Page 488 - Practical Machinery Management for Process Plants Major Process Equipment Maintenance and Repair

Gas Turbines 465

be exercised to ensure that the part recovery procedure is proven and ec-
onomic in terms of cost versus additional life expected. Newer and better
repair techniques are being developed rapidly. As confidence in these re-
manufacturing procedures increases, it is expected that recycling of hot
gas path components will become a more accepted practice in the process
industries.

Controls

Gas turbine control systems are without doubt the most complex con-
trols on any form of rotating machinery. Driven by advances in digital
technology, these systems are presently undergoing rapid changes. To gener-
alize about controls is almost impossible, since nearly every gas turbine
manufacturer uses his own control system. Moreover, even these are not
always consistent from one model to another.
Reliability is the key to all control systems. Reliable starting, stopping,
and governing are the basic objectives. The type of execution used to
achieve this objective has developed from pneumatic and relay-based
systems, through solid state analog systems to fully redundant digital sys-
tems. Figure 9-11 shows the type of control panel which was commonly

Figure 9-1 1. W191 Control panel (courtesy Westinghouse Canada).