An accurate representation of the magnetisation curve including the incremental permeability curve, is presented. It is based on selected powers of B (not generally integer) with positive coefficients giving a power series. The fit is shown to be superior to those obtained with polynomial and rational fraction polynomial representations.

Power transformers are vital assets in electric power systems, as they are essential in maintaining a reliable supply and very high in cost. Nowadays, society has become more and more dependent on the availability of power, putting pressure on the reliability, availability and cost efficiency of power supply. These assets operate under high electric stresses and although transformers are extremely energy efficient, the dissipated heat is a limiting factor for the maximum loading of power transformers. The insulating medium must be capable of dealing with large electric stresses, strong electro-mechanical forces and high temperatures. The life of a power transformer mainly depends on the condition of the paper-oil insulation system. Manufacturers often define the expected life of power transformers to be between 25 and 40 years. Some transformers in service are now approaching this age, and it is important to estimate their remaining lifetime in order to prevent premature shutdown of transformers. Knowing the condition of the transformers is an essential factor to make an economical decision for transformer replacement and maintenances. This paper presents a mathematical model to estimate the remaining life through assessment of furfural content in the oil and degree of polymerization of the insulating paper.

Detection of open live conductors is a challenging task in the power system operation since it acts as a high impedance fault. High impendence faults (HIF) characteristically has a very low current value which is often not detectable using conventional over current protection devices. Several methods of detecting these HIF have been put forward. These methods involve spectral analysis of currents, algorithms based on residual current analysis and detection of unbalanced voltages produced by the fault at the end of distribution line. This paper presents a method of detecting open conductor faults based on the sequence current component. Here the ratio of negative sequence current to positive sequence current is used as the detecting parameter and fault is detected through the unbalanced resulted in the system with the occurrence of the fault.