A transient based protection technique for future DC grids utilising travelling wave power

This paper presents a novel time domain protection technique for application to DC grids. The technique utilises the power developed by the forward and backward travelling waves produced by a fault to distinguish between internal and
external faults. For an internal fault, the calculated travelling wave power must exceed a predetermined setting otherwise the fault is external. The ratio between the forward travelling wave power and the backward travelling wave power
provides directional comparison. For a forward directional fault, this ratio is less than unity whereas the ratio is greater than unity for reverse directional faults. To improve the sensitivity of the protection scheme for long distance remote
internal fault, a second element utilising the concavity of the forward travelling wave power is proposed. The proposed technique is time domain-based and does not require complex mathematical or DSP technique; and as such can be easily
implemented since it will require less hardware resources. All simulations were carried out in PSCAD/EMTDC and the results presented considering wider cases of fault scenarios including 500Ω remote internal fault shows the suitability of
the proposed scheme as all fault scenarios indicated were identified within 500µs following the application of the fault.