Microsoft PowerPoint - NFPA Lightning & Electrical Arc Damage to CSST

Size: px

Start display at page:

Download "Microsoft PowerPoint - NFPA Lightning & Electrical Arc Damage to CSST"

当姚
5 years ago
Views:

1 Michael F. Stringfellow Chief Scientist PowerCET Corporation

2 Hole size proportional to energy dissipated Power proportional to product of current and voltage Voltage at arc/metal interface approximately constant Energy proportional to time integral of current (charge) For CSST of 0.25mm wall thickness Hole area in sq mm ~ 3 x charge in coulombs 2mm diameter ~ 1 coulomb

3 Most often to ungrounded metallic roof penetrations ti Melting on metal components most liable to be struck Chimney flues Heater vents Mechanical damage to non-conductors Current flows through all available paths to earth Electrical, telephone and cable TV lines Structural metalwork, metal-foil-clad insulation Water, HVAC and gas pipes Model simulation May also initiate power system faults

4 Chimney caps and flues Furnace vents TV antennas Satellite dishes

5 Lightning-related g event with no evidence of direct strike to structure Evidence of nearby strike Damage to trees or non-metallic objects Melting on nearby metallic objects Power line damage

6 Not precise enough to locate exact point of strike Location done by radio location of lower channel ~ 500m errors Will locate many (not all) strokes of multistroke flash May identify separate channels

7 Negative flashes: One or more impulsive return strokes 30 ka 10x100 µs (5 coulomb impulse charge) One continuing current in some flashes 100 A, 100ms (10C) Positive flashes One return stroke 100 ka 30x µs (100C)

8 Unconnected leader to metallic roof penetrations Short duration (µs), high voltage (>100 kv), low energy and charge (~0.001C) 001C) Electromagnetically-induced surges Medium duration (10 µs), high voltage, low energy and charge (~0.001C) Surges on incoming services round-potential rise Longer duration (100 µs), medium voltages (10 kv), moderate energy and charge (~0C)

Likely serial from multiple-stroke lightning flash Power system only

10 Multiple adjacent holes of similar il size Frequently reported from indirect lightning Adjacent arcs unlikely l to exist concurrently Likely serial from multiple-stroke lightning flash Power system only source likely to deliver similar energy in successive arcs Computer simulation

11 Direct Lightning Strikes Indirect Lightning Strikes Fraction of lightning current flows onto CSST through arc Return stroke Continuing current Sufficient current magnitude and duration to cause observed damage Indirect lightning currents too small and too short duration to damage CSST Indirect overvoltage (> 50 kv) causes multiple flashovers, including AC power system to cause observed damage AC power fault current flows through arc Sufficient current magnitude and duration to cause observed damage Power fault currents also likely cause of many fires not involving ggas pp pipes

12 Leader1kA DC: Amps undefined AC: Amps 1.0 AC: Phase Tran: Exp 0 to 1000 Distort: Sine undefined RFlue kA Leader + Bond Transient - New, Residence Fireplace Lightning Transient Leader.Sch + Residence Fireplace Lightning Transient Leader.Anl, 27 June 2011 VCSST (right) VFurnace (right) y E+4 aslinecurrent (left) ArcCurrent (left) x E-7 LFlue 4.4uH K roundwirecurrent R L1 4.4uH aslinecurrent FoundationR 5 IbeamL 100uH K roundwire RCSST.132 IbeamR K Lroundwire LCSST 2uH TPi1 VCSST ArcCurrent R4 L2 R5 R9.132 L7 2uH Raspipe.005 R1 10k C1 50pF R32 10 TPv1 + Vc -- Vc Vsw1 Ron: 0.1 Roff: 1e6 Vthres: 15.1 Vhyst: 14.9 Init Cond: OFF RDuct.0019 LDuct 4uH R K 50.0K L3 Laspipe L8 4uH VFurnace 250 R6 R R K L4 L12 L9 200 R7 R R K L5 L13 Rasground 500 L K R8 R L2maspipe 1.6uH R L6 L R17 L15 R2maspipe.002 RBond LBond 2uH L11 RPanelroundLPanelround PanelEarth 3uH K K n 100n 150n 200n 250n 300n 350n 400n 450n 500n Time

13 FaultR 1 R56 L53 R55 L52 LineR FurnaceVoltage LineL R54 9 L51 4uH DuctR 9 DuctL 4uH R60 1 L55 ArccurrentR Fireplace AC Simulation Bonded Transient - New, Fireplace AC Simulation Flexconnect.Sch + Fireplace AC Simulation Flexconnect.Anl, 28 June 2011 FaultCurrent (left) Arccurrent (right) y E+2 x E-2 BondL 3uH BondR R52 L49 R51 L48 R50 L47 BlackIronRBlacIronL CSSTR CSSTL R CSSTLoop 1uH Fireplacevoltage L50 3uH CableL 12uH R53 PanelroundR 20 TPdv Cable asground 500 R40 R38 L35 R39 L36 R41 R42 L37 L38 L39 R43 L40 R46 R34 L43 L31 C10 R44 C1 Vs1 DC: Volts undefined AC: Volts 170 AC: Phase 0 Tran: Sine 170 (peak) Freq 60 Distort: Sine undefined L41 C9 R45 C2 BranchCircuit14g BrachCircuitL R33 L42 L30 C8 R47 C3 R35 L44 L32 C7 R48 C4 R36 L45 L33 C6 R49 C5 R37 L46 L34 Title Number Connectors 0 FaultCurrent Fireplace A C Simulation PowerCET Corporation Date June Size A Sheet 1 of 1 Rev 1.1 File: Fireplace AC Simulation Flexconnect.Sch m 6.00m 9.00m 12.0m 15.0m 18.0m 21.0m 24.0m 27.0m 30.0m Time

14 Direct Strikes Indirect Strikes Install at least minimal round ungrounded lightning protection roof penetrations system Preferably through Bond all metal services lightning protection system to main building and power system ground Bond all metal services to main building and power system ground Including gas pipes on building side of service All gas pipes, not just CSST! Including gas pipes on building side of service Evaluate benefit of earth-leakage relays on AC power system

15 Should there be a mandated minimum requirement for lightning protection in vulnerable structures, including residences? Do we need to define lightning withstand requirements for services in unprotected structures? (Proceed with caution!) Electrical lines & equipment as pipes & appliances Telephone & cable wires & equipment Water pipes

16 Include ALL gas pipe p systems in study Compare and contrast type and incidence of damage to rigid pipe systems to that of CSST Long reported lightning damage to rigid pipe systems not investigated t or understood d Joints, flex connectors or appliance valves? Identify relative importance of direct and indirect strikes tik for gas and electrical ti l fires Computer simulation very helpful Solutions may be different Would replacing CSST by rigid pipes improve overall fire incidence? Leaks & breaks much more significant cause of fires than lightning

a) Rating and Characteristics Disk Type 05D *Rated Rated Peak Varistor Clamping Typ. cap. Series Part No. Rated Voltage Energy Rated Power Current(8 2

a) Rating and Characteristics Disk Type 05D *Rated Rated Peak Varistor Clamping Typ. cap. Series Part No. Rated Voltage Energy Rated Power Current(8 2 ZR NR Series (Radial type) Disk type general use ZR type (Low voltage) and NR type (Medium/High Voltage) are for protection of electronics and control eqiupments from surge and noise. 1. Features Superior