HPS). The HPS is made up of solar photovoltaic (PV), diesel generator (DG), wind turbine (WT) and battery energy storage system (BESS). Two university campuses are used as case study to investigate the efficiency of the proposed HPS. The objective function is formulated such that each campus load is met by the renewable energy source (RES) when available and the DG only swicthes on when the output of the RES is not eneough to meet the load. The resulting non linear optimization problem is solved using a function in MATLAB called “quadprog”. The results of the simulation are analyzed and compared with the base case in which the DG is used exclusively to meet the entire load. The results show the effectiveness of the optimized HPS in saving fuel when compared to the base case and reflect the effects of seasonal variations in fuel costs.Item The use of the carrier to noise ratios (C/N0) to alleviate the problematic GNSS phase multipath(IEEE, 2022-01-25) Madonsela, Bheki; Davidson, Innocent; Mukubwa, EmmanuelThe Global Navigation Satellite System (GNSS) multipath caused by the large time delays of the reflected signal causes errors to the output of the GNSS receiver, the Position, Velocity and Time (PVT). These errors are mitigated by the technology and architecture of the GNSS receiver. Numerous research has been conducted to reveal the correlation between the Signals to Noise Ratio (SNR). Various multipath-mitigating techniques uses the concept of SNR measurements during the data processing in the GNSS receiver to ease the impact of the signal multipath if the signal is imitated. In this paper, we define and analyse the concept of the multipath mitigation techniques that are dependent to the SNR measurements. Hence, all signal components that are found in GNSS signal such as phase, code, time and SNR will be utilized to estimate impact of the GNSS phase multipath. The technique of the C/V0 is incorporating the density power ration to the SNR measurements and this is used to calculate reliability of the GNSS signal tracking.Item Thermocouple signal conditioning using augmented device tables and table look-up neural networks, with validation in J-Thermocouples(IEEE, 2022-01-25) Maseko, Moses L.; Agee, John T.; Davidson, InnocentThe relatively high accuracy, large measurement range, and durability of thermocouple devices make these devices to probably be the most-widely used temperature measuring devices in industrial applications. The ability of thermocouples to sense temperature is derived from the generation of thermoelectric voltages arising due to temperature differences between the hot and cold junctions of the thermocouple. Thermocouple temperature measurement processes suffer from inaccuracies arising from both the unwanted or undetected variations in the cold junction temperature of the thermocouple, and nonlinearities in the generated thermoelectric voltage. This paper presents an enhancement of thermocouple temperature measurement using a combination of augmented thermocouple tables generated from thermocouple polynomial functions, look-up MLP neural networks trained to accept the thermocouple output voltage, and the cold or reference junction temperature measurements: to produce improved hot-junction temperature outputs. Experimental validation of the current approach for a J thermocouple, using data from augmented device tables, reproduced the measured temperature values with a worst-case error of 0.0094%.Item A new technique for improvement differential relay performance in power transformers(IEEE, 2022-01-25) Ngema, Philani; Buraimoh, Elutunji; Davidson, InnocentTransformer protection devices are often used to identify internal or external transformer problems and act to either prevent damage or unnecessarily disconnect power transformers. This study proposes a new differential element that combines harmonic restraint, security, and reliability with harmonic blocking speed to improve the relay performance in a power transformer. Under high load, a negative-sequence differential element adds more sensitivity for internal turn-to-turn failures. External fault detection monitoring enhances security in an external problem involving current transformer (CT) saturation. Furthermore, overcurrent elements may be configured to vary dynamically in operation is provided. This element enhances protection coordination for various operating conditions without requiring modifications to the transformer group settings. The balance of the paper discusses the use of an under-load tap changer using a time-synchronized phasor monitoring system to reduce loop current and losses in parallel transformer applications.Item Investigation and mitigation of temporary overvoltage caused by de-energization on an offshore wind farm(MDPI AG, 2020-08) Akinrinde, Ajibola O.; Swanson, Andrew; Davidson, InnocentThe Ferranti effect could cause a rise in voltage along the cables on a wind farm if the circuit breakers at the receiving ends are switched off. Ferroresonance could also occur due to stuck pole(s) of the circuit breaker during de-energization. This paper reports on the temporary overvoltage (TOV) arising from the de-energization of the circuit breaker connecting the wind turbine to the feeder, the feeder breaker connecting an array of wind turbines to the point of common coupling (PCC), and the opening of the circuit breaker connecting the onshore to the offshore substation. Ferroresonance was characterized using a phase plane diagram and Poincaré map and was identified to be chaotic. The effect of the nonlinear characteristic of the wind transformer core on the ferroresonant overvoltage was examined and increased with the steepness of slope of the transformer curve. A damping resistor, shunt reactor and surge arrester were used to mitigate the overvoltage experienced during the ferroresonant event. The damping resistor was able to reduce the overvoltage to 1.24 P.U. and damped the ferroresonance from chaotic to fundamental mode.