SKM Power*Tools for Windows

SKM Power*Tools for Windows
Electrical Power Systems Design and Analysis Software PTW is an Integrated Software Tool for Electrical Engineers – for You

“I introduced into my ears two metal rods with rounded ends and joined them to the terminals of the apparatus” “I introduced into my ears two metal rods with rounded ends and joined them to the terminals of the apparatus”

a crackling and boiling”
“At the moment the circuit was completed, I received a shock in the head – and began to hear a noise – a crackling and boiling” “At the moment the circuit was completed, I received a shock in the head – and began to hear a noise – a crackling and boiling”

“This disagreeable sensation, which I feared might be dangerous, has deterred me so that I have not repeated the experiment” “This disagreeable sensation, which I feared might be dangerous, has deterred me so that I have not repeated the experiment”

Alessandro Volta Volta made this statement in the early 1800s – a shocking experience so to speak But from the statement – no arc flash was experienced – otherwise we might not have Volta’s statement

Arc Flash Today we are going to work with Arc Flash
In this example, an arcing fault occurs in a distribution substation. The protection doesn’t clear the fault for several seconds, resulting in catastrophic damage. Fortunately no one was present within the substation flash boundary area when the arcing fault occurred.

What is the purpose of an arc flash study?
To determine the protective clothing requirements for persons working on live equipment Living with what one has and minimize the risks Designing electrical safety into the power distribution design Because I am a person of Iron And a full-fledged masochist Thank you and Have Great Afternoon!

Why Integrated Software For Arc Flash Evaluation?
Why use integrated software, even for Arc Flash?

Why Integrated Software?
We all love Microsoft (we own stock)? I can’t find that NFPA book to do it by hand ? I lost my calculator? The boss wanted the PPEs yesterday? (Humor voice) We all love Microsoft?? I can’t Find my NFPA book? I lost my calculator? You want the PPE labels WHEN?

Why Integrated Software?
In Real Estate, it’s location In Arc Flash, it is Accuracy You have heard in real estate – it’s location, location, location In Arc Flash, it’s accuracy, accuracy, accuracy, Garbage in - Garbage out Rule of thumb question - rule of thumb answer

Standards Related to Safety
NEC NFPA 70E IEEE Std. 1584 Also we have OSHA & The Occupational Health and Safety Act and its regulations More specifically, the arc flash labeling requirements in NEC article , arc flash calculation requirements in NFPA 70E, and expanded calculation methodology and procedures in the IEEE 1584 standard. We will also review some examples, and explore important concepts and issues.

Electrical Hazards Shock Flash Burns Blast Pressure
Arc Flash and Shock hazards have been around since the first person was electrocuted in 1893. What has changed is the recognition for the safety of those who must work around and with electricity.

NEC® 2002 Article Flash Protection. Switchboards, panelboards, industrial control panels, and motor control centers in other than dwelling occupancies, that 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. Reprinted from NEC® 2002 NEC Article requires arc flash warning labels. The article states: Flash Protection. Switchboards, panelboards, industrial control panels, and motor control centers in other than dwelling occupancies, that 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.

This picture demonstrates minimum labeling requirements based on the 2002 NEC. The labels state only that a flash hazard exists.

NEC® 2005 Article 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 Z535.4 – 1998, Product Safety Signs and Labels for application to products. Reprinted from NEC® 2005 NEC Article requires arc flash warning labels. The article states: Flash Protection. Switchboards, panelboards, industrial control panels, and motor control centers in other than dwelling occupancies, that 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.

Requirements for safe work practices Addresses hazards: Shock
NFPA 70E Requirements for safe work practices Addresses hazards: Shock Arc Flash Requirements for shock and arc flash boundaries Requirements for personal protective equipment Incident Energy and flash boundary calculations (<1000V, 5kA-106kA) NFPA 70E Standard for Electrical Safety Requirements for Employee Workplaces 2004 Edition NFPA70E is the standard for electrical safety requirements for employee workplaces. Originally requested by OSHA the National Fire Protection Association developed 70E as a standard for electrical safety. This document provides requirements for: electrical safe work practices electrical shock and arc flash boundaries and proper personal protective equipment This standard addresses safe work practices for both qualified and unqualified workers.

NFPA 70E 130.3 Flash Hazard Analysis. A flash hazard analysis shall be done in order to protect personnel from the possibility of being injured by an arc flash. The analysis shall determine the Flash Protection Boundary and the personal protective equipment that people within the Flash Protection Boundary shall use. Requirements for safe work practices NFPA 70E Standard for Electrical Safety Requirements for Employee Workplaces 2004 Edition NFPA70E is the standard for electrical safety requirements for employee workplaces. Originally requested by OSHA the National Fire Protection Association developed 70E as a standard for electrical safety. This document provides requirements for: electrical safe work practices electrical shock and arc flash boundaries and proper personal protective equipment This standard addresses safe work practices for both qualified and unqualified workers.

NFPA 70E (B) Protective Clothing and Personal Protective Equipment for Application with a Flash Hazard Analysis. Where it has been determined that work will be performed within the Flash Protection Boundary by 130.3(A), the flash hazard analysis shall determine, and the employer shall document, the incident energy exposure of the worker (in calories per square centimeter). The incident energy exposure level shall be based on the working distance of the employee’s face and chest areas from a prospective arc source for the specific task to be performed. Flame-resistant (FR) clothing and personal protective equipment (PPE) shall be used by the employee based on the incident energy exposure associated with the specific task. Recognizing that incident energy increases as the distance from the arc flash decreases, additional PPE shall be used for any parts of the body that are closer than the distance at which the incident energy was determined As an alternative, the PPE requirements of 130.7(C)(9) shall be permitted to be used in lieu of the detailed flash hazard analysis approach described in 130.3(A). FPN: For information on estimating the incident energy, see Annex D. NFPA70E is the standard for electrical safety requirements for employee workplaces. Originally requested by OSHA the National Fire Protection Association developed 70E as a standard for electrical safety. This document provides requirements for: electrical safe work practices electrical shock and arc flash boundaries and proper personal protective equipment This standard addresses safe work practices for both qualified and unqualified workers.

Addresses Arc Flash Calculations: Arcing Fault Incident energy
IEEE Std Addresses Arc Flash Calculations: Arcing Fault Incident energy Flash boundary Valid Ranges 208 V to 15 kV 700A to 106kA Gap 13mm to 153mm Out of Range Use Lee Equation IEEE Standard 1584 is a standard released in 2002 and revised in 2004. It provides Empirical Equations to estimate arcing fault current, incident energy and flash boundary distances for work in 208 Volt to 15 kV 3-phase electrical systems

! WARNING Arc Flash and Shock Hazard Appropriate PPE Required 24 inch
Flash Hazard Boundary 3 cal/cm 2 Flash Hazard at 18 inches 1DF PPE Level, 1 Layer 6 oz Nomex ®, Leather Gloves Faceshield 480 VAC Shock Hazard when Cover is removed 36 inch Limited Approach 12 inch Restricted Approach - 500 V Class 00 Gloves 1 inch Prohibited Approach - For improved safety and worker compliance, it is recommended to provide additional information on the label including the flash hazard boundary, working distance and required Personal Protective Equipment, PPE. While it’s obvious that insufficient PPE is dangerous, over-clothing workers may also increase the risk of an arcing fault due to limited mobility and visibility. Equipment Name: Slurry Pump Starter Courtesy E.I. du Pont de Nemours & Co.

To do Arc Flash Evaluations
Start with an accurate one line Have accurate one line component definitions Have accurate Short Circuit potentials Have knowledge of the protective devices’ opening times An accurate description of the operation And it is all kept up to date The Arc Flash Evaluation starts with an accurate one line and model of the power distribution system. The more accurate the input the more accurate the output. One can calculate the potential short circuits including for multiple and parallel contributions. Based on manufacturers’ Time-Current-Curves, one can determine the protective device’s opening time. And we need to take into account the possible facility power situations, such as all motors running with a supply voltage drop on a hot summer’s day to few motors running with a supply voltage 5% over nominal over a Spring holiday weekend. And it should be up to date just in case your friendly OSHA inspector walks in or the company’s safety director.

Role of Integrated Software
Provide a one-line and system model of the power system Run studies for sizing and analysis (studies are required for worker safety, protection of equipment, and reliable operation) Other than the first time for gathering data (very time consuming), the studies are mostly number crunching. That’s what a program and a computer do best.

Studies (Examples) Load Analysis is used to verify that equipment is sized properly for continuous loads. Short Circuit Analysis is used to verify that equipment is sized properly to withstand and interrupt short circuits. Protective Device Coordination sets protective devices to allow normal system operation while protecting equipment from damage and workers from injury. Harmonic Analysis is used to minimize harmonic distortion and verify the equipment is sized properly to withstand harmonic current and voltage. Arc Flash Hazard Analysis is used to calculate the incident energy released when an arcing fault occurs. Here is a partial list of the types of studies that one can do by hand or with the use of a program. A dynamic integrated program does just that; it integrates the data in the calculations and may automatically go through several iterations before presenting the results. You can read the information on the slide as well as I could. So I won’t – you can.

In reality These studies are not always performed
(When changes are made or about to made) Plant operating conditions vary Assumptions (issues) have to be made But with Arc Flash today, studies need to be up to date At some point reality sets in. In doing these studies, as one “digs in”, more questions arise than answers. Or short cuts are taken. Accuracy could be become compromised. Models need to be kept up to date and assumptions validated.

Preparing to Work Safely What do we need to know or do?
Documented Procedures Know Fault Current Calculations Know Safe Approach Distance Know Arcing Fault Clearing Time Know the Incident Energy Exposure Calculations Know Hazard Risk Category

Documented Procedures Job briefing (written work processes & procedures) Energized work permit Know Fault Current Calculations Know Safe Approach Distance Know Arcing Fault Clearing Time Know the Incident Energy Exposure Calculations Know Hazard Risk Category Job briefing (written work processes & procedures) Energized work permit

Safe Work Practices OSHA (a) (1) & NFPA 70E 130.1 not to work “hot” or “live” except when Employer can demonstrate: 1. De-energizing introduces additional or increased hazards 2. Infeasible due to equipment design or operational limitations OSHA regulations state in (a) that workers should not work on live equipment (greater than 50 volts) except for one of two reasons: 1. Deenergizing introduces additional or increased hazards (such as cutting ventilation to a hazardous location) or 2, it is 2. Infeasible due to equipment design or operational limitations (such as when voltage testing is required for diagnostics). Note: NFPA 70E – states essentially the same requirement, and adds, when it is necessary to work on equipment “live”, you must follow safe work practices, which include assessing the risks, wearing adequate PPE and using the proper tools. Note that even when de-energizing the system, performing a voltage test requires proper PPE.

NFPA 70E Appropriate safety-related work practices shall be determined before any person approaches exposed live parts within the Limited Approach Boundary by using both shock hazard analysis and flash hazard analysis. Appropriate safety-related work practices shall be determined before any person approaches exposed live parts within the Limited Approach Boundary by using both shock hazard analysis and flash hazard analysis.

NFPA 70E A flash hazard analysis shall be done in order to protect personnel from the possibility of being injured by an arc flash. The analysis shall determine the Flash Protection Boundary and the personal protective equipment that people within the Flash Protection Boundary shall use. A flash hazard analysis shall be done in order to protect personnel from the possibility of being injured by an arc flash. The analysis shall determine the Flash Protection Boundary and the personal protective equipment that people within the Flash Protection Boundary shall use.

NFPA 70E The incident energy exposure level shall be based on the working distance of the employee’s face and chest areas from a prospective arc source for the specific task to be performed. 480V MCC The incident energy exposure level shall be based on the working distance of the employee’s face and chest areas from a prospective arc source for the specific task to be performed.

NFPA 70E If live parts are not placed in an electrically safe work conditions (i.e., for the reasons of increased or additional hazards or infeasibility per 130.1) work to be performed shall be considered energized electrical work and shall be performed by written permit only. If live parts are not placed in an electrically safe work conditions (i.e., for the reasons of increased or additional hazards or infeasibility per 130.1) work to be performed shall be considered energized electrical work and shall be performed by written permit only.

Documented Procedures Know Fault Current Calculations Bolted Fault Arcing Fault Know Safe Approach Distance Know Arcing Fault Clearing Time Know the Incident Energy Exposure Calculations Know Hazard Risk Category Know Fault Current Calculations Bolted Fault Arcing Fault The class ran short circuit studies earlier this week to obtain potential bolted faults.

Bolted Short Circuit Arcing Short Circuit A B A B
To understand the arc flash hazard, it’s important to understand the difference between an arcing short circuit and a bolted short circuit. When a bolted short circuit occurs, the circuit path by-passes the load and shorts the circuit. The current that flows can be hundreds or thousands of times the normal load current. In this case the power of the fault current is dissipated throughout the circuit from the generation source to the bolted short. Typically the energy is not released into the environment however there are serious hazards associated with bolted short circuit currents such as protecting components from rupturing and ensuring overcurrent protective devices have adequate interrupting ratings. In contrast, an arcing fault is the flow of current through the air between phase conductors or between phase conductors and neutral or ground. The load is also by-passed which results in currents higher then the load current. Arcing fault currents can be extremely high in current magnitude approaching the bolted short- circuit current. However, arcing faults are typically less than the bolted short circuit. The magnitude of an arcing fault is subject to many variables and therefore is difficult to predict. A B A B

Test Rig for Bolted SC

Test Rig for Arching SC Two clips (Test 5 and Test 3)

Hot Air-Rapid Expansion
Arcing Short Circuit Extreme Heat 35,000 °F Molten Metal Pressure Waves Sound Waves When an arcing fault occurs, the result can be extremely high temperatures, a tremendous pressure blast and shrapnel hurling at high velocity. An accidental slip of a tool, or a lose part tumbling across live parts can initiate an arcing fault in the equipment. If a person is in the proximity of an arcing fault, the flash can cause serious injury or death. The point of the warning label is to remind qualified workers of the arc flash hazard when working on electrical equipment. This slide identifies some of the effects of an arcing fault including: Extreme Heat, Pressure waves, Loud sound waves, Molten Metal Copper vapor, Intense Light, Shrapnel A phase to ground or phase to phase arcing fault can quickly escalate into a three phase arcing fault due to the expansive cloud of conductive copper vapor which can engulf all phase conductors STOP- Shrapnel Copper Vapor: Solid to Vapor Expands by 67,000 times Hot Air-Rapid Expansion Intense Light

Documented Procedures Know Fault Current Calculations Know Safe Approach Distance Limits of approach Flash boundary Know Hazard Risk Category Know Arcing Fault Clearing Time Know the Incident Energy Exposure Calculations Know Safe Approach Distance Limits of approach Flash boundary This is an area that you will review

Note: shock boundaries dependent on system voltage level
Flash Protection Boundary (FPB) Must wear appropriate PPE FPB dependent on fault level and time duration. Equipment The arc flash hazard must be assessed prior to working on equipment and NFPA 70E stipulates three shock boundaries and a flash protection boundary that must be known and observed. The shock boundaries are dependent on the system voltage and can be found in a NFPA 70E table. NFPA 70E also provides methods to determine the flash protection boundary. It is possible to calculate the Flash Protection Boundary and Incident Energy Exposure level, when the available bolted short circuit current, the minimum sustainable arcing fault current, and the trip time of the protective devices are known. NFPA 70E provides the formulas for this critical information as well as other important information on safe work practices, personal protection equipment and tools to use. A qualified worker should not enter the flash protection boundary to work on live parts unless he/she is wearing the PPE for the level of hazard that could occur. Limited Shock Boundary: Qualified or Unqualified Persons* * Only if accompanied by Qualified Person Prohibited Shock Boundary: Qualified Persons Only. PPE as if direct contact with live part Restricted Shock Boundary: Qualified Persons Only Note: shock boundaries dependent on system voltage level

Flash Boundary DB arc flash boundary (mm) at incident energy of 5.0 (J/cm2) DB = [ Cf En (t/0.2) (610X / EB) ]1/X where EB incident energy set 5.0 (J/cm2) Cf 1.0 for voltage above 1 kV and for voltage at or below 1 kV t arcing duration in seconds x distance exponent x Equipment Type kV Switchgear <= Panel <= Switchgear > 1 2 all others The flash boundary is essentially a reverse calculation to determine the distance where the incident energy is equal to 1.2 calories per square centimeters.

Documented Procedures Know Fault Current Calculations Know Safe Approach Distance Know Arcing Fault Clearing Time Time current curves Coordination studies Know the Incident Energy Exposure Calculations Know Hazard Risk Category Know Arcing Fault Clearing Time Time current curves Coordination studies Yesterday the starting class learned “played” with TCCs

Documented Procedures Know Fault Current Calculations Know Safe Approach Distance Know Arcing Fault Clearing Time Know the Incident Energy Exposure Calculations NFPA 70E Method IEEE 1584 Method Know Hazard Risk Category

NFPA 70E Annex D: Sample Calculation of Incident Energy and Flash Protection Boundary 1) NFPA 70 Method with 100% and 38% of Bolted Fault 2) IEEE 1584 Empirical method NFPA 70E Annex D outlines two methods for calculating the incident energy and flash protection boundary. One method follows equations originally published in the NFPA 70E and calculates values using 100% of the bolted fault current and 38% of the bolted fault current. The other method uses the IEEE 1584 empirical equations. ---STOP---

Use IEEE 1584 Calculations Preliminary IEEE 1584 work used in NFPA 70E
NFPA 70E equations limited to < 1000V IEEE 1584 equations expanded to 15,000V NFPA 70E 38% Arcing Fault Current is overly conservative and doesn’t guarantee worst case incident energy. Most engineers follow the IEEE 1584 method because the empirical equations provide a more accurate estimate of the arcing fault current, more test data and variables were used to develop the IEEE 1584 incident energy equations, and the IEEE 1584 equations are valid over a wider range of voltages and fault currents.

Incident Energy Energy Per Unit of Area Received On A Surface Located A Specific Distance Away From The Electric Arc, Both Radiant And Convective, in Units of cal/cm2. As the video showed, electric arcs release a lot of energy, which takes many different forms and may be destructive. One form of arc energy is incident energy which is the arc radiant/convective energy per unit area. Incident energy causes burns, which is a major hazard to individuals from an arc flash

Incident Energy log (En) = K1 + K log (Ia) G En Incident energy (J/cm2) normalized for 0.2s arcing duration and 610mm working distance K1 –0.792 for open configuration –0.555 for box configuration (switchgear, panel) K2 0 for ungrounded and high resistance grounded systems for grounded systems Ia Arcing fault current G gap between bus bar conductors in mm solve En = 10 log En The incident energy is calculated in two steps, including a calculation normalized to a 0.2 second arc at a working distance of 610mm followed by an adjustment to the actual trip time and working distance. The first calculation includes variables for open air versus in a box, grounded versus ungrounded equipment, the arcing fault current, and the gap between the bus bar conductors.

Incident Energy Incident Energy convert from normalized: E = Cf En (t/0.2) (610X / DX) E incident energy (J/cm2) Cf 1.0 for voltage above 1 kV and for voltage at or below 1 kV t arcing duration in seconds D working distance x distance exponent x Equipment Type kV Switchgear <= Panel <= Switchgear > 1 2 Cable, Open Air The second equation includes variables for voltage, the normalized incident energy, arc duration, working distance, and the type of equipment.

Documented Procedures Know Fault Current Calculations Know Safe Approach Distance Know Arcing Fault Clearing Time Know the Incident Energy Exposure Calculations Know Hazard Risk Category NFPA 70E Know Hazard Risk Category NFPA 70E You will be working with this later today

Appropriate PPE The NFPA 70E 2004 standard provides 5 Arc Rating levels of PPE. Class 0 for incident energy up to 1.2 calories per square centimeter. Class 1 for incident energy up to 4 calories per square centimeter, Class 2 for incident energy up to 8 calories per square centimeter, Class 3 for incident energy up to 25 calories per square centimeter, And Class 4 for incident energy up to 40 calories per square centimeter,

Preparing to Work Safely We need to know or do:
Prepare to work safely Know Fault Current Calculations Know Safe Approach Distance Know Arcing Fault Clearing Time Know the Incident Energy Exposure Calculations Know Hazard Risk Category But Why?

NFPA 70E A flash hazard analysis shall be done in order to protect personnel from the possibility of being injured by an arc flash. The analysis shall determine the Flash Protection Boundary and the personal protective equipment that people within the Flash Protection Boundary shall use. A flash hazard analysis shall be done in order to protect personnel from the possibility of being injured by an arc flash. The analysis shall determine the Flash Protection Boundary and the personal protective equipment that people within the Flash Protection Boundary shall use.

Ok, it’s required But How?

Break So Let’s introduce you to: PTW’s Arc Flash Evaluation

Perform an Arc Flash Study Analysis
Arc Flash Calculation Step Review Determine System Modes of Operation Calculate Bolted Fault Current at each Bus Calculate Arcing Fault Current at each Bus Calculate Arcing Fault Current seen by each Protective Device Determine Trip Time for Each Protective Device based on Arcing Fault Current Calculate Incident Energy at Working Distance Calculate Arc Flash Boundary Determine Required PPE

Bolted Fault Current The bolted fault current should be as accurate as possible. While assuming an infinite source is conservative for sizing equipment, it is generally not conservative for arc flash calculations. When accurate data is not available, it is prudent to apply a minimum and maximum tolerance for the utility contribution and component impedance values when calculating the bolted fault currents.

Arcing Fault Current For bus voltage < 1 kV and 700A  IB  106kA log (IA) = K log (IB) V G V log (IB) – G log (IB) where log log10 IA arcing fault current K –0.153 for open configuration and –0.097 for box configuration IB bolted fault current – 3phase sym rms kA at the bus V bus voltage in kV G bus bar gap between conductors in mm For bus voltage >= 1 kV and 700A  IB  106kA log (IA) = log (IB) The above equations are reprinted with permission from IEEE 1584 *Copyright 2002*, by IEEE. The IEEE disclaims any responsibility or liability resulting from the placement and use in the described manner. From IEEE 1584 Copyright 2002 IEEE. All rights reserved.* The IEEE 1584 standard provides an empirical equation to estimate the arcing fault current. The calculated arcing fault current varies with voltage, bolted fault current, gap between the conductors and whether the arc occurs in open air or in a box.

Identify Environment Working Distance Grounded / Ungrounded
480V MCC Working Distance Grounded / Ungrounded Equipment Type Open Air Switchgear Panel / MCC Cable Bus Bar Gap 15kV Swgr 152mm 5kV Swgr 104mm LV Swgr 32mm Panel / MCC 25mm Cable 13mm Additional environmental variables are needed to calculate the incident energy, including: Working distance, whether the equipment is grounded or ungrounded, and the Equipment type with related bus gap.

There are Issues!

Arc Flash Let’s look at an actual Arc Flash Incident.
In this example, an arcing fault occurs in a distribution substation. The protection doesn’t clear the fault for several seconds, resulting in catastrophic damage. Fortunately no one was present within the substation flash boundary area when the arcing fault occurred.

Arcing Fault Clear Time
0.5 1 10 100 1K 10K 0.01 0.10 1000 CURRENT IN AMPERES tcc3.tcc Ref. Voltage: Current Scale x10^0 TIME IN SECONDS A4BQ Fuse Min Max Trip Time for Low Arcing Fault The substation example highlights one of the most important considerations of arcing fault calculations, that is how long it takes the upstream protection device to clear an arcing fault. Since the arcing fault current is less than the bolted fault current (typically between 38% and 89% of the bolted fault), it may take substantially longer to clear an arcing fault. It is prudent to think of the arcing fault current as a possible range of current using assumptions that produce a minimum and maximum arcing fault current. This slide depicts a fuse melting curve and a tolerance of arcing fault currents. At the maximum arcing fault current, the fuse will melt before 0.01 seconds and may operate in the current-limiting range. However, at the minimum arcing fault current, the fuse will take 100 seconds to clear the fault. The amount of energy released is a combination of the current and the time. As seen in the substation example, the long trip time was catastrophic. The point here is that smaller currents may be worse than larger currents since the trip time may be substantially longer.

Arc Flash Incident 480 Volt System 22,600 Amp Symmetrical Fault
Motor Controller Enclosure 6-Cycle Arcing Fault (0.1 sec) Let’s look at another example of an Arc Flash Incident Filmed in a Lab. In this case, the system is 480 Volts The available fault current is 22,600 Amps The protective device clears the arcing fault in 6 cycles (0.1 sec).

Each slide represents approximately 1 cycle
Copyright IEEE Used by Permission

During the first cycle, the arc releases significant energy including light and heat…

At 2 cycles, vapor and debris can be seen.

At 3 cycles, the pressure and sound waves begin to move the worker.

At 4 cycles, the equipment and worker are engulfed in flame.

At 5 cycles smoke rises from the fire.

At 6 cycles the fault is cleared, but the damage is already done.

Issues – Current Limiting
In Current Limiting Range Operates in < ½ Cycle Limits Current from 0 to >90% Limits More at Higher Currents Current limiting protective devices can reduce incident energy by clearing the fault more quickly and by reducing the let-through fault current. These current limiting effects are typically only applicable at high fault currents. Since the arcing fault current is often substantially less than the bolted fault, the current-limiting effects must be evaluated carefully. When the fault current is in the current-limiting range, it is usually sufficient to use the faster trip times associated with current-limiting devices without making adjustments for reduced let through current. Arcing faults that clear in ½ cycle, as required in current-limiting devices, will typically not result in high incident energy. Current Limiting Range

Arc Flash Incident 480 Volt System 22,600 Amp Symmetrical Fault
Motor Controller Enclosure Current Limiting Device with < ½ Cycle operation (.0083 sec). Note that Arcing Fault must be in current limiting range. Faster operating times and current limiting devices can reduce arc-flash exposure. The following example uses the same conditions as the previous lab example: 480 Volt, 22,600 Amp Fault Current However this time a current-limiting device is used that clears the arcing fault in less than ½ cycle. Note that the faster operating time only occurs in the current-limiting range of the protective device and the minimum arcing fault current may be below the current-limiting range.

Again each slide represents approximately 1 cycle.

During the first half cycle some light and energy is released, but the fault has already been cleared. Copyright IEEE Used by Permission

At 2 cycles, the environment begins to return to normal.

3 cycles Copyright IEEE Used by Permission

4 cycles Copyright IEEE Used by Permission

5 cycles. For this case, by clearing the fault is less than ½ cycle, there is no perceivable damage - STOP- Copyright IEEE Used by Permission

Issues – Current Limiting
Ignoring Current-Limiting Effects Operates in 0.01s 2.4 Cal/cm2 at 200 kA 2.3 Cal/cm2 at 100 kA 1.2 Cal/cm2 at 50 kA As an example, using the 0.01 total clear time from the fuse curve and an 18 inch working distance, even 200 thousand amps only results in incident energy of 2.4 calories per square centimeter. Reducing the fault current to 100 thousand amps results in incident energy of 2.3 calories per square centimeter. Reducing the fault current to 50 thousand amps results in incident energy of 1.2 calories per square centimeter. Even for 200 thousand amps, clearing the fault in 0.01 seconds results in Class 1 clothing. The point here is that clearing the fault faster is more important than limiting the current. The real advantage of current-limiting devices in terms of arc flash is that they clear the fault more quickly.

Issues – Fault Values Maximum Faults used for Equipment Selection
Minimum Faults Often Worst Case for Arc Flash Requires accurate utility fault contribution (not infinite source) Consider lowest pre-fault voltage Consider operating conditions with minimum motors Consider operating conditions with/without generators Consider stand-by operating modes Traditionally fault calculations have been performed to provide a basis for conservative equipment selection. Utility contributions were often represented as an infinite source. For arc flash hazard analysis, it is important to estimate the available fault current as accurately as possible. As we have seen, this is because smaller fault currents often produce larger incident energy because the protective devices take longer to operate. It is also important to evaluate alternative operating modes that may result in lower fault currents.

Minimum and Maximum Faults of Devices

Issues – Long Trip Times
Arcing Fault Minimum Tolerance Arcing Fault Maximum Tolerance Artificial 2 second maximum arc duration Note that for long trip times, the incident energy will be extremely high, even for low arcing fault current. For these cases, you may want to evaluate a maximum arc duration such as 2 seconds. If the energy released over the first 2 seconds is relatively small and proper PPE is worn, in most cases the worker will have an opportunity to move away from the arc. Use of a maximum arc duration requires engineering judgment and should be evaluated on a case by case basis. ---STOP---

Issues - Faster Trip Times
Arcing Fault Minimum Tolerance Arcing Fault Maximum Tolerance Trip Time for Minimum Arcing Fault The challenge with faster trip times is further complicated by the lower arcing fault currents, especially when a tolerance is used to estimate a range of possible fault currents. The yellow bar represents the range of arcing fault currents. With the existing protective device settings, the high tolerance arcing fault would be cleared by the instantaneous function of the breaker (0.07 seconds), however the low tolerance arcing fault current would be cleared by the long time delay function of the breaker ( 10 seconds). Trip Time for Maximum Arcing Fault

Issues - Coordination Coordination Traditionally used for Equipment Protection and System Reliability Arc flash requirements brings new safety focus to coordination studies looking at minimum faults and setting faster trip times. Faster trip times may cause more nuisance trips. Alternative protection schemes may gain popularity (differential protection, zone interlocking, light sensors, etc.) Traditionally protective device coordination has been used to protect equipment and provide reliable system operation. Arc Flash protection requires a new safety focus for coordination studies, often needing faster trip times that includes the lower arcing fault currents. Alternative protection schemes such as differential, zone-interlocking, and arc-sensing trip units may also gain popularity.

Issues - Faster Trip Times
The faster you can clear the arcing fault, the less energy will be released. However faster trip times often cause less power system reliability through reduced selectivity and an increased chance of nuisance tripping. Life safety concerns always take precedence. Before After

Issues - Coordination Coordinated
Traditionally protective device coordination has been used to protect equipment and provide reliable system operation. Arc Flash protection requires a new safety focus for coordination studies, often needing faster trip times that includes the lower arcing fault currents. Alternative protection schemes such as differential, zone-interlocking, and arc-sensing trip units may also gain popularity.

Issues - Coordination Miscoordination
Traditionally protective device coordination has been used to protect equipment and provide reliable system operation. Arc Flash protection requires a new safety focus for coordination studies, often needing faster trip times that includes the lower arcing fault currents. Alternative protection schemes such as differential, zone-interlocking, and arc-sensing trip units may also gain popularity.

An exercise to show mis-coordination

Mis-coordination

In Options Screen

Issues – Parallel Contributions
30 kA Short Circuit Current from Utility clears in 0.5 sec. Most arcing faults are fed from parallel sources. It is important to understand that the energy at the fault location will be based on the total fault current from all of the sources, while the time required to clear the fault will be based on the portion of the fault current that flows through the protective device. It is also important to understand that some fault sources, such as utility feeds, are constant, whereas other fault sources, such as induction motors, are transient and only contribute current for a few cycles. For the example shown here, the 30,000 amp utility fault contribution to the arcing fault is cleared by the protective device in 0.5 seconds. The 5000 amp motor fault contribution decays to zero during the first few cycles. To be conservative, let’s assume that the motor contribution is constant and drops to zero at 5 cycles. Fault Location 5 kA Short Circuit Current from Motor decays in 5 cycles (0.08 sec).

Issues – Parallel Contributions
Energy Accumulation (Reduction) Utility + Motor for sec Current Utility only for remaining 0.42 sec. A bar chart of the energy profile is shown. For the first 5 cycles, the worker is exposed to current from the utility and the motor. For the next 0.42 seconds, the worker is exposed to current only from the utility, since the transient motor contribution is removed. Using the total fault current at the bus to calculate the trip time and the incident energy will produce erroneous results. It is important to consider both fixed and transient contributions and to determine the fault clearing time based on the portion of the fault current that flows through the protective device. Time

Fault on 003-HV SWGR And a full-fledged masochist
Because I am a person of Iron And a full-fledged masochist Thank you and Have Great Afternoon!

Arc Flash Calculation on 003-HV SWGR
I (kA) R7 Trips R6 Trips R2 Trips R3 Trips R M8 Trips R M10 Trips 6.93kA 6.46 kA 4.77 kA 1.73 kA 1.45 kA 0.64 kA R7 + R6 + R2 + R3 + RM8 + RM10 R6 + R2 + R3 + RM8 + RM10 R2 + R3 + RM8 + RM10 R3 + RM8 + RM10 RM8 + RM10 RM10 T (s) 0.083s 0.374s 0.222s 1.321s 1.321s 1.321s Incident Energy from branches (cal/cm2): 1.60 4.4 2.3 4.7 0.0 0.0 Total Incident Energy at the fault bus(cal/cm2): 1.60 6.0 8.3 13.0 13.0 13.0 %Arc Current Cleared: 6.03% 31.65% 77.64% 81.28% 91.70% 100%

Break So Let’s introduce you to: PTW’s Arc Flash Evaluation

Issues – Line Side Activities

Run Arc Flash Calculations

Detail View or Summary View
Detail View lists all protective devices at branches that contribute current to the faulted bus. This will vary from the Summary View only for buses that have multiple contributions. Summary View: If the Report Option is set to “Report Last Trip Device”, the Summary View will list the last device to trip whereby the accumulated current tripped meets or exceeds the specified threshold percent (ie… when at least 80% of total fault current has cleared). If the Report Option is set to “Report Main Device”, the Summary View will list the device that carries the largest percentage of the fault contribution to the bus.

Bus Detail generates a detailed label Standard or Custom Label:
Other Tabs Bus Detail: Bus Detail generates a detailed label Standard or Custom Label: Generates standard and custom arc flash warning labels Work Permit: Produces energized work permits based on the calculated incident energy Re-run Study: Allows one to re-run the study to display the most up to date results, if you have made changes in the table Because I am a person of Iron And a full-fledged masochist Thank you and Have Great Afternoon!

Options Tab So Let’s introduce you to: PTW’s Arc Flash Evaluation

For Equipment < or = to 240v ac
In NFPA 70E, Article 130, Table (7)(9)(a) with Notes 1 and 3 (for <10kA short circuit current available, the hazard /risk category required may be reduced by one) Pages 70E-29 thru 31. The Table shows hazard /risk categories of 0 and 1, but all would be 0 given note 3 conditions. In IEEE 1584, dated 2002, on page 6, fourth paragraph, last sentence – “Equipment below 240 V need not be considered unless it involves at least one 125 kVA or larger low impedance transformer in its immediate power supply.” Also on page 25, third paragraph, last sentence within the model and testing discussion – “The arc-flash hazard need only be considered for large 208 V systems: systems fed by transformers smaller than 125 kVA should not be a concern.” So Let’s introduce you to: PTW’s Arc Flash Evaluation

Cleared Fault Threshold
Cleared Fault Threshold, determines the portion of the Total Arcing Fault current at the Bus that needs to be interrupted by protective devices to extinguish the arc. Therefore the remaining portion of Arcing Fault current, if any, can not sustain the arc and will not be considered in the accumulated incident energy. Enter a value in percent of the total bus fault current, the default value is 80%, which means that the final arc fault trip time is based on when 80% or more of the total fault current at the bus has been cleared. In the Summary View, the last device to trip that reaches the cleared fault threshold is the only protective device that will be listed under the bus, and the data from the device will be used in the Bus Detail report and Bus Label. The cleared fault threshold value is also used to determine which branches are searched for mis-coordination. So Let’s introduce you to: PTW’s Arc Flash Evaluation

Report Options Bus option – The bus report assumes that the fault occurs at the equipment bus. If the bus has multiple contributions, the devices that trip each branch contribution will be listed in the order they trip, and incident energy will be accumulated until a significant percentage of the fault current has tripped. The significant portion is defined by the “Cleared Fault Threshold” percentage you specify. So Let’s introduce you to: PTW’s Arc Flash Evaluation

Report Options Protective Device Load Side option – The load side report applies a fault at the load side (To End) of each protective device whose line side (From End) is connected directly to a bus without having an impedance device between the bus and the protective device. The protective device being evaluated is the one that clears the fault. The fault current through the device will be used to calculate the arcing fault current and obtain the trip time from the TCC. You can then select to include Line + Load Sides Contributions (to represent both ends hot) in calculating the incident energy, or to include Line Side Contributions only in which case the load side contributions are not included (now working as if the load side is disconnected). Protective Device Line Side option – The line side report applies a fault at the line side (From End) of each protective device whose load side (To End) is connected directly to a bus without having an impedance device between the bus and the protective device. You can then selected to include Line + Load Sides Contributions or to include Line Side Contributions only. The first case represent both ends hot, this occur if the main breaker failed to open, and the next upstream device is the one that must clear the fault. If there is more than one contribution when there is a fault at the line side, incident energy will be accumulated up to the fault contribution percentage specified. If Line Side Contributions Only is selected, the load side contributions are not included and it is now working as if the load side is disconnected. So Let’s introduce you to: PTW’s Arc Flash Evaluation

Report Options Bus + Line Side option – This option combines the bus report option and the line side report option into one report. Calculated result for the bus and line side will be listed next to each other for easier comparison of worse case scenario. A special custom label is supplied by PTW to put both bus and line side results in one single label. So Let’s introduce you to: PTW’s Arc Flash Evaluation

Scenario Manager Use Scenario Manager to evaluate alternative operating scenarios for the power system, including minimum and maximum fault conditions, and proposed design changes. The scenario manager can be used to evaluate alternative operating scenarios. Each alternative operating scenario should be evaluated to determine the largest possible incident energy. The scenarios can also be used to evaluate the effect of proposed design changes. ---STOP---

Data Visualizer Screen

Issues Fault Values Parallel Contributions (number of motors or generators running and off) Line/Load Side Activities Coordination Here are some areas where assumptions and rules of thumbs are experienced. (wait a moment for the audience to read the slide)

What is the purpose of an arc flash study?
Living with what one has and minimize the risks Designing electrical safety into the power distribution design To determine the protective clothing requirements for persons working on live equipment Because I am a person of Iron And a full-fledged masochist Thank you and Have Great Afternoon!

PPE Table And a full-fledged masochist I am a person of Iron Because
Thank you and Have Great Afternoon!

Labels using the Bus Detail button

Labels using the Standard Label button

Labels using the Custom Label button

Produce Work Permits

One-line with Arc Flash Data

Role of Integrated Software
Integrated Software allows you to: Use NFPA 70E methods in determining PPE Or IEEE 1584 Run scenarios (of options, conditions, modes of operations) and visualize their results simultaneously so good engineering judgments can be made and documented Print Reports, Permits, and Labels It becomes part of the on-going safety program Integrated Software allows you to run Arc Flash calculations using either the NFPA method or with the IEEE 1584 calculations. But the most important reason for using integrated software is that one can run scenarios and “what ifs” within the studies to very quickly get what might happen under those various situations. And it does give us data so that good judgment decisions can be made. In Arc Flash, accuracy is elusive but as we continue to question our assumptions and validate our data we improve our chances.

Costs of Not Performing Arc Flash Studies
OSHA Fines Lost Productivity Medical Costs Legal Costs Possible costs associated with not performing arc flash calculations can be high and include non-compliance fines, lost productivity, increased repair costs, medical expenses, legal costs, and most importantly loss of life.

So… why do I want to do studies by hand, with the calculator or tables?

Have Great Evening! Because And a full-fledged masochist
I am from Texas And a full-fledged masochist Have Great Evening! Because I am a person of Iron And a full-fledged masochist Thank you and Have Great Afternoon!

So Let’s introduce you to: PTW’s Arc Flash Evaluation

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