Seattle City Light Arc Flash: Application and Case Study May 23 rd 24 th. Ryan Cook

Transcription

1 Seattle City Light Arc Flash: Application and Case Study May 23 rd 24 th Ryan Cook 1

2 Overview (Pre Study) What is Arc Flash Hazard Mitigation Labeling Procedures Calculation Goals and Methods Boundary Case Study

3 Overview (Post Study) Worker Response Results PPE Labeling Continuing education Future research DC Studies

4 What is Arc Flash Electrical Explosion Resulting From a Low Impedance Fault Two Types of Incidents Bolted Faults: energy dissipated through equipment Arcing Faults: energy dissipated through air Causes Conductive dust buildup Poor maintenance Equipment failure Insulation

5 Factors Influencing Arc Flash Hazards System Conditions System voltage, loading Size and Shape of Enclosures Atmospheric Conditions Temperature, humidity Protective Devices TCC coordination studies Time to clear fault Distance From Fault

6 Why Is It Important? NESC (2007) Article 410.A.3 States Effective as of January 1,2009 employer shall assess potential exposure to electric arcs for employees who work on or near energized parts or equipment. Employer shall require employees to wear clothing with an effective arc rating no less than the anticipated level of arc energy. 2,000 People/Year Treated for Burns 5-10 incidents/day Easily Exceed $10 Million Per Case 5 th leading Cause of Industrial Fatalities

7 Calculation Goals Flash Protection Boundary Available Incident Energy Level (cal/cm^2) At Each Piece of Equipment Resulting PPE Requirements To Make Information Available With Labeling

8 Arc Flash Protection Boundaries Flash Protection Boundary Safe Approach limit at a distance from an exposed live part where a person could receive a second degree burn Limited Approach Boundary Approach limit at a distance from an exposed live part in which a shock hazard exists. Crossed only by qualified personnel Restricted Approach Boundary Approach limit at a distance from an exposed live part in which there is an increased risk of shock. Crossed only by qualified personnel with appropriate PPE Prohibited Approach Boundary Approach limit at a distance from an exposed live part in which working within is the equivalent of making contact with the live part. Crossed only by qualified personnel with appropriate PPE

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10 Personal Protection Equipment Established by NFPA 70E (2009) For Incident Energy Exceeding 1.2 Cal/cm 2 (2nd Degree Burn) Category Energy Level Needed Cal/cm 2 0 N/A Typical PPE Examples Non-melting or untreated natural fibers 1 5 FR shirt and FR pants 2 8 FR shirt and FR pants and face protection 3 25 FR clothing with overall and face protection 4 40 Flash suit with hood

11 Equipment Labeling Adopted Into 2002 NEC Required To Warn of potential hazard and appropriate PPE needed Be in a location providing clear visibility to workers Required On Switchboards and panel boards Motor control centers

12 Sample Label Default Format Generated by Our Software Very Cluttered Labels are only mandated to specify incident energy or PPE requirement We are Leaning Towards a Simpler Design

13 SCL Warning Labels Warning Labels Orange bar on top States Arc Flash/Shock Hazard is present Specifies appropriate PPE is required Includes arc flash boundary, incident energy level, flash hazard distance, PPE category, and equipment name For equipment rated CAT.0 CAT.4 PPE

14 SCL Danger Labels Danger Labels Red bar on top States no safe PPE exists Tells to de-energize before working Includes arc flash boundary, incident energy level, flash hazard distance, and equipment name For equipment rated higher than CAT.4 PPE

15 IEEE Provides empirical formulas from laboratory testing for incident energy and approach boundary calculations Preferred in industry but does not replace NFPA 70E Voltages between 208 V 15 kv, three phase, operating in Hz range NESC Article 410 Provides arc flash hazard data for higher voltage studies NFPA Standards Used for Study 70E-2004 (applies to industry) Personal Protective Equipment (PPE) requirements Establishes Arc Flash protection boundaries

16 Available Software SKM Power Tools Widely utilized in industry Employs IEEE 1584 calculation methods Used in Boundary station service arc flash study ARCPRO Industry standard for high voltage arc flash studies Relies on NESC arc hazard data for incident energy calculation Used in Boundary switchyard arc flash study

17 Calculation Methods: Step 1 Collect Field Data Transformer Impedances, ratings, grounding methods Conductors Type, size, length Fuse and breaker ratings Equipment type MCC, switchgear

18 Calculation Methods: Step 2 Model the Electrical System and Identify All Possible System Operating Modes Perform short circuit studies Perform protective coordination studies With this information we can calculate incident energy levels and the flash protection boundary at each fault location

19 Boundary Case Study: Station Service Scope of Arc Hazard Analysis per IEEE 1584 Includes the Following: Service areas fed from > 75kVA transformer 3 phase panels rated > 208V System voltages < 13.8kV

20 Boundary Station Service Operation Scenarios Normal Operation Two 13.8kV feeders Scenario 1: Reduced Operation One 13.8kV feeder Scenario 2: Backup Power 2a : Only 750kW generator running 2b : Only 250kW generator running

21 Station Service Normal Operation One Line Diagram

22 Station Service Results Worst Case Normal operation Highest incidents of equipment >CAT.3 PPE Problem Areas: Switchgear WA, WB, and NA Panels L27, L8, NE, and VH Paint booth

23 Boundary Case Study: Switchyard No Specific Formulas Govern Systems >13.8kV NESC Arc Flash Calculation Data Used for This Study

24 Switchyard One Line Diagram

25 Switchyard Results I Using arc flash calculation data from NESC and fault current calculations from ASPEN, ARCPRO is used to calculate incident energy LOCATION HIGHEST AVAILABLE INCIDENT ENERGY LEVEL (CAL/CM 2 ) FIELD PPE RECOMMENDATION BOUNDARY ROSS/DIABLO CEDAR FALLS TOLT GORGE 2.6 1

26 Switchyard Results II Incident Energy Threat Much Lower than Station Service Due To: Faster breaker opening times Greater working distance from fault Equipment generally not worked live

27 Recommendations Dangerous! De-energize when working near or around equipment Category 4 If working live, adjust instantaneous settings to pickup lower fault magnitude. De-energize recommended Category 3 Adjust protective device settings to decrease interrupting time

28 In Retrospect: Overall Study Labor Intensive SKM modeling limitations System Configurations Protective relay settings Scope of data collection Some Questionable Results Due to: Miscoordination of protective devices Long breaker opening times Missing data

29 In Retrospect: Labeling Industrial Label Maker by Brady Global mark 2 Around $4000 Expensive replacement tape Locations Front/rear access of switchgear Independent breaker cubicles Under panel label

30 In Retrospect: PPE Rollout Provided by Work Rite Daily wear Electrical constructors Cat 2: 5 shirts, 5 pants, coveralls, rain coat, and jacket Cat 3 and 4 available upon request Alternative catalog selection Laundering stipend Intermediate wear Engineers/ Other powerhouse staff Cat 2: 2 shirts, 2 pants, coveralls, and jacket

31 Ongoing Work System changes CIP Projects Increased generation Education Availability of Results Powerhouse binders DPP/SOP Documentation General guidelines New employee training

32 Future DC study High potential risk Research being conducted by NFPA Establishing safety guidelines PPE recommendations Not conducted at SCL Other utilities?

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