Study: Milton distribution largely sound but flags 53‑year‑old substation transformer, IT gaps and backup-tie needs

Milton — Consultants from Quanta Technology told the Milton City Council study session on Sept. 8 that the city’s electric distribution “looks pretty good” under normal conditions but identified near‑term vulnerabilities that require planning and capital work. The presentation urged the city to pursue a replacement for the Surprise Lake substation transformer, improve interconnections with Puget Sound Energy (PSE), and complete several information‑technology and asset‑management upgrades.

The finding matters because a transformer failure or loss of external backup will leave Milton’s utility without a spare at the Surprise Lake substation, potentially forcing longer outages or reliance on external ties that are changing. “The Surprise Lake substation transformer is very old. It’s 53 years old,” Don Hall, executive adviser for Quanta Technology, said during the presentation. Hall and colleague Elliot Tanis described recommended capital and IT work that they say will allow the utility to serve customers reliably through 2035 if implemented.

Quanta’s analysis combined field measurements, engineering models and stress testing across extreme summer and winter scenarios for the next 10 years. The firm reported that Milton’s three feeders can meet an n‑minus‑1 contingency (the loss of one feeder) using the remaining circuits, but the study flagged several operational weaknesses. Hall said field crews found temporary jumpers that should be replaced with permanent construction and a switching device serving the Bridgepoint development that should be upgraded to avoid single‑phasing a three‑phase customer.

The presentation identified a critical gap in backup supply. Milton currently uses a limited backup tie with Tacoma Public Utilities (TPU) that Quanta said will be severed when a Washington State Department of Transportation (WSDOT) project proceeds. Consultants recommended the city pursue at least three tie points with Puget Sound Energy; Quanta could not model PSE’s feeders because PSE data were not available, so the firm made tie‑point assumptions and recommended a joint study with PSE and Bonneville Power Administration (BPA).

Hall and city staff also described several IT and data shortfalls that slowed the study and pose operational risk: the city’s asset accounting module (Cartograph) is not fully populated; the ArcGIS system lacks detailed asset attributes; the metering/monitoring (AMI) data were delayed by a third‑party service provider; and the SCADA‑style metering, monitoring and control system at the substation is not working. “We weren’t able to get the [PSE] information on their side,” Hall said; he recommended the city coordinate a PSE study before closing ties.

Quanta’s recommendations included replacing temporary construction and the identified switching device, taking additional phase‑balance readings on Feeder 1, negotiating with BPA to replace or fund a second transformer at Surprise Lake substation to provide redundancy, establishing at least three PSE tie points, implementing a program of asset evaluation and depreciation planning, auditing and revising AMI contracts, hiring permanent GIS expertise, and replacing the nonfunctional SCADA metering/monitoring system. The consultants recommended repeating the distribution analysis every five years.

City staff said earlier meter failures indicate the AMI fleet (installed in 2017) is approaching end of life and that a capital line item for meter replacement will appear in upcoming budgets. Quanta and city staff also discussed storage and inventory handling improvements for spare equipment.

Council members asked for timing and next steps. Director Dustin Madden told the council that Milton met with BPA and that BPA will initiate a study with PSE on the distribution connection; staff and consultants said that work will take time but that they will pursue it with the goal of having a new arrangement in place before the TPU tie is severed. No formal motions or votes were taken; the presentation will return with report materials and an ordinance proposal on rates in October.

The study’s authors and city staff emphasized that many of the recommendations require cooperation with outside utilities and vendors, and that some work (for example, replacing the Surprise Lake transformer) depends on BPA decisions and financing.