# BPA Energizes Upgraded 500 kV Series Capacitor Banks and 1,300 MVA Transformer at Slatt Substation

> The Bonneville Power Administration (BPA) has completed commissioning of modernized 500 kV series capacitor platforms and a 1,300 MVA 500/230 kV autotransformer bank at Slatt Substation in Oregon, reinforcing the Pacific AC Intertie by 600 MW.

- **Publish Date:** 2026-09-24
- **Category:** transmission-substations
- **Reading Time:** 5 min
- **Original Source Citation:** [Bonneville Power Administration (BPA) Transmission Services](https://www.bpa.gov/about/newsroom/news-releases/bpa-slatt-substation-500kv-series-capacitors-energization-september-2026)
- **Tags:** BPA, 500 kV, Series Capacitors, Substations, USA, Pacific Intertie, Grid Stability
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## Mitigating Transient Reactance on Long 500 kV Corridors

Slatt Substation is a vital switching hub along the Pacific AC Intertie, routing bulk federal hydropower from Columbia River dams toward California and intermountain load centers. The newly energized series capacitor banks provide 45% inductive compensation, slashing electrical impedance across the 500 kV transmission lines.

The upgrade incorporates state-of-the-art metal-oxide varistors (MOV), triggered spark gaps, and optical bypass switches engineered to ride through extreme 63 kA short-circuit fault currents without platform flashover.

## Boosting Regional Transmission Transfer Capability

In tandem with the series capacitors, BPA commissioned a replacement 1,300 MVA 500/230 kV autotransformer bank featuring low-loss step-lap cores and fiber-optic winding hot-spot sensors.

The completed project increases southern transmission capacity by 600 MW, preventing severe voltage sagging during high summer transfer periods across the Western Interconnection.

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