Page 483 - Handbook of Electrical Engineering

472 HANDBOOK OF ELECTRICAL ENGINEERING

by the recipient, can suffer through translation. Some of the international standards, e.g. IEC60034,
60050, 60079, include sub-sections or clauses for defining words, phrases and terms. Sometimes
these definitions are not easy to grasp.

It is recommended that particularly important words, phrases, terms and abbreviations are
defined in the specification itself, especially if they differ in use from say those given in an IEC
specification. (An example that regularly appears is the difference in meaning between ‘shall’ and
‘should’.)
Some of the material in this section could equally well be placed at the end of the document
as an appendix.

19.2.6 Performance or Functional Requirements

Somewhere in the specification, or the data sheet, should be stated the expected life duration of the
equipment, e.g. 25 years, and a reasonable duration of continuous service between major maintenance
operations, e.g. 3, 4 or 5 years. These durations will depend upon the type of equipment, but for
major items such as large generators, large high-voltage motors, switchboards, motor control centres,
power transformers, these durations can be regarded as typical for the oil industry.
If equipment is to be specified for use in hazardous areas, e.g. Zone 1, Zone 2, then the
equipment as purchased should not have been modified in any manner that could invalidate its
hazardous area certification. Components that can be vulnerable to modification are terminal boxes,
gland plates and threaded entries.

The basic requirements for performance can be categorised as follows:-

• Starting up.
• Normal continuous operation.
• Permissible but limited overloading.
• Short-circuit withstand.
• Shutting down.

It will be useful to the recipient to have an understanding of the power system or network into
which the equipment will belong. This is especially important when specifying the high-voltage gen-
eration and distribution equipment, and some of the main low-voltage equipment such as switchgear.
The modes of operation of the power system may have some bearing upon the design of the equip-
ment being specified, e.g. method of earthing neutrals, minimum and maximum fault currents, dips
in system voltage and frequency, normal and abnormal switching configuration.
The owner may have some restriction on how to start up and shut down equipment, e.g. limits
on starting currents of motors, voltage dip limits at switchgear, duration of start up or shut down,
purging with safe air or inert gas, interlocking schemes, manual or automatic sequences.
For some equipment, especially generators and their prime-movers, the normal or rated duty
may need to be emphasised so that the correct rating for the prime-mover is chosen, and an adequate
margin for short-term permissible overloading exists. Emergency generators used offshore may need