On novel protection algorithm for distribution network with distributed generations

When distributed generations (DG) and storages are introduced into distribution network, power flow in the network is no longer single direction, in consequence, over-current relay, which is commonly used in distribution network cannot fulfill sufficient protection functions. Thus, more complicated protection principle, for example, directional protection may be needed in this situation. On the other hand, load and the outputs of DGs in distribution network are variant, which causes considerable frequency fluctuation in distribution network; moreover, non-linear loads and devices deployed in distribution network introduce harmonics and inter-harmonic, traditional protection algorithms, such as the Fourier algorithm, do not have good performance under this circumstance. This paper proposes a novel protection algorithm, which is based on time-frequency transform (TFT). TFT is able to estimate fundamental voltage and current phasor as well as derived electrical parameters accurately and with satisfactory dynamic response. The TFT based protection algorithm does not suffer from system frequency fluctuation, harmonic as well as inter-harmonic components even without synchronous sampling. Thus, the proposed algorithm can be well used in above mentioned protections for distribution network including DGs and storages. Finally, MATLAB simulation results verify effectiveness and correctness of the proposed algorithm.