ARC FLASH ANALYSIS Final Report Fall Semester 2010 Todd J Vedder Prepared to Partially Fulfill the Requirements for ECE402 Department of Electrical and Computer Engineering Colorado State University Fort Collins, Colorado 80523 Project Advisor: Dr. George Collins . 1 ABSTRACT I chose to do my senior design project on the topic of Arc Flash Analysis. The last few years have developed a great increase in the awareness of arc flash hazards. The analysis is applied to the overall electrical system of utility companies. The purpose of the study is to develop the best way to limit the amount of an arc flash a lineman can be exposed to while doing maintenance in the field. The National Electric Safety Code (NESC)-2007 Rule 410 states "employers shall ensure that an assessment is performed to determine the potential exposure to an electric arc for employees who work on or near energized parts or equipment. If the assessment determines a potential employee exposure, greater than 2 cal/cm2 exists, the employer shall require employees to wear clothing or clothing systems that have an effective arc rating not less than the anticipated level of arc energy." Electricity has proposed a serious hazard since its discovery by Benjamin Franklin. Why though, after over a hundred years, is the awareness of this hazard drawing so much attention? Arc flash analysis can propose a serious problem to utility companies. Most injuries that occur out in the field with lineman who work for power utility companies don’t result from electrocution, but rather from an arc flash. Over the years, these companies install protective devices all throughout a system. However, much effort, time and cost is involved to ensure these protective devices coordinate with other devices and are used to their best efficiency. These protective devices cannot be changed instantaneously to help arc flashes. One job of a consulting engineer is to calculate the arc flash incident energy at the point of contact. It then can be determined if the up line protective device is adequate, or if a recommendation to their protective devices needs to 2 be applied. When the first arc flash assessment was created there were a few key design questions that needed to be thought about: 1. What are the requirements? 2. How long do we have to design? 3. How will it be tested? 4. What recommended improvements can be made to client? This study has shown that a procedure can be implemented for utility companies. Steps and procedures were developed to perform an accurate arc flash analysis. However, is this the best method that can be used? How accurate are these calculations? Although it has been learned that there isn’t a 100% right solution, an accurate and reliable analysis can be created. Future work for this study will be to come up with the most accurate and reliable method. 3 Table of Contents Title Page.................................................................................................................................... 1 Abstract....................................................................................................................................... 2 Table of Contents..................................................................................................................... 4 List of Figures............................................................................................................................ 5 Introduction .............................................................................................................................. 6 Arc Flash Characteristics ...................................................................................................... 8 Why perform an arc flash assessment? ................................................................................................. 8 How might an arc flash occur? .................................................................................................................. 8 What are the results of an arc flash and why is it such a concern? ........................................... 9 Dependents of survivability from arc flash.......................................................................................... 9 Units of measurement................................................................................................................................... 9 Degree of burns..............................................................................................................................................10 Steps Necessary to Prepare for Arc Flash Analysis ....................................................10 Checklist Completed by Utility Company ......................................................................11 Checklist for arc flash studies for electric distribution systems...............................................12 How Does an Arc Flash Operate?......................................................................................15 Jacob’s Ladder Test ......................................................................................................................................15 Incident Energy Calculations IEEE 1584........................................................................16 Arc Flash Analysis Calculations ........................................................................................17 Improvements/Recommendations .......................................................................................................18 Official Calculation Spreadsheet ......................................................................................19 Arc Flash Boundary ..............................................................................................................21 Arc flash boundary formula......................................................................................................................22 Economic Tradeoff ................................................................................................................22 Future Changes.......................................................................................................................24 Conclusion................................................................................................................................25 Appendix ..................................................................................................................................26 Official calculation spreadsheet..............................................................................................................27 Budget analysis ..............................................................................................................................................28 Definitions ........................................................................................................................................................29 Recommendation for project continuation .......................................................................................32 References........................................................................................................................................................33 Acknowledgements ......................................................................................................................................34 4 List of Figures & Tables Fig 1: Power System Flow Layout ................................................................. 7 Fig 2: Jacob’s Ladder Test............................................................................ 15 Fig 3: Existing System Model ...................................................................... 17 Fig 4: Hazard Category as a Function of Incident Energy Table ................. 18 Fig 5: Recommended System Model............................................................ 19 Fig 6: Variable Factors For Different Types of Equipment ......................... 20 Fig 7: Fuse vs. Recloser Economic Cost ...................................................... 22 Fig 8: Fuse vs. Recloser Payoff Chart .......................................................... 23 Fig 9: Blank Calculation Spreadsheet........................................................... 27 Fig 10: Time Current Curve ......................................................................... 30 5 Introduction: With the development of technology, society has seen an increase in benefits. Things have become easier, more precise, and satisfying. Technology has brought a significant increase to the world of power and electricity. Arc Flash injuries have been a concern since the discovery of electricity. So why is it that these hazards are only drawing high attention over the past few years? A primary reason is the high increase in magnitude and volume to electricity being generated over the world. Many companies are requiring more power and higher voltages. Probably the most important reason is the increased need to perform work on energized equipment. If a line has to be de-energized in order to perform maintenance, then buildings and homes must go without power. This provokes not only a loss in revenue for the Power Company, but can upset many customers. The exponential increase in technology has made it difficult for companies to keep up with training standards to keep employees aware of the risk of arc flash hazard. The last important reason arc flash hazards have become a concern is the increase in liability from lawsuits. Companies are adopting procedures and methods relating to arc flash hazards not only to provide safety to their employees, but the company as well. The focus of this study will be on the distribution side of the power utility system. This is the final stage of delivery of power to end consumers. A distribution system carries power from the transmission system and delivers it to its consumers. The diagram below shows how power is developed starting at a power plant, traveling to transmission lines where it feeds into a power substation. The power substation downsizes the voltage (typically from 69k volts to 12.47k volts). Here power is traveled 6 throughout the town until it reaches the transformer drum and downsized (typically from 12.47k volts to 480 volts). Here power is supplied to houses and commercial industries. Figure 1: Power System Flow Layout According to the NESC an arc flash is the result of a rapid release of energy due to a short circuit between two conductors, or conductor and ground. The arc flash is not the direct short between two conductors but rather it is the arc created in the air after a short circuit occurs. During an arc the air acts as a conductor. This develops problems for utility companies who have lineman working on energized equipment. Majority of accidents that occur in power utility companies are not from the result of electrocution, but instead from an arc flash. Why is an arc flash important to understand? It can kill you! 7 Arc Flash Characteristics Why perform an arc flash assessment? The following statement comes from Rule 410A3 of the National Electric Safety Code: “Effective as of January 1, 2009, the employer shall ensure that an assessment is performed to determine potential exposure to an electric arc for employees who work on or near energized lines, parts or equipment.” In the event that an employee exposure is greater than 2 cal/cm2 exists, the employer shall: A. Perform a detailed arc flash assessment to determine the effective arc rating of clothing or clothing system to be worn by employees working on or near energized lines, parts, or equipment at voltages 50-800,000 volts. The arc flash assessment shall include a calculation of the available short circuit current, time it takes for arc to clear, and the distance from arc to employee. B. Require employees to wear clothing or a clothing system with an effective arc rating not less than the anticipated level of arc energy. Unless flame resistant, when exposed to an electric arc or flame, clothing or a clothing system made from acetate, nylon, polyester or polypropylene shall not be worn. How might an arc flash occur? Arcing fault current can be easily created through poor electrical contact, failed insulation and carelessness. There is no way to eliminate arc fault hazard when working on an energized line, but we can decrease the amount of energy dissipated from an arc and the injury it can create to a lineman. 8 What are the results from an arc flash and why is it such a great concern? Injury is the primary reason we are focused on studying the system analysis of arc flashes. Temperatures up to 35,000 degrees Fahrenheit are created at the point of contact (4 times greater than the sun)! Upon contact molten metal is blasted forward from terminal material resulting in serious burns to victims. A large shockwave is produced that could throw a human off ladders or against walls. The light developed from a flash contains UV rays that can cause blindness. The sound pressure from a blast is enough to cause serious ear injury. If an arc occurs and a worker is in close proximity, the survival rate of the worker is dependent upon the following: Dependents of Survivability from Arc Flash 1. Clearing time- time of the over current protective device to operate. It determines how fast the device will create an open in the circuit and clear arc fault. 2. Magnitude-amount of arc fault current created. 3. Distance-length worker is away from point of contact (arc). 4. Personal Protective Equipment (PPE)-clothing material worker is wearing to protect him or herself. Units of Measurement There are two different units in measuring an arc flash. A joule is a standard unit of energy in general scientific application. 1 joule = 1 watt/second of dissipated energy. A calorie is a unit of heat and is a form of kinetic energy. It takes 1 calorie of heat energy to raise one gram of pure liquid water 1 degree Celsius. 1 calorie = 4.1868 joules 1 joule = 0.2388 calorie 9 Degree of Burns 1st degree burns: Affects outer layer of skin. It can be painful, but it is usually not permanent or life threatening. 2nd degree burns: Causes tissue damage. Creates blistering to the skin. It also destroys outer skin layer. 3rd degree burns: Causes complete destruction of skin. Small areas may be recovered through skin graphs. Arc flash protection is aimed to limit the injury to no more than a 2nd degree burn. Even though this is the goal for a system study, it can still cause a serious burn. 1.2 cal/cm2 is the threshold of 2nd degree burns. Steps Necessary to Prepare for an Arc Flash Analysis 1. Review the existing data a. Existing sectionalizing/fault current study b. Substation size/impedance/voltage/grounding configurations c. Source impedance of transformers d. Breaker/recloser settings 2. Collect new data (per substation area) a. Update source impedance b. Update substation size/impedance c. Update engineering software model d. Locate large 3 phase pad mounted transformer locations 10 i. Since pad mount transformers are in an enclosed area they produce more energy to a lineman compared to an open aired transformer where the energy is dissipated to open air. e. Update all recloser/breaker settings, TCC opening/closing times etc f. Fuse information: manufacturer, type, size/rating, speed (standard/slow), and current limit of fuse. g. Relays: Are they electronic or mechanical? Need type, manufacturer, settings, current transformer rating, and opening/clearing times. h. Transformer Data: kVA rating, primary/secondary voltage, impedance percentage, connection configuration (Y-Y or Delta-Y) i. Engineering model: Need all circuit configurations, wire size/section lengths, operating voltages, and circuit configuration 3. Determine Personal Protective Equipment Settings (see above Arc-flash Hazard Category table). 4. Conduct an Analysis Report: a. Report should contain data collected from utility companies including: Substation names, transformer sizes, primary/secondary voltages, working distance, available bolted and arcing fault current, incident energy level, and risk category for each scenario. Checklist completed by utility company: The following is a series of questions that a consulting firm is to ask utility company. Questions answered are taken into consideration when performing arc flash 11 assessment. The checklist must be thorough and answered as accurate as possible to have the most precise assessment. CHECKLIST FOR ARC FLASH STUDIES FOR ELECTRIC DISTRIBUTION SYSTEMS A. Current utility safety procedures and PPE clothing 1. Clothing, a. What is the calorie rating of the shirt/pants typically worn by employees? b. When do line workers use eye protection? i) When do they wear safety glasses? ii) When do they wear safety glasses and a face shield? c. Hearing protection. When is it used? d. When do line workers use special arc flash protection clothing beyond the normal fire retardant clothing? 2. Hot line work a. When working on an energized primary line, does the utility set the substation or closest circuit reclosers/breaker to non-reclose? b. What are the minimum pickup settings and what curves are used on the recloser/breaker for the non-reclose operation? c. Working distances i) Rubber gloving, 17 inches to chest? d. Hot sticks, 4 feet? e. When is line work done energized with i) Rubber gloves? ii) Hot sticks? f. Secondary work, when is the 277/480 or 480 volt work done while the 480 volts is energized: i) Visual checking, no contacts? ii) Voltage measurements? 12 iii) Making connections? iv) Replace equipment? v) Metering work, change meters? B. Transmission line data 1. Voltage(s) 2. Source substation transformer base kVA and impedance 3. Conductor size(s) 4. Type of construction 5. Is work done while a transmission line is energized? If yes what type of work? a. Installing and removing grounds b. Phase checking, voltage measurements c. Inter-setting a new pole d. Changing insulators e. Replacing an existing pole f. Others explain. C. Substation 1. Primary voltage(s). 2. Secondary voltage(s) 3. Transformer MVA capacities and impedances. 4. Available fault currents 5. Type of transformer and secondary bus protection a. Fuses (type, speed and size) b. Relaying. i) Type and settings, ii) Differential, does it protect only the transformer or does it also protect the secondary bus up to the load side of the circuit breakers? 6. Work practices within the substation while substation is energized. a. Visual inspections, no electrical contacts. b. Installing and removing grounds. c. Primary switching, pull or replace primary fuses? 13 d. Low side: change arresters, circuit breaker by-pass, reclosers/breakers and isolating switches? e. Energized work practices. i) Working distances from energized equipment. ii) Current PPE, calorie rating, face and eye protection iii) Are changes feasible? D. Primary distribution lines, voltage(s) i.e. 12.47/7.2 kV or 24.9/14.4 kV? 1. Recloser types and settings. i.e. “L,” “VWVE,” “E”? 2. Primary fuse type and sizes used to protect laterals and underground risers. 3. Does the utility have a policy of setting the reclosers to non-reclose while working on energized primaries? a. Substation b. Line reclosers c. Alternate fast trip capability? 4. Voltage and phase checking with hot sticks? 5. Energized work procedures a. Rubber glove? b. Hot sticks? c. When is insulated cover up used? 6. Pad-mounted primary switchgear including pad-mounted transformers. a. Work practices, hot sticks for removing and connecting load break elbows? b. Opening and closing pad-mounted load break switches? c. Working distances? 7. Distribution transformers a. Pad-mount 277/480 volt. i) Size(s) ii) Impedance(s) iii) If riser fuses protect pad-mount transformers, type & size? iv) Do the transformers have bayonet fuses, if yes type and size. b. Overhead three-phase 277/480 banks 14 i) Size(s) ii) Impedances iii) Fusing standards, type and size 8. Metering for 277/480 volt services. a. Work energized or de-energized? b. To check voltage or make amp measurements? c. Replace meter. d. Check CT ratio. Conductor, type, size and length to meter. How does an arc flash operate? Jacob’s Ladder Test Figure 2: Jacob's Ladder Test http://sub.allaboutcircuits.com/images/quiz/00561x01.png The Jacob’s Ladder is a device, which is used to show how electric sparks operate. The figure above shows a Jacob’s ladder, more formally known as a high voltage-traveling arc. This is a device designed to produce a continuous train of large sparks, which rise upwards. The top of the figure shows two wires that start close together and gradually diverge away from each other to form the “V” shape. 15 The high-voltage transformer creates a potential difference between the vertical wires. The electrons repel from each other causing them to jump from one wire to try and get as far apart as possible. When high enough voltage is applied to the bottom of the wires a spark forms across them, which quickly changes into an electric arc. Air breaks down around 30 kV/cm factoring in humidity, temperature etc. Besides the anode and cathode voltage drops, the arc behaves as a short circuit, drawing as much current as the electrical power supply can deliver, and the heavy load dramatically reduces the voltage across the gap. Since hot air rises, the spark continues to climb until the voltage provided by the power source is not enough. It then dies and a new spark starts at the bottom again. A spark can jump between two conductors, which relative to each other can carry a high voltage. The gases in the atmosphere are pulled apart, at an atomic level, by the high electric fields generated between such conductors. The air can conduct, just like a wire, but with a few side effects like light and sound (like thunder and lightning but on a much smaller scale). Incident Energy Calculations (IEEE1584): To determine the incident energy at the worker location: • Incident Energy = 4.184 x Cf x Ea[(t/0.2) x (610x/Dx)] • Log(Ea) = k1 + k2 + [1.081 x (log(Ia))] + 0.0011G • Ea = 10(Log Ea) • Ea is normalized for 0.2 sec. and 610 mm gap. For actual Incident energy……….. • Incident Energy = 4.184 x Cf x Ea[(t/0.2) x (610x/Dx)] Ia=Arcing fault current in kA G = conductor gap in millimeters (mm) K1=Open air or in a box factor K2 = ground/ungrounded factor 16 Cf = calculation factor t = arcing time in seconds X = Distance exponent Arc Flash Analysis Calculations: The following illustration shows a Milsoft model being used to calculate the incident energy that a lineman could be exposed to. Figure 3: Existing System The previous example shows the calculations for distribution transformers. The substation is providing 12.47k volts to a distribution transformer. Here the 12.47k volts are stepped down to 480 volts, which is supplied to a commercial building. A 30-amp fuse is currently protecting the transformer since the current carrying capacity of transformers is 23.2 amps. The bold black circle simulates a lineman working on the secondary side of transformers. Power remains constant through a transformer. Since the equation for power is P=volts x amps, if the voltage decreases the amperage must increase providing more danger to the lineman. The calculated data box shows results of 17 what happens if a lineman creates a short circuit while doing maintenance. With a distance of 431.8mm (17inches) between point of contact and worker’s face/body and arcing fault current of 5.027k amps, there are 57.34 joules (13.704 cal/cm2) of energy exposed to the lineman. The following chart shows the hazard category levels as a function of incident energy. 13.704 cal/cm2 has a risk factor of 3. Figure 4: Hazard Category as a Function of Incident Energy Improvements/Recommendations After reviewing the chart of “Hazard Category as a Function of Incident Energy”, we can see that this provides a risk category of 3. If the goal is to try and maintain a category of 2 or lower some recommendations are applied. The following illustration shows transformers being protected by a 70-4H hydraulic recloser. 18 Figure 5: Recommended System It can be seen that the working distance and arc fault current remain constant. However, the incident energy and clearing time of reclosers have decreased substantially, providing incident energy levels of 18.59 joules (4.4441cal/cm2). After reviewing the chart we can see that this puts us at a risk category of 2. Reclosers act differently than fuses in that they can operate on an instantaneous setting where as a fuse has melting time. Reclosers are much more precise in reactance time and helps reduce incident energy levels extremely. Official Calculation Spreadsheet: The appendix of this report on page 27 shows a blank calculation spreadsheet used to insert the incident energy calculations along with necessary information. The spreadsheet is designed to be a quick reference to locate what the incident energy calculation is at a particular spot. The following is a brief description of what each column heading represents 1-18 respectively. 19 1. Sub - Lists substation short circuit calculation is taken from. 2. Item of Interest – Indicates what piece of equipment the calculation is taken from. Typically load side of transformer indicating size and location on the system. 3. Dist. From Sub (Miles) – Distance calculation is taken from substation. 4. Protective Device – Lists type and size of protective device that is up-line from calculation. Generally device will be fuse or recloser. 5. Phase – Generally listed as three phase. However if single phase, which phase is being concentrated on, A B or C phase? 6. Primary Voltage – What is the source side voltage of transformer 7. Service Voltage – What is the load side voltage of transformer 8. Bolted Fault Current – Short circuit current rating creating shortest path between two conductive materials. 9. Arc Fault Current – Arcing current formed from bolted fault current but uses air as the conductor. 10. Gap (mm) – Distance between two terminals of transformer measured in millimeters. Following table lists the typical distances. 11. Gap (in) – Distance between two terminals of transformer measured in inches. Typical bus distance, in Distance Equipment class mm X-Factor Open air 10-40 2.000 Low-V switchgear 32 1.473 15 kV switchgear 152 0.973 5 kV switchgear 104 0.973 Low-V MCCs and panel boards 25 1.641 Cable 13 2.000 Figure 6: Variable factors for different types of equipment 20 12. Distance Factor – Calculation factor for different scenarios. Previous tables list these as the “x-factor”. 13. % of max – Use 85% of fault current when during calculations on equipment that is protected by fuses. This is to give more of a worst-case scenario. The lower the current the longer the fuse will take to clear, since fuses are dependent on time. 14. Arc Clearing Time – time it takes for up-line protective device to clear short circuit measured in seconds. 15. Oper. Dist (in) – distance from arc to workers face/body measured in inches 16. J/cm2 – Incident energy calculated in joules per centimeter squared. This is 4.168 times greater than calories per centimeter squared. 17. Cal/cm2- Incident energy calculated in calories per centimeter squared 18. NESC level – National Electric Safety Code category level to determine what type of personal protective equipment to wear. Levels are based on a 0-4 scale. Arc Flash Boundary A perimeter must be set up around an area where maintenance is being done on energized equipment. The perimeter is measured as distance from energized part. Only qualified personnel must cross this boundary. Unqualified personnel may not cross boundary unless escorted by a qualified person. The same PPE is required in this boundary as if direct contact is made with live part. This is done to maximize safety and minimize possible arc flash. 21 Arc Flash Boundary Formula Dc=[2.65 x MVAbf x t]1/2 • Dc = Distance in feet of person from arc source based on limit of having incident energy of 1.2 cal/cm2 • MVAbf = Bolted fault current in Mega volts at location of maintenance. • T=time of arc exposure measured in seconds Example: What is the flash protection boundary for the secondary side of a 3,750kVA transformer rated at 480 volts line to line with short circuit current of 50,000 amps and clearing time of 0.1 seconds (6 cycles)? The utility company provides this information. 6 cycles is the standard instantaneous time of protective device to operate. MVAbf = [50,000amps x (1.74)1/3 x 480volts] = 41.57 MVAbf Dc = [2.65 x 41.57 MVAbf x 0.1sec] ½ = 3.319 feet Economic Tradeoff As previously stated, it shows no question that a company might want to install a recloser into their system to help the efficiency of arc flash hazards. However, is the economic tradeoff worth the safety? The costs of fuses and reclosers, along with their labor charges, are listed in the table below. FUSE RECLOSER Material Cost(per phase) Material Cost(all three phases) Cost of Installation $150 $450 $150 $1,500 $4,500 $450 Figure 7:Fuse vs Recloser Economic Cost 22 Total $700 $4,950 Fuse vs. Recloser These values do not include the cost to maintain these protective devices. Reclosers have the capability to reclose on their own in the event a fault is cleared, such as a tree branch falls on a power line. A fuse would stay open until a maintenance crew came out to replace the fuse. Also, a recloser has the capability of being installed further up line from the transfer and therefore is able to protect possibly 3 or 4 transformers. So in this scenario we have one recloser protecting 4 transformers vs. 4 transformers being protected by 4 different fuses. The initial cost of installing three reclosers (one recloser per phase) with labor is approximately $5000. The cost of installing three fuses (one fuse per phase) with labor is approximately $700. Since reclosers can reclose on their own, no replacement or labor charges were affected after initial installation. Figure 8: Fuse vs Recloser Payoff Chart It can be seen that in order to have the recloser payoff the economic value of the fuses, the fuses would have to blow and be replaced after 7 times. Utility companies 23 have to determine if this is feasible. If a company is looking to improve their system through arc flash incidents, then yes, they might want to invest their money by installing reclosers. If the company wants to invest their money in other areas of the industry, then they may want to pass on this opportunity and replace the fuses. Future Changes Changes are currently being made to the National Electric Safety Code (NESC) Rule 410 that effect arc flash assessments. Some future changes are as follows: 1. The original intent of Rule 410 was to limit the possibility of technicians or the general public to contact two metallic surfaces that may be at different voltage levels and thus receive an electric shock. It is appropriate that the proper rule be presented as a mandatory “shall” requirement, and not as a present “should requirement”. 2. “For work below 1000 volts, applicable rules required by this part and engineering controls shall be utilized to limit exposure. In lieu of performing an arc hazard analysis, clothing or a clothing system with a minimum effective arc rating of 4 cal/cm2 shall be required to limit the likelihood of ignition. 3. One except to the clothing rule is if the clothing that is required by arc flash assessment produces additional and greater hazards than the possible exposure to the heat energy of the electric arc, then clothing with an arc rating or arc thermal performance value less than that required by the rule can be worn. 24 Conclusion: An arc flash assessment for a power systems utility company can be a complicated process. For recommendations, much more detailed analysis must be provided that is out of the scope of this report. Conducting this report I have learned that you cannot just jump into a project and focus only on the next step. As an example when recommending reclosers, the decision can’t be made just on the arc flash assessment side, but affects on the system as a whole need to be considered. Every protective device in the system needs to coordinate with each other in relation to timing. You don’t want protective devices upline clearing before protective devices down line do. This will cause unnecessary outages and provide no purpose for the down line protective devices. I also learned that although it may be easy to consider installing reclosers numerously throughout the system, the economic tradeoff is not worth it. A majority of the injuries that occur in power utility companies are not the result of electrocution, but rather from an arc flash! This is a new problem to the electrical engineering world but something that needs to be resolved or else more injuries will occur. Results from improvements suggested by an arc flash analysis will not only save lives, but also save a company from economic tragedy in the event of lawsuit or equipment damage. Once my report is finally completed, I plan to provide a reliable method to conduct an arc flash analysis; a benefit not only to myself, but also to the power industry as a whole. 25 Appendix 26 Figure 9: Blank Calculation Spreadsheet 27 Budget Analysis Software Budget: 1. Milsoft/Windmil i. Initial Cost = $15,000 per license ii. Annual Fee = $1,200 per license 2. ArcPro i. One time fee = $1,500 per license 28 Definitions Arch Flash Hazard- Dangerous condition associated with the release of energy caused by an electric arc. Arc Fault Current- Fault current flowing through electric arc plasma. Available Fault Current- The electrical current that can be provided by the serving utility and facility-owned electrical generating devices and large electric motors, considering the amount of impedance in the current path. Bolted fault current- Electrical contact between two conductors at different potential in which the impedance or resistance between the conductors is essentially zero. Arc Fault Current- Current that flows from a conductor to either ground or another conductor when energized, due to an abnormal condition. Flash Hazard Analysis- Method used to determine the risk of personal injury as a result of exposure to incident energy released from an electrical arc flash. Incident Energy- Amount of energy impressed on a surface, a certain distance from the source, generated during an electrical arc event. Shock Hazard- Dangerous condition associated with the possible release of energy caused by contact or approach to energized parts. Voltage (nominal) - Nominal value assigned to a circuit or system for the purpose of conveniently identifying its voltage class. Working Distance- Distance between possible arc points and the head and body of the worker positioned in place to perform the assigned task 29 Arc Gap- Distance between two contacts where possible arc(s) can arise. When high voltage is applied to the gap, an arc has the possibility of crossing between two conductors. Clearing Time- Amount of time it takes for an over current protection device to clear once fault occurs and protective device settings are past their settings. An example is below. Figure 10: Time Current Curve The previous graph shows a Time Current Curve (TCC) chart. It denotes the time (located on “y” axis) in seconds and the current amount (located on “x” axis) in amperes. 30 The graph shows the curve settings of an 85 “T” fuse. Notice that as the fault current increases, it takes less time for a fuse to clear. The bottom line of the black curve indicates the time a fuse begins to melt. After a short amount of time, at same fault current, the top line is reached. This line indicates the complete melting time of fuses for which circuit is open and arc flash has diminished. 31 Recommendations for Project Continuation Arc flash events are a serious hazard that can potentially put people in life threatening situations. National Electric Safety Code and OSHA are in the process of introducing changes to electrical safety rules that require electric utilities to perform arc flash hazard analysis of all electric facilities operating at and above 1000 volts. In 2008, EPRI started a supplemental project to research arc flash issues with over 20 utility members. This effort uncovered new areas where further research could improve arc flash protection approaches. 2008 unveiled that there is still much concern for arc flash when network systems were the main topic for worry when most utilities were sought the need for future improvements. Open-air medium voltage systems, after recent testing and analysis of monitoring data revealed several insights on arc characteristics. One of the findings is that realistic arc lengths under work-type scenarios are longer than the 2 to 6 inch lengths assumed in the National Electric Safety Code table 410-1. Better personal protective equipment is still needed and requires testing to help understand the best assessment approaches and protection options for specific utility equipment. As arc flash assessments can still be conducted and used as professional studies, there are still improvements that can be incorporated to achieve improved arc flash analyses. 32 References T2G Technical Training Group “www.brainfiller.com” Jim Phillips, P.E. ESC Engineering, Jerry Hager, P.E. IEEE1584 Based Arc Flash Calculator and Warning Label Creator, http://www.arcadvisor.com/arcflash/ieee1584.html Electrical Solutions with Energy and Integrity “Mayer Electric,” http://mayerelec.com/arc.htm Arc Flash Information Resource Center: IEEE 1584 Arc Flash Calculations, http://www.arcflash.me/ieee-1584-arc-flash-calculations.php 33 Acknowledgements I would like to acknowledge the following individuals with their help in this project: Dr. George Collins – Professor Colorado State University, Electrical and Computer Engineering – http://www.engr.colostate.edu/ece/facultystaff/facultypage.cfm?pass=9 Gerald H. Hager - ESC engineering: Vice President, Senior Engineer P.E. 34