Engineering

Arc Flash Hazard Analysis

WHAT IS AN ARC FLASH?

An arc flash is a current flowing through air that flashes from one exposed live conductor to another conductor or to ground. When an arc flash happens, the temperatures can reach up to 35,000 degrees Fahrenheit. This is four times the temperature on the surface of the sun. The result can be the destruction of equipment, fire, and injury.

WHAT CAUSES AN ARC FLASH?

An arc flash occurs when electrical clearances are reduced or compromised by deteriorating insulation or human error. The arc flash follows a conductive path between two hot (energized) wires or between a hot wire and ground.

WHY IS AN ARC FLASH ANALYSIS IMPORTANT?

Without an arc flash study, you will not know the actual level of danger or the appropriate personal protective equipment (PPE) required for employees. Electrical systems are dynamic and change over time. Internal changes, such as adding new equipment can affect the level of arc flash energy. A study must be updated every time the system changes. External changes, such as a utility changing transformers or changes at your utilityʼs closest sub-station, can severely impact your level of arc flash energy.
 

HERE ARE THE FACTS…

The Federal Government (OSHA requires that all “Non-Dwelling” facilities have an ARC Flash Hazard Analysis done to determine:

  • The Arc Flash Boundary
  • The Level of PPE Required
  • The Presence of a Flash Hazard

NFPA 130.7 (E) SAYS THIS:

“Safety signs, safety symbols, or accident prevention tags shall be used where necessary to warn employees about electrical hazards that might endanger them. Such signs and tags shall meet the requirements of ANSI Z535…”

NFPA 70E 130.3 SAYS THIS:

“An arc flash hazard analysis shall determine the Arc Flash Protection Boundary and the personal protective equipment that people within the Arc Flash Protection Boundary shall use…”

NFPA 70E 400.11 SAYS THIS:

“Electrical 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…”

REFER TO:

OSHA 29 CFR Part 1910.302-308 & 1910.331-335
US Department of Labor, Occupational Safety & Health Admin
National Fire Protection Association, NFPA 70E

PENALTIES FROM OSHA CONCERNING ARC FLASH

These are the types of violations that may be cited and the penalties that may be proposed:

OTHER THAN SERIOUS VIOLATION

A violation that has a direct relationship to job safety and health, but probably would not cause death or serious physical harm. A proposed penalty of up to $7,000 for each violation is discretionary. A penalty for an other-than-serious violation may be adjusted downward by as much as 95 percent, depending on the employer’s good faith (demonstrated efforts to comply with the Act), history of previous violations, and size of business. When the adjusted penalty amounts to less than $100, no penalty is proposed.

SERIOUS VIOLATION

A violation where there is substantial probability that death or serious physical harm could result and that the employer knew, or should have known, of the hazard. A mandatory penalty of up to $7,000 for each violation is proposed. A penalty for a serious violation may be adjusted downward, based on the employer’s good faith, history of previous violations, the gravity of the alleged violation, and size of business.

WILLFUL VIOLATION

A violation that the employer knowingly commits or commits with plain indifference to the law. The employer either knows that what he or she is doing constitutes a violation, or is aware that a hazardous condition existed and made no reasonable effort to eliminate it.

Penalties of up to $70,000 may be proposed for each willful violation, with a minimum penalty of $5,000 for each violation. A proposed penalty for a willful violation may be adjusted downward, depending on the size of the business and its history of previous violations. Usually, no credit is given for good faith.

If an employer is convicted of a willful violation of a standard that has resulted in the death of an employee, the offense is punishable by a court-imposed fine or by imprisonment for up to six months, or both. A fine of up to $250,000 for an individual, or $500,000 for a corporation, may be imposed for a criminal conviction.

REPEATED VIOLATION

A violation of any standard, regulation, rule, or order where, upon re-inspection, a substantially similar violation can bring a fine of up to $70,000 for each such violation. To be the basis of a repeat citation, the original citation must be final; a citation under contest may not serve as the basis for a subsequent repeat citation.

FAILURE TO ABATE PRIOR VIOLATION

Failure to abate a prior violation may bring a civil penalty of up to $7,000 for each day the violation continues beyond the prescribed abatement date.

DE MINIMIS VIOLATION

De minimis violations are violations of standards which have no direct or immediate relationship to safety or health. Whenever de minimis conditions are found during an inspection, they are documented in the same way as any other violation but are not included in the citation.

Source: https://www.osha.gov/doc/outreachtraining/htmlfiles/introsha.html

Device Evaluation

Device evaluation is performed to identify which components do not meet the short circuit or load rating requirement based on the results obtained from the short circuit analysis or load flow analysis. An equipment evaluation study compares component short circuit ratings and continuous ratings with calculated short circuit and operating conditions. It is an extension of a short circuit study.

Harmonic Studies

Harmonic studies are performed to determine the effects of harmonic-producing devices (such as furnaces, large adjustable-speed drives, static VAR compensators, and HVDC rectifiers) on other equipment in the system to determine potential resonance issues. Harmonic studies are typically associated with the installation of capacitor banks or reactors, and for designing and evaluating the performance of harmonic filter banks.

Ground Mat Analysis

Ground Mat Analysis is performed to determine the step and touch potential voltages that could be present, posing a serious danger to personnel. The analysis is performed to help optimize grid design or reinforce existing grids of any shape.

Load Flow, Voltage & Power Factor Studies

A low flow study calculates the currents, voltages and voltage drops, and phase angles for each bus in your system. This information is used to determine the proper sizing of current-carrying equipment, to identify overload devices, and to determine locations where power factor correction may be required. Load flow studies are performed using computer software (e.g., EasyPower) to simulate actual steady-state power system operating conditions in order to evaluate bus voltage profiles, real and reactive power flow, and losses.

Conducting a load flow study using multiple scenarios helps to ensure that the power system is adequately designed to satisfy desired performance criteria for the most economical expenditure of initial capital investment and future operating costs.

Load flow studies are commonly used to investigate:

  • Component or Circuit Loading
  • Bus Voltage Profiles
  • Real and Reactive Power Flow
  • Power System Losses
  • Proper Transformer Tap Settings

Short Circuit Analysis

Short Circuit Analysis is performed to determine the currents that flow in a power system under fault conditions. If the short circuit capacity of the system exceeds the capacity of the protective device, a dangerous situation exists. Since the growth of a power system often results in increased available short-circuit current, the momentary and interrupting rating of new and existing equipment on the system must be checked to ensure the equipment can withstand the short-circuit energy. Fault contributions for utility sources, motors, and generators are taken into consideration. The results of a Short Circuit Analysis are also used to coordinate electrical protective devices selectively.

Short circuit calculations determine the magnitude of abnormal currents flowing throughout the power system at various time intervals after a “fault” occurs.

The study is based upon utility positive and zero sequence source impedance information supplied by the utility.

Motor Starting Studies

Motor Starting Studies are performed on a power system to determine unexpected consequences of starting a large motor. There are many considerations to starting a motor other than effectively connecting it to the line voltage. Nuisance tripping and excessive running currents, as well as dimming of lights, are signs that a power system isn’t performing correctly.

During starting, an AC induction motor or AC synchronous motor will draw greater-than-normal running current, typically about 600% of rated full-load current, and will last as long, although diminishing in magnitude, as the motor goes to full speed. If a motor is started with a mechanical load connected to the shaft, an inrush current will be drawn for a longer period of time. However, it will not be greater in magnitude than if the motor was started with no load.

The power system should be able to supply inrush to any motor on the system while supplying normal service for the rest of the system. If the system does not have sufficient capacity, there will be excessively low voltage drops and insufficient capacity for motor starting.

Motor starting calculations determine the expected voltage dip and acceleration time for a motor and examine the impacts of a motor starting on an electric power system.

Alternate starting methods, such as across-the-line or reduced voltage can be also be explored.

If system voltage dips >20% are a concern, we can propose the appropriate solutions. For calculating more precise acceleration times, the dynamic motor starting simulation requires motor and load rotational moment of inertia data.

Power System Assessments

Power System Assessments identify power quality, reliability concerns, and code compliance for your facility. Up-to-date assessments are critical for your facility to maintain safe operating conditions.

IKRA Engineer performs Power System Assessments as stand-alone services or as part of a design project upgrade. This process encompasses a walkthrough of your facility and the collection of data that will be compiled for formal risk analysis.

Protective Device Coordination Studies

Protective Device Coordination studies are performed to ensure that transformers, capacitor banks, electric motors, and cables are protected against damage from short circuit currents. These studies are used to select appropriately rated protective devices and their settings. The objective is to minimize the impact of short circuits in the electrical system by isolating faults as quickly as possible while maintaining power to the rest of the system. The rating and settings of protective devices recommended from the coordination study would represent an exercise of judgment as to the best balance of the two goals-protection and selectivity.

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