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A Modern WAN—Simple, Economical, Elegant

A Modern Wan


City Utilities of Springfield wanted to improve their communications system. They had an older T1 multiplexer that was starting to fail, and their communications network was complicated and outdated. It was using eight rings with HCB relays, which were intolerant of the network delays associated with their T1 multiplexer.

Customer Profile


  • Customer: City Utilities of Springfield
  • Location: Springfield, Missouri
  • Industry: Electric Utility
  • Application: WAN Communications



SEL suggested a simple, economical solution that would improve the performance for both the City Utilities communications network and power system.

Rather than making expensive accommodations in a new communications system for the outdated HCB relays, SEL recommended upgrading to SEL-387L Line Current Differential Relays. This upgrade would allow City Utilities to use the SEL ICON with an IEEE C37.94 interface in place of their old T1 multiplexer, eliminating expensive copper wiring and HCB interfaces. And, with IEEE C37.94, they would also have a “clean” interface, free from conditions such as ground potential rise. The SEL solution would also allow City Utilities to convert their eight-ring system into a simpler three-ring system.


Migrating to SEL’s modern, three-ring system allowed City Utilities to reduce their number of nodes from 61 to 49. At a savings of approximately $16,000 (USD) per node, they saved $192,000. In addition, the solution delivers the communications performance required for protection circuits. Upgrading was not only smart but also economical.

City Utilities of Springfield had originally chosen a more complicated system because their HCB relays could not tolerate the delay characteristics of their T1 multiplexer. After replacing their T1 multiplexer with an SEL ICON, the utility no longer has this restriction.

City Utilities was very pleased with their modernized communications system and with SEL’s customer service. The new solution eliminates the tradeoffs required with the older, more complicated system. Now, City Utilities can run their communications on a completely modern system that was specially designed to handle their needs.

Customer Service

At SEL, we take pride in customer service. If a problem can’t be solved over the phone, our engineers will visit the site.

If they’ve had to come onsite, they’re onsite the next day... [They] put people in a corporate jet and have them on the ground at four o’clock the next morning.

David Thompson, General Supervisor Substation Operations, City Utilities of Springfield

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Innovation, Persistence, and a New Beginning

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Innovation, Persistence, and a New Beginning