A safety in electrical systems is a constant concern, especially when considering the risk of fires caused by electric arcs.
These events, triggered by insulation failures, can generate high levels of energy and put both equipment and people at risk. To ensure the safety in electrical installations, it is essential to carry out a detailed analysis of the risk of electric arcs.
It analysis allows to determine the incident energy, that is, the amount of energy released by an electric arc at a given point. Based on this value, it is possible to define the level of protection individual necessary for professionals working in these places.
O Ampere software, used in electrical projects, offers an efficient solution for arc flash hazard analysis. It uses the calculation models established by IEEE 1584-2018 standard to determine the incident energy and arc flash limit, facilitating the risk analysis and definition of appropriate PPE.
Furthermore, the software allows to identify the devices of protection against electric arcs, contributing to risk mitigation.
O Electro Graphics electrical network calculation software increases safety in electrical engineering by enabling precise definition of PPE and arc protection devices. With it, you scales electrical projects safely and efficiently.
Electrical systems must minimize and mitigate the effects of electric arcs, especially in the operation of energized lines, which can be caused by short circuits accidentally triggered by operators close to energized electrical parts.
At an industrial level, fault currents and voltages can create explosive electrical arcs, with molten material projected and dangerous radiation.
Normally, an analysis is made of the degree of danger of the electric arc that can develop in an electrical , defined by the value of the incident Energy calculated at the working distance.
The incident energy determines the level of protection of the personal protective equipment (PPE) that personnel responsible for carrying out activities on energized lines must use.
Other risk mitigation initiatives involve choosing appropriate equipment and systems, such as fault current-limiting circuit breakers and arc flash sensors designed to quickly interrupt power.
Ampère software applies the calculation models provided by IEEE 1584-2018 to determine the Incident Energy (E) and the Arc Flash Threshold (AFB). The table below relates the Incident Energy values to the level of personal protective equipment required.
The definition of Arc flash limit is removed from the standard NFPA 70E: the distance from which Arc Flahs occur and at which you definitely do not have fatal burns (3rd degree) and have a 50% chance of having 2nd degree burns. If the radiated energy is reduced to 1,2 cal/cm2 (5 J/cm2), no PPE is required for Arc Flash.
The values provided by the standard are the interpolation of the results obtained from tests carried out on three typical s, with operating voltages equal to 600, 2700 and 14300 V respectively.
Validation limits
The main field of application of the calculation involves line supply voltages from 208 V to 15.000 V. The circuits must be in alternating current with operating frequencies of 50 or 60 Hz. The fault currents must have values between:
- de 208V to 600V: 500A to 106.000A;
- from 601 V to 15.000 V: 200 A to 65.000 A.
The distance between conductors for different voltage ranges:
- de 208V to 600V: 6,35mm to 76,2mm;
- from 601V to 15000V: 19,05mm to 254mm.
Frames must have the following size limits:
- Maximum height and width 1244,6 mm;
- Maximum opening area 1.549 m2;
- The width must be at least 4 times the distance between the conductors.
Fundamental to the calculation is the variable time, i.e. the duration of the arc. The opening time of the protections against arc current Iarc is calculated, to which 0.05 seconds is added for the minimum non-delayed opening time.
It should be noted that the standard calculates the Incident Energy (E) as the higher of two scenarios, in which two arc current values are considered, one nominal and the other reduced. Reducing the current may affect the opening times, resulting in a final value higher than the full current.
Arc Flash Calculation
Let's analyze the tool offered by the software to calculate the Energy incident on electrical s. To perform the analysis, it is necessary to enter the Edit data window and select the tab Arc-Flash Hazard.
The window below is used as a “calculator” to check the danger level of a as a whole, or of a specific . A particular case could be a containing several MT/AT Cells, for which it may be necessary to perform a spot check. Such s are highlighted in the list by a suffix [MT/AT Cell] next to the name.
Reference for calculation
In the window it is possible to choose one of the s belonging to the board, or with the command Find the biggest fault in the board, the software proposes the with a greater degree of danger.
The working voltage and fault current used are displayed. The IEEE 1584 standard prioritizes three-phase fault currents, although they are not the worst case among faults.
For single-phase or two-phase circuits, the software uses the Ikm max fault current. The window also provides information related to the impossibility of performing calculations such as:
- without power;
- Zero fault current;
- Voltage less than 208 V;
- Voltage greater than 15 kV;
- Working frequency other than 50 or 60 Hz;
- Fault current greater than 106 kA (for voltages less than 600 V);
- Fault current greater than 65 kA (for voltages greater than 600 V);
- Frame width less than 4 times the distance between electrodes.
Frame Properties for Arc Flash
In the window you can enter the Working distance and three properties of the frame. The incident energy, therefore the level of danger of the electric arc, is calculated at the assumed working distance of the operator.
Being a presumed and theoretical value, the window allows an analysis at different distances suggested by the standard, providing a series of four energy values and the corresponding levels of PPE required. Below, we have the Electrode configuration:
- VCB: Vertical electrodes in a frame;
- VCBB: Vertical electrodes with insulating barrier in a frame;
- HCB: Horizontal electrodes in a frame;
- VOA: Open air vertical electrodes;
- HOA: Outdoor horizontal electrodes.
A Distance between electrodes must be chosen considering that the working voltage imposes a range of accepted values, as suggested by the comment below the command. Finally, the frame size complements the “physical” information.
If the frame carpentry is already inserted, the dimensions are automatically entered by the software. Attention: For MT/AT cells, managed as individual s, it may be necessary to enter the dimensions of the individual cell, rather than the overall frame.
Results with Iarc at 100%
The window also displays the calculations for the first scenario with full arc current. This determines the protection opening times, which are identified by the software upstream of the reference .
The Arc Flash Limit (AFB) is the distance at which an incident energy of 5 J/cm2 is expected, the first threshold beyond which a degree of personal protection is required. Finally, it contains a table with the distances, incident energies and corresponding protection levels, expressed in [mm]/[in] and [J]/[cal], customizable units of measurement.
Results with reduced Iarc
The window displays the calculations for the second scenario with reduced arc current. The fault currents that can develop in a switchgear have a range of values due to the external conditions that influence the fault, such as the operating temperature and the supply voltage.
Therefore, in paragraph 4.5, the IEEE 1584 standard provides the equation for calculating the reduced values of the arc current. As already mentioned, it is important because it can increase the Arc time T at a value that provides a final result of incident Energy greater than at full current.
Printing the results
Finally, the window allows printing of the results of the calculations carried out applying the IEEE 1584 standard, mainly for the creation of electric arc hazard warning signs to be placed in risk areas.
The software provides some templates as shown in the figure below and also allows you to create custom templates through the template manager edit templates.
Note. Among the models proposed by the software, the Arc Flash (model) provides all the useful commented tags as a starting point for any custom document concerning the study of the electric arc.
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