Analysis and Research on Factors Affecting the Reliability of Medium Voltage Power Supply

Over the past 10 years, the use of distributed generation (DG) has become one of the important directions in the development of the electric power industry in many countries across the world. According to its purpose, DG is used to supply remote electricity consumers. In conditions of market uncertainty in the development of the energy sector, one of the most profitable solutions for increasing the reliability of consumer power supply is to install a small-scale generation near the distant loads. Under such option the risks of energy shortage and loss of power supply from power source of the main network are reduced, reliability of power supply is improved, the energy quality parameters are improved, power and energy losses are reduced. However, the growth of the DG penetration in electric power systems (EPS) has not only positive aspects, but also creates certain technical problems that are associated with fluctuations of EPS parameters as well as with DG controllability under normal and emergency conditions. These problems can be solved but at the cost of more complex EPS dispatch and automatic control. The solution requires new mathematical models to substantiate the development of EPS and power supply systems, to analyze and to manage their state. In this article the authors propose a novel mathematical model for DG planning and optimization basing on integral quality criterion that incorporates power supply quality and reliability.

This research investigates the integration of renewable energy sources such as solar and wind into Nigeria’s power grid. The main objective is to develop a simulation model that examines how renewable energy systems affect power reliability and supply efficiency under different load and generation conditions using MATLAB. The simulation setup includes solar photovoltaic arrays and wind turbines connected to the grid through inverter systems and controlled using standard power system techniques. Changes in solar radiation and wind speed are introduced during the simulation to reflect real-life variations in renewable energy generation. The results show that, despite their variable nature, solar and wind systems can support the grid effectively when combined with proper control, forecasting, and storage technologies. The study demonstrates that integrating renewable energy into the grid can reduce power shortages, improve electricity access, support a more stable and reliable power supply as well as contribute to sustainable development goals by promoting the use of renewable energy in Nigeria.

Improving the reliability of electric power supply has always been one of the main tasks. The relevance of the task of ensuring of reliable electric power supply is particularly high for the agricultural enterprises with industrial type, especially for the livestock farms. High technical and economic requirements to the quality and efficiency of agricultural technological processes determine the necessity of solving the problem of ensuring reliability of the electric power supply systems of the enterprises involved in agricultural production. In such systems there is a great number of switches, devices of protection and control. These devices operate in heavy-duty with a large number of various perturbations, leading to a substantial reduction of the standard life and the occurrence of switching malfunctions, causing to a decrease in ex-operational reliability. The known methods and technical means of control and registration of emergency situations are not effective enough, narrowly specialized, complex, expensive. Consequently, the development on the basis of new methods of control effective technical means to remotely control the state of electrical equipment in operation, operated in terms of agriculture is a relevant and practically important task nowadays. In this article, the authors propose a new method of remote control of switch's state in the partitioned lines. This method allows to control the state of the switch upon the occurrence the short circuit, happened after the installation of the switch. The proposed method of control is implemented in the remote control of switches of the power lines on the basis of the analog-to-digital converters with following processing of the receiving data with special computer program. The implementation of this method remote control switch enables to increase the reliability of power supply of agricultural consumers.

Power supply reliability (rate) directly reflects the capability of a network in supplying power to its customers. Through reliability analysis, it is possible to locate major factors in links of power generation, transmission and distribution that affect the reliability of power supply and to put forward measures for improvement. This paper makes an analysis of the reliability of the urban power supply of the Shandong power network, China, in 1995. (5 pages)

When grid-connected micro grid operates in island mode, the energy output of micro sources and the capacity of energy storages cannot ensure the power supply for all micro grid loads, it is necessary to remove part of micro grid loads in order to maximally guarantee the power supply for the important loads and extend the power supply time of all loads as far as possible. In this paper, an optimal load shedding strategy of micro grid based on improving the reliability of load power supply is presented, according to the power prediction of micro sources and loads during the operation of the island, charging and discharging power and surplus energy of energy storages are predicted, and the switching time of loads at different level are determined by optimization. The application of this strategy improves the power supply reliability of all the loads in the micro grid while ensuring the continuous and reliable power supply of important loads. A micro grid simulation system based on the load shedding strategy is established, and the simulation results show the correctness and practicability of the strategy.

Hippopotamus algorithm for optimal sizing of hybrid renewable energy system

A low voltage, high current, modular 50 V, 700 A dc power supply has been developed to bias 35 number of 500 W, 505.8 MHz solid state RF amplifiers. This power supply incorporates 7 number of 50 V, 100 A ac-dc power modules, operating in parallel to share the load current. This power supply has two unique attributes namely modular hot swappability and active redundancy. Hot swappable feature incorporated in power modules enables isolation of faulty power modules and facilitates their online replacement without affecting the operation of RF amplifiers and remaining power modules. Active redundancy increases reliability of the power supply significantly. Both these features reduce the down time and increase the availability of the overall system significantly. This paper presents comparison of system reliability of this modular dc power supply with other modular dc power supplies of same output voltage and current rating and having different number of power modules. Suitable mathematical expressions for system reliability of these modular dc power supplies have been evaluated. This power supply also has a digital controller for monitoring the status of 35 number of RF amplifiers and 7 number of power modules as well as controls load current sharing among the power modules. This power supply achieves current THD ≤ 6.2%, input power factor ≥ 0.98, output voltage stability ≤ 0.4% and peak to peak output ripple ≤ 0.2% with overall system reliability and availability approaching near 100%.

The reliability of power supply for users is an actual reflection of power supply enterprises in sustained power supply for users. The current statistical methods of power supply reliability for users adopted currently are mainly based on medium-voltage distribution transformer statistics, which is hard to truly reflect the genuine reliability level for users. This paper has put forward reliability statistical evaluation methods, carried out statistical analysis and calculation to the power supply reliability of medium-voltage users and low-voltage users, and analyzed the impact of different statistical methods for the power supply reliability index. Finally, the feasibility of the calculating modes has been verified by choosing some areas of Shanghai as an example of application, and suggestions on improvement of power supply reliability statistical evaluation for low-voltage users implemented by power supply enterprise have been expounded.

To realize the extension of the reliability index statistics from medium to low voltage and express the power supply reliability comprehensively and accurately, we have developed a low-voltage (LV) customer power supply reliability statistic and assessment system consisting of 4 parts, namely, main station computer system, concentrator, gathering terminal and communication network thus putting into effect the statistics and analysis of the average interruption hours for customers (AIHC), rate of reliability of supply (RS), average interruption times for customers (AITC), net loss of LV systems, voltage acceptance rate, etc. The system has been operating stably and reliably since February 200 Since February 2004 when it began to operate, thus providing an efficient technological means for enhancing power supply quality and customer management. (5 pages)

The research on the rapid secondary reclosing technology proposed by Shandong Electric Power Grid (short delay primary reclosing + long delay secondary reclosing) and boundary switch reclosing and fixed value matching system within the framework of the grid is introduced in this paper. The different distribution network structure identifies the selection of relevant matching principle and secondary reclosing scheme, which changes the current mode which puts emphasis on the safe operation of the system side. The secondary reclosing shortens the user power outage time, achieves the reliability of the user's power supply, improves the quality of power, and provides a high quality distribution network for the users. By continuously optimizing the reclosing strategy and the corresponding protection configuration setting principles, the system to respond to the actual user needs is fully coordinated to improve the reliability of power supply of distribution network.

The reason for the appearance of the first distributed generation in Russia was the high requirements to the reliability of power supply to power consumers of a special group of the first category of reliability. Diesel generating units were used to ensure uninterrupted operation. High costs for technological connection of consumers of the 1st and 2nd categories of reliability have strengthened the tendency to install a backup energy source in the enterprises' own power supply systems. However, setting reserves leads to a decrease in economic efficiency. There are additional costs for maintaining the reserve in a working condition. As a result, enterprises transfer the backup units to the mode of the main power source, and that of the backup function to the centralized power supply system. The creation of such industrial MiniGrid operating in a mode without power supply to the grid increases the cost of electricity for other consumers. Besides, with the departure of industrial enterprises from the centralized power supply, the share of communal and non-industrial consumers is growing. This requires an increase in the manoeuvrability of energy sources. The creation of balanced Energy Cells for energy supply to the population and small and medium-sized businesses that provide services to the population is not accompanied by the negative effects indicated above. In Russia, there are isolated examples of such systems, similarly operating in a mode without supplying power to the grid. Changes are needed to allow active consumers to supply excess capacity to the grid during peak hours in the UES of Russia, for which the grid companies need to be allowed to operate at least in a mode without supplying power to the grid, which will not lead to a decrease in grid companies' revenues from electricity transmission services. The introduction of these changes does not only lead not only to an increase in the reliability of power supply but also to an increase in the economic efficiency of the UES, which will reduce the price of electricity.

This article examines the impact of measures aimed at improving power quality on the reliability of electricity supply to consumers. The main power quality indicators and their effects on the operation of electrical equipment and power system components are analyzed. Measures intended to improve power quality are considered, and the effectiveness of these measures is assessed in terms of reducing failure rates, decreasing power losses, and improving electricity supply reliability indicators. The research results confirm that a comprehensive approach to power quality improvement contributes to enhanced stability and reliability of power supply systems.

With the increasing frequency of large-scale events, the demand for the reliability of power supply is more stringent. In order to ensure the reliability of the power supply system during the event, this paper proposes a method of reliability evaluation and weak link identification for stadium power supply system. Firstly, fault tree model was constructed with any load power supply failure as the top event, and the corresponding minimum cut set was quickly obtained by Binary decision diagram algorithm. Secondly, the two-state model of the system was established based on Monte Carlo simulation, and the operating states of the system and components were obtained by random sampling simulation. System reliability evaluation and component importance evaluation are conducted to assess system power supply capacity and quantify the contribution of each component to system failure. Finally, the proposed method is applied to a typical stadium power supply system to verify the effectiveness.

In Thailand, electric supply services have all been taken over by the state and operated under state enterprises since 1968. Under a law empowering its monopoly, state utilities accumulated assets and built up their manpower to expand and operate the power system to serve the whole country. During the time of high growth in power demand in early the1990 s, the government initiated a move to privatize state electric utilities, the pace of which was firmed up after 1997, the year of the financial crash. Engagement of independent power producers (IPPs) through the use of long-term power purchase agreements (PPAs) for supply of electric power into the system operated by state electric utilities was also initiated from the mid 1990s. Total capacity of IPPs and Small Power Producers (SPPs) that sell excess power from cogeneration on to the system) rose and by the late 1990s started to create a constraint on system economic dispatch. In 1999 the National Energy Policy Council (NEPC) approved a recommendation of international consultants to transform the electric supply industry into a structure similar to the system in the United Kingdom. The transformation was proposed to precede corporatization and privatization of state electric utilities. The objectives of deregulation were to revoke the monopoly in ESI, to improve transparency in electricity pricing, to reduce debts of state enterprises, and to improve economic efficiency. Industry participants have voiced strong objection to the industry model proposed. With the change of market structure in UK to the New Electricity Trading Arrangement (NETA), the secretariat of NEPC also proposed a new structure similar to NETA. More acceptance from industry participants have been received for the new structure. However, it has been assumed that the proposed structure would bring improvement in system reliability, drawing investment into power generation in a manner that would be efficient. Tariff has also been expected to become lower because of the competition in power generation and retail trading. The authors argue that, for developing countries, issues of timely investment in new generation and delivery capacity, stable and reasonable price of electricity, reliability of power supply, fuel diversity and security, equitable access of supply and promotion of social equity are important. Maintaining a functioning ESI that meet the broad objectives of providing reliable power supply to serve social and economic development needs could be prioritized over introduction of complete competition in wholesale generation and retailing. The authors examine the present situation of the industry and propose a transitional model that would serve the broad objectives and introduce gradual competition in the industry. The proposed design would unbundle generation from transmission and retailing. It would aso eventually promote intra-regional interconnection and electricity trading.

Compared with the ground secondary power supply, the aerospace secondary power supply puts forward higher requirements for reliability and safety. This research works to promote the safety and reliability requirements based on resonant reset forward converter. Firstly, the working process of resonant reset forward converter considering parasitic parameters was analyzed, the working mode and waveform were given in detail. Secondly, the parameters of resonant capacitor and excitation inductance were analyzed, which ensure reliable reset for excitation current of the transformer and the voltage spike, which satisfied the derating requirements of MOSFET. Thirdly, the selection and heat consumption of resonant reset capacitor were conducted, and an effective solution was proposed. Finally, a low-power power supply prototype was developed for further experimental analysis. Then the waves of key components were measured. The experiment results showed that reasonable parameters for the selection of resonant reset capacitor can ensure the effective reset of the excitation inductance for the transformer, reduce the peak of MOSFET, improve the EMI, reduce the voltage and thermal stress of the resonant capacitor which improve the reliability of the secondary power supply for aerospace. The converter technology based on resonant reset forward can satisfy the application requirements of high reliability and miniaturization of the aerospace secondary power supply, and will promote the technical accumulation and progress of aerospace power supply.