A Study on Protection Coordination Method in 5 kV MVDC Off-Grid MG System

Abstract

MVDC(Medium Voltage DC) distribution system has been on the rise for large transmission capacity with low energy loss, undersea power transmission, and so forth. Recently it has been a key factor of renewable energy transmission in the smartgrid. However, in the process of the design and the implementation of the protection devices for the grid, engineers face the difficulties to find out MVDC equipments, especially commercialized protection coordination devices, such as hybrid CB, VCB, ACB, MCCB, fuse, power contactors(CTR), etc. And those equipments have generally provided the narrow range of the DC rated voltage and the rated current and the power capacity, and given few types of the protective relay with narrow range. It gives a big restriction to design the protection elements and apply the equipments into the grid. This paper presents the protection coordination methods to design and operate the actual application for 5 kV MVDC grid with distributed generators(DG). And also, this paper performs the modeling of 5 kV MVDC grid including protection devices such as fuse, MCCB, CTR based on the PSCAD/EMTDC. From the simulation results of the operation characteristics of protection device according to the potential scenarios, it is confirmed that appropriate protection devices have been selected for the MVDC off-grid MG system, and protection cooperation is properly performed for all possible fault locations.