SS IMPLICATIONS OF SUBSEA PROCESSING POWER DISTRIBUTION &lt; SUBSEA SWITCHGEAR MODULE - A KEY ENABLING COMPONENT IN SUBSEA INSTALLATIONS&gt;
Authors: Hazel Terence , Alessandrini Raphael , Andrea Pierrick , Eschbach Jean-Luc , Pana Stanel 
Published: July 2010

Subsea high and low voltage switchgear is a key enabling component for subsea process units. Locating the switchgear module at the heart of the subsea load center avoids having to provide any top-side facilities, greatly reduces the operation expenditures and reduces the cost of the power lines. The subsea environment has a very strong influence on the design, fabrication, assembly and testing of the module, both the enclosure itself and the switchgear equipment inside of the enclosure.

After the introduction and some general information regarding the subsea switchgear module, the feasibility study and various conceptual design calculations performed during the development of the switchgear portion will be described. Since this is the first time that such a large electrical distribution system has been installed in a subsea environment, the main purpose of these studies was to ensure a very high availability of the switchgear to provide power to the process loads. Reliability studies combined with mechanical and thermal analyses were performed to ensure correct installation and operation in a subsea environment at about 1000m below sea level. Electromagnetic compatibility studies were also performed to avoid any nuisance operations of the switchgear and controlgear which could result in loss of production.

After the information about the switchgear portion, the design, fabrication and testing of the enclosure itself will be described. There are two main criteria for the enclosure. The first is the high pressure due to installation on the seabed. The second is the requirement for the installation of the switchgear within the enclosure prior to its submersion, and also access to the switchgear during maintenance operations at the surface. This criterion requires removable enclosure parts that must have adequate sealing to prevent any leakage when submerged. Also very important are the constraints due to the handling of the complete module when installing it and also when it requires servicing.

Finally the integration of the switchgear portion within the enclosure will be described.

Introduction

In recent years, the offshore industry has seen a clear trend for production facilities to be installed on the seabed. Such a system is particularly suited for challenging environments such as deepsea and artic, and provides an efficient and economical subsea-to-beach solution which eliminates the need for a floating production unit. There are several advantages of installing process equipment close to the source of the product. Up until now, each item of process equipment was powered from the surface. This is reliable but very costly. In order to reduce the cost of the power supply but not reduce its reliability, it was decided to place the electrical distribution system also on the sea bed. Thus the electrical equipment will be located near the load center which is common practice on all on-shore designs.