OVERCURRENT PROTECTION OF TRANSFORMERS: TRADITIONAL AND NEW FUSING PHILOSOPHIES FOR SMALL AND LARGE TRANSFORMERS

摘要

Over the years, both fuse manufacturers and users have generally agreed on the use of low fusing ratios* when protecting transformers against secondary-side faults and slowly evolving internal faults. This fusing philosophy is still appropriate for small three-phase power transformers used on industrial, commercial, and institutional power systems, and small-to-medium size three-phase power transformers used in utility substations. Low fusing ratios are necessary if low-magnitude faults are to be detected and quickly cleared to minimize damage to these transformers. Protection against secondary-side faults, in particular, is extremely important when considering the critical nature of the process loads served by these transformers. Not to mention that replacement transformers are not readily available.