Page 400 - Offshore Electrical Engineering Manual

CHAPTER
1
Reliability

INTRODUCTION
This chapter has been included as an introduction to the use of reliability analysis in
aiding the offshore electrical system designer in his or her quest to produce a system
that not only is fit for its purpose when all its component parts are working but also
will continue to function in some fashion dependent on the severity of the problem
when certain of its components fail or incidents occur on the installation which affect
the system’s integrity.
Reliability analysis encompasses a number of graphical, mathematical and textual
operations which present the known facts, statistical data and/or experience about the
proposed system or similar systems in a way which highlights its weaknesses or
ranks the effectiveness of the options available to the designer.
It is very important when carrying out any form of reliability analysis that specific
goals are selected. The availability of an electrical supply at a particular point in a
system will be very much dependent on the configuration of the system and where
that point is located in it. Therefore a vague instruction such as ‘quantify the reliabil-
ity of the supply system’ is very unhelpful and it would be necessary to discuss with
the client concerned about what particular supplies were of particular concern and
then consider each in turn. For example, if the object was to maintain full produc-
tion then only the equipment required to maintain supplies to the production switch-
boards would need to be considered. However, if supplies to essential equipment
only were being analysed, the availability of all generation and all the routes which
could be used to connect it to the essential equipment would need to be taken into
account and, hopefully, in comparison, a much higher figure for the availability of
supply would be obtained.

DUPLICATION AND REDUNDANCY
Provided that good quality assurance procedures are adhered to throughout a design
and construction project, to the extent that all equipment purchased for installation
on the platform is fit for its purpose, theoretically there should be no benefit to be
gained by the replacement of one item of equipment with another one of similar
function from another manufacturer. Practically, this is not the case, as we know by
experience that certain devices are better obtained from a particular company. For
obvious reasons, information of this kind in the form of usable data is difficult to

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