Review of HRESs based on storage options, system architecture and optimisation criteria and methodologies

The fast-growing awareness of depleting fossil fuel and the adverse impact of conventional energy generation methods on the environment has brought passionate attention to renewable energy sources (RE source). Owing to stochastic nature of energy production from renewable energy system (RES), two or more sources are combined to form hybrid RE system (HRES). Optimisation of size, cost and reliability of power production of HRES are important factors in the planning of HRES. This study presents a review of optimisation tools and constraints on which HRES system is optimised. The types of storage/backup system available for HRES are also presented in this study.http://digital-library.theiet.org/content/journals/iet-rpghj2018Electrical, Electronic and Computer Engineerin

A decisive evaluation of parks transformation based commonly used voltage detection method

The abc-to-dq0 based voltage detection technique is commonly employed in static transfer switch (STS) applications, which are targeted to protect sensitive loads against variety of disturbances. The technique is quite fast and precise especially in case of balanced disturbances. However balanced events seldom occur as compared to unbalances in supply system. Also there is every possibility that sensitive load may comprise of combination of single phase and three phase loads and therefore to offer a ride through capability during most of events, it is equally important to maintain good power quality at both single-phase and three-phase levels. The effectiveness and the capacity of the detection scheme are analyzed against common disturbances, routine operations of power system, under balanced variations which are within acceptable limits and against unbalances of hybrid nature (simultaneous presence of the sag and swell events). The impact of control elements on the detection process is also discussed.http://www.skit.ac.in/academics/skit-research-journal.htmlam2017Electrical, Electronic and Computer Engineerin

Reactive power and harmonic compensation : a case study for the coal-mining industry

This study reports on a case study in Grootegeluk Mine: Exxaro Coal, Lephalale, South Africa, in terms of power factor correction (PFC), load flow, harmonic frequency scans and harmonic voltage distortion anal-yses. The DIgSilent PowerFactory software was used for network simulations. Harmonic and reactive power compensation techniques were compared in terms of filter type evolution and technology advancement, with the use of simple trade-off criteria such as cost-effectiveness versus performance. It was found that both pas-sive and hybrid filters were more favourable and could effectively compensate all voltage and current har-monics and reactive power for large nonlinear loads. The installation of switched PFC filter banks tuned at the fifth harmonic order accommodates future network growth and this solution can be rolled out to any mining industry as a benchmark to lower energy cost and maximise savings achievable on the electricity bill.http://journals.assaf.org.za/jesaam2020Electrical, Electronic and Computer Engineerin

A review on DC collection grids for offshore wind farms with HVDC transmission system

Abstract: Traditionally, the internal network composition of offshore wind farms consists of alternating current (AC) collection grid; all outputs of wind energy conversion units (WECUs) on a wind farm are aggregated to an AC bus. Each WECU includes: a wind-turbine plus mechanical parts, a generator including electronic controller, and a huge 50-or 60-Hz power transformer. For a DC collection grid, all outputs of WECUs are aggregated to a DC bus; consequently, the transformer in each WECU is replaced by a power converter or rectifier. The converter is more compact and smaller in size compared to the transformer. Thus reducing the size and weight of the WECUs, and also simplifying the wind farm structure. Actually, the use of offshore AC collection grids instead of offshore DC collection grids is mainly motivated by the availability of control and protection devices. However, efficient solutions to control and protect DC grids including HVDC transmission systems have already been addressed. Presently, there are no operational wind farms with DC collection grids, only theoretical and small-scale prototypes are being investigated worldwide. Therefore, a suitable configuration of the DC collection grid, which has been practically verified, is not available yet. This paper discussed some of the main components required for a DC collection grid including: the wind-turbine-generator models, the control and protection methods, the offshore platform structure, and the DC-grid feeder configurations. The key component of a DC collection grid is the power converter; therefore, the paper also reviews some topologies of power converter suitable for DC grid applications

Protection Of Microgrids Using Voltage-Based Power Differential And Sensitivity Analysis

ArticleMicrogrids are emerging as an alternative mode of operation for distribution systems integrated with Distributed Energy Resources (DERs). With appropriate management and control of the DERs, a section of a distribution system can operate isolated from the main grid thereby enhancing the reliability and security of supply to consumers. However, the integration of DERs has raised many technical challenges including protection. The traditional distribution system protection cannot provide reliable protection to the microgrid in the isolated mode due to the limited short-circuit capacities of the converter-interfaced DERs. This paper proposes the application of a new voltage-based relay type for the protection of microgrids. The relay algorithm achieves its protection function through active power differential and sensitivity calculations based on voltage measurements within a specified protection zone. In the paper, the new relay type is modelled in Digsilent PowerFactory software and installed at the nodes of a microgrid test system. The performance of the relay type is investigated under variety of faults. The relay is shown to operate correctly and effectively to detect and identify faults in both radial and meshed microgrids integrated with inverter-interfaced DER technologies

Performance Evaluation of Power Differential and Sensitivity Based Protection for Active Distribution Systems

ArticleProtection performance is characterized by qualities that include selectivity, speed, sensitivity and stability. Generally, selectivity and speed present conflicting requirements on the protection design, as do sensitivity and stability requirements. The integration of distributed generation (DG), in particular at the distribution level, further compromises satisfactory achievement of these performance qualities. A recent paper by the authors introduced a protection algorithm based on active power differential and sensitivity analysis (APdSA) for the protection of active distribution systems and microgrids. This paper investigates the performance characteristics of this algorithm with respect to selectivity, sensitivity, stability, and speed. It is shown that, with an important modification to the protection zoning arrangement, the APdSA algorithm is able to selectively clear faults in a DGintegrated distribution system with high sensitivity, stability, and speed, with more than 95% reach over a wide range of fault resistances. The algorithm is also tolerant to communication failure

Visual Fields at Presentation and after Trans-sphenoidal Resection of Pituitary Adenomas

Purpose: To evaluate visual field changes in patients with pituitary adenomas following trans-sphenoidal surgery. Methods: Eighteen patients with pituitary adenomas underwent a complete ophthalmic assessment and visual field analysis using the Humphrey Field Analyzer 30-2 program before and after trans-sphenoidal surgical resection at the Himalayan Institute of Medical Sciences over a one year period. Visual acuity, duration of symptoms, optic nerve head changes, pattern of visual field defects, and variables such as mean deviation and visual field index were compared. Results: Thirty-six eyes of 18 patients including 10 male and 8 female subjects with mean age of 35.1±9.9 years and histologically proven pituitary adenoma were included. Mean visual acuity at presentation was 0.29 logMAR which improved to 0.21 logMAR postoperatively (P = 0.305). Of 36 eyes, 24 (66.7%) had visual field defects including temporal defects in 12 eyes (33.3%), non-specific defects in 10 eyes (27.8%), and peripheral field constriction in 2 eyes (5.6%). Mean deviation of visual fields at presentation was -14.28 dB which improved to -11.32 dB postoperatively. The visual field index improved from 63.5% to 75% postoperatively. Favorable visual field outcomes were correlated with shorter duration of symptoms and absence of optic nerve head changes at presentation. Conclusion: Visual field defects were present in two thirds of patients at presentation. An overall improvement in vision and visual fields was noted after surgical resection. An inverse correlation was found between the duration of symptoms and postoperative visual field recovery, signifying the importance of early surgical intervention

Experimental evaluation of matrix converter for wind energy conversion system under various abnormal conditions

This paper presents the experimental evaluation of reversed indirect matrix converter (MC) interfaced wind energy conversion system (WECS), where space vector pulse width modulation together with adaptive fuzzy logic control is effectively used to enhance the performance of system under various abnormal conditions like abrupt change in wind speed, disconnection from grid, misfire in the converter, sudden out of one phase, change in load etc. The proposed adaptive control system is realized using dSPACE DS1104 board. Selective experimental results are presented using a laboratory 1.2 kW prototype of WECS to demonstrate the resulting improvements of the developed system under abnormal conditions.http://www.ijrer.org/ijrer/index.php/ijreram201

A motor management strategy for optimising energy use and reducing life cycle costs

With increasing energy costs and renewed focus on using energy in ways that support the environment, a structured approach is required to ensure that energy is used efficiently. A comprehensive motor management strategy to reduce motor life cycle costs while increasing reliability is presented. The application of energy management principles is combined with benefits that can be obtained from using energy-efficiency motors. An economic model for determining the optimal time a motor should be replaced with a higher efficiency motor is proposed. The strategy presented incorporates benefits that can be obtained from using in-situ motor efficiency estimation and condition monitoring techniques as part of a motor management system.http://www.scirp.org/journal/jpeeam201

Optimization of an isolated photo-voltaic generating unit with battery energy storage system using electric system cascade analysis

This paper presents an improvement to the iterative method of electric system cascade analysis (ESCA) for the optimisation of an isolated PV system with battery energy storage system (BESS) for a residential load. The ESCA algorithm is implemented on MATLAB software environment with Final Excess Energy (FEE), Loss of Power Supply Probability (LPSP) and system cost as optimization constraints. The load, temperature and solar radiation profiles are considered for a year, based on historical data. Practical losses in solar radiation reaching the PV collector surface are considered for analysis. Change in PV efficiency due to variation in temperature and change in charge/discharge efficiency of the battery based on current state of charge (SOC) of BESS are taken into consideration which further bolsters the credibility of the ESCA methodology. The ESCA methodology is used to optimize a PV-BESS system for a residential load with average daily consumption of 26.1 kWh. The optimized result obtained from improved ESCA are compared and verified with benchmark HOMER software.http://www.elsevier.com/locate/epsr2019-11-01hj2018Electrical, Electronic and Computer Engineerin