CITY COUNCIL AGENDA ITEM
ACTION REQUESTED:
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Accept the record of Emergency Procurement 24-255, Tollway Substation Power Transformer (30xa) Evaluation, to Power Substation Services for an amount of $58,697
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DEPARTMENT: Electric Utility
SUBMITTED BY: Brian Groth, Director
BACKGROUND:
The Electric Utility (Utility) is responsible for maintaining electric service for customers throughout the City of Naperville. A key component of the substations are transformers that step the 138kV transmission voltage down to lower voltages for distribution. At the Tollway Substation, the City owns a three-winding transformer, known as 30XA. The unit is filled with 14,000 gallons of mineral oil that serves as both electrical insulation and cooling. This transformer serves distribution circuits and customers, but also serves the 34kV Sub-Transmission network that feeds smaller substations (Indian Hill and Washington).
The transformer tripped offline during a 12kV bus fault on September 7, 2024. After clearing the bus and disconnecting the transformer from both 12kV and 34kV loads, an attempt to re-energize the transformer resulted in another trip after three seconds. Subsequent analysis of the oil through laboratory testing showed an alarming increase in combustible gases, including acetylene, suggesting internal arcing within the tank of the transformer. Further electrical testing of the unit resulted in specific evidence of a secondary winding to ground failure on one of the 12kV windings. A winding to ground failure would be fatal to the transformer.
Due to redundancy in design of the system, the loss of this one transformer has not created any extended ongoing outages; however, the Utility is now in a backup contingency configuration. This means that a critical system element is out of service, and staff must put stress on the backup/alternate equipment to maintain service to customers.
Under peak loading conditions, or if another critical component of the system goes off-line, it is uncertain that the Utility could maintain service to customers. Replacement or repair of the transformer is estimated to be between $2M and $4M. It is important to be 100% certain that the unit has failed prior to proceeding down one of these very expensive paths.
Expediting a third-party independent evaluation is the critical next step to either being able to return the unit to service or being able to decide on repairing or replacing the transformer. The sooner this information is known, and decisions can be made, the lower the risk of loss of service to customers. Timeframes to repair or replace the transformer are between six months and four years.
DISCUSSION:
The Emergency Procurement was approved by the Chief Procurement Officer on September 8, 2024, per Section 1-9B-4:6 Emergency Procurements, of the Naperville Procurement Code. The Utility sent requests for quotations to the six contractors below who are either known to be capable of performing this work, or who have expressed interest in quoting this type of work. Power Substation Services provided the lowest cost proposal and had the earliest crew availability to perform the work.
1. Power Substation Services - $58,697
2. Reinhausen - $92,009
3. Delta Star - $104,755
4. GE/Prolec/Waukesha/SPX - $137,380
5. Emerald - Incomplete proposal
6. Hitachi - No proposal
This work includes several components. First, the contractor will conduct tests and a visual inspection of the transformer. Under the best-case scenario, the contractor will determine the transformer does not need to be repaired or replaced and will prep the transformer to be returned to service.
FISCAL IMPACT:
CIP #: EU022
The transformer evaluation will be expensed to the Other Professional Services account listed below. The expense can be accommodated within the 2024 budget/
|
Account Number |
Fund Description |
Total Budget Amount |
|
40251300-531309 |
Electric Utility Fund |
$748,000 |