Page 40: of Maritime Reporter Magazine (April 2022)

TECH FEATURE UNDERSTANDING ARC FLASH

Arc Flash in

Marine Installations

By Will Ayers, P.E., Chief Electrical Engineer, Elliott Bay Design Group &

Taylor Herinckx, P.E., Electrical Engineer/Naval Architect, Elliott Bay Design Group he use of electrical energy aboard • Heat from an arc can cause severe inside each electrical panel. The danger ships and marine structures has ? ash burns many feet away (tempera- is measured in calories per centimeter increased in recent decades and is tures can reach 19,500°C, four times the squared (cal/cm2). This is the energy that

T anticipated to grow further. With temperature at the surface of the sun) [1]. would potentially be projected onto the the increase in energy and power levels, • This massive energy discharge burns front of a worker at roughly arm’s length the hazards associated with electrical in- the bus bars, vaporizing the copper, from the electrical arc. See Figure 1.

stallations also grows. One of the major causing an explosive volumetric expan- It has been found that 1.2 cal/cm2 of hazards is an arc ? ash event. Knowing sion conservatively estimated to have an thermal energy applied to a person’s about arc ? ash can protect your employ- expansion ratio of 67,000 to 1 [1]. By- skin for a short period of time generally ees and your ? rm from a tragic accident. products from the arc, such as molten produces a second-degree burn, which

An arc ? ash is a rapid release of energy metal spatter, can cause severe injury. is not a permanent injury. This thresh- due to an arcing fault between a bus bar • Pressure waves caused by the rapid old is typically used as the upper limit and another bus bar, neutral or a ground, expansion of air and vaporization of to which personnel may be exposed during which the air is the conductor. metal can distort enclosures and cause without extra arc ? ash speci? c personal

While arc ? ashes can be precipitated at doors and cover panels to be ejected protective equipment (PPE). Arc ? ashes any time, they are much more likely, and with severe force, injuring personnel. are generally limited to systems where the consequences much more severe, • Sound levels can damage hearing. the bus voltage is equal to or in excess while maintenance and repair operations • In addition to personnel hazards, an of 208 volts [6]. Lower voltage levels on energized equipment are under way. arc ? ash generally results in equipment normally will not sustain an arc.

These operations introduce the com- damage, which requires clean up and re- The arc ? ash hazard analysis is a pounding effects of bringing personnel pair, and causes system down time. natural extension from two related stud- into proximity with energized conductors, Anywhere from 3,500 to 30,000 arc ies that may already be required for the and the removal of covers from electrical ? ash incidents occur every year [2], and installation: components. In the majority of cases, it is countless have been investigated. Many • Short circuit study human error rather than equipment fail- of these have revealed new insights into • Circuit breaker coordination study ure that leads to the arc ? ash event. Unin- the danger. In particular, a number of If you have these two common stud- tentional arcing in power equipment can accidents occurring at the U.S. Depart- ies, you already have the basis to per- in? ict several different types of hazards: ment of Energy have been very well form an arc ? ash hazard analysis.

documented and the accident reports are EBDG has extensive experience available online [3] [4] [5]. performing these arc ? ash studies for

There have been countless studies marine electrical systems. We utilize a done on a multitude of aspects of the arc powerful software package called SKM ? ash danger. However, most of these are Power Tools for WindowsTM to per- focused on shore-side installations. This form the arc ? ash calculations. Never- paper, in contrast, will focus on what is theless, an intimate understanding of the unique for the marine application. electrical engineering underlying this software is critical in its application.

The purpose of calculating the arc

ARC FLASH HAZARD ANALYSIS

An arc ? ash hazard analysis allows us ? ash numbers is not to have them buried to quantify the arc ? ash energy lurking in a report for the life of the system. In 40 Maritime Reporter & Engineering News • April 2022

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