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Incorrect responses from protective devices weaken the reliability of microgrids. This paper investigates the effects of the protection system on the reliability performance of a microgrid integrated with weather-dependent microsources. It relies on a stochastic model to simulate the challenges existing in current protection schemes designed for microgrids. Abnormal operating conditions, including overcurrent, overvoltage, and undervoltage, which are detected by a deficient protection scheme, are analyzed by a defined fuzzy virtual setting value. Their contributions, along with the conventional random failure rate achieved by statistical results, are jointly used to evaluate the short-term outage rate of a feeder. A series of fuzzy reliability indices is further proposed for the short-term and periodical reliability of both microgrid system and customers. Subsequently, an evaluation strategy, combined with fuzzy simulation and load restoration, is presented as a solution tool. Simulations on a test system are provided to support the necessity of considering the effects of protection operation in evaluating microgrid reliability. [ABSTRACT FROM PUBLISHER]

This paper is a theoretical and experimental assessment of the solder joint reliability of an advanced high-density interposer-based 2.5-D IC integration technology on-board under drop impact in accordance with the JEDEC standard. Focus is placed on the influences of underfill on the solder joint reliability. The transient dynamic responses of the packaging technology are simulated using Input-G finite element analysis, with the use of the Johnson-Cook model for describing the constitutive behaviors of the solder interconnect materials. Furthermore, an energy-based model is utilized for predicting the drop impact solder joint fatigue life. The effectiveness of the proposed theoretical models is demonstrated through comparison with the drop test experiment. Finally, the effects of some essential factors including the allowed JEDEC shock pulse tolerances are examined in order to establish a design guideline for enhanced shock resistance capability. Results show that underfill and even partial underfill can significantly improve the drop impact solder joint reliability of the 2.5-D IC integration technology. The solder joint reliability turns out to be considerably affected by the shock pulse tolerances, suggesting that there is a crucial need to regularly calibrate the precision of drop testers for minimizing the prediction uncertainty. [ABSTRACT FROM PUBLISHER]

The reliability prediction of hybrid electric vehicles (HEVs) is of paramount importance for planning, design, control, and operation management of vehicles, since it can provide an objective criterion for comparative evaluation of various configurations and topologies and can be used as an effective tool to improve the design and control of the overall system. This paper presents a mission-profile-dependent simulation model based on MATLAB for quantitatively assessing the reliability of the electric drivetrain of HEVs. This model takes into consideration the variable driving scenarios, dormant mode, electrical stresses, and thermal stresses. Therefore, more reliable and accurate prediction of system reliability has been achieved. The methodology is explained in detail, and the results of reliability assessment based on a series HEV are presented. Based on reliability analysis, two control strategies are proposed to increase the mean time to failure of HEV powertrains: 1) variable dc-link voltage control and 2) hybrid discontinuous pulsewidth modulation scheme. These novel control schemes reduce the power losses and thermal stresses of power converters, and consequently, enhance system reliability. Numerical simulation results verify the benefits of two proposed control strategies in terms of power losses and reliability. [ABSTRACT FROM PUBLISHER]

In the condition settings of a power-frequency withstand voltage test for substation equipment, an approach based on insulation reliability evaluation using Weibull distribution is available. In this method, temporary overvoltage is evaluated using an ?independence model?. This ?independence model? assumes no remaining influence of voltage application (i.e. the model obeys the failure probability distribution starting at time 0 each time the voltage is applied). However, the authors have conducted insulation characteristics tests by applying a voltage multiple times at intervals and clarified that the influence of voltage application remains to a certain extent (i.e. the effect assumed in the ?accumulation model? appears) as well as the degree of influence depending on the conditions for oil-immersed transformer. The present paper proposes an evaluation method with the degree of influence of voltage application history taken into consideration. In the proposed method, the portions following an ?independence model? and an ?accumulation model? are respectively assumed and combined after multiplying the relevant coefficient representing the respective degrees of influence. According to the trial calculation based on the proposed method, the required withstand voltage decreased by several percentage points, while it was confirmed that the existing method is on the safer side as a means of evaluating the insulation reliability of temporary overvoltage. [ABSTRACT FROM PUBLISHER]

This paper develops new models and concepts for incorporating the effect of protection system failures into power system reliability evaluation. The two types of protection failures, i.e., undesired-tripping mode and fail-to-operate mode, and their impact on reliability modeling are discussed. A complete Markov model for current-carrying components is established and its simplified form appropriately describes the overall reliability situation of individual components. Concepts of self-down state and induced-down state are introduced and used to build the composite unit model for quantitatively assessing the influence of protection failures on modeling system states. Finally, a Markov model of power systems with protection failures is proposed for system reliability evaluation. The proposed methodology is then illustrated in detail. [ABSTRACT FROM PUBLISHER]

Due to the lack of feeder corridors, the Chinese utility companies frequently choose the technique of putting multiple overhead feeders on a same tower (MFST) to meet the load demand in a heavy load area. In many situations, the distance among the feeders of MFST in an electrical distribution network (EDN) is usually too small to meet the requirements of safety regulation for repairing and maintenance. Therefore, when a fault occurs on a feeder of MFST, the other feeders have to be in a triggered passive outage (TPO) state to assist the repairing of the failed feeder. This paper presents a reliability evaluation algorithm for EDNs containing MFST using the section technique. The definition of TPO and the equivalent TPO rate and TPO duration are also proposed. Based on the TPO parameters and the section technique, the reliability evaluation algorithm containing the MFST can be obtained. Case studies on the modified RBTS-BUS6 and the EDNs of three districts in Dongguan city, China, show that the MFST has a significant impact on the EDN reliability and should be considered in the reliability evaluation. The results also show the effectiveness and applicability of the proposed approach. [ABSTRACT FROM PUBLISHER]

Appropriate wind speed modeling is an important requirement in the reliability evaluation of wind integrated electric power systems. This paper examines and illustrates the effects on the generating capacity adequacy indices of a small test system of using different wind speed modeling procedures in Monte Carlo simulation and analytical reliability assessment. Wind speed data for a number of different time periods at two quite diverse locations in Canada are used in the studies. Wind speed is represented using hourly observed data, hourly mean wind speed data, autoregressive moving average (ARMA) time series, moving average (MA) time series, Normal distribution, and Markov chain models. [ABSTRACT FROM PUBLISHER]

This paper proposes a reliability model for a superconducting fault current limiter (SFCL), which is a new alternative in limiting the fault current recently increasing in a network. An evaluation technique for distribution reliability that uses the improved failure rate of all protective devices in a network, depending on the location of the SFCL, is also proposed. As a result, it is expected that the SFCL makes the reliability of adjacent equipment on an existing network improve, and these changes are analyzed. In addition, in order to apply the effect of the intermittent output of renewable-energy sources, distribution reliability indices were redefined in this paper. Case studies verify that the SFCL is effective in reducing fault currents and improving distribution reliability. These effects are analyzed with respect to the location of the SFCL in a case study system. [ABSTRACT FROM AUTHOR]

Provides information on a study which proposed an algorithm based on Monte-Carlo simulation method for composite system reliability evaluation. Main idea of the algorithm; Rules of failure effect analysis (FEA); Conclusions of the study.

Extends the infinitesimal perturbation analysis (IPA) to complex Monte Carlo based generating system reliability programs. Development of a reliability model; Computation of systems and unit sensitivity measures.