This paper comprises the development of a directional definite-time earth fault protection based on virtual polarisation and Commercial-off-the-Shelf (COTS) components. The earth fault protection is intended to be sensitive for high-resistive and remote faults. The challenge of those type of faults is the low magnitude of the zero-sequence voltage measured at the relay location, which is often used as the polarising quantity for directional sensing. A conventional approach is to use a current transformer (CT) in the neutral-to-ground path of a wye-connected power transformer at the corresponding substation. Since this approach exposes some additional costs and efforts in terms of CT installations and engineering, a virtual polarisation approach has been implemented, which has been introduced by the IEEE Power System Relay Committee. Thus a reliable polarising quantity is gained. The platform architecture has been design based on standardised hardware and software products, considered as COTS components. This effort has been made in order to yield a cost-efficient solution as well as to reduce the time-to-market of the development process. In the end the functional performance of the protection system has been tested utilising a hardware-in-the-loop (HIL) approach.