Page 26 - Offshore Electrical Engineering Manual

CHAPTER

The Offshore Electrical 2

Environment

INTRODUCTION
Some background information on oil and gas production is given in Appendix A.
This chapter discusses the more general criteria governing offshore electrical sys-
tems and equipment design.

SAFETY
The environment on an offshore installation is not inherently safe because of the
heavily salt-laden atmosphere and the highly conducting nature of the structure and
virtually all the equipment it contains. It must not be possible for personnel to come
into contact with live or moving parts either by accident or while performing their
normal duties.
Protection against electrical shock relies on the safe design and installation of
equipment, training (making personnel aware of the dangers and ensuring that the
necessary precautions are taken) and the use of special safe supplies for most por-
table equipment.
An electrical current of only a few milliamperes flowing through the human body
can cause muscular contractions and, in some circumstances, will be fatal. The cur-
rent may result in local burning or some involuntary reaction which in itself may lead
to injury. Additionally, of course, varying degrees of pain will be experienced.

ISOLATED SITUATION
Except in the case of one or two installations, the electrical system is totally isolated
from any other means of electrical supply. The system must be designed and config-
ured in such a way that it is never dependent on one small component or electrical
connection to continue in operation. This point may sound rather obvious, but it is the
author’s experience that hidden vulnerabilities may be designed into systems which
are both costly and disruptive in their first effects and in their eradication. The fol-
lowing examples of actual occurrences illustrate the point.
Example 1 A platform reinjection compressor is driven by a 500 kW 3.3 kV
motor having a lube oil system pressurised by auxiliary lube oil pumps driven by
low-voltage motors. Both the lube oil pump motors and the control supply for the

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