This is written to describe the type of machinery that can be found in a typical fossil fuel (gas, oil or coal-fired) electric generating plant to better understand what type of instrumentation is being used for vibration monitoring.

Typical Power Plant

A typical power plant will usually have 5 or 6 power generators of several sizes. It might have 2 larger capacity units, 2 or 3 medium capacity units, and 1 or 2 "peaking units" that have a small generating capacity each. Peaking units are used during periods of high demand for electricity, like hot summer nights, thus the name. Otherwise they sit idle in a stand-by mode. Peaking units use gas turbines or diesel engines to drive the electric generators. Large steam turbines are the most common type of machine used to drive medium and large electric generators.

Power plants are rated by the combined generating capacity of all of the units at the site, in megawatts. Following is a generalized size breakdown based on the generating capacity of each unit.

Monitoring Practices
All power generating units consist of primary or major machinery and secondary or BOP machinery. With little exception, all major machinery is monitored with a permanently installed continuous monitoring system. Most plants monitor their BOP machinery on a periodic basis using a portable data collector and database program. The continuous monitoring system for a medium or large steam turbine generator is called a Turbine Supervisory Instrumentation System (TSI System). A TSI System includes the typical radial displacement vibration and axial position measurements associated with high speed rotating machinery but also includes measurements that are unique to the long and heavy rotors and machine cases required for steam turbines. Among these are; case expansion, differential expansion, runout (shaft bow), zero speed, valve position, and absolute shaft vibration.

Periodic monitoring provides a great solution for power plants for BOP machinery. This is because of the large number of points to be monitored each month, usually 700 or 800. When you consider taking vertical and horizontal readings at each bearing and one axial reading on each machine case, the numbers add up quickly. Too many to have continuous monitoring on all of them!

Still, some plants have moved some of their measurement points (on periodic monitoring) to continuous monitoring (using vibration transmitters, signal conditioners, scanning monitors and even API 670 type monitors) for various reasons. The reasons include; machines with higher than normal maintenance, personnel safety (must climb to reach measurement points), better operating condition visibility, hard to get to machines (like cooling towers), and increased workloads for personnel.

Following is a list of the typical machines found in a single unit in a power plant.

Air supply, fuel supply, lubrication, coal-fired plants have coal handling and processing machinery

To get a perspective of how much machinery a power plant has, multiply the number of steam turbine generators times the numbers in this table for each group of machines!

Written by Hardyinst, originally posted: www.automation.com