A truly digital substation, that is, a substation that employs fiber optics or another form of communications in lieu of conventional copper connections, is safer, less expensive, more reliable and more flexible than its predecessors. New digital substations may employ fiber optics throughout: at the station level, between the station and the bays, the process bus, and even at the primary equipment level. Partially converted facilities that still contain conventional CTs and PTs, for example, may employ merging units to convert analog to digital signals, or special Ethernet switches to transmit sampled values of high-priority data over standard Ethernet links.
Challenging decisions are often necessary regarding the technology for communications within substation sites and between facilities. The choices include wired Ethernet, fiber, WiFi, radio and cellular. Cost reductions and technology enhancements have made two way radio communications one of the most popular means for industrial communications today. Radio communications are utilized for connectivity in a range of mission-critical utility communications including automated meter reading (AMR), advanced metering infrastructure (AMI), distribution automation (DA) and supervisory control and data acquisition (SCADA).
Within the radio communications genre there are two major approaches: point-to-multipoint network architecture using privately licensed spectrum signals; and a mesh network architecture using publicly available spectrum signals. ABB’s TropOS technology is an example of a mesh network system capable of intra-substation communications as well as network wide communications for programs such as asset health monitoring.
Issues to consider when selecting a radio or any communications system include: cost, signal-to-noise ratio, latency, range, interference, bandwidth requirements, transmission capacity and security. Additional factors include weather hardiness, maintainability, geographic conditions and area, scalability, interoperability and longevity. An informative white paper that prioritizes wireless characteristics based on common utility uses is available at this web site.
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