# Hydro-Québec Awards Major Contract for 735 kV Single-Phase Autotransformers for Hertel and Chamouchouane Substations

> To secure the bulk transmission corridor linking James Bay hydropower with southern load centers and the Champlain Hudson Power Express interconnector, Hydro-Québec has ordered nine 370 MVA 735/315 kV single-phase autotransformer units with enhanced cold-climate insulation.

- **Publish Date:** 2026-09-24
- **Category:** transformers-grid
- **Reading Time:** 5 min
- **Original Source Citation:** [Hydro-Québec TransÉnergie Engineering Division](https://www.hydroquebec.com/press/transenergie/735kv-autotransformers-chamouchouane-hertel-september-2026.html)
- **Tags:** Hydro-Québec, 735 kV, Autotransformers, Substations, Canada, CHPE, Hydropower
- **Canonical URL:** https://voltformer.com/news/hydro-quebec-orders-735kv-autotransformers-hertel-chamouchouane-substations
- **Markdown Source:** https://voltformer.com/news/hydro-quebec-orders-735kv-autotransformers-hertel-chamouchouane-substations.md

## Reinforcing the 735 kV Extra-High-Voltage Backbone

Hydro-Québec TransÉnergie operates the world’s pioneer commercial 735 kV transmission system, traversing subarctic terrain subject to ambient temperatures below -45 °C and heavy freezing rain icing. The new 370 MVA single-phase units will form three redundant 1,110 MVA three-phase autotransformer banks at Hertel and Chamouchouane substations.

The transformers feature specially engineered low-viscosity naphthenic mineral oil, high-grade silicon steel cores, and automated nitrogen-injection fire protection systems (NIFPS) to ensure uncompromised dielectric resilience against severe geomagnetic induced currents (GIC).

## Enabling Clean Power Exports to New York and New England

The substation upgrades are vital for operating the 1,250 MW Champlain Hudson Power Express (CHPE) HVDC transmission line at continuous full load while maintaining provincial N-1-1 reserve margins.

Factory acceptance testing at 735 kV full lightning impulse (BIL 2,050 kV) will be completed by mid-2027, with site energization slated for early 2028 under Hydro-Québec’s 2035 Grid Master Plan.

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