Caledonia Combined Cycle Relay Replacement

Tennessee Valley Authority (TVA) | Steens, Mississippi

To improve plant reliability, protection and control relays were replaced throughout the Tennessee Valley Authority’s (TVA’s) Caledonia Combined Cycle Plant. In total, 98 protective relays (the majority of which were GE Multilin) were replaced and combined into 65 new Schweitzer Engineering Laboratories (SEL) relays. The new design also included arc flash mitigation and maintenance mode switches.

The Merrick team provided complete engineering services, on-site installation supervision, and commissioning support for the replacement of the protective relays. Design efforts included:

  • Updated the existing plant ETAP model, performed load flow, short circuit, arc flash analysis, and performed selective coordination studies
  • Developed relay setting sheets and relay programming database files
  • Updated plant one-line and three-line drawings
  • Developed control DC and AC schematic diagrams
  • Developed wiring drawings for the new SEL relays
  • Created a relay test plan and procedure

Merrick provided on-site supervision of relay demolition and installation, NERC compliant CT/PT ratio testing, and wiring construction during the outage. After completion of installation and commissioning, Merrick produced as-built drawings.

The protective relays included: generator protection, generator step-up transformer (GSU) differential protection, 4.16kV switchgear feeder and motor protection, 480V auxiliary feeder protection, and the plant standby diesel generator (SDG) protection relay.


Electrical Engineering;Engineering; Commissioning Support; Installation Oversight
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