Specification of a Turbine Supervisory
Instrumentation (TSI) system can be an exacting process when the
individual parameters must be specified. This application note is
supplied to provide a guide to be used in selecting an appropriate TSI
system. TSI systems not only measure bearing vibration levels, but also
can include shell expansion, differential expansion, valve position,
turbine speed and acceleration, thrust position, phase angle, and
When an existing TSI system is being
retrofitted the immediate indication is that a one-for-one replacement
of each original parameter is sufficient. This approach may be adequate
if the original system was a complete package.
Recent experience with retrofitting TSI systems
has brought to light that many of the existing systems could be
enhanced with additional parameters. Also, certain parameters should be
considered for complete replacement with a different type sensor.
The information required under this topic will define and
describe the turbine generator along with who will perform and/or supply
the various tasks and parts of the TSI installation. The time frame for
the system installation should get consideration at the point.
Describing the turbine generator involves
listing the number of bearings, type of bearings, turbine/generator
manufacturer, the number and function of each rotor segment, etc. This
information may be obtained from the OEM operation and maintenance
manuals and is required whether a retrofit or an entirely new
installation is being specified.
Documentation of the proposed TSI should
include who supplies the individual components and service of the new
system, along with the number of operation and service manuals and/or
For more information about installation
services see the STI Application Note, Field Service, FS. STI
Application Note, Field Wiring Installation, FWI covers many topics of
particular concern prior to and during the electrical system
Selecting the monitor follows the process of detailing the
turbine generator layout. The monitor selection generally involves
deciding what the monitor should do and how the user will interface with
it. The monitor can be specified to be a stand-alone output with user
interface or to interface with an existing output device such as PLC or
Radial vibration is usually the heart of the TSI system. It gets the most attention and generally
gives the first indication of out of specification conditions.
Most OEM TSI systems utilized a shaft rider transducer system to monitor
vibration with a shaft absolute output signal. An exact replacement
transducer system can be supplied, but most customers and OEMs are
specifying an Eddy Probe Systems. A complete vibration system would
install two sensor systems per bearing with the sensors located 90° from
For more information about Eddy Probe Vibration Sensors and their application see the STI Application Note, Eddy Probe Transducer Installation, Part 1- Radial Vibration.
Thrust position indication includes one or two Eddy Probe
Systems to observe the position of the thrust collar within its
bearings. This system is an internal installation and need not replace
the existing system because many original installations utilize a
differential pressure system that interfaces with the turbine hydraulic
For more information about thrust position sensors and their application see the STI Application Note, Eddy Probe Transducer Installation, Part 2-Thrust Position.
Shell expansion is the measure of a turbine case or shell moves
in relation to a fixed location usually measured with a Linear Variable
Differential Transformer (LVDT). Some existing OEM systems still use
spindle micrometers or dial indicators that are subject to mechanical
damage and human error. Although many systems installed with only one
LVDT are adequate, a complete TSI system specification should consider
two LVDTs located at each corner of the turbine shell. A second sensor
will monitor shell cocking or uneven thermal growth, which is a fairly
common occurrence during startup when the sliding feet may have
For more information about shell expansion systems and applications see the STI Application Note, Shell Expansion, TSI Part-4.
measurements are an important parameter receiving much attention
during turbine startup and warming. This parameter measures how the
turbine rotor expands in relation to the turbine shell, or casing. A new
differential expansion system using Eddy Probes can be retrofitted to
any existing system. An Eddy Probe is more reliable and robust than OEM
supplied induction coil systems. For more information about differential
expansion systems and applications see the STI Application Note,
Differential Expansion, TSI Part-3.
Correct valve positioning is required to efficiently operate a
steam turbine. Some turbines may require several throttle valves be
monitored and some turbines will instrument the main stop valve(s) to
determine when they crack from their seats.
Retrofit valve position measurements use DC
LVDTs or DC Rotary Potentiometers. All OEM TSI systems include valve
position measurement(s) as a startup and operation parameter. Some OEM
systems utilized AC LVDTs while others use mechanical linkages and
scales for indication. A retrofitted system can be installed in the same
position or at relocated to a more accessible or protected position.
For more information about valve position systems and applications see STI Application Note, Valve Position, TSI Part-2.
A rotor which has been sitting idle during overhaul or has been
inadvertently stopped during coast down for an extended period will
develop a bow or bend. This condition must be corrected by turning gear
operation and, possibly, with auxiliary heating prior to high speed
operation to prevent internal clearance rubbing.
Eccentricity systems installed by OEMs monitor
the turbine stub shaft or a shaft collar using induction coils. A
retrofit Eddy Probe system will monitor the same location and many times
use the same bracketry.
For more information about eccentricity systems and applications see STI Application Note, Eccentricity, TSI Part-1.
Turbine speed indication supplied by OEMs come in many forms:
observing a gear wheel located inside the front standard, electrically
converting the generator output frequency, or monitoring the turning
gear. A retrofitted system using Eddy Probe's can be specified to
observe any multi-toothed gear wheel.
Applications monitoring generator output
frequency without an integral turning gear may require installation of a
custom gear wheel. Speed indication may be specified as an analog
display or as a digital display and can be interfaced to a zero speed
system for turning gear engagement.
Rate of Acceleration
The rate of acceleration parameter is usually monitored during
startup to prevent over-torquing the rotors, as the turbine approaches
critical speeds, and as the operating speed is reached prior to line
synchronization. Once the generator has been synchronized and is being
controlled by load dispatchers the acceleration rate is not monitored.
Acceleration rate measurements use a speed
input to derive its output display. Eddy Probe systems can be installed
as a replacement or supplement an existing application. See STI
Application Note, Eddy Probe Transducer Installation, Part-1 Radial Vibration for relevant information about this type of sensor.
Phase, or phase angle, is a measure of the relationship of how
one vibration signal relates to another vibration signal and is commonly
used to calculate the placement of a balance weight. This parameter is
not usually displayed continuously but is monitored periodically to
determine changes in the rotor balance condition, deviations in system
stiffness such as a cracked shaft.
Phase angle measurements are sometimes not
supplied by OEMs, but can be installed using an Eddy Probe system.
Installation involves locating or installing a once-per-turn event such
as a key or notch that the Eddy Probe will view. An Eddy Probe viewing a
notch is easier to install and adjust, but the installation of the
notch requires special tooling to cut the notch. Keys are easier to
apply using glues or epoxies and are subject to coming off due to
Bearing temperature is a measure of the how hot a bearing is
operating. It may be due to overloading, miss-alignment, improper
lubricant pressure and/or flow. Nearly all turbine generator bearings
were originally installed or retrofitted with bearing temperature
sensors. These sensors may be thermocouples or RTDs. This parameter is
often overlooked possibly due to the OEM output display located at some
other panel not within the vicinity of the retrofitted TSI system. Any
bearings that were not originally equipped with temperature sensors can
be retrofitted to accept thermocouples or RTDs.
Congested control boards may preclude installing the TSI rack
requiring a stand-alone cabinet. This cabinet can house auxiliary
equipment associated with the new TSI system, such as power supplies,
termination strips, external relays, etc. The cabinet can be configured
to many differing designs depending upon the user's requirements.
Cabinets should be sturdy enough withstand environmental conditions,
such as moisture content, explosive atmospheres, temperature, etc.