Page 139 - Offshore Electrical Engineering Manual

126 CHAPTER 12 Process Drives and Starting Requirements

FIGURE 2.12.2
Typical torque requirements over one cycle of reciprocating compressor operation, full
load.

GAS COMPRESSORS
It is worth remembering that large gas compressors, whether using induction or
synchronous motors, are highly dependent on their auxiliaries for reliable and safe
operation. The following is a list of basic requirements:

1. hazardous area ventilation fans,
2. main and standby lube oil pumps,
3. main and standby seal oil pumps,
4. cooling water pumps,
5. motor ventilation fans.

This list is not exhaustive, as it does not include the various installation utilities
and safety systems which have to provide continuous permissive signals to allow
starting or continued running of the compressor package.

DIRECT CURRENT DRILLING MOTORS
The conventional arrangement in a drilling rig is to utilise 750 V direct current (DC)
machines run from phase angle-controlled thyristor units.