2×1250 kVA SF6-Free Substation for E.ON

How we maximised urban grid capacity by fitting two 1250 kVA transformers alongside bulky eco-friendly technology into a single enclosure, completing development with minimal customer involvement.

Reference details:

Location: 

Sweden
Timeline: Delivered as a critical expansion milestone in 2025.
Client: E.ON Sweden
Scope of work:

Spatial optimization, IP-class type-testing, and turnkey logistics for dual-transformer outdoor concrete compact substations (HEKA C).

Technical specification:
  • Model / CSS Name: HEKA C
  • Configuration: HEKA1VB1250-2 / Dual-Transformer
  • Power Capacity: Up to 2×1250 kVA
  • Enclosure Type: Heavy-duty concrete (outdoor)
  • Safety Rating (IAC): Up to 20 kA / 1s
  • Enclosure Class: K15
  • IP: Fully type-tested and certified
  • MV Switchgear: Up to 5 bays, completely SF6-free RMU

Challenge

Fitting Dual Transformers and Green Switchgear into One Urban Footprint

Densely populated urban centres require rugged, visually integrated concrete substations. For its 2025 local grid expansion, E.ON faced a massive hurdle: they needed to establish high-capacity connection points up to 2×1250 kVA using exclusively new, environmentally friendly SF6-free switchgear.

Because greenhouse gas-free RMU components are significantly larger than traditional models, fitting both the bulky eco-friendly switchgear and two massive transformers into a standardised urban footprint was a major engineering challenge. Failing to solve this would force E.ON to install multiple substations, doubling infrastructure costs and taking up valuable urban real estate.

Solution

Radical Internal Space Optimization and Full IP Certification

Harju Elekter re-engineered the HEKA C concrete substation configuration to unlock maximum internal space efficiency. Our design teams optimised the layout, mapping out a way to integrate the bulkier SF6-free RMU, dual 1250 kVA transformers, and secondary low-voltage panels into a single, compact concrete footprint.

To ensure strong resilience against outdoor weather elements in public spaces, we fast-tracked manufacturing and successfully type-tested the new multi-transformer design for strict IP (Ingress Protection) classification. Additionally, we took full responsibility for transport logistics and cross-party component coordination.

Result

Double the Power in a Single Certified Urban Asset

E.ON successfully deployed a certified, high-density, “plug-and-play” urban grid asset that satisfies new environmental laws while delivering double the power capacity. By managing the extreme spatial redesign, rigorous IP-validation, and complete material supply chain, Harju Elekter lightened the client’s project management burden.

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