IRIS POWER ON-LINE PRODUCTS

Iris Power RFAIIII-RTM

Periodic Rotor Flux Analyzer: a second generation advanced tool to find rotor windingshorted turns in turbine generators and high speed synchronous motors during service

QUALITROL-IRIS POWER IS THE WORLD’S LARGEST PROVIDER OF MONITORING AND TESTING EQUIPMENT FOR MOTOR AND GENERATOR WINDINGS

IRIS POWER RFAIIII-R

The insulation in round rotorsmust withstand severe electrical,mechanical and environmentalstresses. Insulation failures canresult from many factorsincluding:

• mechanical wear, especially thatcaused by frequent start/stopcycles

• distortion, breakage andmigration due to centrifugalmechanical loading andthermally induced expansion/contraction during load cycles

• overheating due to overloading/over excitation or inadequate ordiminished cooling

• local overheating at highresistance brazed joints and atshorted turns

• contamination in cooling gas orcopper dusting resulting insurface tracking between turnsor to ground

• overvoltages induced fromsystem events or from firingcircuits in static exciters.

An insulation failure can translateinto electrical connections betweenturns, and eventually a winding toground fault.

A turn-to-turn short is the mostfrequent rotor insulation failuremechanism. Turn shorts can result in:

• thermal imbalance of the rotorleading to mechanical vibrations

• magnetic imbalance in the fluxresulting in mechanicalvibration of the rotor

• increased rotor temperatureand subsequent insulationdegradation

• overheating resulting ininsulation failure and a groundfault with the potential for asecond catastrophic groundfault

• inability to reach the ratedMVA rating for the machine.

Magnetic flux monitoring viapermanently mounted air gap fluxprobes is a proven technology insynchronous machines todetermine if turn-to-turn shortshave occurred in the rotorwinding. Flux measurementprovides the most direct means ofmonitoring the condition of rotorwindings on-line, yieldinginformation on the integrity of thecoils’ interturn insulation. Thisinformation is critical in planningmaintenance, diagnosingabnormal vibrations, and verifyingnew and rewound rotor integrity.

IRIS POWER ON-LINE PRODUCTS

The Iris Power RFAII-R technology is a second generation rotor flux analyzer that revolutionizes the analysis ofthe flux data by providing an initial diagnosis of the rotor winding condition usually even if the generator loadis constant! This portable instrument can collect and analyze flux data from any flux probe in real time,providing the user with data on potential shorted turns. The Iris Power RFAII-R’s high-speed acquisition, highresolution capability and totally new analysis algorithms allow it to collect and analyze data over an entire unitrun-down or start-up (with the shaft sync signal connected). Once configured, the Iris Power RFAII-R requiresno user intervention and is ideal for profiling the rotor insulation condition before a machine outage or after arefurbishment.

SYNCHRONOUS GENERATOR AND MOTOR ROTOR WINDINGS CAPABILITIES

• Instant analysis of roundrotor winding conditionusually at any operatingload

• Where needed, ability toanalyze tests at differentloads for a more certainprediction of rotorwinding condition

• Able to perform a spotmeasurement, orautomatically acquireresults over days duringnormal generator loadchanges, without operatorintervention

• Works with conventionalwedge-mounted fluxprobe, or the stator tooth-mounted Iris PowerTFProbeTM, which canoften be retrofitted withthe rotor in-place

TYPICAL APPLICATION

The condition of the rotor windinginsulation is difficult to assess duringminor or major generatormaintenance outages. Access to thewinding is severely restricted withoutremoval of the retaining rings and ofthe winding wedges. The off-linetests for detection of shorted turnsand ground fault locations can alsobe frustratingly ineffective due tothe frequently intermittent nature offaults at speed and at standstill.Therefore, on-line measurements aremuch preferred to off-line tests andinspections.

On-line measurements require thepermanent installation of a fluxprobe on the stator to measure theslot leakage flux. Most machineOEM’s offer a flux probe which isattached to a stator winding wedgeprotruding into the airgap. Qualitrol-Iris Power now offers an alternativeprobe, the Iris Power TFProbe,which is a small, thin, flexible,printed circuit board transducer Iris Power TFProbe

affixed to a tooth of the stator. TheIris Power TFProbe measures thetotal airgap flux, rather than just theleakage flux as do older styleprobes. The Iris Power TFProbe iseasy to install, and requires noinvasive drilling of stator wedges.Frequently, it can be installed withthe rotor still in place! In the case ofhydrogen-cooled machines, theleads from the flux probe are routedout of the machine through ahermetically sealed feed-through.

Regardless of the probe technology,data from permanently installed flux probes can be measured viasoftware, with the Iris Power RFAII-R, or continuous on-linemonitors like the Iris PowerFluxTracIITM. Once the data areacquired, analysis techniques mustbe applied to compare the fluxmeasurements across various rotorslots to determine if the turn shortsare present.

Typical voltage waveform from a flux probe

Iris Power TFProbe glued to a turbine generator stator tooth

THEORY OF FLUX MONITORING

Flux monitoring relies on measurements of the localmagnetic field emanated by each coil in the rotor. Theleakage flux is determined by the total ampere-turns fromeach rotor slot. Any change in the ampere-turns within acoil due to shorted turns produces a change in theleakage flux.

To measure the leakage flux, a flux probe sensor ispermanently installed on the stator. During machineoperation, the flux from each passing slot will induce avoltage in the flux probe. The difficulty in measuring theleakage flux is that the main radial magnetic flux is ordersof magnitude greater than the leakage flux. To maximizethe sensitivity to shorted turns in all rotor coils, the signalsfrom the flux probe need to be measured under differentload conditions ranging from no load to full load. At azero crossing of the total flux (which is the function of thereal and reactive load of the machine), the sensitivity to the leakage flux is the highest. Thus the flux readings with the older,first generation equipment must be taken at various load points depending on the number of slots in a pole.

The graph shows a typical voltage waveform from a flux probe. Each peak of the voltage represents the leakage flux aroundone rotor coil. An inter-turn short in a coil reduces the peaks associated with the two opposite slots containing the faulted coil.By analyzing the voltage waveforms at various generator load points, it is possible to identify any slots with shorted turns. Thenew technology used in the Iris Power RFAII-R usually does not require the load changes.

IRIS POWER RFAIIII-R

IRIS POWER ON-LINE PRODUCTS

IRIS POWER RFAIIII-R

Iris Power RFAII-R, Iris Power TFProbe and Iris Power FluxTracII are Trademarks of Qualitrol-Iris Power.

Windows is a registered trademark of Microsoft Corporation in the United States and other countries.

FEATURES

• Rugged portable instrumentwith USB and Ethernetcomputer interfaces

• Custom built, ultra-highresolution digital dataacquisition and on-boardswitchable attenuation formaximum resolutionmeasurements using anymanufacturer’s flux probe

• High speed acquisition withdeep memory for completeand accurate data collection

• Capable of storing over onehundred and fifty fluxwaveforms

• Can be synchronized to apower frequency signal, orideally to an external shaft sync signal (key phasor)

• Use with 2-pole or 4-polerotors

• Predictions of turn-shorts inany slot, often regardless ofthe generator load pointduring data acquisition

• A high-speed acquisition modeimmediately creates a table ofresults covering each coil ateach load point, including fluxwaveforms

• Stand-alone mode where theIris Power RFAII-R can collectdata automatically as thegenerator goes through normalload changes

• User friendly Windows™ basedsoftware for data display,analysis, and trending

• Analysis software capable ofreading and analyzing data filesfrom other manufacturers’portable instruments

• Systems are available for remoteand continuous monitoring

• Optional mode for findingshorts in spin pits with the rotoroperating at different speeds

• Optional instrument that canbe used with both round rotorsand salient pole rotors

Pole A to Pole BComparison

Software outputshowing location

of turn shorts

QUALITROL-IRIS POWER HAS BEEN THE WORLD LEADER IN MOTOR AND GENERATOR WINDING DIAGNOSTICS SINCE 1990,PROVIDING A FULL LINE OF ON-LINE AND OFF-LINE TOOLS, AS WELL AS COMMISSIONING AND CONSULTING SERVICES.

Iris Power LP3110 American DriveMississauga, ON, Canada L4V 1T2 Phone: 1-905-677-4824Fax: 1-905-677-8498sales.iris@qualitrolcorp.com

Qualitrol Company LLC1385 Fairport RoadFairport, NY, USA 14450Phone (585) 586-1515Fax (585) 377-0220

www.irispower.com

Ver 3 • 08/10

www.qualitrolcorp.com