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Investigation Report
Power Transformer Tank Rupture and Mitigation - Current State of Practice and Knowledge
by the Task Force of IEEE Power Transformer Subcommittee
March 09, 2010 Houston, TX.
CONTENT
1.Investigation and Analysis -10 minutes 2.Utility Experience (15 minutes) 3.Manufacturer’s Perspective (25 minutes) 4.PRD (10 minutes)5.Conclusions (10 minutes ) 6.Q&A (5 minutes)
Analysis of Transformer Tank Ruptures
Electric Power Research Institute
Wayne [email protected]
Nick [email protected]
2
Survey On Transformer Rupture
Objectives• Develop an understanding of the tank rupture process
associated with internal faults.• Develop tools, and methods, for evaluating the influence
of tank designs on rupture characteristics
3
Background
• 42 transformer failures (tanks ruptured or deformed without rupture)
• 22 utilities • 10-year period (1980-1990)• 7 transformer manufacturers• Different voltage levels• Different designs: (GSU’s, Auto,
Phase Shifters, etc.)
4
Conclusions
• The arc energy is the critical rupture parameter • Differences in transformer design and application are not major
discriminators in the tank rupture • The fault energy capacity of a tank can be increased by increasing
the tank rupture pressure limit and tank flexibility. – The pressure at which tanks rupture can be increased by local
strengthening of weak points, while the tank flexibility can be increased by replacing large beams with a number of smaller beams (which permit greater deflection at a given stress level).
• Venting to conservators or to auxiliary tanks was not found to be effective for heavy faults (those with arc power greater than 300 MW)
5
Conclusions
• A long arcing time is not necessary for rupture: – About 75% of the cases
occurred with arcing times less than 4.5 cycles.
• Since arc energy is proportional to I2t, where the t is duration in seconds, the parameter which offers the most opportunity for control of the risk of rupture is the magnitude of the current, and specifically, the peak crest value of the first half cycle of the fault current (and the associated X/R of the circuit).
Graph of Tank Deformation Rupture as a function of fault
current and fault duration.
Power Transformer Tank RuptureA Utility's Experience
Marc FoataIEEE Transformers CommitteeHouston, March 2010
22
PresentationPresentation
AssessmentAssessment of the of the riskriskStatisticsStatisticsArc Arc energyenergy
PreventionPrevention of tank ruptureof tank ruptureVentingVentingContainmentContainment
SpecificationSpecification of a Tank pressure of a Tank pressure withstandwithstandrequirementrequirement
33
AssessingAssessing the the riskrisk -- StatisticsStatistics
44
AssessingAssessing the the riskrisk -- StatisticsStatistics
55
AssessingAssessing the the riskrisk -- StatisticsStatistics
66
Arc Arc energyenergy -- 4 MJ4 MJ
77
Arc Arc EnergyEnergy -- 8 MJ8 MJ
88
Arc Arc EnergyEnergy -- 12 MJ12 MJ
99
Arc Arc EnergyEnergy -- 14 MJ14 MJ
1010
Arc Arc energyenergy vs Damagevs Damage
1111
Arc Arc EnergyEnergy -- CalculationCalculation
I I –– Arc Arc currentcurrent: : EvaluatedEvaluated fromfrom shortshort--circuit circuit levellevelT T –– Fault clearing time: Fault clearing time: DependsDepends mainlymainly on on protectionprotectionV V –– Arc voltage: Arc voltage: VeryVery difficultdifficult to to evaluateevaluate0.9 0.9 –– Factor Factor introducedintroduced for square for square waveformwaveform of Vof V
tIVEarc 9.0=
1212
Arc Arc EnergyEnergy -- RecordingsRecordingsUnité Support et analyses - DESTT
A
205 210 215 220 225 230 235 240 245 250 255(ms rel. à 05:34:32.2870)
-80
-60
-40
-20
0
20
40
60
80
100
(kV
)
E BN TT MAIS MICOUA E BN L-7019 MICOUA E BN L-7011 MICOUA E BN L-7027 MICOUA
2008-09-12 05:34:32.499 MICOUA 735-02 TENSION RÉSIDUELLE DÉFAUT TRANSFO T8-B
205 210 215 220 225 230 235 240 245 250 255(ms rel. à 05:34:32.2870)
-1 0 1 2 3 4 5 6 7 8 9
101112
(MJo
ules
)
ÉNTERGIE TOTALE (TT MAIS)ÉNTERGIE TOTALE (TTC 7019)ÉNTERGIE TOTALE (TTC 7011)ÉNTERGIE TOTALE (TTC 7027)
2008-09-12 05:34:32.499 MICOUA 735-02 ESTIMÉ DE L'ÉNERGIE TOTALE DANS LE DÉFAUT TRANSFO T8-B
190 200 210 220 230 240 250 260 270(ms rel. à 05:34:32.2870)
-20000
-15000
-10000
-5000
0
5000
10000
15000
20000(A
)
COURANTS CÔTÉ 735 kVCOURANTS APROX. CÔTÉ 315 kV
2008-09-12 05:34:32.499 MICOUA 735-02 COURANTS DE DÉFAUT TRANSFO T8-B
Lundi 15 Septembre, 2008\\VECTEUR\DONNEES\PARTAGE\@AUTOMATISMES\COMPORTEMENT\RAPPORT\RAPP_2008\TOSC_ANA\20080912_053432499_ENERGIE_T8-B_MICOUA.TOS
1313
Arc Arc EnergyEnergy -- EvaluationEvaluation of Arc of Arc VoltageVoltage
6060--100 V/cm range 100 V/cm range isis oftenoften referredreferredFor 40 kV, For 40 kV, thisthis meansmeans an arc an arc lengthlength of of more more thanthan 4 m !!4 m !!
1414
Arc Arc EnergyEnergy -- Pressure Pressure EffectEffect
Constant 55 V/cmConstant 55 V/cmL L isis arc arc lengthlength (m)(m)P P isis absoluteabsolute pressure (pressure (atmatm))Pressure in the Pressure in the gasgas bubblebubble at arc ignition at arc ignition cancan reachreach extremelyextremely highhigh valuesvalues
PLV 55=
1515
PreventionPrevention of tank rupture of tank rupture ––VentingVenting SimulationsSimulations
1616
PreventionPrevention of tank rupture of tank rupture ––VentingVenting SimulationsSimulations
1717
PreventionPrevention of tank rupture of tank rupture –– VentedVentedvs Nonvs Non--ventedvented ExampleExample
1818
PreventionPrevention of tank rupture of tank rupture ––Conclusions on Conclusions on ventingventing
Pressure Pressure reductionreduction fromfrom a single 25 cm a single 25 cm aperture aperture isis lowlow and and becomesbecomes negligiblenegligiblewhenwhen the arc the arc isis more more thanthan 1 1 metermeter awayaway..An effective pressure An effective pressure ventingventing strategystrategywouldwould requirerequire eithereither a a veryvery large large ventingventingductduct or or numerousnumerous smallsmall apertures in the apertures in the close close vicinityvicinity of the arc.of the arc.
1919
PreventionPrevention of tank rupture of tank rupture --ContainmentContainment
2020
PreventionPrevention of tank rupture of tank rupture --ContainmentContainment
PresentPresent design design cancan containcontain up to 10 MJ up to 10 MJ for the for the largestlargest tanks (735 kV)tanks (735 kV)More More resistantresistant tank design tank design cancan bebeachievedachievedNeedNeed to to implementimplement specificationsspecifications with with minimum minimum energyenergy requirementrequirement to to meetmeet..EnergyEnergy requirementrequirement willwill bebe a compromise a compromise betweenbetween the the feasibilityfeasibility and the and the likelihoodlikelihood..
2121
New New SpecificationSpecification -- PhilosophyPhilosophyPriorityPriority isis givengiven to the protection of the to the protection of the workersworkersWorstWorst energyenergy levelslevels maymay not not alwaysalways bebecontainablecontainable by the tankby the tankFirst rupture point must First rupture point must bebe the the covercoverRequiredRequired calculationcalculation toolstools must must bebeaccessible to transformer designersaccessible to transformer designersMust Must taketake intointo accountaccount the the highlyhighly dynamicdynamicphenomenaphenomena involvedinvolvedMust Must bebe easilyeasily verifiedverified
2222
New New specificationspecification -- FormulaFormula
Ps Ps –– CalculatedCalculated tank pressure tank pressure withstandwithstandF F –– DynamicDynamic (time & location) amplification(time & location) amplificationE E –– Fault Fault energyenergy levellevel to to withstandwithstandK K –– Arc Arc energyenergy conversion factorconversion factorC C –– Tank expansion coefficientTank expansion coefficient
⎥⎦
⎤⎢⎣
⎡−+= 50
10041100
CkE
s FP
2323
New New specificationsspecifications –– DynamicDynamicfactorfactor
Time Time relatedrelated dynamicdynamic factor (pressure and factor (pressure and deformationdeformation))ProximityProximity relatedrelated dynamicdynamic factorfactorTakesTakes intointo accountaccount tank volumetank volume
1
1,5
2
2,5
3
0 20 40 60 80 100 120 140 160 180 200
C/V (x 10 -5 kPa-1)
F
2424
New New specificationspecification : : HydroHydro--Québec'sQuébec'sEnergyEnergy ContainmentContainment RequirementsRequirements
Voltage Class Arc Energy
2525
New New specificationspecification -- ImplementationImplementation
All transformer All transformer supplierssuppliers sincesince 1992 have 1992 have shownshownadequateadequate tank tank withstandwithstand calculationcalculation capabilitiescapabilities..SinceSince implementingimplementing energyenergy levellevel requirementsrequirements(2006), (2006), manufacturersmanufacturers have been have been forcedforced to to improveimprove theirtheir tank design.tank design.DetailedDetailed analysisanalysis by a by a numbernumber of of manufacturersmanufacturersconfirmedconfirmed thatthat all the all the specifiedspecified energyenergyrequirementsrequirements cancan bebe met.met.
Transformer Tanks - Some Factors Related to Rupture
A Manufacturers Perspective
IEEE Transformers Committee Houston, March 9, 2010
by Bill Darovny, P.Eng.Siemens Canada
Facts about Liquid Filled Transformer Tanks
• C57.12.00 and C57.12.10 define the operating pressures for transformer tanks– full vacuum = -101.4 kPa (-14.7 psig)– pressure 25% above the normal operating
pressure
• Transformer tanks are not pressure vessels– are not required to be designed to the ASME
Boiler and Pressure Vessel Code.• ASME code is mandatory when operating
pressure exceeds 2 atmospheres (203 kPa).
Facts about Liquid Filled Transformer Tanks
• C57.12.10 requires a pressure relief device to be mounted on the tank cover – Typically activate at 34.5 to 69 kPa (5 to 10 psig)
• Most rectangular tanks will sustain internal pressures of 140 to 210 kPa (20 to 30 psig) before rupture
• A tank on its own cannot be made strong enough to resist all magnitudes of internal pressure
Transformers have been saved from rupture by common protection devices
• Pressure Relief Devices• Gas Detector Relays• Rapid Pressure Rise Relays• Real time Gas Monitors
Provided the alarm signals are quickly recognized and the transformer is
de-energized
Pressure Relief Device in Action
Not Every Tank Rupture Results in a FireUnit gassing, GDR alarmed, long delay in response to alarm,
ambient -30°C, reaction force to rupture shifted unit on the pad.
Some Units Burn After Tank Rupture- 750 MVA 500kV
Same Rating Different Supplier
The Location Where a Tank will Rupture is a Function of:
1. the rate of change of the pressure increaseSlow rate:• Pressure has time to distribute throughout the tank
Fast rate:• Results in a pressure build-up at the source
2. the co-ordinates of the pressure source inside the tank
3. the closest weak spot to those co-ordinates
Slow Rate of Pressure Increase- Failed at 2 locations on the Cover- Tensile end reactions tore the welds at the ends of the stiffeners- Cover end angle rotated and the weld to tank flange cracked
Moderate Rate of Pressure Increase
• Tank failed at the cover joint
• Some stiffeners on the tank wall were permanently deformed
• There were no cracks in the oil containment welds in the tank body
Rapid Rate of Pressure Increase
• Co-ordinates of pressure source was about 1/3 tank height
• Wall plate fracture started at the corner welds and ran almost full height of the tank
• Tank wall to bottom weld joint also failed
Rapid Rate of Pressure Increase
• Cover weld did not fail
• Tank failed at the high stress points in welds at the tank corners and wall penetrations then propagated through the wall plates
• Unit was returned to the factory and rebuilt
Weakest Points of a Rectangular Tank
• Main cover to tank wall flange - weld joint
• Tank wall corners - weld joint
• Tank wall to base plate - weld joint
• High stress points at throats and large penetrations through the tank plates
• High stress points at ends of stiffeners where the end reaction force is transmitted to the tank plate
Main Cover to Tank Wall Flange Mode of Weld Failure
Typical Cover Welded Joint
Upward and outward forces due to internal pressures
Stress is concentrated at the weakest point - the root of the weld.
Weld crack progresses outward from the root
Typical Rectangular Tank Corner Joints
Stresses are on the face of the weld.
The face of the weld is stronger than the root of the weld.
Adding corner gussets will reinforce this joint
Cylindrical Tanks are Inherently Stronger than Rectangular Tanks
• 110MVAR 735 kV shunt reactor
• The tank wall is stressed in hoop tension
• Typically the cylinder walls can sustain pressures > 350 kPa (50 psig)
• Weakest point is the cover weld
Design to Help Reduce Tank Rupture
• Design in service systems to detect faults early & de-energize quickly
• Use detection & relief accessories– Real time gas monitors– Gas detector relays - ensure gas collection
system / piping functions as intended – Rapid pressure relays– Pressure relief devices
• To be effective, relief devices must be located close to the pressure source
• Standard size relief devices may not prevent all tank ruptures
Design to Help Reduce Tank Rupture
• The best location for a tank to fail is at the welded cover joint as this will minimize fluid loss
• Strengthen the tank below the cover joint– Reinforce tank corners and wall to bottom joints
with plates / gussets
– Distribute stiffener end reaction forces with reinforcements or by connecting to stiffeners on adjacent walls
– Reinforce around wall penetrations to reduce the high stress points
Transformer Tank Rupture and Mitigation Transformer Tank Rupture and Mitigation TutorialTutorial
March 9, 2010March 9, 2010
Mitigation Research and Example Techniques
Presented by Craig SwindermanMitsubishi Electric Power Products, Inc.
Research on Transformer Tank Rupture Research on Transformer Tank Rupture MitigationMitigation
• Joint research performed in the mid-1980’s by three large Electric Utilities in Japan, Tokyo University, and several transformer manufacturers.
• Goal was to study ways of reducing the risk of transformer tank explosion in urban substations/ underground substations.
• Full scale model testing performed.
• Arc energies calculated and gas generation rate observed.
• Pressure rise models developed.
• Tank construction countermeasures developed.
Summary of ResearchSummary of Research
Internal Pressure Increase
Tank Explosion
Tank Explosion Tank Explosion ProcessProcess
Arc Test in Oil Tank
Pressure Rise Test
using Full Scale Tx
Verification Verification TestsTests
Study Process for Internal FaultStudy Process for Internal Fault
Estimation of Fault Condition① Arc Current ② Arc Voltage ③ Time ④ Dissolved Gas Generation Volume
Pressure Rise AnalysisDynamic Analysis considering Oil Motion
Comparison between Internal Pressure and Tank Strength
Countermeasure① Tank Strength Improvement ② Protection Relay Improvement
③ System Improvement ④ Pressure Restrained Structure
Internal FaultDissolved Gas
Generation
Internal Pressure
> Tank Strength
Dynamics of Internal Fault (1)Dynamics of Internal Fault (1)
Arc Test in Oil TankArc Test in Oil Tank
Arc Current : 1.3 to 40.9 kA
Time : 3Cycle (0.05sec)Arc Energy : 0.11 to 2.64 MJGap Length : 100 to 300 mm
Oil
Electrode
Arc100
1000
10000
10 100 1000Arc Length (mm)
Arc
Volta
ge (V
)
Gas Volume
0.01
0.1
1
0.1 1 10Arc Energy (MJ)
Gas
Vol
ume
(m3)
*Reference – T. KAWAMURA, M. UEDA, K. ANDO, Y. MAEDA, Y. ABIRU, M. WATANABE, K. MORITSU “Prevention of Tank Rupture Due to Internal Fault of Oil Filled Transformers”, CIGRE, 12-02, 1988.
Dynamics of Internal Fault (2)Dynamics of Internal Fault (2)Pressure Rise Test using Full Scale model for verifying pressure risePressure Rise Test using Full Scale model for verifying pressure rise
Combustion Container
Gas Outlet
(Φ12*72)
Cartridge increment(Max.7500g)
Φ300,L570Upper Tank
Middle TankLower Tank
Transformer : 275kV 300MVAArc Energy : 142,000kW、
Time : 80msec(Single Line-Ground Fault at Upper Tank)
- Pressure rise at internal fault can be simulated by powder combustion, considering nozzle area of container and powder amount.
- Dead space (steel tank) was set for simulating internal parts(Core,Coil).in the tested tank.
Pres
sure
Pres
sure
Pres
sure
Time
Time
Time
Middle Tank
Upper Tank
Measured ResultsAnalytical Results
Lower Tank
*Reference – T. KAWAMURA, M. UEDA, K. ANDO, Y. MAEDA, Y. ABIRU, M. WATANABE, K. MORITSU “Prevention of Tank Rupture Due to Internal Fault of Oil Filled Transformers”, CIGRE, 12-02, 1988.
Results of AnalysisResults of Analysis• Decomposed gas generation calculated to be around
0.5L/kW sec for larger 275 kV class transformers at HV lead.*
• Dynamic oscillation of fault pressure wave (kinetic energy) has a considerable influence on the pressure rise. (Dynamic Load Factor approx. 1.3 was recommended)*
• Tank expansion characteristics and tank strength are important in determining the transformer’s capability to resist rupture.
• Reinforcements can be made at the joining flange between the tank and cover (or flange between upper and lower tank for shell-form) to significantly improve the tank strength against rupture.
*Reference – T. KAWAMURA, M. UEDA, K. ANDO, Y. MAEDA, Y. ABIRU, M. WATANABE, K. MORITSU “Prevention of Tank Rupture Due to Internal Fault of Oil Filled Transformers”, CIGRE, 12-02, 1988.
Example of Tank Strength ImprovementExample of Tank Strength Improvement
Alleviation of Stress Concentration
Improvement of Connecting Part Strength by Tie Reinforcement
Conventional Type Improved Type
Connecting Part
• Diaphragm type Conservator Tanks can be used as effective pressure reducing space if the connection duct to the main tank is short, the cross sectional area of the duct is large (approx. 1.4 m dia.), and the air space in the conservator diaphragm is adequate
Pressure Reducing SpacePressure Reducing Space
•Tests on 300 MVA, 230 kV units have verified ability to withstand 15,000 MVA short circuit capacity without rupture of the tank.•Still requires operation of protective relays and circuit breakers to clear fault within approx. 60 - 80 ms.
Transformer main tank
Conservator TankDiaphragm (bladder)
Connection duct
Gas Insulated Power TransformersGas Insulated Power Transformers
•Use SF6 Gas as the insulating and cooling medium instead of insulating oil.
•First units produced in 1967.
•Several thousand units of various sizes now in service worldwide, several manufacturers.
•Transformer applications: From Distribution class units up to 400 MVA, 345 kV ratings.
•Primarily used in substations located in urban areas (including inside buildings, underground) due to safety benefits.
Features of Gas Insulated TransformersFeatures of Gas Insulated Transformers
• Use SF6 Gas as insulating and cooling medium, instead of oil.
• Typically use special internal insulation materials such as plastics, special paper, and pressboard.
• SF6 has excellent dielectric properties, but not as good for heat transfer.
Benefit of Gas Insulated TransformersBenefit of Gas Insulated Transformers
0
20
40
60
80
100
0 0. 2 0. 4 0. 6 0. 8 1
0
20
40
60
80
100
0 0. 2 0. 4 0. 6 0. 8 1
Tank Strength
Oil-Immersed Transformer
Gas Insulated Transformer
Fault Time (sec)
Pres
sure
Ris
e (%
)SF6 Gas Insulation: non-flammable, compressible gas
Pressure rise during an internal fault is slower than oil-immersed (non- compressible fluid), thus SF6 gas reduces the chances of tank explosion
15MVA, Three phase, 50Hz, Continuous Rating,Core-Form,Forced-Gas Natual Air,with On-Load Tap ChangerGNAN/GFAN
H.V. 64.5kV +10/-10% StarL.V. 6.6kV Delta
For underground substation beneath office building
Application ExampleApplication Example
Transformer Tank Rupture and Mitigation - March 9, 2010 J.Herz,
Qualitrol
A VERY BRIEF HISTORY:A VERY BRIEF HISTORY:
PRESSURE RELIEF DEVICES PRESSURE RELIEF DEVICES (PRDs) AND THEIR USE ON (PRDs) AND THEIR USE ON POWER AND DISTRIBUTION POWER AND DISTRIBUTION TRANSFORMERSTRANSFORMERS
BEFOREBEFORE
THERE WERE RETHERE WERE RE--SEALABLE PRDsSEALABLE PRDs……
Rupture DiscsRupture Discs
GOOSENECK CAN ADD TO BACK PRESSUREGOOSENECK CAN ADD TO BACK PRESSUREHAD TO BE REPLACED AFTER OPERATION HAD TO BE REPLACED AFTER OPERATION -- LEFT LEFT THE TRANSFORMER OPEN TO ATMOSPHERIC THE TRANSFORMER OPEN TO ATMOSPHERIC MOISTURE IN THE INTERIMMOISTURE IN THE INTERIMTYPICALLY WITH NO ALARMTYPICALLY WITH NO ALARM
More RecentlyMore RecentlyTHEY HAVE BEEN USED IN MULTIPLE SETS ALONG THEY HAVE BEEN USED IN MULTIPLE SETS ALONG THE TOP AND BOTTOM OF A SINGLE TRANSFORMER THE TOP AND BOTTOM OF A SINGLE TRANSFORMER TO MAXIMIZE THE PRESSURE RELIEF AREA AND TO TO MAXIMIZE THE PRESSURE RELIEF AREA AND TO BE LOCATED AS CLOSE AS POSSIBLE TO ANY BE LOCATED AS CLOSE AS POSSIBLE TO ANY POTENTIAL FAULT LOCATION. POTENTIAL FAULT LOCATION. THEY ARE THE RELIEF MECHANISM FOR THEY ARE THE RELIEF MECHANISM FOR COMBINATION PRESSURE RELIEF/FIRE COMBINATION PRESSURE RELIEF/FIRE SUPPRESSION SYSTEMSSUPPRESSION SYSTEMS
THERE WERE SEVERAL DIFFERENT THERE WERE SEVERAL DIFFERENT DESIGN APPROACHES TO REDESIGN APPROACHES TO RE--SEALING SEALING PRDs MADE BY VARIOUS PRDs MADE BY VARIOUS MANUFACTURERS MANUFACTURERS
IN THE LATE 1950IN THE LATE 1950’’s THE INDUSTRY s THE INDUSTRY SETTLED OVERWHELMINGLY ON ONE SETTLED OVERWHELMINGLY ON ONE DESIGN.DESIGN.
THE DESIGN IS STILL IN FREQUENT THE DESIGN IS STILL IN FREQUENT USE TODAY. IT OFFERS SIMPLICITY USE TODAY. IT OFFERS SIMPLICITY AND DURABILITY IN ADDITION TO AND DURABILITY IN ADDITION TO RERE--SEALABILITY. SEALABILITY.
REFINEMENTS SINCE HAVE TO DO REFINEMENTS SINCE HAVE TO DO WITH IMPROVING THE SEAL, WITH IMPROVING THE SEAL, SHIELDING AND PROTECTION, SHIELDING AND PROTECTION, SWITCH CAPACITY, CORROSION SWITCH CAPACITY, CORROSION RESISTANCE, ETCRESISTANCE, ETC
WHEN OPERATING PRESSURE IS REACHED, TOP SEAL OPENS WHILE SIDE SEAL REMAINS BRIEFLY CLOSED
WITH OPERATING PRESSURE ACTING ON THE LARGER AREA CIRCUMSCRIBED BY THE SIDE SEAL, THE SPRING IS RAPIDLY COMPRESSED AND THE VALVE EXHAUSTS QUICKLY
8400 SCFM AT 50% OVERPRESSURE ON A 10 PSI PRD WAS TYPICAL. NOW THERE ARE DEVICES WHICH GO TO 12,600 SCFM.
Most frequent question: Will it protect? Most frequent question: Will it protect?
Most frequent answer is: Depends.Most frequent answer is: Depends.
•• location of faultlocation of fault•• magnitude of faultmagnitude of fault•• duration of faultduration of fault
The test tank was approximately 6 ft in diameter and 4 ft deep, The test tank was approximately 6 ft in diameter and 4 ft deep, with the with the PRD mounted in the center of the 6 ft. diameter cover. PRD mounted in the center of the 6 ft. diameter cover. The gas space was 10 inches below the cover which resulted in abThe gas space was 10 inches below the cover which resulted in about 700 out 700 gallons of oil and 23 cu. ft. of gas (air). gallons of oil and 23 cu. ft. of gas (air). Ball nosed copper electrodes (2) were threaded with a small coppBall nosed copper electrodes (2) were threaded with a small copper wire to er wire to trigger the arc, the highest of which was 25K amps and 20K voltstrigger the arc, the highest of which was 25K amps and 20K volts. Oil, . Oil, smoke, mist, spray blasted out of the relief device over a radiusmoke, mist, spray blasted out of the relief device over a radius of about 40 s of about 40 feet. feet.
TEST 1: 1958 AT GE SCHENECTADY
In tests performed by Jim Barr on a transformer with NO COIn tests performed by Jim Barr on a transformer with NO COVER , the fault VER , the fault was introduced near the bottom of the tank and the bottom of thewas introduced near the bottom of the tank and the bottom of the tank BLEW tank BLEW OUT, at 10K amps and 10K volts.OUT, at 10K amps and 10K volts.
TEST 2: 1958 AT GE SCHENECTADY
Transformer Tank Rupture and Mitigation - March 9, 2010 J.Herz,
Qualitrol
There are thousands of events where rupture There are thousands of events where rupture discs and rediscs and re--sealable PRDs have successfully sealable PRDs have successfully protected transformers: protected transformers:
““Internal arcing, breaker insulation break Internal arcing, breaker insulation break down, load tap changer problems, phase down, load tap changer problems, phase angle regulator problems, and internal angle regulator problems, and internal winding problemswinding problems””
are some of the more are some of the more
common.common.
CONCLUSIONS
TTR is a complex problem. The severity is a function of arc location, arc I and T as well as oil volume and tank expansion characteristics.
It’s possible to reduce the risk of TTR by performing modifications to the tank.
PRDs help to protect the tank against low energy internal arcing faults.
Fluids with high fire point will reduce the consequences of a tank rupture; however it is not yet proven if these fluids will prevent tank rupture.
GITs will eliminate the risk of tank rupture.
Improved electrical protection and electrical system design can also help prevent TTR.
The IEEE currently has no standards that provide guidance on TTR mitigation.
Power Transformer Tank Rupture and Mitigation- A Summary of Current State of Practice and Knowledge
by the Task Force of IEEE Power Transformer SubcommitteeNick Abi-Samra, Javier Arteaga, Bill Darovny, Marc Foata, Joshua Herz, Terence Lee, Van Nhi Nguyen,
Guillaume Perigaud, Craig Swinderman, Robert Thompson, Ge (Jim) Zhang, and Peter D. Zhao
IEEE TRANSACTIONS ON POWER DELIVERYVolume: 24 Issue: 4 Date: Oct. 2009 Page(s): 1959 - 1967
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