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POWER TRANSFORMERFREQUENCY RESPONSE ANALYSIS

TEST SETMODEL FRA-100

The PHENIX Technologies model FRA-100 Frequency Response Analysis test system is a portable,off-line system designed to detect winding movements resulting from shipping damage, subjection tolow impedance through faults, or general looseness of clamping structures brought on by the normaleffects of aging, in distribution and power transformers. The technology used in this highly sophisticateddiagnostic tool was developed in the United States by the National Electric Energy Testing, Research andApplications Center (NEETRAC), a center of Georgia Institute of Technology. PHENIX Technologiesand NEETRAC have teamed together to bring this powerful testing technique to the electric powerindustry.

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THEORETICAL BACKGROUND:The test is accomplished through the application

and subsequent analysis of a series of low voltageimpulses of varying duration, and approximately 300V magnitude. Based on the resulting current impulsemeasured by the current probe, the frequency responseis calculated for frequencies up to 5 MHz. Thistechnique is designed to detect winding shifts throughnon-destructive methods, and can either be used as astand alone test to detect winding damage, or as adiagnostic tool to pinpoint damages discovered in othertest results such as insulation power factor tests,dissolved gas analysis, or short circuit impedance.

The testing software provided calculates objectiveestimates of the degree of movement based on twodifferent patented analysis techniques, the WeightedNormalized Difference (WND) number is used inanalysis of all types of transformers, and the ObjectiveWinding Asymmetry (OWA) percentage, for useespecially on three phase transformers and single phaseidentical sister units.

Basic WND analysis allows comparison toprevious FRA “fingerprints”, baseline data that mayhave been made on the transformer at the factory, or atan earlier date in the substation. This alone can be usedas an effective technique to detect winding damages.

The more advanced OWA technique has beendeveloped especially for use in cases where no baselinedata exists, but a condition assessment of themechanical integrity of the windings is still required.This technique may be used very effectively in casesboth with and without baseline data to detect andpinpoint damages to a specific phase and winding. Thisis accomplished through an objective (numerical)comparison of the three individual phase responsesagainst each other, and a knowledge of the fact thatwhile the individual phase responses of a three phasetransformer are not identical, they should differ fromeach other in a predictable manner based on thesymmetrical design and construction of thetransformer.

Even though the OWA test method has beenshown to be very successful in locating mechanicalwinding shifts without historical data, developmenttesting has shown that the most sensitive indicator ofwinding damage may result from the combination ofthe OWA test and the historical comparison.Comparison of a previous OWA test result to a presentOWA test result on a given transformer provides ameans of comparing differences in the frequencyresponse records obtained from the same transformerat different times that is largely unaffected by variablessuch as temperature and oil condition, since changesin these parameters have a common influence on thephase-to-phase frequency response comparison.

Extensive development testing has been doneover a wide range of transformers in the power rangeof a several hundred kVA distribution transformersthrough several hundred MVA Class I, Class IIsubstation and generator step up transformers todetermine the evaluation criteria used in the PHENIXTechnologies FRA-100 system. The OWA technologyhas been the only technology to date that has shownthe ability to detect and locate problems ontransformers even after they have been de-tanked, andhave had their leads cut and bushings removed!

Typical 3-Phase TransformerTransfer Function Plots withOWA Results Displayed

IMPULSE SOURCE:An internal 300 V impulse source provides the exciting

impulses required for the FRA test. The pulse source isautomatically controlled by the PC, with all pulseapplication and data collection being managed by the testcomputer, following an initiation command by the testtechnician to acknowledge that the test leads have beenconnected to the proper terminals of the transformer, andthat all personnel are clear of the test leads.

For each connection configuration, the PC will collectdata from a series of ten applied impulses. Each impulse isof approximately 300 V magnitude, with a steep rise timeon the order of a few hundred nanoseconds, and a variabletime to chop that is controlled by the test set computer thatranges over a time interval of approximately 10 to 90microseconds during the series of 10 applied impulses.

“FRA-100 Test System Components”

HARDWARE:System Power Requirements

Battery Operated for Onsite Use100 to 240 VAC, 50 or 60 Hz source for charging

Digitizer DataResolution: .................................... 12 bitNumber of Channels: .................... 2Sampling Rate (per Channel) ........ 50Ms/sec

Lap Top PC (included)Processor: ...................................... Intel PentiumOperating System: ......................... WindowsMonitor: ........................................ Color LCDCompact Disc Drive: ..................... CDRWPower Supply: ............................... 100 to 240 VAC,

50 or 60 Hz, withinternal battery foron site use

Current Probe

Type: .............................................. Low InductanceShunt

Resistance: ..................................... 10 Ω

Test LeadsAll required test leads and clamps are provided, with pulseoutput and signal measuring leads provided in 60 Ft lengths.This allows the test technician to locate the PC and pulsesource at ground level while performing the test.

Note: Due to continual development, specifications aresubject to change without notice.

DIMENSIONS AND WEIGHTS:FRA-100 Pulse Source with Digitizer14" W x 11" D x 6½" H; 21 lbs.

Laptop Computer13" W x 11" D x 1½" H; 8 lbs.

Cable Lead Bag19" W x 10" D x 10" H; 17 lbs.

COMPANY PROFILEPHENIX TECHNOLOGIES is a leading manufacturer of high voltage, high current, and high power test systems

and components. Our test systems are in operation around the world satisfying the testing requirements of our customers.Our 65,000 square foot headquarters is a modern manufacturing facility where all the major components of our

systems are produced. All aspects of electrical and mechanical design, software design and actual production are performedin this facility and controlled by an ISO9001 quality program. Our engineers offer a unique blend of theoretical knowledgeand practical experience. Our ever-expanding Service & Calibration Department stands ready to assist you during andafter installation to insure years of trouble free service.

Our engineering resources, manufacturing capability and commitment to flexibility have earned us the reputation asthe supplier of choice. From portable test equipment to large, cutting edge automated test systems, PHENIX Technologiesprovides solutions for your testing needs. You owe it to yourself to discuss your testing requirements with PHENIXTechnologies today.

Main Test Screen Shot

A test report can be generated and stored that providesthe results of the comparison of any two test records selected,and that provides written application guidelines that promptthe test technician about possible reasons for the resultsobtained, based on the type of transformer and the resultsencountered. The guidelines are based on the extensivedevelopment investigations performed during the developmentof the FRA-100 test system, and provide valuable insight intothe results. Additionally, the software generates a Green/Yellow/Red condition assessment as an immediate visualindication to the test technician of whether a significant changeexists between frequency responses under comparison. Thisvisual condition assessment can be used as the basis indeciding whether additional electrical tests or internal visualinspections should be made on the transformer beforeapproving it to be energized in service.

SOFTWARE ANALYSIS AND DATAMANAGEMENT PACKAGE

The FRA-100 software package is a Windows basedapplication that provides both testing control as well as datamanagement functions.

Upon selecting the type of transformer from a list ofstandard single phase, three phase and auto connections,the software provides prompts to the user to connect theleads and initiate each sequence of impulses. Built in safetychecks will prompt the user if there is a problem with thelead connection that is recognized by the computer, basedon the data collected.

In addition, on three phase transformers the testtechnician can select whether or not he or she wants toperform an OWA test on the transformer. The OWA test isrecommended on all three phase transformers even if acomparison to historical data is also desired. The OWA testhas been shown to be generally the most sensitive to actualmechanical changes in the winding geometry, while at thesame time looking over changes that commonly affect allthree phases, resulting from temperature differences, oilcondition, etc.

The data management portion of the software providesfor convenient storage and retrieval of test records, allowingthe comparison of both WND results and OWA results onany two transformer test records that are selected. Thisallows comparison between historical data and present data,as well as comparison with the frequency response of sisterunits if it is desired to make this comparison.

Your Local Representative is:

75 Speicher DriveAccident, MD 21520 USA

Tel: 301-746-8118 • Fax: 301-895-5570e-mail: info@phenixtech.comhttp://www.phenixtech.com4/05 © Copyright—Phenix Technologies, Inc., 2004. All rights reserved

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