Innovative solution concept for process bus based on IEC 61850 with real-time Ethernet improves data communications in high voltage substations

The IEC 61850 communications standard uses Ethernet bus technology with its high data rate not only for the station bus for intercommunication between protection and bay devices and the station control unit. The process bus for transmitting instrument transformer data and circuit-breaker commands is also defined in the standard. For the use of non-conventional instrument transformers, for example optical instrument transformers or instrument transformers based on Hall sensors, the sampled currents and voltages must be time-synchronized. Whereas in the past highly accurate time synchronization was transmitted via an additional fiber-optic link to the upstream recording units (merging units), according to the new concept synchronization is now carried out directly over the real-time Ethernet process bus.

This solution still offers increased redundancy. Since the signals are transmitted in both directions simultaneously in a ring bus structure so that no messages are lost if the communication route is interrupted, there is no need to allow for any reconfiguration time for real-time Ethernet. In the past the transmission of triggering signals, so-called trips, for circuit-breakers as a form of intelligent local control was virtually inconceivable, but the new communications concept also makes this kind of control system possible.

The Siemens concept, described at the Cigré as a further milestone on the way to the digital substation, uses the Ethernet enhancements available in IEC 61784-2 (CP3/6) without modification of the data structures of the IEC-61850 process bus. For this reason, communication with and without the real-time enhancements can be set in the Siemens merging unit. Network components, for example switches that add real-time features to existing IEC-61850-9-2 components would also be feasible. This enables merging units and protection devices to be connected easily without real-time enhancement.

The use of the new real-time Ethernet solution presented by Siemens at the Cigré means highly efficient and reliable data communications for switching station operators. It also means that they can save investment costs and space when extending existing systems, because non-conventional instrument transformers such as optical instrument transformers or Hall sensors are much smaller than their conventional counterparts which frequently even need special foundations. They can save cabling and engineering costs, and subsequent maintenance of the system is also made easier. The Siemens concept also provides the basis for maintenance according to the state of the system. Fewer different devices in the system reduces the spare parts inventory needed. Adapting the equipment to changes in the load flow is also easier because it is only necessary to change the parameters instead of exchanging equipment.