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J. C. Das - Arc Flash Hazard Analysis and Mitigation

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Название:
Arc Flash Hazard Analysis and Mitigation
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J. C. Das
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unrecognised / на английском языке
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Arc Flash Hazard Analysis and Mitigation: краткое содержание, описание и аннотация

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This new edition of the definitive arc flash reference guide, fully updated to align with the IEEE's updated hazard calculations An arc flash, an electrical breakdown of the resistance of air resulting in an electric arc, can cause substantial damage, fire, injury, or loss of life. Professionals involved in the design, operation, or maintenance of electric power systems require thorough and up-to-date knowledge of arc flash safety and prevention methods.
is the most comprehensive reference guide available on all aspects of arc flash hazard calculations, protective current technologies, and worker safety in electrical environments. Detailed chapters cover protective relaying, unit protection systems, arc-resistant equipment, arc flash analyses in DC systems, and many more critical topics.
Now in its second edition, this industry-standard resource contains fully revised material throughout, including a new chapter on calculation procedures conforming to the latest
. Updated methodology and equations are complemented by new practical examples and case studies. Expanded topics include risk assessment, electrode configuration, the impact of system grounding, electrical safety in workplaces, and short-circuit currents. Written by a leading authority with more than three decades' experience conducting power system analyses, this invaluable guide:
Provides the latest methodologies for flash arc hazard analysis as well practical mitigation techniques, fully aligned with the updated
Explores an inclusive range of current technologies and strategies for arc flash mitigation Covers calculations of short-circuits, protective relaying, and varied electrical system configurations in industrial power systems Addresses differential relays, arc flash sensing relays, protective relaying coordination, current transformer operation and saturation, and more Includes review questions and references at the end of each chapter Part of the market-leading
the second edition of Arc Flash Hazard Analysis and Mitigation remains essential reading for all electrical engineers and consulting engineers.

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Technology	Arc-Flash Mitigation	Incremental Commissioning Complexity	Protection for Intentional Exposure	Protection for Incidental Exposure	Foot-print	Capital Expense	Operational Expenditure	Equipment Survivability	Arc Flash Incident Energy Reduction	Typical Application
Prevention	Barriers	Low	Limited	Limited	No change	Low	Low	Moderate impact	None	LV switchgear switchboard
	ANSI compartmentalization	Low	Limited	Limited	No change	Low	Low	Moderate impact	None	LV switchgear switchboard
	IEC-4b compartmentalization	Low	Limited	Limited	No change	Low	Low	Moderate impact	None	LV switchgear switchboard
	HRG	High	Limited	Limited	Increased	Medium	Low	Moderate impact	SLG fault only	480V to 5 kV
	Shielding barriers	Low	Limited	Limited	No change	Low	Low	No impact	None	LV arc-resistant switchgear
	Adm. controls	N/A	Limited	Limited	No change	Low	Low	No impact	None	All, training requirement
Containment	Arc-resistant equipment	Low	No	Yes	Increased	High	Low	No impact	None	LV/MV switchgear
	Solid dielectric bus	Medium	Yes	Yes	No change	Low	Low	Moderate	None	MV switchgear
Reduction	Differential protraction	High	Yes	Yes	No change	High	Medium	impact	Significant	LV/MV switchgear
	ZSI	Medium	Yes	Yes	No change	Low	Medium	Moderate	Significant	LV switchgear/ switchboard
	Transfer trip	High	Yes	Yes	Increased	High	Medium	impact	Significant	LV switchgear fed from transformers of >750 kVA

TABLE 1.16. Measures for Mitigating Arc Flashes at Key Locations in Data Centers

System Location	Issue	Recommendations
LV service entrance equipment	Protection on HV side of transformer does not respond quickly for LV faults	Transfer trip, differential protection along with ZSI
UPS input/output switchboards	Selectivity requirements lead to extended clearing times	ZSI or optical detection
PDU secondary (480 V to 208/120 V)	Low fault levels and P combined with transformer inrush currents extend arc-clearing times	Maintenance switch, compartmentalization of PDU with administrative controls
Generator paralleling equipment	Low fault levels combined with multiple sources extend arc-clearing times	Bus differential or optical detection, adaptive relay settings
MV distribution equipment	Multiple utility sources and/or generator sources result in high fault currents	High-speed shorting switch, bus differential, and optical relaying

Figure 1.11. An outﬁt for PPE HRC4.

Figure 1.11shows a PPE outﬁt for HRC=4. It looks like a space suit and hampers the mobility of a worker to render fine tasks. The arc flash energy must be reduced to no more than 8 cal/cm 2with appropriate measures.

1.15.2 Arc Flash Labels

Computer-based software can generate a variety of arc ﬂash labels. The format, size of the label, and even colors can be modiﬁed according to user’s choice. NFPA speciﬁes minimum data that should be included in an arc ﬂash label. Generally, the labels are laminated to withstand weathering effects. Figure 1.12shows a specimen arc ﬂash label.

Figure 112 A specimen arc ﬂash label REVIEW QUESTIONS 1 The calculated - фото 41

Figure 1.12. A specimen arc ﬂash label.

REVIEW QUESTIONS

1 The calculated symmetrical three-phase bolted fault in a 480-V switchgear assembly is 40 kA. Using IEEE equations, calculate the arc fault current. Assuming that the fault is cleared in 0.1 seconds, both for Ia and 85% Ia, calculate the incident energy release and arc ﬂash boundary. Use the gap length and working distance as per IEEE tables. The 480 V three-phase system is high resistance grounded.

2 Repeat with Lee’s equations.

3 Repeat using Equation (1.9)of the text.

4 Consult NFPA 70 E and the text in this paper and specify the PPE outﬁts for category 3 and 4 hazard levels in detail.

5 What is the IEEE intent of calculating a second arcing fault current at 85% of Ia?

6 List ﬁve points in order of their importance for worker’s safety.

REFERENCES

1 W.A. Brown and R. Shapiro, “Incident energy reduction techniques,” IEEE Industry Applications Magazine, vol. 15, no. 3, pp. 53–61, May/June 2009.

2 T. Gammon and J. Mathews, “Conventional and recommended arc power and energy calculations and arc damage assessment,” IEEE Trans. Ind. Appl., vol. 39, no. 3, pp. 197–203, May/June 2003.

3 T. Gammon and J. Mathews, “Instantaneous arcing fault models developed for building system analysis,” IEEE Trans. Ind. Appl., vol. 37, no. 1, pp. 197–203, Jan./Feb. 2001.

4 V.V. Terzija and H.J. Koglin, “On the modeling of long arc in still air and arc resistance calculations,” IEEE Trans. Power Deliv., vol. 19, no. 3, pp. 1012–1017, July 2004.

5 A.D. Stokes and D.K. Sweeting, “Electrical arcing burn hazards,” IEEE Trans. Ind. Appl., vol. 42, no. 1, pp. 134–142, Jan./Feb. 2006.

6 H.B. Land, III, “Determination of the case of arcing faults in low-voltage switchboards,” IEEE Trans. Ind. Appl., vol. 44, no. 2, pp. 430–436, March/April 2008.

7 H.B. Land, III, “The behavior of arcing faults in low-voltage switchboards,” IEEE Trans. Ind. Appl., vol. 44, no. 2, pp. 437–444, March/April 2008.

8 R. Wilkins, M. Allison, and M. Lang, “Effects of electrode orientation in arc ﬂash testing,” in Proc. IEEE IAS Annual Meeting, Hong Kong, pp. 459–465, 2005.

9 IEEE 1584, IEEE Guide for Performing Arc-Flash Hazard Calculations, 2002.

10 J.C. Das, “Arc ﬂash hazard,” in McGraw-Hill Year Book of Science and Technology, pp. 18–20, McGraw-Hill, New York, 2008.

11 R. Lee, “The other electrical hazard: Electrical arc blast burns,” IEEE Trans. Ind. Appl., vol. 1A-18, no. 3, pp. 246–251, May/June 1982.

12 R. Lee, “Pressure developed by arcs,” IEEE Trans. Ind. Appl., vol. IA-23, no. 4, pp. 760–764, July/Aug. 1987.

13 R.L. Doughty, T.E. Neal, T.A. Dear, and A.H. Bingham, “Testing Update on Protective Clothing and equipment for arc exposure,” IEEE Industry Applications Magazine, vol. 5, no. 1, 37–49, Jan./Feb. 1999.

14 R.L. Doughty, T.E. Neal, and H.L. Floyd, II, “Predicting incident energy to better manage the electric arc hazard on 600-V power distribution systems,” IEEE Trans. Ind. Appl., vol. 36, no. 1, pp. 257–269, Jan./Feb. 2000.