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In early 2003, Valero Refining faced a situation of having inadequate capacity in their 69 kV main substation and 12.47 kV plant distribution to reliably serve their plant expansion plans. The Valero service provider, American Electric Power (AEP) did not have capacity in their 69 kV transmission system to support any plant load additions and recommended that the plant be served from the newer 138 kV transmission system.


Colwell was retained by Valero to develop a project to construct a new 138 kV substation and to cutover the existing plant electrical system without a plant electrical outage. Colwell performed an initial site study to determine the optimum substation location considering constructability and future maintenance as well as tie- ins to AEP’s transmission system and to the plant distribution system. A conceptual design was developed and an AFE package was prepared, submitted and approved.


Colwell then provided detailed engineering design for the project which included a 138 kV, six breaker, 3000 amp ring bus, box structure substation with two incoming AEP transmission lines. Two 35/62.5 MVA transformers were provided to step down from 138 kV to 12.47 kV and supply plant power to a 4 bus, main-tie-main 3000 amp, 12.47 kV metal-clad switchgear arrangement. Two switchgear assemblies were located in separate, climate controlled and pressurized switchgear buildings and were connected by a 3000 amp underground cable bus tie circuit through a current limiting reactor. Twelve new 12.47 kV underground feeders were installed through a new underground duct and manhole system to reconnect to existing plant distribution system.


The two existing 69 kV AEP incoming lines were removed and the 69 kV substation bus was reconnected to the new primary sub through a 30/50 MVA autotransformer and 138 kV and 69 kV underground feeder cables. Provisions were made in the design for future demolition of the 69 kV substation and reconnection of the plant generators and 13.8 kV motors directly to a 13.8 kV switchgear bus served from the autotransformer.


Colwell engineers provided system planning, multi-discipline detailed design engineering and construction administration services for this project and, additionally performed short circuit and protective device coordination studies and equipment evaluation studies for the existing system.

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