turbine supervisory instrumentation

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Sales Technology, Inc. 2911 South Shore Blvd., Ste. 170, League City, TX 77573

Phone: 281.334.0766 Fax: 281.334.4255 Web: www.stiweb.com

Specification of a Turbine Supervisory Instrumentation (TSI)system can be an exacting process when the individualparameters must be specified. This application note issupplied to provide a guide to be used in selecting anappropriate TSI system. TSI systems not only measurebearing vibration levels, but also can include shell expansion,differential expansion, valve position, turbine speed andacceleration, thrust position, phase angle, and bearingtemperatures.

When an existing TSI system is being retrofitted theimmediate indication is that a one-for-one replacement ofeach original parameter is sufficient. This approach may be

adequate if the original system was a complete package.

Recent experience with retrofitting TSI systems has broughtto light that many of the existing systems could be enhancedwith additional parameters. Also, certain parameters shouldbe considered for complete replacement with a different typesensor.

General

The information required under this topic will define anddescribe the turbine generator along with who will performand/or supply the various tasks and parts of the TSIinstallation. The time frame for the system installation shouldget consideration at the point.

Describing the turbine generator involves listing the numberof bearings, type of bearings, turbine/generator manufacturer,the number and function of each rotor segment, etc. Thisinformation may be obtained from the OEM operation andmaintenance manuals and is required whether a retrofit or anentirely new installation is being specified.

Documentation of the proposed TSI should include whosupplies the individual components and service of the newsystem, along with the number of operation and servicemanuals and/or drawings required.

For more information about installation services see the STIApplication Note, Field Service, FS. STI Application Note,Field Wiring Installation, FWI covers many topics of particularconcern prior to and during the electrical system installation.

Monitor

Selecting the monitor follows the process of detailingthe turbine generator layout. The monitor selectiongenerally involves deciding what the monitor shoulddo and how the user will interface with it.

The monitor can be specified to be a stand-aloneoutput with user interface or to interface with anexisting output device such as PLC or DCS.

Radial Vibration

Radial vibration is usually the heart of the TSIsystem. It gets the most attention and generallygives the first indication of out of specificationconditions. Most OEM TSI systems utilized a shaftrider transducer system to monitor vibration with ashaft absolute output signal. An exact replacementtransducer system can be supplied, but mostcustomers and OEMs are specifying an Eddy ProbeSystems. A complete vibration system would installtwo sensor systems per bearing with the sensorslocated 90 from each other.

For more information about Eddy Probe VibrationSensors and their application see the STI ApplicationNote, Eddy Probe Transducer Installation, Part 1-Radial Vibration.

Thrust Position

Thrust position indication includes one or two EddyProbe Systems to observe the position of the thrustcollar within its bearings. This system is an internalinstallation and need not replace the existing systembecause many original installations utilize adifferential pressure system that interfaces with theturbine hydraulic control system.

For more information about thrust position sensorsand their application see the STI Application Note,Eddy Probe Transducer Installation, Part 2-ThrustPosition.

Field Application Note

Turbine Supervisory Instrumentation TSI


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Shell Expansion

Shell expansion is the measure of a turbine case or shellmoves in relation to a fixed location usually measured with aLinear Variable Differential Transformer (LVDT). Someexisting OEM systems still use spindle micrometers or dialindicators that are subject to mechanical damage and humanerror. Although many systems installed with only one LVDTare adequate, a complete TSI system specification shouldconsider two LVDTs located at each corner of the turbineshell. A second sensor will monitor shell cocking or uneventhermal growth, which is a fairly common occurrence duringstartup when the sliding feet may have inadequate

lubrication.

For more information about shell expansion systems andapplications see the STI Application Note, Shell Expansion,TSI Part-4.

Differential Expansion

Differential expansion measurements are an importantparameter receiving much attention during turbine startupand warming. This parameter measures how the turbinerotor expands in relation to the turbine shell, or casing.

A new differential expansion system using Eddy Probes canbe retrofitted to any existing system. An Eddy Probe is morereliable and robust than OEM supplied induction coil systems.

For more information about differential expansion systemsand applications see the STI Application Note, DifferentialExpansion, TSI Part-3.

Valve Position

Correct valve positioning is required to efficiently operate asteam turbine. Some turbines may require several throttlevalves be monitored and some turbines will instrument themain stop valve(s) to determine when they crack from their

seats.

Retrofit valve position measurements use DC LVDTs or DCRotary Potentiometers. All OEM TSI systems include valveposition measurement(s) as a startup and operationparameter. Some OEM systems utilized AC LVDTs whileothers use mechanical linkages and scales for indication.

A retrofitted system can be installed in the same position or atrelocated to a more accessible or protected position.

For more information about valve position systemsand applications see STI Application Note, ValvePosition, TSI Part-2.

Eccentricity

A rotor which has been sitting idle during overhaul orhas been inadvertently stopped during coast downfor an extended period will develop a bow or bend.This condition must be corrected by turning gearoperation and, possibly, with auxiliary heating prior tohigh speed operation to prevent internal clearancerubbing.

Eccentricity systems installed by OEMs monitor theturbine stub shaft or a shaft collar using inductioncoils. A retrofit Eddy Probe system will monitor thesame location and many times use the samebracketry.

For more information about eccentricity systems andapplications see STI Application Note, Eccentricity,TSI Part-1.

Speed

Turbine speed indication supplied by OEMs come inmany forms: observing a gear wheel located insidethe front standard, electrically converting thegenerator output frequency, or monitoring the turninggear. A retrofitted system using Eddy Probe's can bespecified to observe any multi-toothed gear wheel.Applications monitoring generator output frequencywithout an integral turning gear may requireinstallation of a custom gear wheel.

Speed indication may be specified as an analogdisplay or as a digital display and can be interfacedto a zero speed system for turning gear engagement.




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Rate of Acceleration

The rate of acceleration parameter is usually monitoredduring startup to prevent over-torquing the rotors, as theturbine approaches critical speeds, and as the operatingspeed is reached prior to line synchronization. Once thegenerator has been synchronized and is being controlled byload dispatchers the acceleration rate is not monitored.

Acceleration rate measurements use a speed input to deriveits output display. Eddy Probe systems can be installed as areplacement or supplement an existing application. See STIApplication Note, Eddy Probe Transducer Installation, Part-1

Radial Vibration for relevant information about this type ofsensor.

Phase

Phase, or phase angle, is a measure of the relationship ofhow one vibration signal relates to another vibration signaland is commonly used to calculate the placement of abalance weight. This parameter is not usually displayedcontinuously but is monitored periodically to determinechanges in the rotor balance condition, deviations in systemstiffness such as a cracked shaft.

Phase angle measurements are sometimes not supplied byOEMs, but can be installed using an Eddy Probe system.Installation involves locating or installing a once-per-turnevent 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 cutthe notch. Keys are easier to apply using glues or epoxiesand are subject to coming off due to centrifugal forces.

Temperature

Bearing temperature is a measure of the how hot a bearing isoperating. It may be due to overloading, miss-alignment,improper lubricant pressure and/or flow.

Nearly all turbine generator bearings were originally installedor retrofitted with bearing temperature sensors. Thesesensors may be thermocouples or RTDs. This parameter isoften overlooked possibly due to the OEM output displaylocated at some other panel not within the vicinity of theretrofitted TSI system. Any bearings that were not originallyequipped with temperature sensors can be retrofitted toaccept thermocouples or RTDs.

Custom Cabinet

Congested control boards may preclude installing theTSI rack requiring a stand-alone cabinet. Thiscabinet can house auxiliary equipment associatedwith the new TSI system, such as power supplies,termination strips, external relays, etc.

The cabinet can be configured to many differingdesigns depending upon the user's requirements.Cabinets should be sturdy enough withstandenvironmental conditions, such as moisture content,explosive atmospheres, temperature, etc.



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