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Understanding Manhole Events

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This presentation reviews literature related to the prevention, detection, mitigation and response to events resulting from low voltage cable failures. The most serious outcomes are manhole fires, explosions and contact voltage electric shocks. Smoking manholes, stray voltage (contact voltage) and service quality complaints are less serious outcomes.

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Understanding Manhole Events

  1. 1. C34 – Mitigating Manhole ExplosionsIEEE PES ICC Spring 2013 MeetingUnderstanding Manhole EventsStuart HanebuthPower Survey Companyshanebuth@powersurveyco.com973-344-7116
  2. 2. C34 – Mitigating Manhole ExplosionsIEEE PES ICC Spring 2013 MeetingDo We Need a Trial Use Guide?• There has been a lot of research into causes, preventiondetection, mitigation and response• Little of this work has been consolidated to identifybeneficial strategies and best practices• Significant maintenance and capital spending to preventand respond, oftentimes with limited benefit• Events represent risk to employees and the public• Industry and public do not always speak the samelanguage on these events• Consolidation of prior research, along with utility bestpractices will save utility and ratepayer dollars andimprove public safety2
  3. 3. C34 – Mitigating Manhole ExplosionsIEEE PES ICC Spring 2013 MeetingManhole Event Sources• Transmission and primary cable initiated events• High fault energy• Interrupted quickly by protective systems• Incipient fault detection may be possible• Transformer initiated events• High fault energy• Large fuel source• Primary faults interrupted by protective systems, secondary faultsmay or may not be interrupted• DGOA, visual inspection, and cathodic protection are effectivepreventative measures3
  4. 4. C34 – Mitigating Manhole ExplosionsIEEE PES ICC Spring 2013 MeetingManhole Event Sources• Natural gas initiated events• Large fuel source• Potential for collateral damage to electric facilities• Methane and chemical related events• Less common• Hard to predict4
  5. 5. C34 – Mitigating Manhole ExplosionsIEEE PES ICC Spring 2013 MeetingManhole Event Sources• Low voltage cable events (>95% of manhole events1)• Limiters designed to prevent damage to adjacent sections but notto interrupt fault• Large potential fuel source from cable insulation• Toxic gases produced during decomposition of insulation• Visual inspections provide limited benefit (less than 5% reduction)• Arc fault detection may not provide adequate sensitivity• Contact voltage detection locates conductive faults• Venting demonstrates some benefit in reducing severity5
  6. 6. C34 – Mitigating Manhole ExplosionsIEEE PES ICC Spring 2013 MeetingElectrical Properties• Low Current• Gas generation with a little as 1.28 W/cm1• Sustained Combustion at 18W/cm• Distinctive waveform2-4• May persist for short intervals of seconds to minuteswith long quiescent periods5• Arcing events can energize street level objects andcan be detected with mobile contact voltage detectionsystems66
  7. 7. C34 – Mitigating Manhole ExplosionsIEEE PES ICC Spring 2013 MeetingProtective Systems• Limiters• Designed to protect adjacentsections from thermal overloadsduring three phase faults7• Typically limit in the 1,000-5,000amp range• Not generally effective inpreventing or mitigating gasproducing faults• Arc fault detection• Most sensitive systems seem tobe in the 5 amp – 50 amp range6• May not be able to detect gasproducing faults7
  8. 8. C34 – Mitigating Manhole ExplosionsIEEE PES ICC Spring 2013 MeetingChemistry• A variety of materials have been used for low voltage cable insulation8• Paper Insulated Lead (PILC)• Kerite• Styrene Butadiene Rubber (SBR) 1940 - 1960• Butyl Rubber• Neoprene• PVC• EPR• Variety of duct materials have been used9• Wood• Cellulose-Tar• Concrete• PVC• Each represents different risks and benefits8
  9. 9. C34 – Mitigating Manhole ExplosionsIEEE PES ICC Spring 2013 MeetingCable Failure Outcomes• Majority of failures result in powerquality and contact voltagerelated issues• Smoking manholes are the mostprobable manhole events as aresult of insulation degradation• Manhole fires and explosions canbe further subdivided• Electrically driven events• Chemically driven events9Energized ObjectsFlickering LightsSmoking ManholesManholeFires andExplosions
  10. 10. C34 – Mitigating Manhole ExplosionsIEEE PES ICC Spring 2013 MeetingCollateral Damage Concerns• Primary damage fromlow voltage faults• Damage to nearbynatural gas facilities10• Building explosions fromcarbon monoxideaccumulations10Danny Iudici/for New York Daily News
  11. 11. C34 – Mitigating Manhole ExplosionsIEEE PES ICC Spring 2013 MeetingEvent Prevention Strategies• Post installation testing11• Duct sealing to minimizeairflow12• Filling manholes with inertmaterials to minimize gasaccumulation• Contact voltage testing tofind incipient faults11
  12. 12. C34 – Mitigating Manhole ExplosionsIEEE PES ICC Spring 2013 MeetingVisual Inspections• Analysis of over 55,000visual inspections foundsmall reduction insecondary relatedevents such as13• Smoking manholes• Contact voltage• Power Quality Events• No reduction in manholefires or explosions12Structure CategoryEventProbability
  13. 13. C34 – Mitigating Manhole ExplosionsIEEE PES ICC Spring 2013 MeetingMitigation Strategies• Several cover designs and restraining approaches have been implemented14• Tethering• Self restraining• Venting• Deployment strategies not well established• Is 100% installation the optimal approach?• High density areas• Dense structures• Duct or Cable driven installation• Analysis needed on impacts of deployment• Water• Primary Joints• Customer basements• Debris accumulation• Access• Civil design• Increased duct airflow• At least one “standard” exists for deployment of vented covers15• Office of the Telecommunications Authority Hong Kong. (2010, June, 30). ImplementationGuidelines on Mitigating the Risk of Gas Explosion in Telecommunications Manholes [Online].Available: http://tel_archives.ofca.gov.hk/en/report-paper-guide/guidance-notes/gn_201003.pdf13
  14. 14. C34 – Mitigating Manhole ExplosionsIEEE PES ICC Spring 2013 MeetingResponse Strategies• Area of little consideration by most utilities• Fire department approaches problem different than utility• Variety of agents are available on the market• Some firefighters have written on the topic• Battalion Chief Frank C. Montagna, “Manhole Fires”, http://www.chiefmontagna.com/Articles/manhole%20fires.htm• Battalion Chief Frank C. Montagna, “What You Should Know About 10-25 Reponses”, http://www.chiefmontagna.com/Articles/pdf/Manhole.pdf• Boston Fire Department, “SOP #49B Special Procedures and Precautions for Incidents Involving Manholes”, http://www.firesops.com/wp-content/uploads/2012/02/BFD_SOP_49B_Special_Procedures_and_Precautions_Involving_Manhole_Incidents.pdf• D. Leihbacher, “Managing Manhole Fires”, Fire Engineering Magazine, January 2008, http://www.fireengineering.com/articles/print/volume-161/issue-1/features/managing-manhole-fires.html• Conflicting strategies• Remove covers or leave in place• Flood Structures or leave dry• Apply other firefighting agents• Isolation14
  15. 15. C34 – Mitigating Manhole ExplosionsIEEE PES ICC Spring 2013 MeetingManhole Events Outline• Event taxonomy• Definitions• Literature Review• Low Voltage Cable Insulation Initiated Events• Electrical Properties• Protective Systems• Early Detection Methodologies• Cable Failure Outcomes• Collateral Damage Concerns• Severity Mitigation Strategies• Response Strategies15
  16. 16. C34 – Mitigating Manhole ExplosionsIEEE PES ICC Spring 2013 MeetingManhole Events Outline• Transformer Initiated Events (With similar subtopics fromabove)• Electrical Properties• Protective Systems• Early Detection Methodologies• Outcomes• Severity Mitigation Strategies• Response Strategies16
  17. 17. C34 – Mitigating Manhole ExplosionsIEEE PES ICC Spring 2013 MeetingManhole Events Outline• Transmission and Primary Cable Insulation InitiatedEvents• Electrical Properties• Protective Systems• Early Detection Methodologies• Cable Failure Outcomes• Collateral Damage Concerns• Severity Mitigation Strategies• Response Strategies• Natural gas Initiated Events (With similar subtopics fromabove)17
  18. 18. C34 – Mitigating Manhole ExplosionsIEEE PES ICC Spring 2013 MeetingManhole Events Outline• Natural gas events• Protective Systems• Early Detection Methodologies• Outcomes• Collateral Damage Concerns• Severity Mitigation Strategies• Response Strategies18
  19. 19. C34 – Mitigating Manhole ExplosionsIEEE PES ICC Spring 2013 MeetingConclusion• General need to define common terms to discuss theissue• Low voltage cable failures are at root of most of theseevents• Need wider focus than simply mitigating manhole events,also need to consider:• Prevention• Early detection• Maintenance• Response19
  20. 20. C34 – Mitigating Manhole ExplosionsIEEE PES ICC Spring 2013 MeetingBibliography1. L. Zhang, “Mitigation of Manhole Events Caused by Secondary Cable Failure,” Ph.D. dissertation, Dept. of Elect. and Electronic Eng., Univ.of Conn., Storrs-Mansfield, CT, 20112. D.G. Ece, F.M. Wells and H.G. Senel, “Analysis and Detection of Arcing Faults in Low-Voltage Electrical Power Systems,” in 7thMediterranean Electrotechnical Conference., Antalya, Turkey, 1994, pp. 929-9353. W. Charytoniuk et al., “Arcing fault detection in underground distribution networks feasibility study,” in Industrial and Commercial PowerSystems Technical Conference, Clearwater Beach, Fla, 2000, pp.15-204. B. Koch and Y. Carpentier, “Manhole Explosions Due to Arcing Faults on Underground Secondary Distribution Cables in Ducts,” IEEETrans. Power Del., vol. 7, no. 3, pp. 1425-1433, Jul 19925. Hamel, A. Gaudreau, and M. Cote, “Intermittent Arcing Fault on Underground Low-Voltage Cables” IEEE Trans. Power Del., vol. 19, no. 4,pp. 1862-1868, Oct 20046. N. Weisenfeld, Y. When, “Arcing Fault Detection Projects”, 2010 Jodie S. Lane Public Safety Conference, New York, NY7. F. Heller, and I. Matthysse, “Limiters, Their Design Characteristics and Application” IEEE Trans. Power App. Syst., vol. 74, pp. 924-950, Oct19558. C. Zuidema et al., “A Short History of Rubber Cables,” IEEE Electr. Insul. Mag, vol. 27, no. 4, pp 45-50, Jul/Aug 20119. L. Zhang et al., “The Electro-Chemical Basis of Manhole Events,” IEEE Electr. Insul. Mag, vol. 25, no. 5, pp. 25-30, Sep/Oct 200910. T.J. Parker and D. J. Ward, “Insuring Adequate Spacing Between Underground Distribution Conductors in Conduit and Gas Lines,” IEEETrans. Power Del., vol. 18, no. 1, pp. 291-294, Jan 200311. J.Côté, “Manhole Explosions Discussion Group Hydro-Québec Experience”,http://www.pesicc.org/iccwebsite/subcommittees/subcom_c/C34/Presentations/2011Spring/C17.pdf12. L. Zhang, S.A. Boggs and S. Livanos, “Manhole Events Caused by Secondary Cable Insulation Breakdown,” in Annual Report Conferenceon Electrical Insulation Dielectric Phenomena, Quebec City, Canada, 2008, pp. 107-11013. Consolidated Edison Co. of NY, Inc. Stray Voltage Test and Inspection 2010 Annual Report 04-M-0159, Consolidated Edison Co. of NY,Inc., New York, NY, 201114. W. Black, J.Côté, “Mitigating Manhole Explosions”http://www.pesicc.org/iccwebsite/subcommittees/subcom_c/C34/Presentations/2012Spring/C-21.pdf15. Office of the Telecommunications Authority Hong Kong. (2010, June, 30). Implementation Guidelines on Mitigating the Risk of GasExplosion in Telecommunications Manholes [Online]. Available: http://tel_archives.ofca.gov.hk/en/report-paper-guide/guidance-notes/gn_201003.pdf20

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