Presentation on theme: "Electrical Awareness Arc Flash Overview & Qualifications By: Joseph F"— Presentation transcript:
1Electrical Awareness Arc Flash Overview & Qualifications By: Joseph F Electrical Awareness Arc Flash Overview & Qualifications By: Joseph F. Maida, PE August 18, 2009Fort Washington, PAP FOrlando, FLP FVisit us online at
2Joseph F. Maida, P.E. President Maida Engineering, Inc. Qualifications:BSEE – Drexel University – 1971MSEE – Drexel University (Power) – 1976Licensed Electrical ContractorOfficer - US Army Reserve 1971 – 1979Delmarva Power & Light Co.1972 – 1974Day & Zimmermann, IncMaida Engineering, Inc. – 1978 – PresentPE License – PA (NJ, NY & DE 1976)PE License – ID, MA, RI, NC, GA, FL, TX, IA, WV, AKand Alberta, CanadaLEED Accredited ProfessionalPA UCC Review and Advisory Council
3The National Electrical Code NFPA 70 Why the NEC®?The National Electrical Code NFPA 70- NEC® is the least amended modelcode in the world and no court in theUSA has faulted anyone for using thelatest version of the NEC®, even whenthe local code was not updated.12009 International Building Code hasincorporated the 2008 NEC®.1.
4NEC® Article 110.16 Flash Protection. Equipment such as switchboards, panelboards, industrial control panels, meter socket enclosures, and motor control centers that are in other than dwelling occupancies and are likely to require examination, adjustment, servicing, or maintenance while energized shall be field marked to warn “qualified persons” of potential electric arc flash hazards. The marking shall be located so as to be clearly visible to qualified persons before examination, adjustment, servicing, or maintenance of the equipment.
5NEC® Article 110.16 Flash Protection. FPN No. 1: NFPA 70E-2004, Standard for Electrical Safety in the Workplace, provides assistance in determining severity of potential exposure, planning safe work practices, and selecting personal protective equipment.FPN No. 2: ANSI Z , Product Safety Signs and Labels, provides guidelines for the design of safety signs and labels for application to products.
6NEC® Definition Panelboard. A single panel or group of panel units designed for assembly in the form of a single panel, including buses and automatic overcurrent devices, and equipped with or without switches for the control of light, heat, or power circuits; designed to be placed in a cabinet or cutout box placed in or against a wall, partition, or other support; and accessible only from the front.
7NEC® Definition Switchboard. A large single panel, frame, or assembly of panels on which are mounted on the face, back, or both, switches, overcurrent and other protective devices, buses, and usually instruments. Switchboards are generally accessible from the rear as well as from the front and are not intended to be installed in cabinets.
8Cabinets, Cutout Boxes, and Meter Socket Enclosures NEC® DefinitionMotor Control Center.An assembly of one or more enclosed sections having a common power bus and principally containing motor control units.ARTICLE 312Cabinets, Cutout Boxes, and Meter Socket Enclosures312.1 Scope. This article covers the installation and construction specifications of cabinets, cutout boxes, and meter socket enclosures.
9NEC® Article 409.2Industrial Control Panel. An assembly of two or morecomponents consisting of one of the following:(1) Power circuit components only, such as motor controllers, overload relays, fused disconnect switches, andcircuit breakers(2) Control circuit components only, such as pushbuttons,pilot lights, selector switches, timers, switches, controlrelays(3) A combination of power and control circuit componentsThese components, with associated wiring and terminals,are mounted on or contained within an enclosure ormounted on a sub-panel. The industrial control panel doesnot include the controlled equipment.
10NFPA 70 National Electrical Code®, 2008 Edition NEC® DefinitionNFPA 70 National Electrical Code®, 2008 EditionQualified Person. One who has skills and knowledge related to the construction and operation of the electrical equipment and installations and has received safety trainingto recognize and avoid the hazards involved.FPN: Refer to NFPA 70E®-2004, Standard for Electrical Safety in the Workplace, for electrical safety training requirements.
11Qualified Person. A qualified person shall be: NFPA 70 E Standard for Electrical Safety in the Workplace, 2009 EditionQualified Person. A qualified person shall be:Trained and knowledgeable of the constructionand operation of equipment or a specific workmethodTrained to recognize and avoid the electricalhazards that might be present with respect tothat equipment or work method.
12Qualified PersonNFPA 70 E Standard for Electrical Safety in the Workplace, 2009 EditionQualified persons shall be familiar with the proper use of:The special precautionary techniques,Personal Protective Equipment, includingArc-flash,Insulating and Shielding materials,Insulated tools and test equipment.
13Qualified PersonNFPA 70 E Standard for Electrical Safety in the Workplace, 2009 EditionA person can be considered qualified with respect to certain equipment and methods but still be unqualified for others.
14What is an Arc Flash?QuestionWhat is an arc flash?
15Arc FlashNFPA 70 E Standard for Electrical Safety in the Workplace, 2009 Edition – Appendix KArc-Flash - When an electric current passes through air between ungrounded conductors or between ungrounded conductors and grounded conductors.Exposure to these extreme temperatures both burns the skin directly and causes ignition of clothing, which adds to the burn injury.Arc-flashes can and do kill at distances of 3 m (10 ft).
16What is an Arc Flash?Arc-Flashes occurs when electricity flows through airbetween two (2) parts of a power circuit which are not atthe same voltage. The parts could be two (2) conductorsof different phases or a phase conductor and groundwhen the system is grounded.Arc flashes are more likely to occur where dust orhumidity are present or after an initial electrical shortbecause the vaporized particles provide low impedancemedia for current to flow between the phases or toground.Circuit breakers can explode if subjected to short circuitcurrents higher than their rating.
17What is an Arc Flash?Electricity can flow through any medium but cannot flowthrough a vacuum. Insulated materials present asignificantly high impedance but will conduct moreelectricity as the voltage increases.The majority of hospital admissions due to electricalaccidents are from arc-flash burns.Each year more than 2,000 people are admitted to burncenters with severe arc-flash burns. Almost 5 peopleevery day.Hazards are shown on the following slide.
18What is an Arc Flash? Flame Retardant Clothing Provides added protection from arc flash burns only!Electrical hazards are shown on the following slide.
20Electric Hazards Electric Shock – Electricity, resulting from electromagnetism, passing through the body cancause shock, cardiac arrest and internal burns.Arc-Flash Burns – Caused by air that can reach35,000° F. Hotter than the sun! Hot enough to vaporizemetal.Arc-Flash Blasts – Pressure waves that will throw a person away from the blast into walls and other equipment or off ladders and platforms.
21Electric HazardsIntense Light – Electric arcs can create light that willdamage eyes and may cause cataracts years later.Sound Waves – Noise levels that can cause temporaryor permanent loss of hearingProjectiles – Molten pieces of metal, vapors andshrapnel that can penetrate flame retardant clothing.
22Why now and not before?QuestionWhy now and not before?
23Why now and not before?Electrical power distribution system are being designedto generate and distribute more electrical energy.Personnel are more often exposed to recognizedelectrical hazards that could cause death or seriousphysical harm when “examining, adjusting, servicing,or maintaining electrical equipment”.Understanding of the arc flash hazards has increasedPersonal Protective Equipment (PPE) to prevent deathor severe injuries due to arc flash burns are available.
24Why now and not before?In the early 1980’s, Dupont developed flame retardantmaterial (Nomex).Ralph Lee, a Dupont Consultant, looking for usesfor the new flame retardant material, performed teststo determine the effect “heat” from an electric arc flashwould have on human skin.Ralph Lee developed the first set empirical equations \that could be used to calculate “incident energy”associated with an arc flash. The equations are still usedfor electrical power systems rated above 15,000 Volts.
25Why now and not before?Ralph Lee’s work showed that skin temperatures above96°C for .1 seconds or 6 cycles would result in incurable3rd degree burns and that at a temperature of 80°C theskin would be just curable or sustain a 2nd degreeburn.In 1998, Dougherty, Neill and Floyd developed the firstEquations which considered the effect of an arc in a boxversus an arc in open air. They developed the ArcHazard Classifications for flame retardant clothing. Theirequations are only for systems rated below 1,000 voltswith short circuit currents between 16,000 and 50,000amps. Equations are no longer utilized.
26Why now and not before?An IEEE industry group sponsored by petroleum andchemical industries developed the latest formulas thatare published in the IEEE Standard Guidefor Performing Arc Flash Calculations. It contains:Empirical formulas, derived from tests that can be used for 3Ø power systems up to 15,000 volts and for short circuit currents between 700 and 106,000 amps.Generally, no need for calculation on systems rated at 50 volts or less and on systems rated 240 volt and less that are derived from transformers rated less than 125 KVA. The guide does not state if this rating is for 1Ø and 3Ø transformers.
27Why now and not before?IEEE Standard Guide for Performing ArcFlash Calculations contains equations to calculateArc Flash Incident Energy based on:The short circuit current and duration of an arc thatconsider if the arc occurs within a box or in open airand if the power system is grounded or ungrounded.The short circuit current and the type of fuse or circuitbreaker, if the arc flash current will trip the circuitbreaker or blow the fuse.Incident Energy is the amount of energy impressed on asurface a certain distance from the source.
28Why now and not before?Occupational Safety and Health Administration (OSHA)was created in 1971.OSHA has worked with employers and employees toprovide a better working environment and since itscreation, has helped to cut workplace fatalities by morethan 60 percent and occupational injury and illness ratesby 40 percent while employment in the United States hasdoubled.1OSHA is part of the US Department of Labor.OSHA regulations are written under Title 29 of the Codeof Federal Regulations1.
29Why now and not before?On January 16, 1981, OSHA by reference incorporatedthe relevant requirements from Part 1 of then new NFPA70E as its electrical standard for general industry.The first substantial changes to NFPA 70E wereintroduced in 1995 and included a consensus standardon work practices and PPE application based ontheoretical modeling developed by Ralph Lee.Subpart S of 29 CFR Part 1910 was updated on August13, 2007 to reference NFPA 70E – 2000 and NFPA 70 –2002.
30Why now and not before? Calculations: Methods and Empirical Equations Developed by- Ralph Lee- IEEE Group (1584) – 2002Charts:Published within NFPA 70E – 2004CalculatorsProvided with IEEE 1584 – 2002Computer SoftwareDeveloped by SKM Systems Inc. and others
31Why now and not before? Calculation - IEEE Group (1584) – 2002 Empirical Formulas that consider for many variablesincluding short circuit current and time of exposure.Formulas specific to types of fuses.General Formulas that are based on fuse or breakersizes and available short circuit current.Defines when calculations are not required.Refers to Lee’s equations for systems greater than15,000 Volts.
32Why adhere to NFPA 70E Article 130 - “Working on or near live parts “? QuestionWhy adhere to NFPA 70E Article “Working on or near live parts “?
33Why adhere to NFPA 70 E OSHA Electrical Codes Non-mandatory Compliance Guidelines for Hazard Assessment and Personal Protective Equipment Selection Subpart I App BElectrical CodesNFPA 70 National Electrical Code®, 2008 EditionNFPA 70E Standard for Electrical Safety in the Workplace, 2009 Edition
34Why adhere to NFPA 70 E?With the addition of Article in the 2002National Electrical Code (NEC®), employersand employees have become aware of “electricarc flash hazard”.With the publication of NFPA 70E Standard forElectrical Safety in the Workplace, 2009 Edition,employers and employees have methods tosafeguard employees from at least one of the“electric arc flash hazards”.1: NFPA 70E Standard for Electrical Safety in the Workplace, 2004 Edition
36January 9, 2002Conclusion:Though OSHA does not, per se, enforce NFPA 70EStandard, 2000 Edition, OSHA considers the NFPAStandard a recognized industry practice.The employer is required to conduct hazardassessment in accordance with 29 CR (d)(1).If a arc flash hazard is present, or likely to bepresent, then the employer must select and requirethe employees to use the selected apparel.
37January 9, 2002 assessment, and select and require their Employers who conduct the hazard/riskassessment, and select and require theiremployees to use protective clothing andother PPE appropriate for the task, as statedin NFPA 70E 2000 edition, are deemed incompliance with the Hazard Assessment andEquipment Selection OSHA StandardU. S. Department of Labor – Jan. 9, 2002
38OSHA OSHA commonly uses the “General Duty Clause”, which is paraphrased below or as an alternateuses NFPA 70E or the NEC for citations related to arcflash incidents.General Duty Clause:Section 5(a)(1) of the Occupational Safety and Health Act requires an employer to furnish to its employees “employment and a place of employment which are free from recognized hazards that are causing or are likely to cause death or serious physical harm to his employees”.
39It is the right thing to do! Why adhere to NFPA 70 EAnswerIt is the right thing to do!
41What is and where are Arc Flash Label Required? Arc Flash LabelsQuestionWhat is and where are Arc Flash Label Required?
42Arc Flash Labels Arc Flash labels are required on equipment “such as” panelboards, switchboards, motor control centers,industrial control panels and meter sockets,Arc Flash labels are required on motor starters,variable frequency drives, plug-in bus duct, equipmentcontrol panels and building management panels if theycontain equipment that is 50 volts or higher and are“likely to require examination, adjustment, servicing ormaintenance while energized”.
43Arc Flash Hazard Labels The following arc flash label would suffice in meeting therequirements of NEC Article but may not sufficein meeting NFPA 70E – 2009.Equipment Labeling. Equipment shall be field markedwith a label containing the available incident energyor required level of PPE.1. NFPA 70E 2009
44Arc Flash Hazard Labels Arc flash labels can contain other information that canbe provided by the owner or employer to the employeewhen needed based on the system configuration at thetime
45Arc Flash Hazard Labels Limited Approach: The closest distance an unqualifiedperson can approach unless made aware of the dangerand accompanied by a qualified person.Restricted Approach: The closet distance a qualifiedperson can approach with proper PPE and tools.Prohibited Approach: The minimum distance to preventflashover and arcing.Flash Protection Boundary: The distance where theenergy from the arc will not cause a 3rd degree burn tounprotected skin.
47Electric Shock Hazard Analysis The following chart is the basis fordetermining electric shock boundaries. It iscontained within NFPA 70 E 2009.The actual chart covers voltage as high as800,000 volts.
48Shock Hazard AnalysisTable 130.2(C) Approach Boundaries to Energized Electrical Conductors or Circuit Parts for Shock Protection (All dimensions are distance from energized electrical conductor or circuit part to employeeLimited Approach Boundary Restricted ApproachNominal System Exposed Exposed Boundary; Includes ProhibitedVoltage Range, Movable Fixed Inadvertent Movement ApproachPhase to Phase Conductor Circuit Part Adder BoundaryLess than Not specified Not specified Not specified Not specified50 to ft 0 in ft 6 in Avoid contact Avoid contact301 to ft 0 in ft 6 in ft 0 in in.751 to 15 kV ft 0 in ft 0 in ft 2 in in.15.1 kV to 36 kV ft 0 in ft 0 in ft 7 in in.
49Arc Flash Hazard Analysis Arc Flash Hazard Analysis are performed to determine theArc Flash Hazard CategoryAndArc Flash Protection Boundary
50Arc Flash Labels analysis shall determine the Arc Flash Protection Arc Flash Hazard Analysis. An arc flash hazardanalysis shall determine the Arc Flash ProtectionBoundary and the Personal ProtectiveEquipment that people, within the Arc FlashProtection Boundary, shall use.1The Arc Flash Protection Boundary is thedistance at which a person is likely to receive asecond-degree burn.All parts of the body inside the Arc FlashProtection Boundary shall be protected.11. NFPA 70E -2009
51Arc Flash Hazard Analysis Arc Flash Hazard Category – Is used to definethe appropriate level of Personnel ProtectiveEquipment based on a working distance in frontof exposed electrical parts and circuits.Exposed - Capable of being inadvertentlytouched or approached nearer than a safedistance by a person. It is applied to electricalconductors or circuit parts that are not suitablyguarded, isolated, or insulated.1.1. NFPA 70E -2009
52calculations are as follows: Arc Flash Hazard AnalysisTypical working distances used for incident energycalculations are as follows:Low voltage (600 V and below) MCC and panelboards— 455 mm (18 in.)Low voltage (600 V and below) switchgear— 610 mm (24 in.)Medium voltage (above 600 V) switchgear— 910 mm (36 in.)Reference – NFPA 70E – 2009 Appendix D
53Arc Flash Hazard Analysis Almost all arc flash analysis require knowing theavailable short circuit current.Table 130.7(C)(9) within NFPA 70E can be usedin lieu of arc flash calculations if one know the maximumavailable 3 phase bolted fault current and theovercurrent device clearing time at and for theequipment.Part of the Table 130.7(C)(9) Hazard/Risk CategoryClassifications and Use of Rubber Insulating Gloves andInsulated and Insulating Hand Tools from NFPA 70E –2009 and selected footnotes for the Table are shown onthe following slides.
54Arc Flash Hazard Analysis Table (C)(9) from NFPA 70ETask Performed on Energized Equipment Hazard/Risk V-rated V-ratedCategory Gloves ToolsPanelboards and Other Equipment Rated 240 V and Below— Notes 1Perform infrared thermography and other non-contactinspections outside the restricted approach boundary N NCircuit breaker (CB) or fused switch operation with covers on N NCB or fused switch operation with covers off N NWork on energized electrical conductors and circuit parts,including voltage testing Y YRemove/install CBs or fused switches Y YRemoval of bolted covers (to expose bare, energized electricalconductors and circuit parts) N NOpening hinged covers (to expose bare, energized electricalconductors and circuit parts) N NWork on energized electrical conductors and circuit parts ofutilization equipment fed directly by a branch circuit of thePanelboard Y Y
55Arc Flash Hazard Analysis Footnotes from Table (C)(9) NFPA 70E -20091. 25 kA short circuit current available, 0.03 second (2cycle) fault clearing time.2. 65 kA short circuit current available, 0.03 second (2Generally, the short circuit current must be within theinstantaneous operating time of the circuit breaker or thecurrent limiting range of a current limiting fuse.
56Arc Flash Hazard Analysis Table (C)(9) from NFPA 70EBoth larger and smaller available short-circuit currentscould result in higher available arc flash energies.* If the available short-circuit current increases withouta decrease in the opening time of the overcurrentprotective device, the arc flash energy will increase.* If the available short-circuit current decreases,resulting in a longer opening time for the overcurrentprotective device, arc flash energies could alsoincrease.1.1. NFPA 70 E 2009
60Qualified PersonNFPA 70 E Standard for Electrical Safety in the Workplace, 2009 EditionQualified persons permitted to work within the Limited Approach Boundary of exposed energized electrical conductors and circuit parts operating at 50 volts or more shall, at a minimum, be additionally trained in all of the following:(1) The skills and techniques necessary to distinguish exposed energized electrical conductors and circuit parts from other parts of electrical equipment.
61Qualified PersonNFPA 70 E Standard for Electrical Safety in the Workplace, 2009 Edition(2) The skills and techniques necessary to determine the nominal voltage of exposed energized electrical conductors and circuit parts(3) The approach distances specified in Table 130.2(C) and the corresponding voltages to which the qualified person will be exposed.(4) The decision-making process necessary to determine the degree and extent of the hazard and the personal protective equipment and job planning necessary to perform the task safely
62Task Qualified PersonNFPA 70 E Standard for Electrical Safety in the Workplace, 2009 EditionAn employee who is undergoing on-the-job training and who, in the course of such training, has demonstrated an ability to perform duties safely at his or her level of training and who is under the direct supervision of a qualified person shall be considered to be a qualified person for the performance of those duties.Tasks that are performed less often than once per year shall require retraining before the performance of the work practices involved.
63Qualified PersonNFPA 70 E Standard for Electrical Safety in the Workplace, 2009 EditionEmployees shall be trained to select an appropriate voltage detector and shall demonstrate how to use a device to verify the absence of voltage, including interpreting indications provided by the device. The training shall include information that enables the employee to understand all limitations of each specific voltage detector that may be used.
64Qualified PersonNFPA 70 E Standard for Electrical Safety in the Workplace, 2009 EditionThe employer shall document that each employee has received the training required. This documentation shall be made when the employee demonstrates proficiency in the work practices involved and shall be maintained for the duration of the employee’s employment. The documentation shall contain each employee’s name and dates of training.
65NFPA 70EThe arc flash hazard analysis shall take into consideration the design of the overcurrent protective device and its opening time, including its condition of maintenance.Exception No. 1: An arc flash hazard analysis shall not be required where all of the following conditions exist:(1) The circuit is rated 240 volts or less.(2) The circuit is supplied by one transformer.(3) The transformer supplying the circuit is rated less than 125 kVA.
66Arc Flash Hazard Analysis Therefore, there is NO requirement to determine the following for AC power system rated below 240 Volts and above 50 volts originating from one transformer rated below 125 KVA.Arc Flash Protection BoundaryPersonal Protective EquipmentArc Flash Hazard Category
67Arc Flash Hazard Labels The following arc flash label would suffice in meeting therequirements of NEC Article and NFPA 70E –2009.
68Arc Flash Hazard Analysis NFPA 70 E defines Arc Flash Protection Boundary as follows”“When an arc flash hazard exists, an approach limit at a distance from a prospective arc source within which a person could receive a second degree burn if an electrical arc flash were to occur”
69Arc Flash Hazard Analysis NFPA 70E states the following:When an employee is working within the Arc Flash Protection Boundary he or she shall wear protective clothing and other personal protective equipment in accordance with All parts of the body inside the Arc Flash Protection Boundary shall be protected.
70Arc Flash Hazard Analysis IEEE 1584 – 2002 states the following relative to the use of PPE:“Where used, PPE for the arc-flash hazard is the last line of defense. The protection is not intended to prevent all injuries but to mitigate the impact of an arc flash upon the individual, should one occur. In many cases, the use of PPE has saved lives or prevented injury. The calculations in this guide will lead to selection of a level of PPE that is a balance between the calculated estimated incident energy exposure and the work activity being performed while meeting the following concerns:
71Arc Flash Hazard Analysis The desire to provide enough protection to prevent a second degree burn in all cases.The desire to avoid providing more protection than is needed. Hazards may be introduced by the garments such as heat stress, poor visibility, and limited body movement.”
72Arc Flash Hazard Analysis Without arc flash hazard analysis, which at a minimum requires the determination of the potential short circuit current and knowledge of the overcurrent protective device, short of testing, it is impossible to determine the Incident Energy.Therefore, without arc flash hazard analysis, the only information that can be included on label is the Required Level of PPE.
73Arc Flash Hazard Analysis NFPA 70 E does not define what is meant by the “Required Level of PPE” and it only defines methods that should be used for the selection of protective clothing and other personnel protective equipment for work performed within the Arc Flash Protection Boundary.
74“NO ARC FLASH HAZARD ANALYSIS WAS PERFORMED” Arc Flash Labels used to mark equipment for which arc flash hazard analysis has not been performed should indicate that the Level of PPE shown on the label are“DEFAULT”And“NO ARC FLASH HAZARD ANALYSIS WAS PERFORMED”An Arc Flash Protection Boundary need not be listed on the label.
75Arc Flash Hazard Analysis Considering that the hazard within the equipment could be equivalent to the hazard associated with changing a 120 volt. 100 watt light bulb, the requirement for PPE should depend on the type of equipment.Examples of Level of PEE that could be defined on a label, as determined by the employer, could include:
77Arc Flash Hazard Analysis Even if no Arc Flash Hazard Category is defined, Safety glasses or goggles and hearing protection should be required for any electrical work near exposed energized parts except for circuits originating from Class II power sources as defined by Section 725 of the NEC.
78Arc Flash Hazard Analysis Based on the selection of standard personalprotective equipment (PPE) levels (1.2, 8, 25,and 40 cal/cm2), it is estimated that the PPEis adequate or more than adequate to protectemployees from second-degree burns in 95percent of the cases.
80Arc Flash Hazard Analysis When incident energy exceeds 40cal/cm2 at the working distance, greateremphasis than normal should be placedon de-energizing before working on ornear the exposed electrical conductors orcircuit parts.
81Arc Flash Hazard Analysis What are the formulas?
82Arc Flash Hazard Analysis SKM Software Incident Energy Calculations:To determine the incident energy based on the arcingfault currents, first use empirically derived equationshown on the next slide to determine the log10 of thenormalized incident energy.The equation is based on data normalized for an arc timeof 0.2 second and a distance from the possible arc pointto the person of 610 mm.Afterwards convert from the normalized value using theequations on the subsequent slides.
83Arc Flash Hazard Analysis For Applications with system voltages below 1,000 Voltswhere:lg = the log10Ia = arcing current in kAK = for open air arcs; for arcs-in-a-boxIbf = bolted three-phase available short-circuit current (symmetrical rms) (kA) between 700 and 106,000 ampsV = system voltage in kVG = conductor gap (mm) (See Table on following slide)
84Arc Flash Hazard Analysis For applications with a voltage of 1,000 Volts or higher:where:lg = the log10Ia = arcing current in kAIbf = bolted three-phase available short-circuit current(symmetrical rms) (kA)V = system voltage in kVG = conductor gap (mm) (See Table on previous slide)
85Arc Flash Hazard Analysis Table D.8.2 Factors for Equipment and Voltage ClassesSystem TypicalVoltage Conductor Distance(kV) Type of Equipment Gap (mm) X-FactorOpen-air –0.208– SwitchgearMCCs and panelsCablesOpen-air>1– Switchgear –CablesOpen-air –>5– SwitchgearCables
86Arc Flash Hazard Analysis For all applications two (2) time durations are used to calculate the incident energy from the TCC Curve:“Use 0.85Ia to find a second arcing time. This second arc current accounts for variations in the arcing current and the time for the overcurrent device to open.Calculate the incident energy using both values (Ia and 0.85 Ia), and use the higher value.”
88Arc Flash Hazard Analysis Normalized Incident Energy Calculations:where:En = incident energy (J/cm2) normalized for time anddistancek1 = for open air arcs; for arcs-in-a-boxk2 = 0 for ungrounded and high-resistance groundedsystems= for grounded systemsG = the conductor gap (mm) (See Table on previousslide)
89Arc Flash Hazard Analysis Converting from Normalized Incident Energy:where:E = incident energy in J/cm2Cf = calculation factor= 1.0 for voltages above 1 kV= 1.5 for voltages at or below 1 kVEn = incident energy normalizedt = arcing time (seconds) from TCC CurveD = distance (mm) from the arc to the person (workingdistance)X = the distance exponent from Table onprevious slide
90Arc Flash Hazard Analysis Flash Boundary Calculation:The Flash Protection Boundary is the distance atwhich a person is likely to receive a second-degreeburn. The onset of a second-degree burn is assumedto be when the skin receives 5.0 J/cm2 or 1.2 cal/cm2of incident energy.The formula on the following slides is then used tocalculate the Flash Boundary Distance.
91Arc Flash Hazard Analysis Flash Boundary Calculation:where:DB = the distance (mm) of the Flash Protection Boundary from thearcing pointCf = a calculation factor= 1.0 for voltages above 1 kV= 1.5 for voltages at or below 1 kVEn = incident energy normalizedEB = incident energy in J/cm2 at the distance of the FlashProtection Boundaryt = time (seconds)X = the distance exponent from TableIbf = bolted three phase available short-circuit currentV = system voltage in kV
92Arc Flash Hazard Analysis Equations for estimating incident energy and FlashProtection Boundaries based on statistical analysis andcurve fitting of available test data was produced by anIEEE working group that produced the data from tests itperformed to produce models of incident energy.Based on the selection of standard personal protectiveequipment (PPE) levels (1.2, 8, 25, and 40 cal/cm2), it isestimated that the PPE is adequate or more thanadequate to protect employees from second-degreeburns in 95 percent of the cases.
93Arc Flash Hazard Analysis QuestionWhat can be done to reduce arc flash exposure?
94Arc Flash Hazard Analysis Design with Arc Flash in mindInstall smaller transformers112.5 KVA or less for 240 Volt and 120/208 Volt PowerSystems.CompartmentalizeUse individual secondary main circuit breakers that arein separate compartments or enclosuresRequire designs that have a maximum arc flash hazardincident energy of 8 cals/cm2.
95Arc Flash Hazard Analysis Design with Arc Flash in mindDo not oversize transformersKVASC = KVABASE / ZPUISC = (KVASC X 1000) / (VLL X 1.732)where ISC is in amperes, VLL is in volts, and ZPU isbased on the transformer rated KVAInstall new light sensing relays in medium voltageswitchgearApply overcurrent protective devices properlyUse circuit breakers with a maintenance instantaneoustrip switch.
96Arc Flash Hazard Analysis NFPA 70 National Electrical Code®, Many Editions110.9 Interrupting Rating.Equipment intended to interrupt current at fault levels shall have an interrupting rating sufficient for the nominal circuit voltage and the current that is available at the line terminals of the equipment.Equipment intended to interrupt current at other than fault levels shall have an interrupting rating at nominal circuit voltage sufficient for the current that must be interrupted.
97Arc Flash Hazard Analysis Arc Flash Hazards can be reduced by clearing the arcingfault faster by doing one of the following:Reduce Existing Pickup and Delay Settings whereverpossible.Enable Instantaneous Functions or Retro-fit withInstantaneous FunctionsReduce Fuse Sizes wherever possible.Use Current-limiting breakers or fuses for high arcingfault currentsAdd Differential ProtectionUse Temporary Instantaneous Trip Settings when workis being performedAdd optical sensors to trip when flash occurs
102Arc Flash Hazard Analysis Must consider all of the sources of power includinggenerators run in parallel and motors.Cannot account for services that only have overloadprotection and hence must be consider DANGEROUS.Must account for current limiting fuses operating withinthe current limiting range.Panelboards on the secondary of a transformer maypresent a very high hazard because the trip time of thetransformers primary protection is very long for a fault onthe secondary of the transformer.
104Arc Flash Hazard Analysis Arc Flash Hazards can be reduced by current limitingfuses.The clearing time for a current limiting fuse isapproximately ¼ cycle or second. The clearingtime of a 5 kV and 15 kV circuit breaker isapproximately 0.1 second or 6 cycles. This can bebroken down as follows: actual breaker time(approximately 2.0 cycles), plus relay operating time ofapproximately 1.74 cycles, plus an additional safetymargin of 2 cycles, giving a total time of approximately6 cycles.
105Arc Flash Hazard Analysis Arc Flash Hazards can be reduced by: Current Limiting Fuses and Cable Limiters
106Arc Flash Hazard Analysis Arc Flash Hazards can be reduced by: Current Limiting Fuses and Cable Limiters
107What is required to do an arc flash analysis? QuestionWhat is required to do an arc flash analysis?
108Arc Flash Analysis All analyses require the following: Accurate One Line DiagramsOvercurrent Device Equipment DataRealistic Short Circuit Current CalculationsArc Flash Calculations or Fault Clearing Time.A copy of NFPA 70E Standard for Electrical Safety inthe Workplace, 2004 Edition
109General arc flash study procedure1 Arc Flash AnalysisGeneral arc flash study procedure1Collect field data sufficient to perform a short-circuit and coordination study.Identify the possible system operating modes including tie-breaker positions, parallel generation, etc.Calculate the bolted fault current at each fault location.Calculate the arcing fault current flowing through each branch for each fault location.1. Arc Flash User’s Guide – SKM Power Systems, Inc.
110General arc flash study procedure1 Arc Flash AnalysisGeneral arc flash study procedure15. Determine the time required to clear the arcing faultcurrent using the protective device settings andassociated trip curves.6. Select the working distances based on system voltageand equipment class.7. Calculate the incident energy at each fault location.8. Calculate the flash protection boundary at each faultlocation.1. Arc Flash User’s Guide – SKM Power Systems, Inc.
111What are the overall benefits of an arc QuestionWhat are the overall benefits of an arcflash analysis?
112Why Perform Arc Flash Studies? Overall BenefitsWhy Perform Arc Flash Studies?Possibly prevent worker injury or deathAvoid or reduce litigation expense associated with anelectrical injury.Comply with codes and safety regulations (OSHA,NFPA, NEC) thereby avoiding citations and fines.Insurance requirementsBecause you can and you want to!
113Potential Benefits from an Arc Flash Studies? Overall BenefitsPotential Benefits from an Arc Flash Studies?Lesson injuries caused by an arc flash thus increasingworker safety and productivity.Minimize equipment damage and system down timeIncrease selectivity and hence the reliability of thePower Distribution System.Reduce the cost of future electrical projects.Reduce maintenance cost.
114Arc Flash Summary Proper Maintenance Define and follow necessary PM proceduresKnowledgeUnderstand the true dangers of electricityPlanningDevelop and follow a work plan that includesidentifying the arc flash hazardSTAY ALERT – STAY WELL – STAY ALIVE
115Questions? Joseph Maida 215.542.8700 x141 firstname.lastname@example.org Additional PresentationsARC FLASH OVERVIEWARC FLASH LABELS AND REPORTING REQUIREMENTSFR CLOTHING AND PPEPERFORMING ARC FLASH ANALYSIS VS USING CHARTS & TABLESUNDERSTANDING SHORT CIRCUIT AND ARC FLASH CALCULATIONSAN OVERVIEW IEEE 1584Joseph MaidaPresidentx141