Staff recommends approval of the engineering services work by Booth & Associates related to the swapping of two substation transformers for $42,325.00.
The peak load at the Airport last year was 22 MW. Two transformers serve the load at the Airport; one is a 30 MVA and the other is a 20 MVA. The 30 MVA transformer is able to handle the entire load if the 20 MVA transformer is lost. Depending upon the time of year, if the 30 MVA transformer fails, the load simply cannot be transferred to the other transformer at peak load conditions. An overload, and possible loss of the second transformer, could result. To further exacerbate the problem, one of the main backup feeders was eliminated as a result of the underground conversion along Highway 441, so the load cannot be transferred to another substation.
As a result of the regular dissolved gas analysis, staff knows the 30 MVA transformer at the Airport Substation, which has been in service since around 1982, has been evolving gas combinations indicative of overheating. The transformer has not been placed in an overload condition so these gasses can only be a result of an internal problem. The transformer was examined by the manufacturer soon after its installation and they were not able to determine the nature of the problem, only that an internal problem exists. This unknown problem increases the possibility that a failure could occur in the 30 MVA transformer.
The original plan was to replace the existing 30 MVA transformer with a new 30 MVA transformer, then recondition or rewind the retired transformer and use it to replace the existing 20 MVA transformer. There would then be two 30 MVA transformers at Airport substation, thereby eliminating the overload problem. Since budgetary constraints prevent the purchase of a new transformer, the following transformer swap is proposed.
Picciola Substation has a peak load of 15 MW being served by a 30 MVA transformer and a 20 MVA transformer. The 30 MVA transformer at Picciola Substation can be swapped with the 20 MVA transformer at Airport Substation leaving two 20 MVA transformers in place at the Picciola Substation where the peak load is 15 MW and two 30 MVA transformers at the Airport Substation where the peak load is 22 MW. If the suspicious 30 MVA transformer at Airport Substation fails, the other 30 MVA transformer will be able to carry the load while repairs are made. When budget allows, rather than wait until the transformer fails, staff can remove the suspicious transformer from service and send it away for diagnosis and repair.
The City currently has a continuing services contract with Booth & Associates for this type of engineering service. This work will be covered under the existing continuing services contract and the attached proposal from Booth & Associates.
1. Approve the purchase to Booth & Associates; or
2. Such alternative action as the Commission may deem appropriate
This was not a budgeted project as the original plan was to purchase a new substation transformer. The funds for this project are available in the account listed.
Department: _Electric Department_____
Prepared by: _Mike Thornton_________
Attachments: Yes__X_ No ______
Advertised: ____Not Required __X___
Attorney Review : Yes___ No __X_
Reviewed by: Dept. Head ________
Finance Dept. __________________
Deputy C.M. ___________________
City Manager ___________________
Account No. _041-1099-531.31-10__
Project No. __410012____________
WF No. _____WF453731 / 001____