NFPA 70E: Arc Flash in District Energy
with Distributed Generation Sources
Presented By:
Edd H. Lovette III, P.E., LEED-AP
Jacobs Engineering • July 2, 2012
Arc Flash / Distributed Generation
Introduction
Who is Edd H. Lovette III, P.E., LEED-AP ?
Arc Flash / Distributed Generation
Overview
– Calculation Approach
– Generation Case Study
– Mitigation Methods
Calculation Approach
• Develop the Model
–System Topography
–Utility Fault Currents – Receive from Utility
–Generator Data – Receive from Gen. Mfg.
Calculation Approach
– Behind the Scenes:
• Three Part Process
• Part 1: Short Circuit Analysis
–
–
–
–
Calculate System Available Fault Current
Compare to Equipment Ratings
Identify Deficiencies
Available Fault Current Affects Arc Flash Energy
Calculation Approach
– Behind the Scenes:
• Part 2: Coordination Study
– Model Settings for Relays
– Compare Settings on TCC
Curve
– Available Short Circuit
Current Affects Arc Flash
Energy
– Breaker Operating Time
Affects Arc Flash Energy
Calculation Approach
– Behind the Scenes:
• Part 3: Arc Flash Evaluation
– IEEE-1584 Calculations
– Calculations Performed for Each Component
– Incident (Arc Flash) Energy Identified
– Develop Labels
– Utilizes Short Circuit Current (Isc) from Part 1
– Utilizes Opening Time (t) from Part 2
Calculation Approach
Lets Go Back To This Part
• Part 2: Coordination Study
– Available Short Circuit
Current Affects Arc Flash
Energy
– Breaker Operating Time
Affects Arc Flash Energy
Calculation Approach
Incident Energy
“E”
Calculation Approach
Simplified IEEE1584 Equations
Isc = Short Circuit Current
t = Time
E = Incident Energy
log10(Ia) = 0.00402+0.983*log10(Isc)
log10(En) = K1+K2+1.081*log10(Ia)+.0011G
E = 4.814*C*En*(t/0.2)*(610^x/D^x)
D, C, K1, K2, G = constants, x = distance
1000V< System Voltage < 15,000V
Sample Time Current Curve (TCC)
Calculation Approach
Summary
– 3 Steps
• Short Circuit Study
• Coordination Study
• Arc Flash Evaluation
– Short Circuit Current (Isc)  Significant Impact On Energy
– Time (t)  Significant Impact On Energy
Case Study Analysis
– Case Study:
Solar T60
| 5.5 MW
|
12.47kV
Case Study Analysis
Case Study Analysis
– Case 1: No Protection
– Turbine 3-Phase Isc
• 1949 Amps
– Breaker Opening Time
• 999999 Seconds
– Arc Flash Incident Energy
• Bus – 219,149 cal/cm2
• DANGEROUS
Case Study Analysis
– Case 2: SEL-300G
• 51 Function Only
• I2T Over-current
– Turbine 3-Phase Isc
• 1949 Amps
– Breaker Opening Time
• 5.2 Seconds
– Arc Flash Incident Energy
• Bus – 11.62 cal/cm2
• CATEGORY 3
Case Study Analysis
– Case 3: SEL-300 w/ NGR
• 51N Function Only
• 36 Ohm NGR
– Turbine 1-Phase Isc
• 198 Amps
– Breaker Opening Time
• 0.58 Seconds
– Arc Flash Incident Energy
• Bus – 1.3 cal/cm2
• CATEGORY 1
Case Study Analysis
– Case 4: SEL-387
• Still Includes 300G
• 87 (Bus Differential)
– Turbine 3-Phase Isc
• 1949 Amps
– Breaker Opening Time
• 0.167 Seconds
– Arc Flash Incident Energy
• Bus – 0.37 cal/cm2
• CATEGORY 0
Case Study Analysis
– 1: No Protection
– 2: Over-current Protection
• Traditional
– 3: Neutral Ground Resistor
• Low Current, Low Arcing
• Less Chance to Turn to 3-Phase
• Harder Coordination
– 4: Bus Differential
• Local Protection Only
• Best Protection for Personnel
Case Study Analysis
– Resistance Grounding Reduces The Exposure
But Provides Coordination Challenges
• Low Fault Current
• Affects Downstream Clearing
– How to ground then…?
Grounding Options
– Ungrounded – Not acceptable with
distribution, nor recommended for plant
operations any longer
– Low Resistance Grounded – Standard For
“Unit Connected” Campus Generators
– High Resistance Grounded – Standard For
“IPP Style” Generators With GSUs.
– Hybrid High Resistance Grounded – HRG and
LRG <- Jacobs Recommended for Best Of All
Options.
Case Study Summary
–Not Every Job Is The Same
–Combination of Protection
–System Evaluation Required
Mitigation Methods
– Personnel Protection (PPE)
– Equipment Selection
• Relaying
• Grounding
• Switchgear
– Remote Control
• Racking Devices
• SCADA
– De-energize
NFPA 70E 2012 – Personal Protective Equipment (PPE)
NFPA 70E 2012 – Personal Protective Equipment (PPE)
Types of Electrical PPE
•
•
•
•
•
Clothing (Shirts/Pants/Coveralls/Suits)
Face Protection
Gloves
Shoes
Ear Protection
NFPA 70E 2012 – Personal Protective Equipment (PPE)
NFPA 70E 2012 – PPE
Table 130.7(C)(10) –
Protective Clothing and
Personal Protective
Equipment (PPE)
Matrix
Fine Print Notes:
-Allow Layering, Can Get
Confusing
Equipment Selection
–Relaying
• Specification
–Bus Differential
–Ground Protection
–Light Sensors (Retrofit)
• Settings
–Proper Coordination
–Lower Settings
–Maintenance Mode
Equipment Selection
–Grounding
• Neutral Ground Resistor
• Hybrid High Resistance
Equipment Selection
–Switchgear Rating – Arc Resistant
•
•
•
•
Type 1 – Front Only
Type 2 – Sides
Suffix B – Instrument Compartment Separation
Suffix C – Divided Vertical Sections
Equipment Selection
–Switchgear Rating – Arc Resistant
• ANSI C27.20.7
–Category ZERO With Doors Closed:
»Circuit Breaker Operation
»Circuit Breaker Racking
Remote Control
–Racking Device
–SCADA
NFPA 70E 2012 – Avoid Energized Service
Best Protection?
DO WORK WHILE EQUIPMENT DE-ENERGIZED
NFPA 70E 130.1 Requires Justification for Live
Work
Questions?