INTRODUCTION

The losses that occur within the steam turbine generator can be categorized in various ways. In terms of this work, they will be considered to comprise those that occur within the steam path proper and others. Those represent losses present in bearings, windage losses at couplings, and other similar losses that are generally termed mechanical losses by the manufacturer. There are also generator losses. Within the steam path, the losses can be further categorized and these will be considered in the later sections of this chapter.

A difficulty often faced by operators and those responsible for the maintenance of steam turbines is establishing when a component has deteriorated to the extent it needs to be replaced for reasons of efficiency. When a component has deteriorated structurally and returning the unit to service without remedial action could force the unit from service, the maintenance decision becomes clear. However, deterioration that affects efficiency, with a loss of output and the requirement of extra funds for additional fuel costs, is far more difficult to substantiate and to quantify. Corrective decisions are often delayed to the overall detriment of the unit and system effectiveness.

Decisions about inefficient operation may also be influenced by considerations of unit availability, particularly when power generation is a secondary consideration and process steam is a more immediate concern. This is especially true if unavailability of a unit could close down a major production process.

In the case of structural reliability and the probability of component failure forcing a...