A review of cognitive smart grid communication infrastructure system

Abstract: The reliance on obsolete communication infrastructure and outdated technologies, in order to meet increasing electricity demand, consists of major challenges confronting traditional power grids. Therefore, the concept of smart grids (SGs) has been adopted as an ideal solution. This concept entails the integration of advanced information and communication technologies (ICTs) into power grids, as well as allowing a two-way flow of communication. However, recent development in cognitive technologies internet of things (IoT) smart devices particularly in home area network (HAN) as well rapid growth in wireless applications have enabled the traffic of huge data volumes across SGs. Data gathered in SGs are distinguished by quality of service (QoS) requirements such as; latency, security, bandwidth, etc. In order to support the level of QoS requirements in SGs, stable and secure communication infrastructure is of great importance. Therefore an in-depth review of the stateof- the-art of existing and emerging communication architectures of SGs is conducted. Therefore, this work proposes communication architecture based on fifth-generation (5G) and cognitive radio networks (CRN)

A review of microgrid-based approach to rural electrification in South Africa : architecture and policy framework

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A Predicted-Risk-Based Protection Approach for Turbine Generator Shafts against Fatigue Damage due to Islanding

A distributed generation steam turbine generator (hereafter referred to as turbine generator) improves the supply reliability of the local load when operated as a backup supply during islanding. Interconnection standards recommend removing the utility load from the island. Transient torques induced at the moments of islanding and removing the utility load from the island may cause shaft fatigue life loss and lead to fatigue damage. Therefore, a protection method is proposed in this work. The method is based on predicting the risk of shaft fatigue damage. Induced transient torque is first modeled. Fatigue study determines the local load size required to mitigate shaft torsional vibrations and avoid fatigue life loss during islanding. This is substituted in the torque function to obtain the critical torque. The risk of shaft fatigue damage is predicted by comparing the actual shaft torque with the critical torque. The turbine generator is shut down when the actual shaft torque during islanding exceeds the critical torque. Islanding on the local load is allowed when the actual shaft torque is smaller than the critical torque. The proposed method yields 0.011% shaft fatigue life loss under the most adverse islanding condition against 100% obtained with an online monitoring and protection system (OMPS)

A Predicted-Risk-Based Protection Approach for Turbine Generator Shafts against Fatigue Damage due to Islanding

A distributed generation steam turbine generator (hereafter referred to as turbine generator) improves the supply reliability of the local load when operated as a backup supply during islanding. Interconnection standards recommend removing the utility load from the island. Transient torques induced at the moments of islanding and removing the utility load from the island may cause shaft fatigue life loss and lead to fatigue damage. Therefore, a protection method is proposed in this work. The method is based on predicting the risk of shaft fatigue damage. Induced transient torque is first modeled. Fatigue study determines the local load size required to mitigate shaft torsional vibrations and avoid fatigue life loss during islanding. This is substituted in the torque function to obtain the critical torque. The risk of shaft fatigue damage is predicted by comparing the actual shaft torque with the critical torque. The turbine generator is shut down when the actual shaft torque during islanding exceeds the critical torque. Islanding on the local load is allowed when the actual shaft torque is smaller than the critical torque. The proposed method yields 0.011% shaft fatigue life loss under the most adverse islanding condition against 100% obtained with an online monitoring and protection system (OMPS)

Defining and Specifying Design Considerations for Distribution Transformers in Large-Scale Solar Photovoltaic Plants

In the new era of the renewable energy market in South Africa, there is a knowledge gap in the technical standards relating to distribution transformers, which are exclusively intended to serve in large-scale solar photovoltaic (PV) applications. The problem arises from the reality that these transformers are compelled to facilitate an environment with a potentially high risk of an unacceptable level of harmonics and distortion. What manufacturers currently need is a comprehensive transformer specification for DT transformers in PV applications, as the standards currently in use for regular transformers have so far proven to be inadequate. The latter triggers the need for this work to contribute to the advancement of this knowledge gap by mapping a comparative analysis of defining and specifying the design considerations for solar PV transformers. Initially, the computation of the various transformer losses at multifaceted active-part structures under normal conditions by employing the proposed finite element analysis (FEA) is presented. Then, two design case studies are described and the harmonic load current content to which the transformer will be susceptible during operation is specified and used for the analysis. Lastly, the design losses computed using the proposed FEA are substantiated using practical measurements

A Technique for Transformer Remnant Cellulose Life Cycle Prediction Using Adaptive Neuro-Fuzzy Inference System

This article presents an ultramodern modelling algorithm for predicting the remnant cellulose life cycle for oil-submerged power transformers based on the adaptive neuro-fuzzy interference system (ANFIS). The polymer characteristics, degree of polymerization (DP), and 2-furaldehyde (2FAL) of 100 power transformers were measured and collated, which were apportioned into 70 training databanks and 30 as testing datasets. The remnant cellulose life cycle of the transformer was predicted using the proposed ANFIS model characterized by polymer characteristics, DP and 2FAL as inputs. The proposed approach returns 98.23% training and 99.86% testing reliability. The proposed model was applied to 10 transformer case studies in predicting their remnant cellulose life cycle. To corroborate the proposed ANFIS, a comparative study was carried out by employing existing approaches in predicting the remnant life cycle of the case studies, and significant error margins were observed. At large, the results presented in this article certify the dominance of the proposed ANFIS algorithm over compared models. The proposed ANFIS furnishes a pathway to obliterate the constraints of classical techniques in evaluating the transformer DP and remnant cellulose life cycle

Battery Energy Storage for Photovoltaic Application in South Africa: A Review

Despite the significant slowdown of economic activity in South Africa by virtue of the COVID-19 outbreak, load shedding or scheduled power outages remained at a high level. The trend of rising load-shedding hours has persisted throughout most of the year 2022. Operational issues within the South African power utility inflamed the unpredictable nature of generation capacity, resulting in unscheduled outages at several generating units, mostly due to multiple breakdowns. To forestall substantial spikes in energy costs, an increasing number of enterprises and homeowners have started to gradually adopt renewable energy technologies to sustain their operational demand. Therefore, there is an increase in the exploration and investment of battery energy storage systems (BESS) to exploit South Africa’s high solar photovoltaic (PV) energy and help alleviate production losses related to load-shedding-induced downtime. As a result, the current work presents a comprehensive and consequential review conducted on the BESS specifically for solar PV application and in the South African context. The research investigations carried out on BESS for PV application are crucially examined, drawing attention to their capacities, shortcomings, constraints, and prospects for advancement. This investigation probed several areas of interest where the BESS-PV scheme is adopted, viz., choice of battery technology, mitigating miscellaneous power quality problems, optimal power system control, peak load shaving, South African BESS market and status of some Real BESS-PV projects. The techno-economic case scenario has been proposed in the current research and results yield that lithium-ion batteries are more viable than Lead–acid batteries

Stray Load Loss Valuation in Electrical Transformers: A Review

The electricity production opus in South Africa has transformed over the last few years from predominantly coal power generation to a blend of renewable energy generation. The necessity emerges to ascertain whether electrical transformer design philosophies in local manufacturers are contemporary in reference to customer specifications, under increasing penetration of harmonics and distortion as a result of increasing deployment of decentralized power systems. Accurate computation of transformer stray load loss is imperative in localizing the hotspot regions and design of adequate insulation system and consequently cooling system. This loss must also be met by manufacturers based on the customer specifications to avoid penalties. The review of current scientific works affirms the ongoing interest in utilizing the advancement of computational power for painstaking evaluation and management of stray load loss in electric transformers. This article confers overview research, evolution and application of diverse computer-based tools for analyzing the stray load loss based on over 60 published scientific works. Mathematical formulations that can be practically employed by transformer designers during the design phase under normal and harmonic load current conditions are discussed

Stray Load Loss Valuation in Electrical Transformers: A Review

The electricity production opus in South Africa has transformed over the last few years from predominantly coal power generation to a blend of renewable energy generation. The necessity emerges to ascertain whether electrical transformer design philosophies in local manufacturers are contemporary in reference to customer specifications, under increasing penetration of harmonics and distortion as a result of increasing deployment of decentralized power systems. Accurate computation of transformer stray load loss is imperative in localizing the hotspot regions and design of adequate insulation system and consequently cooling system. This loss must also be met by manufacturers based on the customer specifications to avoid penalties. The review of current scientific works affirms the ongoing interest in utilizing the advancement of computational power for painstaking evaluation and management of stray load loss in electric transformers. This article confers overview research, evolution and application of diverse computer-based tools for analyzing the stray load loss based on over 60 published scientific works. Mathematical formulations that can be practically employed by transformer designers during the design phase under normal and harmonic load current conditions are discussed

A Novel Approach to Predict Transformer Temperature Rise under Harmonic Load Current Conditions

In South Africa, distribution transformers (DTs) facilitating solar photovoltaic applications represent the highest percentage of total ownership cost investment for independent power producers (IPPs). One of the most indispensable variables that regulate DTs’ operational life span is the hotspot temperature. The prevailing analytical approaches designated to guesstimate the transformer thermal necessities were fathered in accordance with the conservative foundation that an electrical transformer is prone to uniform mean daily and monthly peak loads. In order to appropriately puzzle out the transformer thermal necessities, the formation of a more detailed thermal model that operates with real-time contorted cyclic loading, ambient air temperature, and the intrinsic characteristics of the transformer in-service losses is required. In the current work, various regression models are proposed for the modification of the top-oil formula and the hotspot temperature formula in the IEEE loading guide standard to replicate the real harmonic load currents (HLCs) and the fluctuating ambient air temperature (AT) on an hourly and daily basis. The proposed thermal model is examined in various transformers case studies, in which the computed outcomes produce an error margin of no more than 3% throughout all test cases when compared to the measured data