Case Study

Switchgear Replacement Study and Implementation


The units and switchgear for our client’s power plant had been in service for over 60 years, were nearing their end of life and presenting reliability concerns. Our client wanted to install upgrades to the 4kV switchgear and needed to know all of their options to get the project approved and funded.


Three options were investigated and analyzed, with the following goals in mind:

  • Upgrade switchgear, preferably without replacing switchgear by uprating and component replacement
  • Add excitation – 2 additional breakers
  • Reuse as many cables as possible
  • Lower arc flash values to 8 cal/cm2
  • Utilize more capacity from existing 20 MVA transformers, 2780 A available, uprate to 2500A main and bus, 3000A preferred
  • Uprate non-segregated phase bus to at least 2500A, 3000A preferred.
  • Upgrade relaying, replace existing fault bus scheme with more modern protection scheme
  • Consider replacing feeder breakers with contactors
  • Remote racking

Valdes prepared specifications for switchgear and related hardware. The packages were issued for budgetary bids and cost estimates were prepared for two of the options. Valdes submitted a report with the results to client for review and final for internal use in obtaining project approval and funding.
To support the estimates, Valdes also provided the following documents:

  • Revised single line diagram and typical three line diagrams
  • Conceptual general arrangement of switchgear and typical switchgear door layouts
  • Spec for switchgear replacement breakers and bus rerating to obtain quotes
  • Spec for switchgear replacement doors with new relays to obtain quotes
  • Cost estimate (+/- 10%) for the total project itemizing engineering, equipment, construction, commissioning costs, and spare parts
  • Project schedule including time for detailed engineering, procurement, pre-outage work, construction, and commissioning.


The study results were used by the client to approve funding for switchgear upgrades on five additional units. Valdes was awarded the detailed engineering to complete this project on the remainder of the units at this facility, as well as associated upgrades at our client’s other generating stations.