Guide for Transformer Fire Safety Practices

1 537 Guide for Transformer fire Safety Practices Working Group June 2013 iGUIDEFORTRANSFORMER fire Safety PRACTICESW orking Group :Arne PETERSEN(AU) ConvenorRudy BLANC (FR)Kjell CARRANDER (SE)Dayse DUARTE (BR)Yoshihito EBISAWA (JP)Elisa (CA)Marc FOATA (CA)Makoto KADOWAKI (JP)Takayuki KOBAYASHI (JP)Terence LEE (US)Russell MARTIN (UK)Sidwell MTETWA (ZA)Hiroshi MURAKAMI (JP)Uwe RIMMELE (DE)Yukiyasu SHIRASAKA (JP).I memory of Yoshihito Ebisawa san, Ebi as he was known to his friends made significant contribution to the completion of thisbrochure. Ebi passed away on the after the brochure was completed, but before itcould be published. The members of the WG who worked with Ebi will remember him forexceptional competences, his intellectual rigor, and by his remarkable elegance and 2012 Ownership of a CIGRE publication, whether in paper form or on electronic support only infers right of usefor personal purposes.

2 Are prohibited, except if explicitly agreed by CIGRE, total or partialreproductionof the publication for use other than personal and transfer to a third party; hence circulation on anyintranet or other company network is forbidden .Disclaimer notice CIGRE gives no warranty or assurance about the contents of thispublication, nor does it accept anyresponsibility, as to the accuracy or exhaustiveness of the information. All implied warranties andconditions are excluded to the maximum extent permitted by law .iiSUMMARYThe issue of Transformer fire Safety has beenof concern to Cigre SCA2 for some time and it wasevidentfrom discussion of the topic within the Study Committeethat theprobabilityand riskofa Transformer firesand the effectiveness of the various risk mitigation measureswas not alwayswell understoodbymany Transformer users andother thereforedecided toestablish a working group[WG ]toprepare recommendationsforgoodTransformer fire SafetyPracticesthatwould help Transformer designers and users todefine and applybest Practices in the domain of Transformer group WG hasendeavoured to do this by preparing thisTechnical Brochurewhich covers the following aspects of Transformer fire Safety :Chapter 1.

3 An introduction toTransformer fireSafety issues with listing of useful Standardsand Guide Documents with information on Transformer fire 2 :Physics of fires and typical Transformer fire scenarios to give a broad perspective ofthe concepts and issues related to Transformer 3:Providing guidance on the probabilityof a transformerfire eventoccurring basedoninformation available in the public domain and also on how atransformer usermight be able toassess the probability of atransformer fireevent occurring in itstransformer 4:Discusses the physics of arcing within Transformer tank and gives formulas andexamples on how a user might be able to predict the likely range of arcing energy, volume of gasgenerated and likely pressures which might be developed during an internal arcing also provides examples on pressure calculation modelswhich are available forapproximatecalculation ofthe pressures which may be developed during and arcingfault withsomeexamples onpressure venting and pressure containment.

4 Although it must be stressed it isnot possible to ensure with absolute certainty that the arcing energy can be contained within thetransformertank at high energy arcing 5: Provides guidance on issues to considerwhen determiningwhat fire protection maybe required and what should be installed at a specific gives examples on points toconsider when determining the likely performanceof fire protection systemsand providesexamples on the methodologiesavailable when planning and designing a fire protectionsystemfor a Transformer 6: Discusses therisk mitigationoptionsavailableforthe Transformer ,and providessome guidance onthe ranking of the options based the risk reduction effectivenessand thedegree of risk reduction required for the specific 7:Discusses the risk mitigation options available for thesubstations and othertransformer installationsto protect human life, maintain supply or if notpossible minimiselossof supply and to protect adjacent plant and 8 :Provides advice on planning andthe importance ofbeing prepared for a fire event, soas tominimisethe effects andlosses from a fire and be able to recover from the fire 9.

5 Contain conclusions and some recommendation for improvement on Standardsforimproved fire Safety on tanks and cable for Transformer fire Safety PracticesiiiTABLE OF CONTENTSC hapter 1 of transformers of TransformerInstallations and 2:FirePhysics and Typical Transformer fire is a fire ?.. Arcing Rupture Bushing fire Cable Box and Cable Termination Failures fire Effect of a Transformer fire in a of Fires and Extinguishing Resistance of as a fire 3:Probability of a Transformer Failure Rates from Survey Failure Australia New Zealand Reliability on Major Transformer Failures by Australia 2002 Survey on Major Transformer Failures and Failure Rate Russia and Transformer fire Risk Assessment by a Major Canadian Failure and fire Risk Rate in Company Failure and fire Risk Rate-Data Other Causes of Transformer fire Initiated by Bushings and Cable Termination Bushing Initiated Initiated by Cable Termination Initiated by OLTC Initiated by a Tank Probability of Transformer Risk to Potential fire Victims Other Substation 4.

6 Internal Arcing and Tank Calculation Containment for Transformer fire Safety Venting Numerical Numerical Upper Bound 5:FireRisk and Performance the Problem and Identifying System Performance and Risk a fire Risk Management Analysis and Management of Transformer Study of a PoolFire on a Transformer with 40,000 l of Mineral 6: fire Risk Mitigation Options for the Risk of Transformer Tanks with Pressure Safety Margin above PRV Opening Insulating Type Insulated transformers (GIT).. Flammable Insulating of Less-Flammable Molecular Weight Hydrocarbon (HMWH).. Characteristics and Test Design as Protective Strength of the Tank Reducing Cushion of Pressure Withstand Venting & Depressurization asProtective Neck Explosion Relief Valves (PRV).

7 For Transformer fire Safety Protection Systems Based on Rupture Discs and Nitrogen Protection Systems Using Multiple Rupture of Components as Protective Terminations and Cable Liquid Filled Cable Insulated Cable Shut-off 7: Transformer fire Damage Control and Control the Risk of Loss of Life to Protection Barriers / fire Suppression City Impact 8:Plans for a fire Importance of Planning for a fire Response Response of the Emergency Response Planning with Emergency Recovery Continuity 9:Conclusions and to Avoid a Boxes and Insulating to Mitigate the Damage of a for Future for Transformer fire Safety PracticesviTable of FiguresFigure 1: fire 2: Tank Rupture 3: Typical Bushing fire Scenario [22]..13 Figure 4: Cable Box and Cable Termination fire 5: Transformer Failure Rate according to Component and Voltage level Australian NewZealand Reliability 6: Yearly Failure rate according to age Australian New Zealand Reliability Survey-199521 Figure 7: Arc voltage as a function of arc length [29].

8 31 Figure 8: Example of arc energy calculation (8 MJ) based on actual fault voltage and 9: Comparison of gas generation models and experiments from different authors (Gasvolume at Normal Pressure and 2000 K)..34 Figure 10: Variation of the dynamic amplification factor F forEquation 11: Simplified numerical model for venting toadjacent 12: Example of pressure field calculation outputs from hydrodynamic 13: Example of stress field outputs from an explosive simulation of the 14: Example of a real chimney rupture case with an arc simulation 15: Upper bound for venting efficiency (% peak pressure reduction) Arc (3 cyclesduration) located in the immediate vicinity of the 16: Upper bound for venting efficiency (% pressure reduction) Arc (3 cycles duration)located more than 1 m from the 17: Upper bound for venting efficiency (% pressure reduction) Arc (30 cycles duration)not located within the immediate vicinityof the 18.

9 Transformer equipped with a 40 rupture discs depressurization 19: Performance fire Risk 20: Understanding the 21: Transformer fire 22: Reliability of the Water Spray 23: Evaluation of Water Spray 24: Success or Failure of the Agent 25: A Transformer involved in a pool 26: A Pool fire Transformer Superimposed onTransformer 27: Layout of the 28: Deformation of the High Voltage Landing Span Structure after a Transformer 29: Case 1: Temperature versus time and load-bearing capacity versus time graphs to anexposed energy of 19 kW/m ..59 Figure 30: Case 2: Temperature versus time and load-bearing capacity versus time graphs to anexposed energy of 20 kW/m ..60 Figure 31: Case 2: Temperature versus time and load-bearing capacity versus time graphs to anexposed energy of 7 kW/m.

10 60 Figure 32: GIT Structure and 33: GIT 34: Comparative Combustion Test 35: Ideal protective performance of a 36: Example of reinforcement at joining 37: Pressure reduction effect of an expansion for Transformer fire Safety PracticesviiFigure 38: Comparison between Dynamic and Static Pressure 39: Variations in the recommended separation distance between Transformer tank andother 40: Wind direction effect on 41: Suggested separation 42: fire Barrier protecting two adjacent 43: Zone of exposure downwind of burning 44: Exposed building roof downwind of burning 45: Extending building wall to protect exposed roof 46: Side elevation of exposed area of a tall 47: Front elevation of exposed area of a tall 48: fire on 80 MVA Transformer in sound 49: Example of an Oil-Water separation 50: Alternative Oil-Water separation 51: Oil separator 52: Rock filled pit 53: Typical water spray arrangement for Transformer and oil containment 54: Water spray system with rock filled 55: Water curtain protection in 56: Oxygen percentage effect on fire intensity and haemoglobin 57: Transformer sound enclosure with Nitrogen gas fire 58: fire Suppression system using inert gas on transformers installed within soundenclosure 59: Internal design of a city substation with fire protection 60: SF6 underground substation in Sydney [63].