Inter and Intra Substation Communications: Requirements and Solutions

As the substation communication world searches for the “Promised LAN”, it would be helpful to have a roadmap to give direction to the search. Many are the expectations of a LAN flowing with data and able to connect with any Intelligent Electronic Device (IED) that was ever made. Such expectations must be tempered with the cost and complexity of achieving them. This paper presents an outline of the communication requirements of the myriad of IED’s in existence in the substation today as well as the expectations of what second generation microprocessor based devices might be able to do. Requirements will focus on language issues, system capabilities, performance requirements, external interfaces, environmental, and quality issues. Some attention will also be given to the architecture of a solution and some guidelines as to how this structure might be built. Introduction From the introduction of processor based devices, we have had the ability to communicate with these devices. The ability to communicate gives added value to the IED and as such, has hastened their implementation. As time has gone on, we have watched communities of these devices sprout up in the substation typically with no concerted attempt to inter-communicate much less interoperate. As a result, a veritable “Tower of Babble” has arisen inside the substation. Attempts to date to achieve some semblance of common communication have focused around “Rosetta Stone” solutions whereby a translation module of software is located between the IED and host computer. Although this technique achieves today’s goals, translation hardware is usually required and creation of the translation module can be costly and time consuming. Another aspect is that revisions and generations of new IED’s have become a frequent occurrence demanding constant “stone cutting” and “chipping” of translation communication software. Newer IED designs implement faster communication rates, have more data to communicate, and are capable of performing some programmable logic functions. In view of future capabilities and a continuing proliferation of IED’s in the substation, a cry has come from the utility community to create a framework for not only common communication but an architecture that will provide for interoperation. Interoperation implies the ability to “plug and play” and also to be able to “share” data and functions. As an example, a protective relay may be required to provide a “check synchronism” function which requires the magnitude and phase angle comparison of two voltages. The relay performing the function may have intrinsic access to only one voltage. The other voltage may be available from another device in the substation . An interoperable system could then negotiate for access to the other voltage and as such, avoid all the overhead involved in direct wiring. Integration Benefits As substation integration becomes a reality, there are numerous benefits that can be realized. With data sharing, wiring between devices can now be minimized. Distributed data acquisition now becomes the foundation of substation integration. Traditional hardware devices such as the Remote Terminal Unit and the Digital Fault Recorder now become primarily functional entities that draw on other IED’s for their data. Interoperation permits distributed functionality, that is, the data and/or the decisions needed for a particular function may reside among multiple IEDs. Such changes in the substation design paradigm can be measured both quantitatively as well as qualitatively. Quantitatively speaking, substation integration has the potential for the following savings [1]: • Elimination of the station fault recorder & wiring • Elimination of the station Sequence of Events recorder & wiring • Minimization of RTU wiring • Minimization of Breaker Wiring Qualitatively, the integrated system brings with it: • Reduced O&M through “Real Time” condition monitoring • 100% redundancy in fault recording • Rapid fault location • Integrated Protection & Control