Future Proof Your Arc Flash Assessment

Transcription

1 Future Proof Your Arc Flash Assessment 2017 ENERGY CONNECTIONS CONFERENCE TRADE SHOW Presented by: Keith Mullen, P.E. November 9, 2017

2 Agenda > Utility requirements > Study objectives > Applicable standards & methods > Example: Impact of system configuration > Conclusions 2

3 Definition of Arc-Flash Electric Arc-Flashover is defined as the passage of current between two electrodes through ionized gasses and vapors 3

4 Utility Requirements the employer shall ensure that an assessment is performed to determine potential exposure to an electric arc for employees who work near energized parts or equipment. Source: National Electrical Safety Code (NESC) 410A 4

5 Utility Requirements > Prepare arc flash assessment to provide a basis for: > Operating procedures > Equipment needs > Inform employees and contractors of potential exposure Priority #1 SAFETY > Train employees on equipment and operating procedures 5

6 Applicable Standards & Methods > NESC 410.A.3 > NFPA 70E > OSHA 29 CFR, > IEEE Standard 1584 > ARCPRO 6

7 Applicable Methods IEEE 1584 > Voltages in the range of 208 V V, three-phase > Frequencies of 50 Hz or 60 Hz > Bolted fault current in the range of 700 A A > Grounding of all types and ungrounded > Equipment enclosures of commonly available sizes > Gaps between conducts of 13 mm-152 mm > Faults involving three phases Note: A theoretically derived model, based upon Lee s paper [B19], is applicable for three-phase systems in open air substations, and open air transmission and distribution systems. This model is intended for applications where faults will escalate to three-phase faults. Where this is not possible or likely, this model will give a conservative result. Where single-phase systems are encountered, this model will provide conservative results. 7

8 Applicable Methods ARCPRO 8

9 Applicable Standards NFPA 70E Arc Flash Hazard PPE Category (HC) NFPA 70E PPE Categories Calculated Arc Energy (Cal/cm 2 ) (J/cm 2 ) >4 >40 >167.4 > 1.2 Cal/cm 2 is the threshold for a 2 nd degree burn > PPE limits injury to no more than a recoverable 2 nd degree burn 9

10 Applicable Standards OSHA 29 CFR Table 12 Selecting a Reasonable Incident-Energy Calculation Method 1 Incident-Energy Calculation Method 600 V and Less V to 15 kv 2 More than 15 kv 1Φ 3Φa 3Φb 1Φ 3Φa 3Φb 1Φ 3Φa 3Φb NFPA 70E-2004 Annex D (Lee Equation) 3 Y-C Y N Y-C Y-C N N 4 N 4 N 4 Doughty, Neal, and Floyd Y-C Y Y N N N N N N IEEE Std. 1584a Y Y Y Y Y Y N N N ARCPRO Y N N Y N N Y Y 6 Y 6 Key: 1Φ: Single-phase arc in open air 3Φa: Three-phase arc in open air 3Φb: Three-phase arc in an enclosure (box) Y: Acceptable; produces a reasonable estimate of incident heat energy from this type of electric arc N: Not acceptable; does not produce a reasonable estimate of incident heat energy from this type of electric arc Y-C: Acceptable; produces a reasonable, but conservative, estimate of incident heat energy from this type of electric arc 10

11 Revised Standards OSHA 29 CFR Table 14 Selecting a Reasonable Distance from the Employee to the Arc Class of Equipment Single-Phase Arc mm (inches) Three-Phase Arc mm (inches) Cable NA* 455 (18) Low voltage MCCs and panel boards NA 455 (18) Low voltage switchgear NA 610 (24) 5 kv switchgear NA 910 (36) 15 kv switchgear NA 910 (36) Single conductors in air (up to 46 kv), work with rubber insulating gloves 380 (15) NA Single conductors in air, work with live-line tools and live-line bare hand work MAD (2 x kv x 2.54) (MAD (2 x kv /10) ) NA * NA = Not applicable The terms in this equation are: MAD = The applicable minimum approach distance kv = The system voltage in kilovolts 11

12 Revised Standards OSHA 29 CFR Table 13 Selecting a Reasonable Arc Gap Class of Equipment Single-Phase Arc mm (inches) Three-Phase Arc mm 1 (inches) Cable NA 2 13 (0.5) Low voltage MCCs and panel boards NA 25 (1.0) Low voltage switchgear NA 32 (1.25) 5 kv switchgear NA 104 (4.0) 15 kv switchgear NA 152 (6.0) Single conductors in air, 15 kv and less 51 3 (2.0) Phase conductor spacing Single conductor in air, more than 15 kv Voltage in kv times 2.54 (0.1), but no less than 51 mm (2 inches) 3 Phase conductor spacing 1Source: IEEE Std. 1584a NA : Not applicable 3Table 6 of Appendix E of final Subpart V uses a more conservative arc gap that equals the electrical component of the minimum approach distance rather than a value corresponding to the dielectric strength of air for the system voltage which forms the basis for the values in this table. 12

13 Applicable Standards OSHA 29 CFR Exposure Minimum Head and Face Protection None 1 Minimum Head and Face Protection 1 Arc Rated Faceshield with a Minimum Rating of 8 Cals/cm 2 Arc-Rated Hood or Faceshield with Balaclava Single-phase, open air 2 8 Cal/cm Cal/cm 2 13 Cal/cm 2 or higher 2 Three-phase 2 4 Cal/cm Cal/cm 2 9 Cal/cm 2 or higher 3 1. These ranges assume that employees are wearing hardhats meeting the specifications in or (b)(2), as possible. 2. The arc rating must be a minimum of 4 Cal/cm 2 less than the estimated incident energy. Note that (g)(5)(v) permits this type of head and face protection, with a minimum arc rating of 4 Cal/cm 2 less than the estimated incident energy, at any incident energy level. 3. Note that (g)(5) permits this type of head and face protection at any incident energy level. 13

14 The Curve Method Relays > Prepare curves for specific incident energy levels > Compare with device responses for available fault range 14

15 Other Operating Scenarios 15

16 Study Findings Secondary Voltages (2012 NESC) NESC Table Equipment Type Nominal Voltage Range & Cal/cm 2 50V-250V 251V 600V 601V-1000V Self-contained meters / cabinets 4 (2) 20 (4) 30 (8) Pad-mounted transformers 4 (9) 4 (9) 6 (8) CT meters and control wiring 4 (2) 4 (5) 6 (8) Metal-clad switchgear / motor control centers 8 (3) 40 (6) 6 (8) Pedestals / pull boxes / hand holes 4 (2) 8 (7) 12 (8) Open air (includes lines) 4 (2) 4 (7) 6 (8) Network protectors 4 (10) (11) (11) Panel boards single phase (all) / three phase (< 100 A) 4 (2) 8 (12) 12 (8) Panel boards three phase (> 100 A) 4 (2) (13) (13) 16

17 Study Findings Secondary Voltages (2012 NESC) NESC Table Notes 1. This table was developed from fault testing based on equipment type and is independent of fault current unless otherwise noted. Calculations and test data are based on a 46 cm (18 in) separation distance from the arc to the employee. See IEEE Std Other methods are available to estimate arc exposure values and may yield slightly different but equally acceptable results. The use of the table in the selection of clothing is intended to reduce the amount or degree of injury but may not prevent all burns. 2. Industry testing on this equipment by two separate major utilities and a research institute has demonstrated that voltages 50 V to 250 V will not sustain arcs for more than 2 cycles, thereby limiting exposure to less than 4 Cal/cm 2. (See 208-V Arc Flash Testing [B1].) 3. Value based on IEEE 1584 formula for Motor Control Centers. [Gap = 2.54 cm (1 in)] (Xd = 1.641) [46 cm (18 in) distance] 51 ka (Based on a 208 V, 1000 kva, 5.3% Z, served from a 500 MVA system). Maximum duration without circuit protective device operation from industry testing (see 208-V Arc Flash Testing [B1]) is 10 cycles: 46.5 Cal/s/cm 2 x s = 7.8 Cal/cm Industry testing on 480 V equipment indicates exposures for self-contained meters do not exceed 20 Cal/cm Industry testing on 480 V equipment indicates exposures for CT meters and control wiring does not exceed 4 Cal/cm Value based on IEEE 1584 formula for Motor Control Centers. [Gap = 2.54 cm (1 in)] (Xd = 1.641) [46 cm (18 in) distance] 12.7 ka at 480 V (worst-case energy value from testing). (See Eblen and Short [B31].) Maximum duration without circuit protective device operation from tests is 85 cycles: 26.2 Cal/s/cm 2 x 1.42 s = 37 Cal/cm Incident analysis on this equipment indicates exposures do not exceed the values in the table. 8. Engineering analysis indicates that applying a 150% multiplier to the 480 V exposure values provides a conservative value for equipment and open air lines operating at 601 V to 1000 V. 9. Industry testing on 480 V equipment indicates exposures on pad-mounted transformers do not exceed 4 Cal/cm 2. (See Eblen and Short [B31].) 10. Industry testing on 208 V network protectors indicates exposures do not exceed 4 Cal/cm 2. (See 208-V Arc Flash Testing [B1].) 11. Industry testing on 480 V network protectors indicates arcs will not self-extinguish and heat flux rates will exceed 60 Cal/cm 2 /s at 24 in working distance. Perform arc hazard analysis. (See Eblen and Short [B31].) 12. Industry testing on 480 V panels with non-edge mounted bus bars indicates exposures do not exceed 8 Cal/cm 2. (See Eblen and Short [B31].) 13. Industry testing on panelboards with edge-mounted, parallel bus bars indicate arcs will not self-extinguish and heat flux rates will exceed 60 Cal/cm 2 /s at 46 cm (18 in) working distance. Perform arc hazard analysis. (See Eblen and Short [B31].) 14. IEEE 1584 original test data indicates there is no significant difference between heat flux rates for 400 V class equipment verses 600 V class equipment. 17

18 Sample Model System Normal Minimum 3ph fault on Feeder A: 3,200 A 18

19 Arc Flash Results for System Normal > Max Incident Energy: 7.36 Cal/cm 2 19

20 Sample Model Contingency Minimum 3ph fault 1,500 A 20

21 Arc Flash Results for Contingency > Max Incident Energy: Cal/cm 2 21

22 Field Condition Alerts Standard Standard w/ Faceshield Standard Standard w/ Faceshield Standard Standard 22

23 Conclusions > Utility compliance can be maintained by incorporating arc flash assessments into: > System planning and standards > Equipment purchasing > Operations and procedures > The Arc Flash Assessment needs to be a living document > Establish process to manage critical information > Adopt methods to share requirements with field staff and contractors > Stay current on industry regulations and standards 23

24 Thank you! Keith Mullen MANAGING DIRECTOR, SYSTEM PLANNING 131 Saundersville Road Suite 300 Hendersonville, TN Office: Mobile: Visit us at energy.leidos.com 24