Determination of fuselink performance
In the determination of fuselink performance, the performances of fuse links may be determined by testing in circuits such as that is shown in figure 1.10, in which the voltage, current level, and waveform may be controlled. The ability to interrupt very high currents may be ascertained as well as the operating times at lower currents. The minimum fusing current may also be determined. Because of the possible variability of fuses, each individual test must be performed on several fuse links.
When fuselinks are being developed for new applications for which the required characteristics are known, designers rely on their experience. Prototypes are produced in sufficient quantities to enable all the necessary tests to be done. should the performance not meet the requirements, design modifications must be made, further prototypes produced and then the tests must be repeated. This process can be both lengthy and expensive.
There has long been a desire to calculate the performance of fuselinks so that acceptable and optimum designs can be produced without recourse to trial and error methods and lengthy testing procedures. In 1941 Gibson published the results of investigations, done by professor R.Rudenberg, in which the high current pre-arcing behavior of fuselinks with wire elements were determined. Because the times to reach the melting point of the elements was very short, heat transfer from the elements was neglected. The current flow was axial and the current density constant.
With notched elements, the current flow is not axial or of constant density but nevertheless with various assumptions applicable over certain current ranges and by employing finite-difference or other methods, various workers have modeled Pre-arcing performance with high accuracy in recent years. It is now possible to determine the effects of changing the materials in fuselink as well as changing their dimensions and geometry.
The arcing process is more Complex than that which takes place during the pre-arcing period and accurate modeling is, therefore, more difficult. some workers have sought from experimental studies to establish the empirical relationship between the current through a fuse link and the voltage across it when arcing occurs. Gananalingam and Wilkins were able to predict the arcing proper performances of certain fuses with reasonable accuracy using the relationship:
They claimed that the simulation technique is useful for screening preliminary designs and investing the effects of system parameters such as frequency.
Such methods are not based on the phenomena taking place and do not assist in understanding the behavior. They may not be applicable if the use of other element or filling materials are being investigated. For this reason, Wright and Beaumont developed a model based on a number of simplifying assumptions. They considered it to be superior to earlier models because it was based on the process occurring during arcing and took account of energy changes. Work of this type is still proceeding to enable the amount of testing currently required to be reduced greatly in the future. Details of work done recently in this field were given in papers presented at the fourth International Conference of electrical fuses and their applications. It must be accepted, however, that it will be necessary to determine fuselink characteristics experimentally for many years.
Comments
Post a Comment