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An interactive computer-based learning tool with multiple sessions is proposed in this paper, which teaches students to think and helps them recognize the merits and limitations of simulation tools so as to improve their practical abilities in electrical circuit simulation based on the case of a power converter with progressive problems. The common problem of fast simulation and differential equation solver convergence are discussed in detail for the simulation of nonlinear power electronic circuits. Another special ratio for ripple restriction is proposed, taking practical work into consideration. Some design and simulation tradeoffs for corresponding problems are also presented. Such a learning tool can improve students' programming skills and inspire their interest in practical work as well. The practical tests--carried out at the Aichi Institute of Technology, Toyota, Japan, and Southeast University, Nanjing, China--validate the effectiveness of the learning tool. (Contains 2 tables and 12 figures.)

A computer package developed for power system protection design is used to teach protection coordination at City University, London. Examples of package use and experience gained from computer assisted learning in this subject are described. The simulation of protection systems gives students an opportunity to observe the actions of each device after they complete their protection schemes. In order to preserve flexibility within this self-learning environment, an expert system is included in the package. The use of an expert system is to make learning as effective as possible by providing guidance on the teaching material. It plays its role only if it is invoked. In other words, the expert system does not supervise learning, but can provide the necessary guidance if a request is made. If there is any error, the result of the simulation will also show the nature of the problem. The debugging function can help the students to detect the errors they have made and know how the devices work in the system. The potential of a well-designed computer package is not only to strengthen the teaching and learning, but also lead to creative contributions to the educational process. This benefit is not available through traditional lectures and textbooks.

Dissolved gas analysis (DGA) of transformer oil has been one of the most useful techniques to detect the incipient faults. Various methods, such as the IEC codes, have been developed to interpret DGA results directly obtained from a chromatographer. Although these methods are widely used in the world, they sometimes fail to diagnose, especially when more than one fault exist in a transformer. This paper presents a fuzzy logic technique which can diagnose multiple faults in a transformer and quantitatively indicates the likelihood/severity of each fault. Insulation deterioration at each fault location can then be monitored closely according to its trend, which is important for a transformer in critical situation. Tests using this technique on a number of transformers have given promising results. Index Terms--transformer, insulation diagnosis, fuzzy logic, dissolved gas analysis.

Remote end infeed causes problems in distance relay measurement, especially under high resistance earth fault conditions. Although a distance relay set to an ideal operating region can cover the fault resistance at one particular load condition, the operating region is affected by changes in load condition. Hence a distance relay may overreach or underreach when load changes. From the main factors which affect the ideal digital distance relay operating region, a stand alone intelligent digital distance relay which can adapt to these changes is presented. This approach does not need communication links from the remote end of the line or the system control center. Numerous computer simulations have been carried out on realistic system configurations and the results show that there is a high potential for developing an intelligent digital distance relay. Index Terms--Adaptive Digital Relaying, Artificial Intelligence, Protection.