Strategy and Mechanism of Time and Sampling Synchronization of digital Substation in China

Abstract

In recent years, nearly all the new-build substations in China are digital substations with the fully digitalized process level devices, implemented with the conventional ITs and the associated stand-alone merging units. All the related process and bay level devices are connected to the time synchronization network and achieved the sampling synchronization which is essential for the differential relay and etc. The paper firstly introduced the basic principle and architecture of the time synchronization system in digital substation in China. Two master time devices are used simultaneously to track the sources (GPS from USA and Beidou from China),and the redundant maters are synchronized to each other to acquire the higher reliability. The paper then introduces the requirements on time synchronization of the merging unit in China. Analysing the possible pseudo-synchronous caused by the inconsistent synchronization between the merging units, and analysing the hold-over behaviour of the merging unit in case of lost connection with the clock, merging unit with higher hold-over capability is introduced and implemented with the application of OCXO.The mechanism of the adjustment of merging unit during the re-connection is also illustrated, fast adjustment and slow adjustment methods are introduced to eliminate the jitter during the re-connection between the merging unit and the clock. The conclusion is drawn and some suggestions are also made in the end of the paper.