Maintenance strategies affecting equipment performance

Proper maintenance of plant items is crucial for the safe and profitable operation of process plants, The relevant maintenance policies fall into the following four categories: (i) preventivejopportunistic/breakdown replacement policies, (ii) inspection/inspection-repair-replacernent policies, (iii) restorative maintenance policies, and (iv) condition based maintenance policies, For correlating failure times of component equipnent and complete systems, the Weibull failure distribution has been used, A new powerful method, SEQLIM, has been proposed for the estimation of the Weibull parameters; particularly, when maintenance records contain very few failures and many successful operation times. When a system consists of a number of replaceable, ageing components, an opporturistic replacernent policy has been found to be cost-effective, A simple opportunistic rrodel has been developed. Inspection models with various objective functions have been investigated, It was found that, on the assumption of a negative exponential failure distribution, all models converge to the same optimal inspection interval; provided the safety components are very reliable and the demand rate is low, When deterioration becomes a contributory factor to same failures, periodic inspections, calculated from above models, are too frequent, A case of safety trip systems has been studied, A highly effective restorative maintenance policy can be developed if the performance of the equipment under this category can be related to some predictive modelling. A novel fouling model has been proposed to determine cleaning strategies of condensers, Condition-based maintenance policies have been investigated. A simple gauge has been designed for condition monitoring of relief valve springs. A typical case of an exothermic inert gas generation plant has been studied, to demonstrate how various policies can be applied to devise overall maintenance actions.

Simulation of power station protection equipment

Computer programs have been developed to enable the coordination of fuses and overcurrent relays for radial power systems under estimated fault current conditions. The grading curves for these protection devices can be produced on a graphics terminal and a hard copy can be obtained. Additional programs have also been developed which could be used to assess the validity of relay settings (obtained under the above conditions) when the transient effect is included. Modelling of a current transformer is included because transformer saturation may occur if the fault current is high, and hence the secondary current is distorted. Experiments were carried out to confirm that distorted currents will affect the relay operating time, and it is shown that if the relay current contains only a small percentage of harmonic distortion, the relay operating time is increased. System equations were arranged to enable the model to predict fault currents with a generator transformer incorporated in the system, and also to include the effect of circuit breaker opening, arcing resistance, and earthing resistance. A fictitious field winding was included to enable more accurate prediction of fault currents when the system is operating at both lagging and leading power factors prior to the occurrence of the fault.

Perceptions of technological change : the attitude of managers towards group technology in the United States food equipment industry

In the center of today's continued and rapid technological change and ever competitive environment of the next millennium, manufacturers must realize that unless they are ready to consider and evaluate new technologies brought onto them, they may fail to adequately respond to the challenges that lie ahead of them. This research was designed to determine the consistency of the perceptions of technical and non-technical administrators, in manufacturing environment, towards technological change and group technology as an advanced manufacturing system. This research has included a review of literature with references to technological change, justification and implementation processes, and various manufacturing systems including group technology and its benefits. This research has used the research method of empirical analysis (quantitative) and case studies (qualitative) to research perceptions of technical and non-technical administrators towards technological change and group technology. Sixty-four (64) technical and fifty-one (51) nontechnical administrators from fifty (50) manufacturing organizations in the United States of America responded to the mail survey questionnaire used in this research. Responses were analyzed using the Repeated Measures ANOVA procedure to compare mean responses of each group. Two correlation analyses, Cronback Coefficient Alpha and Pearson Correlation Coefficient, were also performed to determine the reliability of the questionnaire as well as the degree of correlation of perceptions between these two groups. This research, through the empirical analysis, has found that perceptions of the technical and non-technical administrators towards group technology were not consistent. In other words, they did not perceive the benefits of group technology in the same manner to the overall organizational performance. This finding was significant since it provided the first clear and comprehensive view of the technical and non-technical administrators' perception towards group technology and technological change, in Food Equipment Manufacturer Industry, in United States of America. In addition, a number of cases were analyzed and the results have supported those of the quantitative analysis. Therefore, this research not only has provided basic data, which was unavailable prior to this investigation, but it also provided a basis for future studies.