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Showing 15 results for Reliability

M. Sefidgaran, M. Mirzaie, A. Ebrahimzadeh,
Volume 6, Issue 2 (6-2010)

Reliability of a power system is considerably influenced by its equipments. Power transformers are one of the most critical and expensive equipments of a power system and their proper functions are vital for the substations and utilities. Therefore, reliability model of power transformer is very important in the risk assessment of the engineering systems. This model shows the characteristics and functions of a transformer in the power system. In this paper the reliability model of the power transformer with ONAN cooling is obtained. The transformer is classified into two subsystems. Reliability model of each subsystem is achieved. Markov process representation and the frequency/ duration approach are employed to obtain a complete reliability model of the subsystems. By combining these models reliability model of power transformer is obtained. The reliability model associated with the transformer is then proposed combining the models of subsystems. The proposed model contains five states. To make the model more applicable, the 5-state model is alleviated to a 3-state one. Numerical analysis and sensitivity analysis relevant to the proposed reliability model are performed for evaluating the numerical values of the model parameters and the impact of different components on the reliability of the model.
Y Damchi, J Sadeh,
Volume 9, Issue 4 (12-2013)

Appropriate operation of protection system is one of the effective factors to have a desirable reliability in power systems, which vitally needs routine test of protection system. Precise determination of optimum routine test time interval (ORTTI) plays a vital role in predicting the maintenance costs of protection system. In the most previous studies, ORTTI has been determined while remote back-up protection system was considered fully reliable. This assumption is not exactly correct since remote back-up protection system may operate incorrectly or fail to operate, the same as the primary protection system. Therefore, in order to determine the ORTTI, an extended Markov model is proposed in this paper considering failure probability for remote back-up protection system. In the proposed Markov model of the protection systems, monitoring facility is taken into account. Moreover, it is assumed that the primary and back-up protection systems are maintained simultaneously. Results show that the effect of remote back-up protection system failures on the reliability indices and optimum routine test intervals of protection system is considerable.
B. Adineh, H. Rajabi Mashhadi, M. E. Hajiabadi,
Volume 10, Issue 2 (6-2014)

The main goal of this paper is to structurally analyze impact of DSM programs on reliability indices. A new approach is presented to structurally decompose reliability index Expected Energy Not Supplied (EENS) by using Monte Carlo simulation. EENS is decomposed into two terms. The first term indicates EENS which is caused by generation contingencies. The second term indicates EENS which is caused by transmission and generation contingencies. The proposed approach can be used to indicate appropriate buses for applying DSM. Furthermore, networks are studied at two levels HLI and HLII. Studies show that in some networks reliability indices are affected mostly at the HLI level. While in some other networks, reliability indices are influenced mostly at the HLII level. It means that in these networks, reliability indices are affected by transmission contingencies. Then, it is shown that the implementation of load shifting is effective in some networks and buses. These are the ones which their EENS is more influenced by generation contingencies. However it is not effective in the ones which their EENS is more influenced by transmission contingencies. The simulation results on the IEEE-RTS and Khorasan network show the efficiency of the proposed approach.
H. Hasanzadeh Fard, S. A. Bahreyni , R. Dashti , H. A. Shayanfar,
Volume 11, Issue 2 (6-2015)

Evaluation of the reliability parameters in micro-grids based on renewable energy sources is one of the main problems that are investigated in this paper. Renewable energy sources such as solar and wind energy, battery as an energy storage system and fuel cell as a backup system are used to provide power to the electrical loads of the micro-grid. Loads in the micro-grid consist of interruptible and uninterruptible loads. In addition to the reliability parameters, Forced Outage Rate of each component and also uncertainty of wind power, PV power and demand are considered for micro-grid. In this paper, the problem is formulated as a nonlinear integer minimization problem which minimizes the sum of the total capital, operational, maintenance and replacement cost of DERs. This paper proposes PSO for solving this minimization problem.


M. Khalilzadeh, A. Fereidunian,
Volume 12, Issue 4 (12-2016)

In this paper, a stochastic approach is proposed for reliability assessment of bidirectional DC-DC converters, including the fault-tolerant ones. This type of converters can be used in a smart DC grid, feeding DC loads such as home appliances and plug-in hybrid electric vehicles (PHEVs). The reliability of bidirectional DC-DC converters is of such an importance, due to the key role of the expected increasingly utilization of DC grids in modern Smart Grid. Markov processes are suggested for reliability modeling and consequently calculating the expected effective lifetime of bidirectional converters. A three-leg bidirectional interleaved converter using data of Toyota Prius 2012 hybrid electric vehicle is used as a case study. Besides, the influence of environment and ambient temperature on converter lifetime is studied. The impact of modeling the reliability of the converter and adding reliability constraints on the technical design procedure of the converter is also investigated. In order to investigate the effect of leg increase on the lifetime of the converter, single leg to five-leg interleave DC-DC converters are studied considering economical aspect and the results are extrapolated for six and seven-leg converters. The proposed method could be generalized so that the number of legs and input and output capacitors could be an arbitrary number.

S. Sivasakthi, R. K. Santhi, N. Murali Krishnan, S. Ganesan, S. Subramanian,
Volume 13, Issue 2 (6-2017)

The increasing concern of global climate changes, the promotion of renewable energy sources, primarily wind generation, is a welcome move to reduce the pollutant emissions from conventional power plants. Integration of wind power generation with the existing power network is an emerging research field. This paper presents a meta-heuristic algorithm based approach to determine the feasible dispatch solution for wind integrated thermal power system. The Unit Commitment (UC) process aims to identify the best feasible generation scheme of the committed units such that the overall generation cost is reduced, when subjected to a variety of constraints at each time interval. As the UC formulation involves many variables and system and operational constraints, identifying the best solution is still a research task. Nowadays, it is inevitable to include power system reliability issues in operation strategy. The generator failure and malfunction are the prime influencing factor for reliability issues hence they have considered in UC formulation of wind integrated thermal power system. The modern evolutionary algorithm known as Grey Wolf Optimization (GWO) algorithm is applied to solve the intended UC problem. The potential of the GWO algorithm is validated by the standard test systems. Besides, the ramp rate limits are also incorporated in the UC formulation. The simulation results reveal that the GWO algorithm has the capability of obtaining economical resolutions with good solution quality.

M. Sedighizadeh, M. Esmaili, M. M. Mahmoodi,
Volume 13, Issue 3 (9-2017)

Distribution systems can be operated in multiple configurations since they are possible combinations of radial and loop feeders. Each configuration leads to its own power losses and reliability level of supplying electric energy to customers. In order to obtain the optimal configuration of power networks, their reconfiguration is formulated as a complex optimization problem with different objective functions and network operating constraints. In this paper, a multi-objective framework is proposed for optimal network reconfiguration with objective functions of minimization of power losses, System Average Interruption Frequency Index (SAIFI), System Average Interruption Duration Index (SAIDI), Average Energy Not Supplied (AENS), and Average Service Unavailability Index (ASUI). The optimization problem is solved by the Imperialist Competitive Algorithm (ICA) as one of the most modern heuristic tools. Since objective functions have different scales, a fuzzy membership is utilized here to transform objective functions into a same scale and then to determine the satisfaction level of the afforded solution using the fuzzy fitness. The efficiency of the proposed method is confirmed by testing it on 32-bus and 69-bus distribution test systems. Simulation results demonstrate that the proposed method not only presents intensified exploration ability but also has a better converge rate compared with previous methods.

R. Mohammadi, H. Rajabi Mashhadi,
Volume 15, Issue 1 (3-2019)

Distribution system reliability programs are usually based on improvement of average reliability indices. They have weakness in terms of distinguishing between reliability of different customers that may prefer different level of reliability. This paper proposes a new framework based on game theory to accommodate customers’ reliability requests in distribution system reliability provision. To do this, distribution reliability equations are developed so that it is recognized how game theory is suitable for this purpose and why conventional methods could not provide customer reliability requirements appropriately. It would be shown that customer participation in distribution system reliability provision can make conflict of interest and leads to a competition between customers. So, in this paper a game theoretic approach is designed to model possible strategic behavior of customers in distribution system reliability provision. The results show that by implementing the proposed model, distribution utilities would have the capability to respond to customers’ reliability requirements, such that it is beneficial for both utility and customers.

S. M. Razavi, S. M. Razavi,
Volume 15, Issue 3 (9-2019)

Probabilistic-based methods have been used for designing noise tolerant circuits recently. In these methods, however, there is not any reliability mechanism that is essential for nanometer digital VLSI circuits. In this paper, we propose a novel method for designing reliable probabilistic-based logic gates. The advantage of the proposed method in comparison with previous probabilistic-based methods is its ultra-high reliability. The proposed method benefits from Markov random field (MRF) as a probabilistic framework and triple modular redundancy (TMR) as a reliability mechanism. A NAND gate is used to show the design methodology. The simulation results verify the noise immunity of the proposed MRF-based gate in the presence of noise. In addition, the values from reliability estimation program show the reliability of 0.99999999 and 0.99941316 for transistor failure rates of 0.0001 and 0.001, respectively, which are much better as compared with previous reported MRF-based designs.

M. Ghayeni,
Volume 15, Issue 4 (12-2019)

In this paper, the new approach for the transmission reliability cost allocation (TRCA) problem is proposed. In the conventional TRCA problem, for calculating the contribution of each user (generators & loads or contracts) in the reliability margin of each transmission line, the outage analysis is performed for all system contingencies. It is obvious that this analysis is very time-consuming for large power systems. This paper suggests that this calculation should be done only for major contingencies. To do this, at first, the contingency filtering technique (CFT) is introduced based on the new economic indices that quantify the severity of each contingency to determine the critical contingencies. Then the results of contingency filtering are used in the TRCA problem. The simulation results are reported for the IEEE 118-bus test system. The obtained results show that by application of CFT in TRCA problem, the simulation time is greatly reduced, but the percentage of error remains within an acceptable limit.‚Äč

S. M. Razavi, S. M. Razavi,
Volume 16, Issue 4 (12-2020)

The Markov random field (MRF) theory has been accepted as a highly effective framework for designing noise-tolerant nanometer digital VLSI circuits. In MRF-based design, proper feedback lines are used to control noise and keep the circuits in their valid states. However, this methodology has encountered two major problems that have limited the application of highly noise immune MRF-based circuits. First, excessive hardware overhead that imposes a great cost, power consumption and propagation delay on the circuits and second, separate implementation of feedback lines that adds further delay to the circuits. In this paper, we propose a novel approach for minimal-cost inherent-feedback implementation of low-power MRF-based logic gates. The simulation results, which are based on 32nm BSIM4 models, demonstrate that besides excellent noise immunity of the proposed method, it has the least propagation delay in comparison with all of the previously reported MRF-based gates due to its inherent feedbacks. In addition, the proposed method outperforms competing ones, which have comparable noise immunity, in other circuit metrics like cost and power consumption. Specifically, the proposed method achieves at least 18%, 29%, and 39% reductions in cost, delay and power consumption with considerable noise immunity improvement compared with competing methods.

A. Mirsamadi, Y. Damchi, M. Assili,
Volume 17, Issue 1 (3-2021)

Power systems should have acceptable reliability in order to operate properly. Highly available and dependable protective relays help to obtain the desirable reliability. The relays should be periodically evaluated during specific intervals to achieve the mentioned characteristics. The Routine Test Interval (RTI) should be optimized in order to economically maximize the reliability of the protection system. The failure rate of the relays plays a vital role in determination of the Optimum Routine Test Interval (ORTI). Human error is one of the effective factors in the failure rate of the relays. Therefore, in this paper, a Markov model is proposed to investigate the impact of human error on the failure rate and the ORTI of the protection system. The model is applied for the protection system of power transformer. The obtained results indicated that human error has a significant impact on the increase of protection system failure, the decrease of the desired reliability indices, and the reduction of ORTI of the protection system.

A. Mohammadi, S. Soleymani, B. Mozafari, H. Mohammadnezhad-Shourkaei,
Volume 17, Issue 2 (6-2021)

This paper proposes an advanced distribution automation planning problem in which emergency-based demand response plans are incorporated during service restoration process. The fitness function of this planning problem consists of various costs associated with fault occurrence in electric distribution systems consisting of the total yearly cost of customers’ interruptions, the total annualized investment cost of control and protection devices deployment, including sectionalizing switches, circuit breakers, and fuses and the total annual cost of performing emergency-based demand response programs in the service restoration process. Moreover, the customers’ behavior in participating in the service restoration process is also modeled through using an S-function. The proposed advanced distribution automation planning method is implemented on the fourth bus of the Roy Bilinton test system in order to evaluate its efficacy. The obtained results show that the reliability indices and the total cost of distribution automation are reduced by about 9% and 12% more than the published methods for distribution automation, respectively.

P. Paliwal,
Volume 18, Issue 1 (3-2022)

The determination of a suitable technology combination for an isolated micro-grid (IMG) based on hybrid renewable energy resources (HRES) is a challenging task. The intermittent behavior of RES leads to an adverse impact on system reliability and thus complicates the planning process. This paper proposes a two-fold approach to provide a suitably designed HRES-IMG. Firstly, a reliability-constrained formulation based on load index of reliability (LIR) is developed with an objective to achieve a minimum levelized cost of energy (LCOE). Multi-state modeling of HRES-IMG is carried out based on hardware availability of generating units and uncertainties due to meteorological conditions. Modeling of battery storage units is realized using a multi-state probabilistic battery storage model. Secondly, an efficient optimization technique using a decentralized multi-agent-based approach is applied for obtaining high-quality solutions. The butterfly-PSO is embodied in a multi-agent (MA) framework. The enhanced version, MA-BFPSO is used to determine optimum sizing and technology combinations. Three different technology combinations have been investigated. The combination complying with LIR criterion and least LCOE is chosen as the optimal technology mix. The optimization is carried out using classic PSO, BF-PSO, and, MA-BFPSO and obtained results are compared. Further, in order to add a dimension in system planning, the effect of uncertainty in load demand has also been analyzed. The study is conducted for an HRES-IMG situated in Jaisalmer, India. The technology combination comprising of solar, wind, and battery storage yields the least LCOE of 0.2051 $/kWh with a very low value of LIR (0.08%).  A reduction in generator size by 53.8% and LCOE by 16.5% is obtained with MABFPSO in comparison with classic PSO. The results evidently demonstrate that MA-BFPSO offers better solutions as compared to PSO and BF-PSO.

Hassan Alizadeh Shyrayeh, Iraj Ahmadi, Mohammad Mirzaie, Masoud Ahmadi Gorji,
Volume 18, Issue 4 (12-2022)

The progressive application of non-linear loads in distribution systems (DS) increases current harmonics flow in DS's apparatuses, especially distribution transformers (DTs). Since DTs' operating temperature rises due to the harmonics flow, their loading should be reduced such that the hot spot temperature (HST) is preserved under its permissible value. This means that DTs' available capacity is influenced by load harmonic content. In this paper, a novel formulation for DTs' failure rate in the presence of harmonics is presented as a function of load harmonic contents. Using the suggested equivalent failure rate, DTs' available capacity in harmonic polluted DS is mathematically formulated. Additionally, the presence of the harmonic increases the HST, leading to DTs' aging acceleration. Therefore, the impact of harmonic components on DTs' aging is arithmetically modeled. To evaluate the efficacy of the suggested reliability model, it is applied to three distinct DTs having respectively industrial, commercial, and residential loads. The obtained results indicate that the available capacity of DTs with the same rated capacity would be different regarding to their load harmonic contents. On the other hand, it is comprehended from the achieved results that the aging acceleration factor (Faa) of the DTs increases owing to their load harmonic contents.

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