IEEE 1584-2018 Arc Flash Incident Energy Calculation
IEEE 1584-2018
The new IEEE 1584-2018 arc flash model supersedes the IEEE 1584-2002 model. The development of this new edition of the standard has taken over fifteen years of work and is a result of thousands of hours of research, development and validation. The following sections provide a summary of the main changes of IEEE 1584. ETAP has actively participated in the development and validation of this model to ensure its correct application in power system analysis software.
Model Development
The new model was developed based on over 1800 tests to incorporate different electrode configurations which was much more extensive than the 300 tests used in 2002.
Summary of tests performed:
Electrode Configuration |
Tests Performed |
Voltage Range |
Current Range |
Gap Range |
---|---|---|---|---|
VCB |
485 |
0.208 ~ 14.8 kV |
0.5 ~ 80 kA |
6 ~ 250 mm |
VCBB |
400 |
0.215 ~ 14.8 kV |
0.5 ~ 65 kA |
6 ~ 154 mm |
HCB |
460 |
0.215 ~ 14.8 kV |
0.5 ~ 63 kA |
10 ~ 254 mm |
VOA |
251 |
0.240 ~ 14.8 kV |
0.5 ~ 65 kA |
10 ~ 154 mm |
HOA |
259 |
0.240 ~ 14.8 kV |
0.5 ~ 66 kA |
10 ~ 154 mm |
Electrode Configuration
The most important step in implementing the calculations based on the new IEEE 1584-2018 model, is to identify which one of the five electrode configurations are present in the equipment being analyzed, while also understanding that it is possible to have one or more electrode configurations present in a piece of equipment.
Table 9 of IEEE 1584-2018 is a good starting point for some guidelines on how to identify the potential electrode configuration(s) present in the equipment.
VCB
VCBB
HCB
VOA
HOA
Range of the Model
The range of the voltage and short-circuit current is similar to that of the previous model. The notable improvement is the range of the gap for medium-voltage equipment, which has almost doubled.
Model voltage, short-circuit current, gap and working distance range:
Voltage Range (3-P kV LL) |
I_{bf}(kA) |
Gap (mm) |
WD (inch) |
Fault Duration (cycles) |
0.208 ≤ V ≤ 0.600 |
0.5 to 106 |
6.35 to 76.2 |
> 12 |
No Limit* |
0.600 < V ≤ 15.0 |
0.2 to 65 |
19.05 to 254 |
> 12 |
No Limit |
Recommended range of the enclosure dimensions:
Enclosure Dimension |
Value |
Height |
14 to 49 (in)* |
Width |
(4 x Gap) to 49 (in)* |
Opening Area |
2401 (in2) |
Parameters used in testing:
Parameter |
Value |
Frequency |
50 ~ 60 Hz |
Phases |
3-Phase |
Configurations |
VCB, VCBB, HCB, VOA, HOA |
IEEE 1584-2018, Section 4.11 still recommends that the model can be used for single-phase systems and expects the results to be conservative.
Summary of the actual sizes of the test enclosures used to develop the model range:
Equipment Class |
Height (mm) |
Width (mm) |
Depth (mm) |
15 kV Switchgear 5 kV Switchgear |
1143* |
762* |
462* |
15 kV MCC 5 kV Switchgear |
914.4 |
914.4 |
914.4 |
5 kV MCC |
660.4 |
660.4 |
660.4 |
Low-Voltage Switchgear |
508 |
508 |
508 |
Shallow Low-Voltage MCCs and Panelboards Cable Junction Box |
355.6* |
304.8* |
≤ 203.2* |
Deep Low-Voltage MCCs and Panelboards Cable Junction Box |
355.6* |
304.8* |
> 203.2* |
Voltage Levels
The voltage range applicable to IEEE 1584 remains unchanged at 208V through 15kV.
Low voltage range is now 208V through 600V.
In previous versions of IEEE 1584 (2002) a reference to the Ralph Lee method allowed the possibility to use this method for this condition, yet its results were found to be totally unrealistic. Also, the physical behavior of the arcs and the mode of failure are totally different for overhead open-air equipment. The following table presents a concise view of the application of different models across voltage levels between 0.208 kV to 15 kV and higher.
Method | 208 V to 600 V | 601 V to 15 kV | 15.1 kV to 38 kV | > 38 kV | ||||||||||
Phases1 | 3ɸa | 3ɸb | 1ɸa | 1ɸb | 3ɸa | 3ɸb | 1ɸa | 1ɸb | 3ɸa | 3ɸb | 1ɸa | 3ɸa | 3ɸb | 1ɸa |
IEEE 1584-2002 | G | G | Y | Y | G | G | Y | Y | Y | Y | ||||
IEEE 1584-2018 | G | G | Y | Y | G | G | Y | Y | ||||||
*ArcFault™ | G | Y | Y | Y | G | Y | G |
Green (G) – Directly Applicable / Yellow (Y) – Extended with Engineering Assumptions
Non-Shaded – Not Applicable
Note that the Ralph Lee method should not be used at all for voltages above 15 kV, however, since it was previously applied by ETAP as an alternative to the IEEE 1584-2002 method, ETAP still has this option available but with a warning.
Arc Current Model (0.208 kV to 0.6 kV)
Perhaps the greatest improvement to the IEEE 1584-2018 model is its capability to model five different electrode configurations and their effect on the arc current. The main areas of improvement are its improved expected arc physical behavior, its increased sensitivity to gap variation, the correction of inconsistencies (such as cases when Ia > Ibf), etc. Please refer to Annex G.5.5 of IEEE 1584-2018 for more details on the improvements to the arc current model. The following plot shows a comparative analysis of the arc current predictions of the new model vs. the IEEE 1584-2002 model.
Arc Current Model (0.6 kV to 15 kV)
Similar to the 2002 method, IEEE 1584-2018 has two different models for arc current. The medium-voltage part of the model is described in section 4.4 and 4.9 of IEEE 1584-2018. The model uses an interpolation approach to apply the effect of the voltage on the arc current. The effect of voltage on the predicted arc current becomes less dominant as the voltage increases.
The new model centers around the calculation of the arc current at three different voltages which are 600, 2700 and 14300 Volts AC. The following plot shows the results of a parameter sweep for short-circuit current for the medium-voltage arc current model.
Arc Current Variation Correction Factor
The arc current is the most important factor to determine the operation time of overcurrent protective devices. This is the reason why the new IEEE 1584-2018 model applied an enhanced arc current model. The arc current predicted by the model is considered to be the average arc current for the duration of the arc. In reality, the arc current can experience variations caused by the ac and dc components of the short-circuit current. Also, the magnitude of the arc current can vary as the arc ignites, persists and extinguishes. The average current model in 2002 does not include the arc current measured during ignition or extinguishing periods of the arc. It includes only the average of all three-phase arc currents.
The physical concept of arc current variation is not changed, however, it was improved. Based on the analysis done during the new arc flash model development phase, it was found that the variation in the arc current was higher at voltages below 480 Volts and far less at voltages such as 600 Volts and 2700 Volts ac.
The value of the arc current variation is no longer fixed to 15% but calculated continuously based on the equations provided in section 4.5 of IEEE 1584-2018.
The arc current variation was determined from the median of the measured variation at each voltage level. The plot below shows the median arc current variation in percent for each of the five electrode configurations.
Low Voltage Arc Sustainability Limit
The reason the limits were revised is because additional electrode configurations such as VCBB used in the testing revealed that arcs can sustain at much lower short-circuit currents than previously presented in the 2002 standard.
Previous versions of IEEE 1584 suggested a limit for sustainability at around 240 Volts ac with approximately 125 kVA (or 10 kA with a 3.5% impedance transformer). This left a substantial amount of equipment out of the scope of incident energy calculations. However, since the limit has been lowered to 240 Volt ac with 2.0 kA of short-circuit current, it means that more systems had to be analyzed. An overly-conservative incident energy correction factor was removed from the low-voltage model for IEEE 1584-2018 as shown in the plot below:
As can be observed in this plot, the incident energy results of the new IEEE 1584-2018 model are more accurate and also less over conservative.
Incident Energy Model – (0.208 kV to 0.6 kV)
The incident energy model is described in great detail in sections 4.3, 4.6, 4.9 and 4.10 of IEEE 1584-2018. The overall incident energy model is different from that of the 2002 model because it includes the additional three electrode configurations. In addition, for enclosed configurations VCB, VCBB and HCB, an enclosure size-correction factor is applied.
The incident energy model follows the same principle as the arc current. An interpolation process is done to determine the incident energy. The interpolation takes place by obtaining intermediate incident energy values at 600, 2700 and 14300 Volts ac.
Incident Energy Model – (0.6 kV to 15 kV)
The plot below shows a comparison of the incident energy for both IEEE 1584-2018 and 2002 models. The results reveal consistently that if the equipment is determined to now be HCB configuration that the incident energy can be significantly more. In the plot below the incident energy for a VCB configuration, using the 2002 model is 20 cal/cm^{2} while it is predicted to be over 45 cal/cm^{2} using the 2018 model if the HCB electrode configuration is used.
Arc-Flash Boundary Model (0.208 to 0.6 kV)
The testing methods used allow the new model to predict shorter boundary distances. The testing and data processing used to develop the new arc-flash boundary model reveal a gain in margin which becomes evident when comparing the results of both methods (2002 and 2018).
Arc-Flash Boundary Model (0.6 to 15 kV)
Similar to the low-voltage model, there is a notable reduction in the predicted arc-flash boundary. The overly conservative IEEE 1584-2002 result consistently produces the highest AFB for similar incident energy values.
The plot below shows the arc-flash boundary vs the arc duration and compares the 2018 AFB vs the 2002 AFB results. This comparison was made for a system voltage of 2700 Volts ac.Effect of Grounding on the Incident Energy
Based on the findings of the development group of the new IEEE 1584-2018 model, the effect of grounding is no longer considered.
ETAP Arc Flash IEEE 1584-2018
ETAP Arc Flash Analysis software is used to perform arc flash analysis for systems from 0.208 kV to 15 kV in accordance with IEEE 1584-2018 “IEEE Guide for Performing Arc Flash Hazard Calculations.” The software determines the incident energy and arc flash boundary values required to comply with NEC equipment labeling. It also provides hazard evaluation for shock protection and arc flash PPE according to NFPA 70E 2018.