ML22307A236
| ML22307A236 | |
| Person / Time | |
|---|---|
| Issue date: | 10/21/2022 |
| From: | Coyne K, Kenneth Hamburger, Mcgrattan K, Nick Melly, Markhenry Salley, Gabe Taylor NRC/RES/DRA |
| To: | |
| References | |
| Download: ML22307A236 (1) | |
Text
Development of Improved High Energy Arcing Fault (HEAF) Target Damage Thresholds and Zone of Influence (ZOI) Models Kevin Coyne, Gabriel Taylor, Kenneth Hamburger, Nicholas Melly, Kevin McGrattan, Mark Henry Salley 26thInternational Conference on Structural Mechanics in Reactor Technology (SMiRT 26) 17th International Post-Conference Seminar on FIRE SAFETY IN NUCLEAR POWER PLANTS AND INSTALLATIONS
Updated Fragility Modeling Physical testing and operating experience to develop fragilities for electrical cables ZOI Development Confirmatory ZOI Analysis Independent confirmation using modified IEEE arc flash model Comprised of three major research activities CFD Simulations FDS development and application to large matrix of configurations
Heliostat and parabolic reflector, generating up to 6 MW/m2 over a 5 cm circle Varied heat flux, duration, cable material, and exposure profile Objective was to develop metrics for evaluating cable failure and quantify threshold criteria SNL Solar Furnace Facility Cable Fragility Experiments
Solar Furnace Testing Methodology Test 1-22 (7 MJ/m2): Surface damage to jacket only Test 1-32 (24 MJ/m2): Sub-jacket shielding visible Test 1-09 (206 MJ/m2): Cable insulation and bare wire exposed
Solar Furnace Testing Results Total of 38 tests conducted, and categorized by damage extent:
jacket damage, insulation exposure, conducting wire exposure Results for initial heat fluxes of >1 MW/m2 are shown (upper plot thermoplastic, lower plot thermoset)
Fragility Working Group Process for data analysis and consensus building 1
2 3
Proposal Development Weekly Meetings Consensus Two teams developed proposals to address the specific technical issues Proposals presented to full working group and resource experts for feedback Technical evaluators and integrators caucused to reach agreement on path forward for each issue
Incident Energy Sustained Ignition Protective Features Fragility Working Group Conclusions The threshold for electrical failure/damage of thermoplastic jacketed cables is 15 MJ/m² and the threshold for thermoset jacketed cables is 30 MJ/m² Sustained ignition is assumed for cables within the enclosure of origin (e.g.
internal cables and components within switchgear and load centers) 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> (or greater) rated Electrical Fire Raceway Barrier System (ERFBS) will prevent ignition inside the enclosure of origin, and damage in the ZOI
FDS Inputs Relative convective/radiative fraction of HRR Radiative Fraction Electrode Mass Loss Rate Mass of electrode vaporized during arc Source Term (HRR)
Volumetric HRR to represent the arc Particle size distribution and extent of oxidation Metal Oxidation
Q
FDS does not include models for electrical/magnetic fields, dissociation of molecules at high temperatures, or formation of plasma Total arc energy can be accounted for using arc voltage, current, and duration A volume was defined in FDS to approximate the arcing region with the same total arc energy Volumetric HRR Definition Heat Release Rate Development
Cressault developed radiative fraction correlations for electrical arcs as a function of electrode material (aluminum, copper) and arc power Stanback developed electrode mass loss rate correlations as a function of electrode material (aluminum, copper) and arc current Data from Literature Radiative Fraction & Electrode Mass Loss
SNL conducted experiments in a closed calorimeter with scaled current densities Experiments determined vapor fraction of lost electrode and extent of particle oxidation Nozzles defined in FDS to emit metal particles with defined oxidation rates at each conductor in the arc volume Experimental Data Metal Oxidation
FDS Validation Full-scale experiments used for model validation; unbiased FDS predictions plotted against experimental temperatures for MV switchgear shown at right 1
10 100 1000 10000 1
10 100 1000 10000 FDS Temperatur Rise (K)
Test Temperature Rise (K)
A matrix of FDS simulations was created to vary the important inputs: energy profile, geometric configuration, electrode material, housing material, and arc initiation location In total, 130+ simulations were run A Python script, FDS template, and parameter file were used to programmatically swap the relevant variables in and out and reduce the chance of human error Scripted Automation Processing the FDS Run Matrix
FDS Results & Conclusions FDS simulations allowed the determination of the distances where 15 MJ/m2 and 30 MJ/m2 would be exceeded.
Sample results shown for medium-voltage switchgear with arc initiated at the main bus bars and a 15 MJ/m2 fragility threshold Dominant factor in ZOI is total arc energy.
Switchgear are sensitive to arc initiation location and geometry. Bus ducts are sensitive to housing material (aluminum vs. steel)
Results not sensitive to electrode composition (aluminum vs. copper) 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 0
50 100 150 200 250 300 ZOI (m)
Arc Energy (MJ)
Back Left Right Top Front
Confirmatory ZOI Analysis Using a modified model based on IEEE guide 1584-2018 Current Voltage Base Model Enclosure Breach Base model developed to estimate incident energy at various distances from an arc flash for personnel safety Base model uses bolted fault current, modified to use arc current. Arc voltage obtained from CIGRE-602 model Base model does not assume a barrier between source and target.
Modified model incorporates a time to breach before target receives energy Decay Current Arc energy profile developed for generator-fed faults during coast down following a trip
Modified IEEE & FDS Models Compared Modified IEEE model results are generally within 20 cm of FDS results.
Considering vastly different nature of the models (empirical vs. CFD) the ZOIs are in fairly good agreement and provide confidence in the results IEEE Max ZOI FDS Max ZOI MV Switchgear (15 MJ/m2) 1.6 m 1.3 m MV Switchgear (30 MJ/m2) 1.06 m 0.97 m NSBD Aluminum (15 MJ/m2) 1.2 m 1.41 m NSBD Aluminum (30 MJ/m2) 0.77 m 0.95 m NSBD Steel (15 MJ/m2) 1.18 m 1.33 m NSBD Steel (30 MJ/m2) 0.76 m 0.89 m
THANK YOU!
https://www.nrc.gov/about-nrc/regulatory/research/fire-research/heaf-research.html