ARC FLASH & PPE UPDATE. Michael Olivo, P.E. Aaron Ramirez, E.I.T.

Transcription

1 ARC FLASH & PPE UPDATE Michael Olivo, P.E. Aaron Ramirez, E.I.T.

2 What is Arc Flash? Arc Flash is the release of heat and light produced when electrical current flows through an air gap between two conductors 2

3 Overview of Arc Flash An arc fault is when air separation between high voltage conductors is compromised allowing electrical current to flow through the air gap between conductors Air separation is compromised by insulation breakdown or accidental contact with the electrical systems Arc fault creates an electrical explosion Light and heat emitted from the explosion is known as arc flash Pressure wave caused by the tremendous temperatures of the arc flash is known as arc blast Arc Flash Arc Fault Electrical explosion Arc Blast 3

4 Arc Flash and Arc Blast Arc Flash Temperatures can reach 35,000 F Exposure to these extreme temperatures burns the skin and causes clothing to catch on fire Arc flash will kill up to distances of 10 ft. Arc Blast Explosive expansion of the air and metal in the arc path Dangers associated with expansion are high pressure waves, sound, and shrapnel Heated metal is expelled away from the arc at speeds exceeding 600 mph 4

5 What causes an Arc Flash? Short Circuit - energized conductor making an unintentional contact with another energized conductor Ground Fault - energized conductor making an unintentional contact with ground 0V The following events will create an arc flash Insulation breakdown Accidental contact with the electrical systems Improper use of tools Dropped tools Corrosion Lack of electrical safety training Lack of preventative maintenance 240V 240V Screwdriver touching 240V and 240V (Short Circuit) 0V 240V 240V Dropped screw touching 240V and Ground (Ground Fault) 5

6 What is incident energy? Incident energy is the temperature produced (in cal/cm²) at a distance (usually eighteen inches) from an arc flash 1 Cal/cm 2 Hand 1 inch over flame for 1 second equals 1 cal/cm² It takes 1.2 cal/cm² to create a second-degree burn A second-degree burn causes skin to blister and become sore 1.2 Cal/cm 2 6

7 PPE Categories Personal Protective Equipment (PPE) 7

8 PPE Category 0 If incident energy < 1.2 cal/cm^2 Use PPE Category 0 Untreated Cotton Long Sleeve Shirt, Pants, Safety glasses, Hearing Protection Number one question asked, "What level of PPE should we use? Note: (*) While the 2015 NFPA 70E Edition no longer recognizes Category 0 as an arc flash hazard, the need for proper personal protective equipment (PPE) remains unchanged. 8

9 Two ways to evaluate Arc Flash Tables in NFPA 70E Arc Flash Study 9

10 Table Method Table 130.7(C)(15)(A)(a) Table 130.7(C)(15)(A)(b) 10

11 Table 130.7(C)(15)(A)(a) 11

12 Table 130.7(C)(15)(A)(a) 12

13 Table 130.7(C)(15)(A)(b) 13

14 Table 130.7(C)(15)(A)(b) 14

15 Arc Flash study How it works We send this form to the District District fills out the form with information from the field District sends back the form to us We will run it in our arc flash calculation software We will print the equipment labels and send back to the District to put on the equipment 15

16 Arc Flash study City Location GPS coordinates Transformer rating Service Drop Conductor sizes Conductor lengths Conductor type Overhead/Underground Service Entrance Conductor sizes Conductor lengths Conductor type 16

17 Arc Flash study Meter Company Meter Code Barcodes Service Breaker brands Breaker sizes Breaker labels Service Information Manufacture Service Code Line voltage Date of manufacture 17

18 Arc Flash study Signal Cabinet Feeder Conductor sizes Conductor lengths Signal Cabinet Breaker brands Breaker sizes Breaker labels 18

19 Results from skm Results from US 290 and George Bush St At the electrical service incident energy is 3.4 Cal/cm 2 PPE Category 1 will be required At the Controller the incident energy is 0.1 Cal/cm 2 PPE Category 0 will be required 19

20 Intersection Example Cal/cm^2 PPE Level Cal/cm^2 PPE Level 1 20

21 Intersection Example Cal/cm^2 PPE Level Cal/cm^2 PPE Level 0 21

22 Intersection Example Cal/cm^2 PPE Level Cal/cm^2 PPE Level 0 22

23 Any Pattern seen in Arc Flash Study? The 3 locations shown are all traffic signals and all have similar configurations but have different incident energy values There is no discernable pattern in arc flash We can t control transformer size We can t control distance between electrical service and traffic signal controller on existing locations Things we can CHANGE are size of breakers and the size of conductors Will that help? 23

24 Design Design circuit with smaller breakers Design circuit with smaller conductors 24

25 Use Smaller Breakers 2P/70 A 1.7 Cal/cm^2 PPE Level 1 2P/60 A 0.1 Cal/cm^2 PPE Level 0 25

26 Use Smaller Wire Sizes 4 AWG 1.5 Cal/cm^2 PPE Level 1 8 AWG 0.5 Cal/cm^2 PPE Level 0 26

27 Smaller Conductor Sizes and Arc Flash Reducing conductor size reduces the incident energy 8.39% cost savings replacing #4 conductor with #6 conductor 17.87% cost savings replacing #4 conductor with #8 conductor Any Hidden Costs? Theft deterrent Smaller conductor size makes criminals less likely to steal and easier on our budget to replace. 27

28 Summary Arc Flash is the release of extreme heat and light Two ways to evaluate Arc Flash - Tables in NFPA 70E or performing Arc Flash Study Arc flash hazard decreases when breaker and conductor sizes are reduced Cost Savings Direct ALL QUESTIONS related to purchasing PPE to Sidney Maloy (512) Sidney.Maloy@txdot.gov 28

29 Questions? 29