Testing Mixed Application of Analog and Process Bus Environment in Transformer Differential Protection

In a digital substation automation system introduced by IEC61850 standard, various technologies may co-exist with multiple vendors and combinations of analog and digital measurement signals. In this paper, a case study of a distribution power substation has been developed. The objective is to test the transformer differential protection during internal and external faults, inrush, sympathetic inrush, and over-excitation while combining both conventional and multi-vendor process bus technologies. The effect of communication network imperfection such as constant and random delay on the packet are emulated and the protection relay response is analyzed. The preliminary test indicates that mixed applications of conventional and process bus is fully functional in case of same vendor combination of merging unit and relay protection. The multi-vendor combination does not affect relay operation during faults, but protection relay shows incorrect blocking signal in case of over-excitation. Network imperfections and delays of more than 2 ms blocks the tripping signal during internal faults. Simulation and experimental results were carried-out for the MUs and differential protection in a multi-vendor environment.