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Science and Technology of Nuclear Installations
Volume 2017 (2017), Article ID 3976049, 11 pages
Research Article

Separation of Transformers for Class 1E Systems in Nuclear Power Plants

Nuclear Power Plant Engineering Department, KEPCO International Nuclear Graduate School, 658-91 Haemaji-ro, Seosang-myeon, Ulju-gun, Ulsan 45014, Republic of Korea

Correspondence should be addressed to Sang-Hyun Lee

Received 2 September 2016; Revised 18 November 2016; Accepted 4 December 2016; Published 2 January 2017

Academic Editor: Arkady Serikov

Copyright © 2017 Sang-Hyun Lee and Choong-Koo Chang. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


In order to supply electric power to the safety related loads, safety and reliability of onsite power have to be ensured for the safety function performance in nuclear power plants. Even though the existing electric power system of APR1400 meets the requirements of codes regarding Class 1E system, there is a room for improvement in the design margin against the voltage drop and short circuit current. This paper discusses the amount that the voltage drop and short circuit current occur in the existing electric power system of APR1400. Additionally, this paper studies with regard to the improved model that has the extra margin against the high voltage drop and short circuit current by separation of unit auxiliary transformer (UAT) and standby auxiliary transformer (SAT) for the Class 1E loads. The improved model of the electric power system by separation of UAT and SAT has been suggested through this paper. Additionally, effects of reliability and cost caused by the electric power system modification are considered.