Upgrading your protective relays — when theory meets reality

In theory, it is easy to see the advantage of upgrading a protective relay installation from Electro-Mechanical Relays or Solid-State Relays to Modern Digital Relays: Required panel space is reduced. Interconnection wiring is reduced. Required maintenance is reduced. Calibration is simpler. Settings can be changed dynamically. More complex relay schemes are possible. Self-diagnosis is built in. And modern digital relays provide abundantly more information than the previous generation of relays supplying data to SCADA systems, helping document compliance with NERC reliability standards, and establishing a cornerstone for many smart grid efforts. But when theory meets reality, an upgrade is never quite as easy as it sounds. Do you still have drawings from the original installation? Are the wires well-labeled? Is the wire insulation still flexible? Do any of your technicians remember how it was actually installed? Do the new relays fit the old relays' holes? If not, can the panel be cut? Do alternate power sources exist such that the circuits can be taken out of service during the upgrade? Will your battery plant have the capacity to power the modern relays? Is your control building large enough? If not, is it expandable? All these questions change the equation. The challenges can be overcome, but need to be considered before the project starts.