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This paper discusses a number of aspects of operational-risk assessment of transmission systems, operational-risk assessment uses techniques developed from reliability analysis to predict the performance of the transmission system during a short period of time (several hours) starting from a well-defined operational state. The influence of weather parameters on the momentary failure rate and the operational...
This paper describes a method for predicting circuit breaker time-to-failures using a probabilistic operational model that incorporates generation capacity growth. Increases in generation capacity may cause fault current levels to approach or exceed circuit breaker ratings. This condition may increase the probability of a circuit breaker failure. Circuit breaker failures result in common-mode multiple...
Knowledge of the reliability of power transformers is of growing importance to the asset manager. A method is presented for determining the reliability of a power transformer based on the mechanical strength of winding insulation paper. In addition to the modelling technique, there is a validation method for the modelling technique presented. The validation method depends on a good data management...
Decisions on maintaining, repairing, refurbishing and replacing cable systems are usually a compromise between what technically is advised and what economically is feasible. To implement an optimal maintenance and/or replacement strategy, asset managers and/or maintenance engineers need appropriate tools to provide them with reliable information on the condition of the cable systems. Partial discharge...
This paper presents an Bayesian approach for the estimation of sojourn time distribution parameters. Expert opinion and condition monitoring data can be used as source of information for the estimation. It is shown how expert opinion and data can be combined and how estimates for the parameters can be calculated by means of numerical methods. It is also discussed how expert uncertainty and systematic...
There is an increasing trend towards using the concept of risk assessment as an important tool in distribution system asset management. In an ongoing R&D project (RISK DSAM), the main objective is to investigate how information about risk exposure can improve maintenance and reinvestment decisions in an electrical distribution company. As the popularity of Bayesian networks (BN) is increasing,...
This paper illustrates the challenges associated with risk assessment for reinvestments decisions. A holistic framework for risk assessment in electricity distribution systems will be described first and then used to structure the analysis and decision making in a case study concerning cable reinvestment. These decisions are generally multi criteria decisions, including risks related to e.g.; economy,...
Markov models are a well established technique widely used for modeling deterioration processes of the electric power equipment and in reliability analysis. Recently, several papers using Markov and semi-Markov models have been published addressing the issue of the calculation of the remaining life, future failure rates and the probability of failure of power equipment. This paper focuses on one such...
This paper deals with the ageing behavior of different circuit-breaker types. Furthermore, the model simplifies the condition control of pieces of equipment and provides the asset manager with information about the yearly capital and operational expenditures (CAPEX and OPEX). Capital expenditures include new installation costs in consequence of replacement and grid enlargement and operational expenditures...
Technology of control command system (or instrumentation and control I&C equipment) has evolved dramatically during last 30 years from electromechanical relay, analog relay to digital relay. Then utilities have to maintain different type of devices. Risks linked to this fact are ageing effect on protection relays and technical life time of piece of equipment. After 20 years of use, manufacturers...
Maintenance managers of today's electrical distribution systems are faced with the problem of where their maintenance resources will be utilized best. In previous work the authors have developed a method for maintenance policy optimization for electrical networks. This paper presents results from an application study performed for a distribution system, including both urban and rural parts, for this...
Electric utilities schedule power transformers in high voltage load stations (customer delivery or regional supply systems) for planned outages such as unit refurbishment, unit replacement, etc. that may last for a few weeks. During the planned outage time, companion units may fail causing a complete loss of supply to customers. Mobile unit transformers (MUT's) could be used in these emergency situations...
This paper introduces the characteristics of relationship between probabilistic reliability (LOLE; loss of load expectation) and deterministic reliability (SRR; supply reserve rate) for 2008 and 2010 years in Korea power system. Korea power system has been using the loss of load expectation criterion (0.5 days/year) to determine the adequacy of installed capacity (ICAP) requirement. The criterion...
Detailed maintenance modeling is indispensable for utilities to determine optimum maintenance policy. Traditional reliability studies assume that transition rates or probabilities in Markov models are accurate. However, in reality, reliability data is either insufficient or mixed with uncertainty. This paper intends to utilize fuzzy set theory to represent parameters for Markov and semi-Markov processes...
This paper presents a reliability assessment of the HVDC converter transformer system (CTS) comparing different component models and configurations. The CTS model is based on the Markov modelling approach, which is shown to be well suited for these relatively small systems. The failure rate data in the models is based on statistical surveys by OGRE. A number of scenarios are calculated in order to...
Cost-effective maintenance scheduling of power system equipment is critical, especially with present economic scenario of power industry. Apart from long-term maintenance policy, asset planners need to come up with revised short term maintenance strategies mainly due to the shrinking budget allocations for various reasons. The problem may be formulated as follows: if it is the same availability of...
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