Arc-flash calculations improve safety

Everyone deserves to go home without injury at the end of the (working) day.

During the course of any kind of work on a power grid there is a risk of short circuits and arc flash hazards occurring. Arc flashes are rare, but the consequences are disastrous. Mechanics, installers and bystanders are at great risk from the massive explosion triggered by an arc. Optimal arc flash protection is an absolute necessity. Predicting the behaviour of the arc flash will increase safety. It will provide insight into risks and how to manange these risks best. Knowing the electrical energy in every distribution board determines the right PPE for all situations.

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HyTEPS provides arc flash calculations and simulations

NEN3140

The most recent NEN 3140 standard has an increased focus on the danger caused by electric arcs. In order to reduce risk and take appropriate protective measures, an RI&E in the field of electric arcs is required. Based on installation data, the arc energy at a specific workplace (for a specific device or part of the installation) needs to be determined. This makes it possible to specify whether arc protection is required, and what this protection would need to consist of. However, determining arc energy is complicated. A variety of  factors need to be taken into account, including the duration of the fault, the level of the current and the distance between individuals and the installation.

HyTEPS provides arc flash calculations and simulations

For every cabinet, HyTEPS can provide you with labels, listing the most important safety data such as short circuit power, and information on which PPMs should be worn for different situations, based on simulations. This simplifies LMRA (Last Minute Risk Assessment) making it efficient to carry this out for each individual cabinet. If desired, this can be linked to a management system, which provides central data allowing you to know which PPMs are necessary at your plant. This increases awareness and supports a safer work culture.

proces of arc flash simulaties

What is an arc flash?

An arc flash is a sustained electrical arc that can result from switching or a failure within an installation. Often, an arc flash will have a negative incremental resistance. This means the arc will grow until a component elsewhere in the installation fails due to overcurrent. Only then will the arc die out.

Characteristics of an arc fault

  • Extreme temperatures in excess of 19,000 degrees Celsius
  • Flying (heated or melted) fragments of the installation
  • A pressure wave with a deafening bang (arc blast)
  • An intense bright light, in both the visible and invisible spectrum (infrared)

Risks for your employees

  • External burns
  • Internal burns due to inhaled ionized gases
  • Blindness (temporary or permanent)
  • Injury
  • Hearing damage (temporary or permanent)
  • Copper poisoning (the inhaled copper fumes will solidify in the lungs, resulting in the permanent presence of copper residue in the lungs.)

In extreme cases the arc fault can mean direct, or indirect (due to the reasons mentioned above) employee loss.

The three most important parameters governing the extent of an arc fault are arcing time, fault current and the distance between operator and installation.

Causes of an arc flash

Most arc flashes are produced by human error. In about 70% of all cases, the cause is careless operation of the installation. Furthermore, faults in the installation can also result in a dangerous arc flash:

  • Incorrectly sized switching gear
  • Decayed or lacking insulation material
  • Bad joints
  • Conduction between phases due to objects such as tools, parts or rodents

Standard for arc flash calculations

Many standards have been developed to calculate arc-flashes. Every standard has its own application domain and method. Some of the most common rules and regulations are summarized in the table below.

IEEE-1584 2018 International standard for calculating arc flashes. This version is extended with additional circumstances.
IEEE-1584 2002 International standard for calculating arc flashes. Main method for calculating arc flashes.
NFPA 70E National fire protection agency guides concerning arc faults.
NEN 3140 Dutch standard concerning operation of electrical installations
EN 50110 European standard for safe operations on and around electrical installations

But also regulations on protective clothing:

ISSA Guidelines about thermal effect of arc flash on PPE
DGVU203-077 Guidelines about thermal effect of arc flash on PPE
IEC 61482-1-1 Test method for PPE against thermal effects and electrical energy
IEC 61482-1-2 Test method for PPE against thermal effects and electrical energy

It is vital to select the right guidelines and regulations for your installation. HyTEPS can advise you in making these decisions.

Dangerous arc flashes: an expensive case

As described, the effects of unwanted arc flashes can be severe. An arc flash can harm people, but also cause major damage to installations such as distribution boards. Due to damage from the arc flash, an installation could be out of service for several days or weeks.  Replacing entire cabinets such as feeder systems might be necessary. This leads to direct financial damage - the cost of replacement parts - but also indirect damage resulting from decreasing production capacity. This could also negatively affect market position and business results.

 

By means of simulations and arc flash calculations, HyTEPS supports you in protecting your employees, and reducing unnecessary risks and unwanted downtime and costs.

Direct Current (DC) Arc Flash Calculations

All distribution boards or panels are subjected to arc flash phenomena, as no electrical installation can guarantee an arc-free situation. Direct Current (DC) installations are exposed to the same hazardous situations as Alternate Current (AC) installations.

Despite most electrical installations being AC, they also present some DC loads – each has an AC/DC converter so it can operate optimally . Moreover, the number of DC loads on  electrical systems is increasing, particularly due to integration of new technologies  such as renewable energy generation, electric vehicles, energy storage systems and LED lighting systems.

As a consequence, partial or complete DC installations are becoming more popular and common, especially in offshore (vessels and platforms), novel installations which are sensitive to Power Quality disturbances, and certain on-shore industries. Research in this field is becoming a hot topic, which means DC installations may become the ‘new normal’.

HyTEPS is also specialized in DC arc flash calculations thus ensuring safety on such electrical installations. The methodology is based on the state-of-art existing research.

DC Standards and Guidelines. Is compliance a ‘must’?

DC systems are not part of the existing guidelines and standards for performing Arc Flash hazard calculations. In other words, there is no official document defining a universal methodology to perform such calculations.

Compared to AC systems, research into the DC arc flash phenomenon is relatively new. Therefore, researchers have been performing real-life tests and documenting their findings in papers, developing a methodology for DC arc flash calculations mostly based on empirical equations.

HyTEPS can perform DC arc flash simulations based on the three most used and widely accepted methods:

  1. Maximum Power Method: Introduced in 2007, based on the maximum power the arc could achieve and the maximum energy that could be released by the arc and exposed to an employee. The maximum power, in watts, is the system voltage times one-half the bolted fault current.
  2. Stokes and Oppelander: Research developed in 1990, empirical equations based on test results. The study was based on a free-burning vertical and horizontal arc between series electrodes or busbars in open air. It also estimates the minimum burning voltage needed to maintain an open arc under different conditions.
  3. Paukert: based on a compilation of published arcing fault data from seven researchers who conducted several arc tests. Based on that, Paukert formulated arc voltage and arc resistance equations that consider electrode gap widths.

The method chosen for the calculation is based on the agreement with the customer, along with HyTEPS advice, as each method has its advantages, disadvantages but also limitations. The selected method is the one that fits customer needs the best.

Depending on the chosen method, extra information on distribution board physical characteristics may be required.

When DC arc flash calculations are recommended

In any DC electrical installations with either battery systems, rectifiers converting AC current to DC, and/or DC motors, it is recommended to perform arc flash calculations on each DC distribution board, mainly to:

  1. Ensure the installation is safe, verifying no unsafe situations are presented
  2. Learn more about the energy levels in case of an arc flash
  3. Advise Personal Protective Equipment (PPE) i.e. extra safety

This is especially important in situations where batteries are connected to the DC busbar and at 100 % state of charge. Depending on the battery size, consequences can be fatal in case of an arc flash on the busbar. Therefore, multiple parameters are involved such as the protection device in front of the battery as well as the cable damping which influences the arc current value. The presence or absence of galvanic isolation will also influence the final DC short-circuit current value and therefore the arc incident energy. Normally, power electronics have a fast current limitation to protect sensitive internal equipment, therefore the main contribution tends to be from DC batteries.

 

 

 

Personal Protective Equipment

The NFPA 70E 2021 standard for electrical safety in the workplace addresses employee workplace electrical safety requirements. The standard focuses on practical safeguards that also allow workers to be productive within their job functions.

Over the years it slowly included and expanded its section on Practical DC guidance. Therefore, it defines situations where PPE are required or not.

 

Therefore, PPE are required when the employee is exposed to live electrical parts which may result on a DC arc flash and the afterwards energy release.

It is of utmost importance the employee knows not only the potential risk he is exposed to but that he also wears the correct safety equipment. This is done by placing a DC arc flash label on the front plate of each distribution board or panel.

The DC Arc Flash Label

HyTEPS has developed a label template which summarizes the DC arc flash simulation results highlighting the hazard category defining the level of PPE required. Its purpose is purely indicative as it cannot be referred to any standard or guidelines. However, it combines HyTEPS expertise in AC arc flash together with the state-of-art research on DC arc flash.

General Information:

  • Warning message: Arc flash / shock hazard risk
  • Distribution board name i.e. cabinet
  • Type of Arc Flash i.e. Direct Current (DC)
  • Method used for the calculation
  • Simulation date
  • ISO number: Unique per label
  • Customer logo
  • HyTEPS logo
  • Warning message: stating that changes to either the system configuration or equipment will invalidate the results and that the label results are based on a simulation report / arc flash study

DC Arc Flash information:

  • Shock hazard when cover is removed
  • Arc Fault current
  • Working distance considered for the simulation
  • Incident energy due to a DC arc flash based on the arc location i.e. enclosure (inside a cabinet with an open front door) or open air (without cabinet at all).

HyTEPS is expert in simulating arc faults

 

We would like to inform you about the possibilities in the area of simulating and reporting arc faults. We strive to deliver tailored solutions, reports and advice, which can be directly applied in order to increase safety and continuity. This improves your knowledge of your own installation, correct operation and security, and answers the question whether the installation has been properly designed for normal as well as emergency operation!