Incorrect use of fuse characteristics in IEC 62271-105 restricts H.V. fuse application in ring main units

摘要

IEC 62271-105 “Alternating current switch-fuse combinations” goes back to IEC 420:1973, when relatively slow acting switches in air and under oil were used in ring main units. SF6 insulated switchgear did not exist in m.v. secondary distribution systems by than. This may explain why no one cared about the limitations in the use of fuse time-current characteristics in a time range below 100 ms. The paper highlights the conflicting claims of IEC 62271-105 to IEC 60282-1 “High voltage fuses” and IEC TR 60787 “Application guide for the selection of high voltage current-limiting fuselinks for transformer circuits” and explains the consequences with respect to h.v. fuse application in combinations with SF6 switches. Indeed, important and well established fuse applications will virtually be ruled out by IEC 62271-105. Alternative proposals are presented to resolve the conflicting situation in the International Standards.