Siemens Subsea Power Grid

Siemens successfully completed the first phase of its shallow water test of the Subsea Power Grid.

The development program was conducted in collaboration with industry partners Chevron, Equinor, ExxonMobil, and Eni Norge.

This will be the world’s first Subsea Power Grid for medium voltage power distribution using pressure compensated technology.

Siemens has successfully concluded the first phase of its Subsea Power Grid shallow water test in Trondheim, Norway. Siemens, in collaboration with industry partners Chevron, Equinor, ExxonMobil, and Eni Norge, is in the final stages of a program to develop a barrier-breaking system that will become the world’s first Subsea Power Grid designed for distribution of medium voltage power using pressure compensated technology.

“There will be more subsea compressors, pumps, processing plants, and in the future entire production facilities placed on the seabed, all of which require power,” said Frode Tobiassen, Head of Subsea at Siemens. “This development is what we are preparing for with the Subsea Power Grid system.”

The Subsea Power Grid system consists of a subsea transformer, subsea switchgear, subsea variable speed drive (VSD), subsea wet mate connectors, and a highly reliable remote control and monitoring system that includes cloud-based user dashboards and data analytics.

Subsea power distribution systems will play a major role in the future of subsea field development projects. The Subsea Power Grid is an enabling technology for subsea processing with multiple seabed power consumers. The system is ideally suited to support enhanced recovery in subsea brownfield projects and tie-back fields, benefitting from single- or multiphase boosting to increase oil recovery.

During the initial test phase at Siemens’ test site in Trondheim, the system operated in a ring loop topology at full load and a predetermined test and verification program was performed. The initial results from the shallow water testing were positive and all units operated within their design parameters.

In agreement with its program partners, Siemens will now move into the next phase with an extended shallow water test to build operational experience and verify long-term reliability. The goal is to accumulate 3,000 hours of runtime on the equipment while performing further system testing.

In parallel, preparations are ongoing for a deep-water pilot program where the equipment will be installed and used on a subsea field.

Powering installations on the seabed

Enabling large-scale subsea processing by powering the subsea fields of the future – down to 3,000 meters.

Subsea Transformers

The step-down transformer is the main interface between the subsea transmission line and the power distribution. As a hermetically sealed, fluid-filled and pressure-compensated unit transformer for variable speed drive of pump motors, it enables step down to a wide range of consumers as well as longer step-outs. Its natural convection cooling reduces maintenance requirements.

Optimized as the main transformer for Siemens Subsea Power Grid, the generic design can be used on subsea distribution transformers in a wide power range. The electrical design is based on traditional onshore distribution transformers, but with an enhanced-efficiency insulation system. All materials have been tested for pressure and fluid compatibility in an extensive qualification program. In addition, the design was verified with an extensive test in shallow water.

The subsea transformer has an integrated sensor and monitoring system that can be seamlessly integrated in the Siemens subsea power control system. This provides the operator with a continuous display of status of transformer integrity and the ability to optimize operations for enhanced safety.

In 2012, the Siemens Subsea Transformer was successfully operated in shallow water in Trondheim harbor. All transformer materials were tested for pressure and fluid compatibility in an extensive qualification program before the design was verified with the test in shallow water.

Technical data

Pressure-compensated
Hybrid insulation
Robust enclosure design with optimized natural cooling properties
Biodegradable and environmentally-friendly MIDEL 7131? fluid filling
Flexible interfaces (dry or wet-mate connections)
Advanced condition monitoring
Also suitable as a step-down transformer for subsea boosting
Qualified for 3,000 meters water depth.

Subsea Switchgear

The subsea switchgear has a modular design. Its main bus bars, wet-mate connectors and measuring transformers are housed in the fluid-filled and pressurized base module.

Technical data

Modular design with vacuum circuit breakers
Fluid-filled base module
Pressure-compensated bus bar base section
Cascadable design for more consumers
Zero differential pressure at all penetration to seawater

Subsea Variable-Speed Drive (VSD)

The variable-speed drive (VSD) features a fault-tolerant multi-cell topology with built-in component redundancy. Designed specifically for sea floor operation, its fluid-filled enclosure and all power electronics can be exposed to full pressure, thereby reducing maintenance requirements.

Technical data

Modular and compact pressure-compensated design
100 % natural cooling
Multicell topology with built-in redundancy
Advanced cell by-pass for maximum availability
Built-in isolation transformer ensures safe operation in Siemens’ Subsea Power Grid
Low harmonics both to motor and to supply

Subsea Power Control

The Subsea Power Control system is a very important component of the Subsea Power Grid. It ensures several important functions in the subsea power distribution:

Direct transfer of every command given in the topside control system to the respective subsea control module,

Transparent communication of status and information from the respective subsea modules like variable-speed drive (VSD) and switchgear to the topside control system,

Delivery of standardized interfaces (e.g. SIIS to other subsea application like sensors and/or pump systems).

Delivery of a transparent communication channel from topside all the way to the subsea variable-speed drive (VSD). This enables configuration of the VSD, update of VSD software, as well as diagnostics and service being done the same way as with a topside VSD.

The Subsea Power Control system is connected with topside control via an embedded fiber in the subsea power umbilical. The fiber is terminated and connected to a subsea electronic power control unit (EPCU) – the “brain” of the Siemens Subsea Power Grid. This controller unit processes commands and information, and generates the correct commands locally to the respective subsea modules like variable-speed drive (VSD) and switchgear. All data flow subsea is sent to and from the respective units via a remote termination unit (RTU) in an Ethernet data network.

The subsea power control system is built up as a redundant system with retrievable units.

Control challenges

High availability and reliability
Flexible size and scalability of grid
Coordination of distributed components
Fast response to commands and failures
High number of (different) interfaces

Control and monitoring system advantages

Flexibility
System can easily be reconfigured for many different topologies
System can operate autonomously

Increased grid life time
Operation can be adapted to increase component life time

Lower engineering and maintenance costs
Standard interfaces reduces interface engineering costs
Remaining life time can be predicted so that maintenance can be planned
Service intervals can be extended to when maintenance is needed

Higher availability
System can continue to operate after faults, either at full or reduced performance
Modular design and advanced fault detection will reduce repair time