Method and apparatus for measuring turbine shell clearance

Abstract

An apparatus for measuring turbine rotor-to-stator clearances and a method for assembling a turbomachine based on the measured clearances are disclosed. In an embodiment, at least one clearance sensor is inserted into a stator of a turbomachine. Using the sensor, tops-on clearance between a rotor blade tip and an inner surface of a stator is measured while an upper stator shell, a rotor, a lower stator shell are assembled together; and a tops-off clearance is measured while the lower stator shell and a rotor are assembled together. A tops-on/tops-off shift, i.e., a difference between the tops-on clearance and the tops-off clearance, is determined. The turbine can be assembled by adjusting a relative position of the rotor and stator to account for the tops-on/tops-off shift.

What is claimed is: 
     
         1 . An apparatus comprising:
 at least one sensor inserted in a stator, the at least one sensor being configured to measure:   a tops-on clearance between a rotor blade tip and an inner surface of a stator, wherein in the tops-on condition, the clearance is measured while an upper stator shell and a lower stator shell are assembled together, and a rotor is installed within the assembled stator, and   a tops-off clearance between the rotor blade tip and the inner surface of the stator while the lower stator shell and the rotor are assembled together, and the upper stator shell is not affixed to the lower stator shell; and   a computing device operably connected with the at least one sensor, the computing device being configured to determine a tops-on/tops-off shift, wherein the tops-on/tops-off shift is equal to a difference between the tops-on clearance and the tops-off clearance.   
     
     
         2 . The apparatus of  claim 1 , wherein the at least one sensor further comprises between about 3 and about 6 sensors axially spaced along the stator. 
     
     
         3 . The apparatus of  claim 1 , wherein the at least one sensor further comprises a plurality of sensors spaced such that one sensor is axially aligned with each of a plurality of stages of rotor blades. 
     
     
         4 . The apparatus of  claim 1 , wherein the sensor further comprises a voltage drop sensor for measuring a voltage drop across a clearance between a tip of the sensor and a point on the rotor. 
     
     
         5 . The apparatus of  claim 1 , wherein the sensor is substantially vertically aligned with a longitudinal axis of the rotor. 
     
     
         6 . A turbomachine comprising:
 a rotor;   a stator surrounding the rotor, the stator including a lower stator shell and an upper stator shell,   a plurality of sensors inserted in the lower stator shell, each of the plurality of sensors being configured to measure:   a tops-on clearance between a rotor blade tip and an inner surface of the stator, wherein in the tops-on condition, the clearance is measured while the upper stator shell and the lower stator shell are assembled together and the rotor is installed within the assembled stator, and   a tops-off clearance between the rotor blade tip and the inner surface of the stator while the lower stator shell and the rotor are assembled together, and the upper stator shell is not affixed to the lower stator shell; and   a computing device operably connected to each of the plurality of sensors, the computing device being configured to determine a tops-on/tops-off shift, wherein the tops-on/tops-off shift is equal to a difference between the tops-on clearance and the tops-off clearance;   wherein the plurality of sensors are spaced such that either:
 one sensor is axially aligned with each of a plurality of stages of rotor blades, or 
 one sensor is axially aligned with every other stage of the plurality of stages of rotor blades. 
   
     
     
         7 . The turbomachine of  claim 6 , wherein the plurality of sensors further comprises between about 3 and about 6 sensors axially spaced along the stator. 
     
     
         8 . The turbomachine of  claim 6 , wherein the plurality of sensors further comprises a plurality of voltage drop sensors for measuring a voltage drop across a clearance between a tip of each sensor and a point on the rotor. 
     
     
         9 . The turbomachine of  claim 6 , wherein the plurality of sensors are substantially vertically aligned with a longitudinal axis of the rotor. 
     
     
         10 . The turbomachine of  claim 6 , wherein the tops-on clearance further comprises the tops-on clearance when the turbomachine is shutdown and cool. 
     
     
         11 . The turbomachine of  claim 6 , further comprising a turning gear for rotating the rotor during measuring of the tops-on clearance. 
     
     
         12 . The turbomachine of  claim 6 , further comprising a motor for rotating the rotor during measuring of the tops-off clearance. 
     
     
         13 . The turbomachine of  claim 12 , wherein the rotating is at a speed of about 0.5 rotation per minute. 
     
     
         14 . The turbomachine of  claim 6 , wherein the plurality of sensors inserted in the lower stator shell further are embedded in an inner stator shell such that a radially outer edge of each of the plurality of sensors is substantially flush with the inner surface of the stator. 
     
     
         15 . The turbomachine of  claim 6 , wherein each of the plurality of sensors are affixed to the lower stator shell by a sensor retainer member.