Circuit-breaker RMU improves MV/LV transformer protection

Abstract

Traditionally MV/LV transformers have been protected by switch-fuses because of the significant cost differential with respect to withdrawable CBs and relays. The main advantage for using RMU with fixed integral low cost CB is that it allows to have an improved transformer protection at an equivalent lifetime cost, thus making transformer CB protection affordable. Today, over 60% of the SF6 RMUs sold by the author's company use CB function.

The smarter single breaker RMU. A fuse-less, single breaker, auto-loop-sectionalizing RMU

“…This further reinforces the need for a significantly improved Stockholm, 10-13 June 2013 For all isolated or Petersen grounded networks and lower Earth-faults in resistance-earthed systems, the HRC fuse is of almost no use, as it is only in the extremely rare cases of high amperage faults, that it would operate. These reasons, as well as the handling of Distributed Generation located in the low voltage, e-car charging and the need to address the islanding phenomenon, reinforce the already established practice of the use of a Breaker for the Transformer protection [1]. All of the above requirements combined with expectation of a modern RMU to perform completely maintenance-free for more than 50 years, reinforce the notion that an ideal "Smart RMU" should utilize three vacuum breakers.…”