Vertical Shaft Plumbness Using a Laser Alignment System potx

Vertical Shaft Plumbness Using a Laser Alignment System

By Daus Studenberg, Ludeca, Inc.

ABSTRACT

Traditionally, plumbness measurements on a vertical hydro-turbine/generator

shaft involved stringing a series of wires along the length of the shaft, attaching a

weight to the end of the wires and then measuring the space from the wire to the

shaft using an electronic micrometer. Although this method was inexpensive

and has been used for many years, it did require access to a long length of the

shaft to achieve an accurate resolution. Also, measurements involve physically

measuring the distance between the wire and the shaft at various elevations on

the shaft, increasing the amount of time and personnel requirement for the

measurement.

Ludeca, Inc. presents their experience with a laser-based system which replaces

the time-consuming wire method. Measurements can now be performed in a

fraction of the time it would otherwise take with the wire measurement method.

Ludeca’s measurement system, known as the PERMAPLUMB®

, uses a self￾adjusting mechanical mirror, always plumb to earth, that reflects a class 1 laser

beam into a detector. It requires only 14ギ of axial space along the shaft. The

mirror and transducer are attached by a bracket that uses magnets on the turbine

shaft. From a single 270-degree shaft rotation, the system calculates and

displays angularity and corrective moves and provides a statistical quality

measurement of the data. A “move” function allows monitoring of corrections as

they are being made. The resolution is better than 0.00002"/ft, (more accurate

than required by NEMA). Adjacent turbines can also continue to operate since

the system is insensitive to vibration.

Introduction

Plumbness is the relationship of a rotating centerline to gravity. It can be thought

of as the verticality of a centerline. In practice, with vertical hydro shaft

measurement, it is actually “un-plumbness” that is being measured, since the

factor quantified is the difference from perfectly vertical as shown in Figure 1.