# 50Hertz Awards Ostwind 4 Marine Assurance to ABL for Baltic Sea’s First 2 GW 525 kV HVDC Offshore Grid System

> German transmission system operator 50Hertz has appointed marine consultancy ABL to deliver comprehensive marine warranty survey (MWS) and engineering assurance for Ostwind 4, the landmark 2 GW offshore transmission system deploying the German Baltic Sea’s first 525 kV subsea HVDC link and offshore converter platform.

- **Publish Date:** 2026-09-29
- **Category:** transmission-substations
- **Reading Time:** 5 min
- **Original Source Citation:** [50Hertz Transmission GmbH & ABL Group](https://www.50hertz.com/en/News/Detail/ostwind-4-baltic-hvdc-marine-warranty-survey-contract-award)
- **Tags:** 50Hertz, Ostwind 4, Baltic Sea, HVDC 525kV, Offshore Converter, ABL Group, Subsea Cable, Germany Grid
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## Pioneering 525 kV Direct Current in the Baltic Offshore Sector

Unlike previous German Baltic grid connections (such as Ostwind 1 and 2) which operated via 220 kV three-phase alternating current, Ostwind 4 represents a technological leap to 525 kV high-voltage direct current (HVDC). The system will evacuate up to 2,000 MW of wind generation from offshore wind areas O-1.3 and O-2.2 located northeast of Rügen island.

The offshore converter platform will house multi-phase step-up transformers, harmonic filters, and Voltage Sourced Converter (VSC) valve halls, stepping up array collection voltages to ±525 kV DC for transmission over 100+ kilometers of subsea and underground cables to the onshore grid interconnection hub near Lubmin.

## Rigorous Marine Assurance for Heavy Topside and Cable Installation

Under the contract awarded in late September 2026, ABL will provide comprehensive marine assurance covering the transportation, heavy lifting, and installation of the multi-thousand-tonne topside structure, jacket foundation piles, and twin extruded XLPE 525 kV direct-current cables.

Technical scope includes verifying mooring systems for specialized heavy-lift vessels, evaluating dynamic cable burial plows across sensitive Baltic seabed substrates, and witnessing warranted offshore installation procedures in demanding sea conditions.

## Anchor Component of Germany’s 2030 Offshore Target

Ostwind 4 is critical to meeting Germany’s statutory target of 30 GW offshore wind capacity by 2030. By deploying 525 kV DC technology, transmission losses over the marine route are reduced by more than 35% compared to high-voltage AC counterparts.

Commissioning of the complete converter and cable system is slated for 2029, establishing a high-capacity clean energy conduit feeding directly into eastern Germany’s extra-high-voltage industrial transmission network.

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