Seattle City Light
Arc Flash: Application and Case Study
May 23rd – 24th
Ryan Cook
1
Overview (Pre Study)
•
•
•
•
•
What is Arc Flash
Hazard Mitigation
Labeling Procedures
Calculation Goals and Methods
Boundary Case Study
Overview (Post Study)
• Worker Response
– Results
– PPE
– Labeling
• Continuing education
• Future research
– DC Studies
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
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
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
• 5th leading Cause of Industrial Fatalities
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
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
Personal Protection Equipment
• Established by NFPA 70E (2009)
• For Incident Energy Exceeding 1.2
Cal/cm2 (2nd Degree Burn)
Category
Energy Level
Needed Cal/cm2
0
N/A
1
5
2
8
3
25
4
40
Typical PPE Examples
Non-melting or untreated natural
fibers
FR shirt and FR pants
FR shirt and FR pants and face
protection
FR clothing with overall and face
protection
Flash suit with hood
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
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…
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
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
Standards Used for Study
• IEEE 1584-2002
– 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
50 – 60 Hz range
• NESC Article 410
– Provides arc flash hazard data for higher voltage studies
• NFPA
– 70E-2004 (applies to industry)
 Personal Protective Equipment (PPE) requirements
 Establishes Arc Flash protection boundaries
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
Calculation Methods: Step 1
• Collect Field Data
– Transformer
 Impedances, ratings, grounding methods
– Conductors
 Type, size, length
– Fuse and breaker ratings
– Equipment type
 MCC, switchgear
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…
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
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
Station Service Normal
Operation One Line
Diagram
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
Boundary Case Study: Switchyard
• No Specific
Formulas Govern
Systems >13.8kV
• NESC Arc Flash
Calculation Data
Used for This Study
Switchyard One Line
Diagram
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/CM2 )
FIELD PPE
RECOMMENDATION
BOUNDARY
1.4
1
ROSS/DIABLO
4.7
2
CEDAR FALLS
1.9
1
TOLT
1.5
1
GORGE
2.6
1
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
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
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
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
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
Ongoing Work
• System changes
– CIP Projects
– Increased generation
• Education
– Availability of Results
• Powerhouse binders
– DPP/SOP Documentation
– General guidelines
• New employee training
Future
• DC study
– High potential risk
– Research being conducted by NFPA
• Establishing safety guidelines
• PPE recommendations
– Not conducted at SCL
• Other utilities?
33