Abstract
When customers demand for very short lead-times and for a strict respect of the delivery schedules, it becomes difficult to avoid the existence of relatively large work-in-process buffers. As the buffers will also increase dramatically the production costs, their design (location and capacity) should be carefully analyzed and optimized, a task that becomes rather complex for large production systems. This paper firstly introduces a series of fundamental concepts related to the reliability of production systems. Then, the rationale of an analysis method oriented to this class of systems will be presented, together with its two main components, the modelling framework and the evaluation algorithm. The method allows analysing several issues of the design and operation of the production systems, namely the redundancy of equipment, the layout of the cells and the maintenance policies. To illustrate its practical usefulness and enlighten the kind of results that the method can provide, a numerical example concerning the design of work-in-process buffers of a just-in-time manufacturing system will be presented in the final part of the paper.

Abstract
The current fixed tariff remuneration for wind energy is not compatible with the deregulation of the electric power industry. The time-varying and location-dependent value of renewable energy is not acknowledged. The newly announced switchable tariff for wind energy in the Spanish electricity market provides a promising solution to compensating renewable energy within the deregulated electric power industry. The new switchable tariff provides wind generators more flexibility in operating wind generation assets. Such flexibilities provide option value in coordinating the seasonality of wind energy, demand on electric power and electricity prices movement. This paper models and valuates the flexibility on switching tariff as real compound options for wind generators. Numerical examples valuate wind generation assets under fixed tariff, spot market price taking, and yearly and monthly switchable tariffs. The optimal switching strategies are identified. The impacts of the switchable tariff on sitting criteria and values of wind generation assets are investigated. An improvement on the yearly switchable tariff is suggested to further reduce the operation risk of wind generators and fully explore the efficiency provided by competitive electricity markets.

Abstract
Reliability models rarely incorporate the uncertainty that is present in most of the reliability parameters, which is an important limitation for the managers of production system. This paper presents a fuzzy-probabilistic methodology that was developed to analyse production systems. The methodology employs probabilistic theory to represent the stochastic behaviour of the failure and repair processes and fuzzy sets to represent uncertainty in the parameters. This approach is based on a fuzzy reliability analysis from which is possible to obtain the fuzzy downtime function of a system in a given period of analysis. This function is a crucial element to obtain two performance measures: a financial measure (the fuzzy cost concerning failures of a production system) and a quality of service measure (the fuzzy frequency of failure on deliveries), as it will be illustrated in the final part of the paper through a practical example.

Abstract
The paper presents a methodology for the analysis of just-in-time production systems that are expected to deliver a fixed quantity of parts to its customers on a periodical basis, and whose equipment is submitted to random failure and repair processes. The methodology is based on the determination of the density function of T-H, the cumulated halting time of the production system between deliveries. The paper firstly shows how this function can be obtained from the internal structure of the system and individual equipment failure processes. Then, it shows how the reliability of the deliveries, and several production costs, e.g., extra work, delivery failures penalties, loss of sales profit, and safety stocks, may be assessed using this function. The practical application and usefulness of the methodology is illustrated in the final part of the paper for a typical production system of the automotive industry.

Abstract
This paper describes a mathematical formulation for the active/reactive dispatch in electricity markets, including a number of issues present in market models used in several countries. Traditional market approaches are implemented considering a sequence of activities namely in terms of active power dispatch and ancillary services. However, these two problems are coupled in the sense that dispatching reactive power is not independent from the active power scheduling of generators. The proposed model admits that it is known the purely economic pool dispatch together with bilateral contracts and then it aims at dispatching reactive resources considering voltage and branch limit constraints and constraints reflecting the alternator capability curve. As a sub-result, this formulation also outputs nodal active and reactive marginal prices that can be useful to build tariff schemes. Finally, the paper includes a case study based on the IEEE 30 bus/41 branch system to illustrate the obtained results and their interest for electricity markets.

Abstract
This paper presents a mathematical formulation for the active/reactive dispatch in electricity markets, recognizing that the typical sequential activities organized in terms of pool markets and the dispatch of ancillary services may lead to economic inefficiencies or technical difficulties. The developed model admits that it is known the purely economic pool dispatch and then it aims at dispatching reactive resources considering voltage and branch limit constraints and constraints reflecting the alternator capability curve. We also admitted that some constraints have a soft nature and used a symmetrical fuzzy decision formulation to model this aspect within an SLP based algorithm. Finally, the paper includes a case study based on the IEEE 24 bus/38 branch system to illustrate the results obtained with the developed approach. © Copyright KTH 2006.