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Handbook of Turbomachinery Second Edition Revised - Ventech!

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Figure 63 Mechanical hydraulic control/governor/actuator system.<br />

Main and Auxiliary Governors<br />

The main governor with a conventional motor operated speed changer<br />

controls the speed or load <strong>of</strong> the turbine. This governor controls the<br />

positioning <strong>of</strong> the steam inlet (or governing) valves through servomotors,<br />

one <strong>of</strong> which is connected to each steam chest.<br />

The main governor produces a governing control oil pressure that<br />

varies in accordance with the turbine speed with a fixed setting <strong>of</strong> the speed<br />

changer. When operating in parallel with a utility system or with large units<br />

in the same plant, the electrical tie <strong>of</strong> the generators controls the turbine<br />

speed. Under such operating conditions, the speed changer actually becomes<br />

a load changer. This is true because changing the steam flow can only<br />

change the torque, while the speed <strong>of</strong> the turbine is scarcely affected.<br />

Accordingly then, there is a different load for every position <strong>of</strong> the speed<br />

changer. The auxiliary governor, mounted on the control block with the<br />

main governor, is hydraulically connected to the governing control oil<br />

system and has no speed changer or speed setting.<br />

In the event <strong>of</strong> the complete or partial loss <strong>of</strong> electrical load, the speed<br />

will rise sharply since the main governor speed changer is in such a position<br />

that the speed with no power load is higher than normal operating speed.<br />

This sudden speed rise will cause the acceleration response feature <strong>of</strong> the<br />

Copyright © 2003 Marcel Dekker, Inc.

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