Page 134 - Offshore Electrical Engineering Manual

CHAPTER

Process Drives and 12

Starting Requirements

INTRODUCTION
This chapter is a continuation of PART 2 Chapter 9.
Machinery drives for offshore installations range in size from fractional horse-
power cabin ventilation fans to the 15 MW or more machines required for gas injec-
tion compressors. Some concern has been expressed over the practicality of installing
very large electric motors offshore because of the stresses imposed on the structure,
especially during starting. A figure of around 25 MW, depending on the application
(e.g., less for reciprocating pump drivers), should be considered as the normal ceiling
figure for offshore electric motor ratings. Where the design is outside general engi-
neering experience/practice, special studies will be required to ensure that structural
resonance, shock, noise and vibration, metal fatigue, electric system dynamics, etc.
are not ‘showstoppers’ and this will add significant cost to the project.
Summarising from PART 2 Chapter 9.

VOLTAGE LEVELS

Voltage Level Rating
1. 415–460 V Up to 150 kW
2. 3300–6600 V Up to 1000 kW
3. 11–13.8 kV Over 1000 kW

Higher voltages such as 22 kV could be utilised, provided the economics is
favourable and proven ranges of machine at these higher voltages are available.

STARTING
Where an individual motor load represents a substantial part of the power system
capacity, it is desirable to obtain designs of squirrel-cage motors with the lowest
starting current characteristics compatible with the driven equipment. Both reduced-
voltage starting of cage motors and the use of slip ring motors will add considerable

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