Low impedance restricted earth fault protection

In today's competitive environment, investments must have a minimum global cost. For protection relays, as for any other electrical device, users need standard, packaged solutions, with a minimum engineering study. Restricted earth fault (REF) protection, as other protections, is a good candidate because it needs no time grading study. Evolution in computer relaying have made this protection available in a multi-functional device for transformer application. In such an implementation a low impedance principle is used. No external stabilising resistor nor class X CTs are needed, making the installation of the protection straightforward. It is thus possible to build a fully packaged cubicle for transformer protection, including CTs and multifunctional relay giving improved transformer protection thanks to a REF protection.