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The design of a new microprocessor based multifunctional relay for use on interconnected 33 kV circuits is described. The relay uses sequence component principles and rented low grade VF communication. It was needed urgently because rented metallic communication circuits, which are in widespread use, are being withdrawn in the UK. The relay development is unusual because of its measurement methods and because it can derive polarising voltage from existing 1 1 kV VTs. The time scales required were such that development, field trials and installation phases overlapped. The field experience is described.

The book is predominantly directed to 'mission-oriented' systems, i.e, those for which the probability of failure (or success) is pre-eminent. In this aspect it provides an excellent coverage of the theory, modelling techniques, evaluation techniques and reliability testing methods as well as presenting a wealth (130 pages) of various statistical information and tables. Many worked examples are also included. The majority of examples in the application area may be considered to be more relevant to mechanical and structural engineers. However, the basic techniques and models are equally applicable to many desciplines including all branches of electrical engineering and therefore a reader should not be off-put by this emphasis.On the other hand, many systems are continuously operated repairable-systems and these only get a cursory mention. Therefore a reader would need to expand his reading considerably to assess such systems. For instance, the technique known as Markov modelling, which is ideally suited to repairable systems, is not discussed but only a reference is given.Despite this, however, the book forms an excellent text within its terms of reference and can be recommended to all those with an interest in or need of reliability techniques. R. N. ALLAN, Department ofElectrical Engineering and Electronics, U.M.IS. T.

INTRODUCTIONIt is only in the last ten years that transistorised equipment has been widely used in power systems. This delay was as a result of reluctance to use modern electronic technology where previously electro-mechanical instruments had been used satisfactorily. It is just a little surprising, therefore, that digital equipment has become accepted during the last three years or so. For example, earlier experience with digital frequency meters had been disappointing. These suffered from electrical interference when installed in the particularly noisy environment of an electrical substation. The interference problems were eventually solved using isolation transformers, RF filters, and optical isolators in the production of digital equipment which has performed well in a growing number of substation installations. The solution of the interference problem was a breakthrough. It permitted manufacturers to offer, with confidence, microprocessor-based equipment which had significant advantages in terms of cost, size and performance over conventional electro-mechanical and electronic alternatives.The main applications of microprocessors in substations are:

Some aspects of undergraduate digital electronics and systems This paper considers some of the problems involved in the design and implementation of syllabi and support experimental and project activities for undergraduate digital electronics and systems. In particular the influence of rapid developments in integrated circuit technology on fundamental design philosophy and the laboratory/lecture interface is discussed.