the effects of means of grounding and asymmetrical current
TRANSCRIPT
The Effects of Means of Grounding and Asymmetrical Current on Arc Flash
por
Jairo Vladimir Chaparro Rodriguez
Proyecto de fin de carrera presentado para obtener el tıtulo deIngeniero Electrico
(Departamento de Ingenierıa Electrica y Electronica)en la Universidad de los Andes
2020
Evaluation Committee:
Gustavo Ramos LopezPaulo de Oliveira
Jairo Vladimir Chaparro Rodriguez
ORCID iD: 0000-0000-0000-0000
© Jairo Vladimir Chaparro Rodriguez 2020
TABLE OF CONTENTS
List of Figures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iii
List of Tabless . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iv
Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . v
Chapter
1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
2 Asymmetrical Current Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3 Arc Flash and Neutral Grounding Means . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.1 Solidly Grounded Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53.2 High Resistance Grounded Systems (HRG) . . . . . . . . . . . . . . . . . . . . 6
4 Short Circuit analysis for Line-to-Ground faults . . . . . . . . . . . . . . . . . . . . . 8
5 Arc Flash Levels Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
6 Arc Flash and Asymmetrical Current . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
7 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
8 Annexes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
ii
LIST OF FIGURES
FIGURE
2.1 Asymmetrical Short Circuit Contribution (4) . . . . . . . . . . . . . . . . . . . . . . 32.2 Asymmetry Factor Graph (4) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3.1 Phase voltages during line-to-ground fault using a solidly grounded system (4) . . . . 63.2 Phase voltages during line-to-ground fault using a High Resistance Grounding system
(4) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
8.1 IEEE 242 system zones . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
iii
List of Tables
TABLE
4.1 IEEE 242 Currents Using Solidly Grounded Method . . . . . . . . . . . . . . . . . . 84.2 IEEE 242 Voltages Using Solidly Grounded Method . . . . . . . . . . . . . . . . . . 94.3 IEEE 242 Currents Using HRG Method on LV Buses . . . . . . . . . . . . . . . . . . 104.4 IEEE 242 Voltages Using HRG Method on LV Buses . . . . . . . . . . . . . . . . . . 10
5.1 Arc Flash Results for IEEE 242 System . . . . . . . . . . . . . . . . . . . . . . . . . 11
6.1 Arc Flash Analysis for Bus F2 4160 of IEEE 242 System . . . . . . . . . . . . . . . . 13
iv
ABSTRACT
Industrial power systems bring considerable challenges in terms of safety and reliability. As anyother power network these type of systems have some specific risks, specially when it concerns toshort circuit faults. These faults create a phenomenon called Arc Flash, which in some cases canbe extremely hazardous for the system equipment, and also for the personnel. The IEEE 1584-2018 standard currently presents a methodology in the calculation of Arc Flash where the incidentenergy level is calculated based on the symmetrical rms bolted fault current value. However, thefirst cycles of the fault current are not symmetrical values. Therefore, it is necessary to analyzewhat happens if the incident energy is calculated as stated in the IEEE 1584-2018 standard, butusing the rms value of the asymmetrical current. This article takes into account the asymmetricalcurrent into Arc Flash estimations. This current value will affect considerably the level of incidentenergy during a fault, specially for systems with a high X/R ratio. Additionally, this article willshow up an analysis to see what happens with Arc Flash levels in industrial power systems usinghigh resistance grounding, and comparing it with solid grounded systems, one of the most commongrounding means in industry. As this study means an improvement on the safeness of electricsystems, simulations were carried out using IEEE 242 system in order to support the content ofthis paper.
v
Chapter 1
Introduction
Arc Flash is a dangerous and sometimes even deadly event that happens during a short circuit. Itcan reach temperatures approximately four times bigger than the temperature of the sun, and theexplosion can create a wave with a pressure around the 700 miles per hour.[1] This incident canoccur due to different reasons. Accidental contact across conductors, component failures, lack ofmaintenance, corroded cables, equipment, or parts are some factors that can cause it. Arc Flashlevel depends on the amount of incident energy, commonly measured in cal
cm2 . This amount ofenergy depends on different aspects, the most important ones are the time that takes to clear thefault, the ground fault current, and the voltage of the system.
Ground fault current level is very important for the Arc Flash calculation. The higher thiscurrent value is, the greater the Arc Flash level is going to be. So, this means that the incidentenergy is going to change depending on the type of fault. However, not all the type of faults havethe same probability to happen. Statistics show that approximately 95 % of all short circuits inindustrial plants are line to ground faults [2]. Therefore, choosing the correct grounding methodwill help reducing the incident energy during a fault of this type.
Grounding means were develop to solve different issues ungrounded systems had. The IEEEStd. 242-2001 establishes four system grounding methods that are normally used in industrialand commercial power systems. The most common ones are solid grounding, high resistancegrounding (HRG), low resistance grounding (LRG), and ungrounded systems. (3)
This document will focus in only two of them, the solidly grounded, and the high resistancegrounded systems. The first method is imperative for the analysis because it’s one of the mostcommon modes used. The second one is the method that should be used in order to attenuate theArc Flash Level. Throughout the document this point is going to be proved, being based on theanalysis related with the short circuit current levels and Arc Flash levels of these two methodsduring line to ground faults.
However, it is useless to show a method that attenuated the incident energy, if there is a proba-bility of an error in its calculation. IEEE 1584-2018 standard only talks about Arc Flash estimation
1
using symmetrical RMS current value. For this reason this document will also focus on showinghow asymmetric current can affect the level of Arc Flash considerably.
2
Chapter 2
Asymmetrical Current Analysis
In a short circuit the current experiences different stages. Initially during the first half cycle of thecurrent wave, the maximum value of the short circuit current is given. This is known as the sub-transitory state of the fault. After the first cycle, the current enters a transient phase where it tendsto stabilize, this usually happens during the first five cycles or so. Finally, the current stabilizesand reaches the steady state after several cycles. This will be its minimum value and will remainin this state until it is cleared.
When sizing the protections for a system, it is very important to take into account the sub-transitory part of the fault current. Usually, during this stage the circuit breakers detect the fault,but are not able to clear it. Therefore, protections must be able to withstand that half cycle currentvalue in order to clear the fault a few cycles later.
During the sub-transitory and transitory state of the fault current a phenomenon called asym-metric current appears. This means that the waveform of the current is displaced, creating a DCcomponent during the fault. Figure 2.1 shows the waveform of the asymmetric current.
Figure 2.1: Asymmetrical Short Circuit Contribution (4)
The magnitude and duration of this asymmetric component depends on two main factors. Theangle at which the voltage was at the time of the fault and the X/R ratio. For an angle closer or equalto zero the value of the magnitude of the asymmetrical current will be greater. The opposite would
3
happen if at the time of the fault there is a greater angle, this would reduce the magnitude of theasymmetrical current. On the other hand, the X/R ratio is inversely proportional to the duration ofthe asymmetrical current. The higher the X/R ratio, the longer it will take for the current waveformto reach its steady state. In order to estimate the value of asymmetrical component, the asymmetricfactor should be used. Figure 2.2 taken from Shoaib Khan’s book, shows how to estimate theassymetrical component multiplying the symmetrical current with the multiplication factor thatcorresponds to the X/R ratio of the system. (4) (9)
Figure 2.2: Asymmetry Factor Graph (4)
4
Chapter 3
Arc Flash and Neutral Grounding Means
In fact, an ungrounded system offers a huge advantage when it is related with Arc Flash. When aline to ground fault takes place, the short circuit current is very low due to the lack of zero sequencepath. In this case the only current that is going to show up will be the charging current of the entiresystem that is typically very low. Nevertheless, ungrounded systems have some issues with steadystate and transient overvoltages, causing several damage to the system equipment’s during groundfaults. That is why, nowadays is considered mandatory the usage of a grounding method in powersystems. (2)
3.1 Solidly Grounded Systems
Networks that use this grounding method will have no overvoltages during a ground fault. Sincethe neutral of the system is connected directly to the ground, it will be always at ground potential,avoiding a neutral offset during these types of faults. Figure 3.1 taken from Shoaib Khan’s book,”Industrial Power Systems” illustrates what happens to phase voltages when a line-to-ground faultoccurs. As can be seen in the figure, the healthy phase voltages will suffer a slightly change de-pending on the distance between the fault and the source. Nonetheless this change on the healthyphase voltage will always be less than the phase-to-phase voltage. Additionally, solidly groundedsystems offer another advantage. This grounding method enables the possibility to attend threephase four wire loads, that are the most common ones at commercial and industrial electric net-works. (2) (4)
5
Figure 3.1: Phase voltages during line-to-ground fault using a solidly grounded system (4)
However, grounding the neutral of the system directly to the ground represents a huge disad-vantage concerning to Arc Flash. In most of electrical systems, the net zero sequence impedanceis lower than the positive and negative sequence impedance. Hence, for solidly grounded networksthe fault current for ground faults will be higher. IEEE Std. 141-1993 states that these type ofsystems have the highest magnitudes of ground-fault current. This implies a huge risk specially forthe 480 and 600 V systems, the most common ones at industrial plants. Systems of this type havethe highest probability of escalating the ground fault into a phase-to-phase or three-phase arcingfault. Additionally, the danger of sustained arcing for phase-to-ground fault probability is also veryhigh. [5]
3.2 High Resistance Grounded Systems (HRG)
High resistance grounding came up with a complete different method in order to reduce groundfault current flow. In this case, the neutral of the system will be grounded through a high impedanceresistor. Thus, the total ground fault current will be limited by the resistance.
The current that flows through this element needs to be a value equal or slightly greater thanthe capacitive charging current of the system. The only way to be sure this happens is to calculatethe impedance of the resistor as equation 1 shows. Therefore, the total current flow will be thevector sum between the current flowing through the resistor and the capacitive charging current.This value is crucial for this method, because capacitive charging current is the lowest groundfault current flow at which overvoltages can be effectively limited.(6) This current depends on thereactive capacitance of the system XCO
R ≤ XCO
3(3.1)
As line-to-ground current fault will be reduce to approximately 8 A to 10 A, the system will be
6
capable of continue working during these incidents, increasing the system reliability.(7) At thesame time the incident energy will decrease considerably, reducing the Arc Flash levels.
Figure 3.2 shows the phase voltages diagram for a line-to-ground fault in a High ResistanceGrounding system. As it can be observed, the healthy phase line-to-ground voltages will increaseapproximately
√3 times line-to-line voltage. This effect happens because the current that flows
between the systems neutral and ground, will create a voltage that goes through the neutral to theground. The magnitude of this potential is almost systems line-to-neutral voltage value. (4) (2)
Figure 3.2: Phase voltages during line-to-ground fault using a High Resistance Grounding system(4)
Apparently figure 3.2 indicates that HRG have the same issue as the ungrounded method re-lated to overvoltages when ground fault occurs. However, with HRG no severe overvoltages willdeveloped due to a line-to-ground inductive fault or an intermittent ground-fault. (6)
On the other hand, this grounding method has some restrictions that need to be consideratebefore applying it. First of all, this system is not able to attend three phase four wire loads. Second,as some overvoltages are experienced in the healthy phases during line-to-ground faults. It is notrecommended to apply HRG on system islands that operate above 5 kV. Above this value, theinsulation of cables can break up easily causing an escalation from line-to-ground fault to line-toground-to line or a three phase fault. Additionally, is highly recommended to install a detectionsystem in order to locate easily the location of the fault. Because of HRG systems are capable ofcontinuous operation during a ground fault, locating the feeder that is faulted will increase systemssecurity and reliability. That way, operators will know when a fault is happening and also theywould be able to find very quickly which is the feeder with problems.
7
Chapter 4
Short Circuit analysis for Line-to-Ground faults
In order to demonstrate the theory mentioned in the previous section, a short circuit analysis wasmade. For this case the electric system that is going to be studied is the IEEE 242 case. Figure8.1, located in the annexes shows up the topology of the system. The short circuit power of thepower grid is equal to 5000MVASC . Analysis was made taking into account the minimum shortcircuit calculation, that represents the 30 cycle fault current. All the calculations for this sectionwere made with the help of ETAP 19.00 software. For all the scenarios the faulted phase is goingto be phase A. Phases B, and C are the non faulted phases, so the software ignores them becausethere values are not relevant for the simulation.
Table 4.1: IEEE 242 Currents Using Solidly Grounded Method
BusPhase A Phase B Phase C
Magnitude(kA)
Angle(°)
Magnitude(kA)
Angle(°)
Magnitude(kA)
Angle(°)
F1 20,918 -82,9 0 0 0 0
F1 480 7,323 -41,1 0 0 0 0
F1 4160 15,032 -78,1 0 0 0 0
F2 13,354 -87,4 0 0 0 0
F2 480 13,182 -62,3 0 0 0 0
F2 4160 16,054 -86,5 0 0 0 0
F3 480 20.171 -80,4 0 0 0 0
F3 4160 13,24 -87,2 0 0 0 0
F4 480 13,24 -87,2 0 0 0 0
8
Table 4.2: IEEE 242 Voltages Using Solidly Grounded Method
BusPhase A Phase B Phase C
Magnitude(%)
Angle(°)
Magnitude(%)
Angle(°)
Magnitude(%)
Angle(°)
F1 0 0 100,01 -120 100,02 120
F1 480 0 0 107,55 -128 110,43 126,8
F1 4160 0 0 92,24 -116,9 99,9 114,7
F2 0 0 99,31 -119,1 99,01 119,2
F2 480 0 0 103,5 -125,4 107,2 124
F2 4160 0 0 94,66 -114,2 94,92 114,1
F3 480 0 0 99,33 -119,6 99,67 119,4
F3 4160 0 0 99,41 -119,3 99,21 119,4
F4 480 0 0 99,41 -119,3 99,21 119,4
Tables 4.1 and 4.2 show up the results obtained from line-to-ground short circuit analysis. Table4.1 shows the current magnitudes and the angles of each phase during the fault. As mentioned inthe previous section solidly grounded systems have high ground fault current values. Anotherdetail that can be observed from the current magnitudes, is the way they decrease on buses locateddownstream. For example, bus F1480 shows a low fault current level in comparison with the otherbuses of the system. This happens because that bus is the farthest from source, so that meansimpedance value is going to be higher. Also, as this is a low voltage bus the impedance of cableswill be greater. However, table 4.2 reveal that healthy phase voltages remain stable demonstratingthe main characteristic of solidly grounded systems.
The second simulation that was made, was the line-to-ground short circuit analysis applyingHRG. The IEEE 242 has several buses that operate above the 5 kV. Applying HRG at these voltagesis not recommended due to overvolatges that can generate an insulation breakdown on healthyphases. Therefore, the blue and red islands shown in figure 8.1 will be kept solidly grounded, asthey operate at 138 kV and 13.8 kV respectively. On the other hand, the islands marked in greenand yellow operating at 0.48 kV and 4.16 kV will be grounded using HRG. Since the secondaryof each transformer operates at different voltages and the capacitance per phase of each branchdownstream of the equipment is different. Resistance values vary, the 480SS TX transformeroperating at 13.8/0.480 kV has a resistance of 27.7 Ω. While the 4160SS TX operating at 13.8/4.16kV has a resistance of 240.1 Ω. In both branches, the line-to-ground fault current will be limitedto 10 A. Tables 4.3, and 4.4 show the results obtained in the simulation.
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Table 4.3: IEEE 242 Currents Using HRG Method on LV Buses
BusPhase A Phase B Phase C
Magnitude(kA)
Angle(°)
Magnitude(kA)
Angle(°)
Magnitude(kA)
Angle(°)
F1 20,918 -82,9 0 0 0 0
F1 480 0,01 -0,1 0 0 0 0
F1 4160 0,01 0 0 0 0 0
F2 13,354 -87,4 0 0 0 0
F2 480 0,01 0 0 0 0 0
F2 4160 0,01 0 0 0 0 0
F3 480 0,01 0 0 0 0 0
F3 4160 13,24 -87,2 0 0 0 0
F4 480 13,24 -87,2 0 0 0 0
Table 4.4: IEEE 242 Voltages Using HRG Method on LV Buses
BusPhase A Phase B Phase C
Magnitude(%)
Angle(°)
Magnitude(%)
Angle(°)
Magnitude(%)
Angle(°)
F1 0 0 100,01 -120 100,02 120
F1 480 0 0 173,1 -150 173,17 150
F1 4160 0 0 173,16 -150 173,23 150
F2 0 0 99,31 -119,1 99,01 119,2
F2 480 0 0 173,15 -150 173,21 150
F2 4160 0 0 173,17 -150 173,24 150
F3 480 0 0 173,17 -150 173,22 150
F3 4160 0 0 99,41 -119,3 99,21 119,4
F4 480 0 0 99,41 -119,3 99,21 119,444
The analysis shows that if the system is grounded by a resistor, the line-to-ground fault currentis effectively limited. The buses downstream of the transformers limited the current to 10 A whenthe fault occurs. However, as far as voltages are concerned, it can be seen that the voltage profilein the buses is 173 %. This is due to the overvoltages generated by the displacement of the neutral,as shown in figure 3.2.
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Chapter 5
Arc Flash Levels Analysis
According to IEEE 1584-2018 the Arc Flash is defined as an electric arc event with thermal energydissipated as radiant, convective and conductive heat. It appears on the switchboards when anelectrical failure occurs. Arc Flash level is measured with the amount of incident energy in J/cm2or in cal/cm2, and its value will depend on different factors. The bolted short circuit symmetricalcurrent is one of the parameters that most affects incident energy levels as same as the clearingtime. The open circuit voltage level at which the network operates is also related to the incidentarc. However, there are also different aspects such as the configuration of the electrodes of theboard, separation distance of the electrodes, working distance, and dimensions of the cabinet. (8)
Table 5.1 shows the results obtained for the Arc Flash analysis in the IEEE 242 system with alltransformers solidly grounded. To perform these calculations the method suggested by the IEEE1584-2018 standard to calculate the incident energy level was used. Although the standard onlysays to take into account the bolted fault current, it does not mention which value of fault currentshould be used (line-to-ground, line-to-line, line-to-line-to-ground, or three-phase) to calculate theincident energy. However in this case the arc current and the incident energy were calculated withthe current values of table 4.1.
Table 5.1: Arc Flash Results for IEEE 242 System
Bus Arc Current(kA)
Clearing Time(Cycles)
Incident Energy(Cal/cmˆ2)
Incident Energy(J/cmˆ2)
F1 20,937 3,6 59,731 249,914504F1 480 7,322 0,25 0,055 0,23012
F1 4160 12,378 1,964 0,591 2,472744F2 12,24 42,68 12,108 50,659872
F2 480 12,38 1,8 0,7 2,9288F2 4160 12,86 30,748 9,614 40,224976F3 480 16,727 7,2 3,867 16,179528
F3 4160 12,32 3,6 1,028 4,301152F4 480 12,319 1,2 0,343 1,435112
11
The results show how the incident energy level changes considerably depending on the shortcircuit current and the clearing time. For example, the bus F4480 has a considerable arcing currentvalue, but its clearing time is very short. Therefore, the incident energy level is relatively low.
Nevertheless, most buses report significant levels of incident energy due to the line-to-groundfault current. But, if HRG was used, the incident energy would be drastically reduced. As theground fault current is limited to some amperes, thanks to the resistor. Arc flash will be easilymitigated due to the low values of short-circuit current, in case of a line-to-ground fault. Which isthe most common type of fault in an electric system. So, using HRG will improve the reliabilityand security of the system significantly.
12
Chapter 6
Arc Flash and Asymmetrical Current
Since the asymmetric current is shown in the first cycles and in addition its value will changeaccording to the X/R ratio. It is important to take it into account when performing an Arc Flashcalculation. The IEEE 1584 standard states that for the calculation of the incident energy, thebolted fault current (RMS symmetrical) should be used. However, this current may not guaran-tee an accurate value in relation to the Arc Flash level. Figure 2.2 shows that depending on theX/R value of the system the asymmetrical fault current can be up to 70 % higher than the sym-metrical component. Therefore, making the incident energy calculation taking into account theasymmetrical current can give more accurate results than using the symmetrical current value.
Table 6.1: Arc Flash Analysis for Bus F2 4160 of IEEE 242 System
X/R SystemRatio
MultiplicationFactor
SymmetricalCurrent (kA)
AsymmetricalCurrent (kA)
Incident Energy(J/cmˆ2)
4 1,2 16,054 19,2648 40,1184
8 1,4 16,054 22,4756 46,4998
10 1,47 16,054 23,59938 48,7266
15 1,52 16,054 24,40208 50,3153
25 1,6 16,054 25,6864 52,8541
Table 6.1 shows the results obtained for the calculation of Arc Flash in the F2 4160 bus ofthe IEEE242 system, using asymmetrical current, and different X/R system ratios. Comparing theresults between table 5.1 and table 6.1, a considerable difference can be observed.When both caseshad the same X/R ratio (X/R = 8), there was a great difference in the Arc Flash level. Incidentenergy was 6 J/cm2 greater in table 6.1 than in table 5.1. In addition, as the X/R ratio increased,so did the incident energy level. Thus, it can be inferred that asymmetrical current does affects ArcFlash considerably, and also the X/R system ratio.
13
Chapter 7
Conclusions
This paper presents an analysis of Arc Flash levels applying High Resistance Grounding, and alsosolid grounded method. Both methods were explained in detail, and a short circuit analysis wasmade. After that an Arc Flash study was mandatory in order to prove that high resistance groundingmitigates the incident energy. For this case the IEEE 242 system was used, and with the help ofETAP 19.0.0 it was possible to do all the analyses. Finally, an analysis to check what happenedwith Arc Flash calculation using asymmetrical current values was made. First of all a brieflyexplanation of asymmetrical current was performed, and then following the IEEE Std 1584-2018the Arc Flash level was estimated using the asymmetrical current value.
It can be concluded that applying HRG improves system security and reliability due to theArc Flash mitigation. Nevertheless, engineers have to take into consideration the conditions andrestrictions under which the HRG system can be implemented. regarding to the asymmetricalcurrent, it was found that the arc flash level can be affected by using this value instead of thesymmetrical current value. However, this will depend on the X/R ratio of the system. For systemswhere this ratio is low, there would be no significant difference. But if the X/R ratio is greater than8, the asymmetrical component should be taken into consideration when calculating the Arc Flash.
14
BIBLIOGRAPHY
[1] ABB, Help Protect Yourself and Your Personel from the Dangers of Arc Flash A guide toGetting Smart about Arc Flash Prevention, 2019.
[2] J. Dunki-Jacobs, F. Shields and C. Pierre, Industrial Power Systems Grounding Design Hand-book. Dexter, MI, USA: Thomson-Shore, 2007, pp. 444-508.
[3] ”IEEE Recommended Practice for Protection and Coordination of Industrial and CommercialPower Systems (IEEE Buff Book),” in IEEE Std 242-2001 (Revision of IEEE Std 242-1986)[IEEE Buff Book] , vol., no., pp.1-710, 17 Dec. 2001, doi: 10.1109/IEEESTD.2001.93369.
[4] S. Khan, Industrial power systems. Boca Raton: CRC Press, 2008, pp. 30-97.
[5] ”IEEE Recommended Practice for Electric Power Distribution for Industrial Plants,” in IEEEStd 141-1993 , vol., no., pp.1-768, 29 April 1994, doi: 10.1109/IEEESTD.1994.121642.
[6] B. Bridger, ”High-Resistance Grounding,” in IEEE Transactions on Industry Applications, vol.IA-19, no. 1, pp. 15-21, Jan. 1983, doi: 10.1109/TIA.1983.4504149.
[7] ”IEEE Recommended Practice for Grounding of Industrial and Commercial Power Systems -Redline,” in IEEE Std 142-2007 (Revision of IEEE Std 142-1991) - Redline , vol., no., pp.1-215,30 Nov. 2007.
[8] ”IEEE Guide for Performing Arc-Flash Hazard Calculations - Redline,” in IEEE Std 1584-2018 (Revision of IEEE Std 1584-2002) - Redline , vol., no., pp.1-341, 30 Nov. 2018.
[9] M. J. S. Ramos, D. P. Bernardon, L. Comassetto, M. Resener and E. B. Daza, ”Analy-sis of short-circuit asymmetrical currents in power distribution systems,” 2012 47th Inter-national Universities Power Engineering Conference (UPEC), London, 2012, pp. 1-6, doi:10.1109/UPEC.2012.6398628.
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Chapter 8
Annexes
Figure 8.1: IEEE 242 system zones
16