Supply Reliability Assessment Research Articles

Power supply reliability assessment for a multistate electrical power network with line loss rates

Power supply reliability assessment for a multistate electrical power network with line loss rates

A systematic method for the optimization of gas supply reliability in natural gas pipeline network based on Bayesian networks and deep reinforcement learning

This study proposes a method based on Bayesian networks (BNs) to optimize the reliability of gas supply in natural gas pipeline networks. The method integrates probabilistic safety analysis with preventive maintenance to achieve the targets of minimizing gas shortage risk and reducing maintenance costs. For this, the tasks of unit failure probability calculation, system maximum supply capacity analysis, gas supply reliability assessment and system maintenance planning are performed. A stochastic capacity network model is coupled with a Markov model and graph theory to generate the state space of the pipeline network system. BN, is then, proposed as the modeling framework to describe the stochastic behavior of unit failures and customer gas shortage. The system maintenance problem is converted into a Markov decision process (MDP), and solved by using deep reinforcement learning (DRL). The effectiveness of the proposed method is validated on a case study of a European gas pipeline network. The results show that the proposed method outperforms others in identifying optimal maintenance strategies. The DRL-optimized maintenance strategy is capable of responding to a dynamic environment through continuous online learning, considering the randomness of the unit failures and the uncertainty in gas demand profiles.

Energy supply reliability assessment of the integrated energy system considering complementary and optimal operation during failure

Integrated energy system (IES) is an effective solution for energy and environment problems. In view of the difficulty of traditional reliability assessment methods to reasonably and effectively assess the reliability of the IES, an energy supply reliability assessment method based on sequential Monte Carlo simulation is proposed in this study. The optimal operation of the system is realised by mobilising the multi-energy complementary characteristics during device failure. The reliability of the system under three different operation objectives is compared and analysed. Three new reliability indices are proposed, which take into account the supply of multiple energy loads and the differences among different energy. Finally, through the analysis of energy supply reliability under different objectives, the reasonability of the proposed indices and the flexible scheduling of energy flow under different objectives are verified; therefore, the IES can realise adaptive and targeted operation strategy during device failure. Also, the influence of different device faults on the system's energy supply reliability is ranked, which is of great significance to find the weak parts of the system and provide a reference for the system to improve energy supply reliability.

Gas Supply Reliability Analysis of a Natural Gas Pipeline System Considering the Effects of Demand Side Management

Abstract At present, China has a developing natural gas market, and ensuring the security of gas supply is an issue of high concern. Gas supply reliability, the natural gas pipeline system's ability to satisfy the market demand, is determined by both supply side and demand side and is usually adopted by the researches to measure the security of gas supply. In the previous study, the demand side is usually simplified by using load duration curve (LDC) to describe the demand, which neglects the effect of demand side management. The simplification leads to the inaccurate and unreasonable assessment of the gas supply reliability, especially in high-demand situation. To overcome this deficiency and achieve a more reasonable result of gas supply reliability, this paper extends the previous study on demand side by proposing a novel method of management on natural gas demand side, and the effects of demand side management on gas supply reliability is analyzed. The management includes natural gas prediction models for different types of users, the user classification rule, and the demand adjustment model based on user classification. First, an autoregressive integrated moving average (ARIMA) model and a support vector machine (SVM) model are applied to predict the natural gas demand for different types of users, such as urban gas distributor (including residential customer, commercial customer, small industrial customer), power plant, large industrial customer, and compressed natural gas (CNG) station. Then, the user classification rule is built based on users' attribute and impact of supplied gas's interruption or reduction. Natural gas users are classified into four levels. (1) demand fully satisfied, (2) demand slightly reduced, (3) demand reduced, and (4) demand interrupted. The user classification rule also provides the demand reduction range of different users. Moreover, the optimization model of demand adjustment is built, and the objective of the model is to maximize the amount of gas supplied to each user based on the classification rule. The constraints of the model are determined by the classification rule, including the demand reduction range of different users. Finally, the improved method of gas supply reliability assessment is developed and is applied to the case study of our previous study derived from a realistic natural gas pipeline system operated by PetroChina to analyze the effects of demand side management on natural gas pipeline system's gas supply reliability.

Assessment method for gas supply reliability of natural gas pipeline networks considering failure and repair

Pipeline networks are the primary means of natural gas transmission, and assessing the gas supply reliability is of great significance for the safe and stable operation of pipeline networks. However, current assessment researches for the gas supply reliability are just conducted on the entire pipeline networks and based on the failed pipeline networks, i.e. the assessment process is static. The individual difference differences among users and the reparability of pipeline networks are neglected, which make the assessment results not comprehensive and objective enough. To address these problems, a new assessment index is defined to assess the gas supply reliability of individual users by combining the gas shortage time and severity in this paper, and the gas supply reliability assessment is carried out from the perspectives of entire pipeline networks, individual users, gas shortage amount and gas shortage time. Furthermore, an operation state determination model of pipeline networks is established based on the failure and repair processes. Finally, a systematic assessment method with dynamic characteristics is proposed. By using the assessment method, the gas supply reliability of an actual pipeline network is assessed. The differences between the assessment of entire pipeline network and individual users are compared, and the importance ranking of components is presented. The assessment results can provide a theoretical basis for an economical optimization of the gas supply reliability of pipeline networks.

Supply reliability assessment of a gas pipeline network under stochastic demands

An integrated methodology to assess the gas supply reliability of a gas pipeline network considering stochastic demands is proposed in this study. Typical scenarios are selected based on the structural reliability calculated by probability theory and stochastic process, including the normal scenario and some failure scenarios with a high probability. For each specific scenario, the gas supply condition is assessed based on the Latin hypercube sampling with the Cholesky decomposition method under stochastic demands. The maximum flow method based on the Dijkstra algorithm is adopted to determine whether the gas demand of customers can be fully covered and optimize the supply scheme under shortages. Finally, the assessment results are demonstrated from the following four aspects: the probability distribution of gas shortages under the normal scenario, identification of units with a high failure probability and vulnerable units, the reasons of gas supply shortages and corresponding probabilities, and the probability distribution of supply reliability for a gas pipeline network and each customer. The methodology is applied to a large-scale gas pipeline network in China. The results of the supply reliability assessment are analyzed in detail, and the sensitivity analysis of the gas demand uncertainty level on gas supply reliability is conducted.

Power Supply Reliability Assessment Including Island Division and Network Reconfiguration

After the power distribution system (DS) fails, a single power supply recovery method will cause certain loads to fail to recover in time. To improve the reliability of distribution systems with distributed generation, this paper proposes a two-stage network restoration reliability assessment method considering island division and network reconfiguration. In the process of network fault recovery, firstly, distributed generation is used to supply power to the load point of power loss, islanding of the network after fault with the aim of minimizing power loss. Then the residual network is reconstructed and optimized by considering the network loss and voltage quality. Finally, the improved ieee33 node network is simulated based on Monte Carlo simulation method. The results show that this method is superior and can realize real-time load transfer, reduce power loss, improve the reliability of DS and the economy of system operation, Considering the continuous change of the network structure, the running state of the system can be described more accurately.

Short-term supply reliability assessment of a gas pipeline system under demand variations

It is the basic responsibility for pipeline companies to satisfy the gas demand of customers. A methodology is proposed to assess the short-term supply reliability of a gas pipeline system under demand variations in this paper. Based on the failure rate and repair rate of the pipe segments and compressor units obtained through historical operational data, the probability under different structural failure scenarios of a gas pipeline system is computed through the stochastic process and probability theory. Indices from aspects of adequacy, availability, and shortage rate are developed to reflect the supply reliability. To reflect the assessment results intuitively, the cumulative probability function is adopted to reflect the supply adequacy and availability, and the probability distribution is adopted to reflect the supply shortage rate during the assessment period. For all scenarios, supply reliability is calculated through batch transient hydraulic and thermal simulations of a gas pipeline system by Stoner Pipeline Simulator considering practical operational processes and legal constraints. The proposed methodology is performed based on the Trans-Asian gas pipeline A-B system, and the functions of cross-over valves on supply reliability of the Trans-Asian gas pipeline A-B system is studied.

Power Supply Reliability Assessment of Distribution Network Considering by Operation, Maintenance and Repair

In order to realize automation and intelligence of power system, it is essential to improve the power supply reliability assessment of distribution network. A comprehensive evaluation system for the reliability was proposed in the paper. An overall index system was integrated to introduce the criteria of the operation, maintenance and repair, which are important for the reliability. Entropy weight method and fuzzy TOPSIS method were combined to propose the evaluation model. Empirical analysis was implemented to verify the practicality of the evaluation system.

Gas supply reliability assessment of natural gas transmission pipeline systems

The uncertainty of market demand and dynamic behaviour of the pipeline system are usually ignored in previous gas supply reliability assessments. With the intent of overcoming these deficiencies, a novel methodology to assess the gas supply reliability of natural gas transmission pipeline systems is proposed in this paper. Considering both gas supply capacity and market demand uncertainties, calculations of these two items are integrated into a single Monte Carlo simulation. On each Monte Carlo trial, the hydraulic analysis of unsteady flow is combined with the state transition process simulation to calculate the gas supply capacity. In terms of market demand, the load duration curve technology is employed to predict the amount of demand. Then, the indicator proposed to quantify gas supply reliability is calculated on each trial. Finally, the average gas supply reliability is obtained based on N Monte Carlo trials. Applications of this methodology are demonstrated through a real transmission pipeline system. Thereafter, the method is compared with previous approaches and differences are discussed. Furthermore, the impacts of supply capacity and market demand uncertainties on the gas supply reliability are investigated and suggestions to improve the gas supply reliability are proposed.

An integrated systemic method for supply reliability assessment of natural gas pipeline networks

A systematic method is developed for supply reliability assessment of natural gas pipeline networks. In the developed method, the integration of stochastic processes, graph theory and thermal-hydraulic simulation is performed accounting for uncertainty and complexity. The supply capacity of a pipeline network depends on the unit states and the network structure, both of which change stochastically because of stochastic failures of the units. To describe this, in this work a capacity network stochastic model is developed, based on Markov modeling and graph theory. The model is embedded in an optimization algorithm to compute the capacities of the pipeline network under different scenarios and analyze the consequences of failures of units in the system. Indices of supply reliability and risk are developed with respect to two aspects: global system and individual customers. In the case study, a gas pipeline network is considered and the results are analyzed in detail.

Analysis and Suggestions for Power Supply Reliability Assessment Index of Distribution Network

The application of micro-grid affects distribution network, while the existing power supply reliability assessment index of distribution network cannot reflect its specific contribution. Based on an analysis of the shortages with the existing power supply reliability assessment index, a new index considering the time and power for evaluating the power supply reliability is proposed. The example indicates that the index proposed can be simply calculated and quantitatively measures the contribution to power supply reliability assessment of distribution network.

Power Supply Reliability Assessment in UPFC-installed Transmission System for ATC Enhancement Considering Transient Stability

With recent development of power electronics technology, power system stability enhancement and optimal power flow control by using Flexible AC Transmission System (FACTS) devices have so far been studied. The FACTS devices to relieve multiple constraints can also make it possible to enhance Available Transfer Capability (ATC) without construction of new transmission lines. The previous research revealed that ATC is expanded by avoiding multiple constraints in OPF using Unified Power Flow Controller (UPFC). For long-term operation of such ATC-expanded power system, it is necessary to evaluate power system reliability. In this paper, the evaluation method of supply reliability for UPFC-installed power system is proposed. Both thermal capacity and transient stability constraints are considered. The effectiveness of the proposed method is shown by numerical examples for IEEJ East10-machine test system.

Reliability Criteria for Power Systems with Inherent Generation and Transmission Deficiencies

Conventional reliability criteria are severely restricted in usefulness for small or less developed systems which are at an early stage of their evolution. Such systems may suffer from partial or chronic generation shortage for certain periods of their growth. The transmission system may also be unevenly interconnected. Some key bus-bars may be well connected while others may have poor alternative infeeds. Nevertheless the system planner needs quantitative reliability indices to guide him. This paper discusses criteria for obtaining such indices or modifying existing indices for use in less developed power systems. Relevant criteria for planning, bulk supply reliability assessment and costing of alternatives are proposed.