Wolfgang Wimmer

Reliability investigations for SA communication architectures based on IEC 61850

The new communication standard IEC 61850 is now introduced to substation automation replacing all wires by serial communication. Based on mainstream communication means like Ethernet it profits from a high flexibility regarding communication architectures. But any solution has to fulfill all reliability requirements resulting from the safety-critical mission of substation automation for a reliable power supply in transmission and distribution grids. To achieve this goal typical types of SA communication architectures are investigated starting from the relevant properties of IEC 61850, using proper reliability definitions and common failure modes. The relevant reliability figures are calculated. Different levels of redundancy, their limits for reliability and impact on the distributed functions are considered. The results clearly indicate what types of architectures have to be applied for the requested reliability of substation automation functions. This includes also function allocation and proposals for amending the standard.

Safety related, distributed functions in substations and the standard IEC 61850

In a substation, a lot of distributed, safety related functions have to be performed. IEC 61850 is intended to replace all wires by serial communication. To achieve this goal IEC 61850 has to fulfill hard real-time criteria. Starting from the definition of these criteria the communication methods of IEC 61850 are investigated. The result shows the feasibility of these methods for interlocking and illustrates their usage. Some application rules are given.

Topology-Based Interlocking of Electrical Substations

Conventional interlocking of substations is usually expressed by Boolean expressions and realized by electro-mechanical relays. Since these expressions are generated by applying verbally stated interlocking rules to a specific substation configuration, any change of the substation or of the operational philosophy affects them in such a complex way that the problem has to be tackled again in most cases from the very beginning. The proposed topology-based approach suited for microprocessors decouples knowledge-base and implementation, i.e. interlocking rules, and substation configuration. It results in interlocking rules that are independent of a single line diagram and can be applied to all known substation configurations. The rules are divided into mandatory and dependent on operational philosophy. The modularity allows for applying exactly those rules specified in the special project. Any new substation does not require new programming. The inherently fault-tolerant implementation in a 765 kV GIS is briefly described.

Use of distributed topology detection for applications in Substation automation

AbstractDistributed functions in substation automation systems typically use distributed data (sensors) and act on more than one switch, i.e. on distributed actuators. The allocation of a distributed function to sensors and actuators is in many cases not fixed but dynamically depending on the actual switchgear topology i.e. of the actual switch states in the single line diagram. The detection of the actual topology is the key, which may be done in one central IED or in many distributed ones. A special problem is the extension of the substation e.g. with one new bay without reengineering the existing SA part and retesting of the existing part of the distributed functions. It is shown that this goal may be reached with a separate topology detection function which serves all distributed functions. The approach uses a topology detection distributed on several IEDs, since there are at least one or more IEDs of the existing system and typically one or two IEDs added by the extension. Application function examples like interlocking, zone protection like busbar protection, breaker failure protection, distributed synchrocheck, CT/VT plausibility control and topology based protections are described.

Investigations of different Function Allocations in SA Systems enabled by IEC 61850

At least since 2006 the standard IEC 61850 for communication in substations is in commercial use providing interoperability in substation automation systems between devices from different suppliers. Its approach is based on the split between applications and communication, functions and implementation and, therefore, supports also the free allocation of functions to IEDs. This allows the question for an optimal allocation regarding the functional requirements of SA, its impact on the communication system, performance of functions, engineering effort and reliability, and on the cost level. Common SA systems are some mix between a total centralized and decentralized allocation providing the well- known functions on station, bay and process level. The two extreme solutions are positioned and it is evaluated if the common mix is an optimal one. The result is a proposal for the best allocation of existing functions to IEDs. Depending on given functional requirements and not too strict boundary conditions, improvements are possible exploiting the full capabilities of IEC 61850, if accepted.