# CAISO and Southern California Edison Approve 500/220 kV Whirlwind Substation Transformer Expansion for Mojave Solar

> The California Independent System Operator (CAISO) and Southern California Edison (SCE) have approved an expedited reliability engineering package for a third 500/220 kV 1,120 MVA autotransformer bank and switchrack reconfiguration at the Whirlwind Substation in Kern County to alleviate Path 26 transmission congestion and absorb gigawatt-scale solar-plus-storage generation.

- **Publish Date:** 2026-09-26
- **Category:** transformers-grid
- **Reading Time:** 5 min
- **Original Source Citation:** [California ISO (CAISO) & Southern California Edison (SCE)](https://www.caiso.com/news-events/news/caiso-sce-whirlwind-500kv-substation-upgrade-approval)
- **Tags:** CAISO, SCE, Whirlwind Substation, 500 kV Transformer, California Grid, Autotransformers, Mojave Desert, Renewable Integration, USA
- **Canonical URL:** https://voltformer.com/news/caiso-sce-whirlwind-substation-500kv-transformer-bank-grid-forming-upgrades
- **Markdown Source:** https://voltformer.com/news/caiso-sce-whirlwind-substation-500kv-transformer-bank-grid-forming-upgrades.md

## Unbottling the Tehachapi and Antelope Valley Renewable Corridor

The Whirlwind Substation serves as a premier extra-high-voltage node in the Tehachapi Renewable Transmission Project (TRTP), bridging major desert solar, wind, and battery storage clusters with the Los Angeles Basin. Surging utility-scale BESS additions and solar repowering projects in Kern and northern Los Angeles counties have pushed existing transformer banks to their maximum thermal ratings.

To eliminate thermal overloads and provide n-1 transmission contingency margins along the Path 26 intertie, SCE is adding a third 500/220 kV autotransformer bank rated at 1,120 MVA.

## Advanced Autotransformer Specs and Low-Noise Baffles

The newly approved autotransformer bank consists of single-phase units utilizing low-loss Step-Lap magnetic cores, natural ester dielectric fluid, and automated on-load tap changers (OLTC).

Because the facility borders sensitive desert habitats and rural communities, the units feature acoustic dampening enclosures engineered to limit operating sound levels below 54 dB(A) at full forced-air (ODAF) rating.

## Switchrack Splitting and Short-Circuit Duty Management

The expansion includes splitting the 220 kV switchrack into isolated operating segments to keep prospective short-circuit fault currents safely below breaker interrupting ratings (63 kA).

Fast-tracked under CAISO’s 2026 Transmission Planning Process, construction is scheduled to begin in 2027 with commercial energization planned for 2028.

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