Cracking the Code for Arc-Flash Mitigation
Transcript of Cracking the Code for Arc-Flash Mitigation
22Littelfuse, Inc. © 2020
Cracking the Code for Arc-Flash Mitigation
Mark Pollock, P.Eng.Global Product Manager, Protection Relays
Industrial Business Unit
Littelfuse, Inc.
4Littelfuse, Inc. © 2020 4
What You Will Learn
1. Overview of an arc-flash event
2. Arc-Flash Hazard Assessments
3. IEEE 1584-2018 Updates
4. Options to Reduce Incident Energy
5. ROI on Mitigation Methods
6. Summary
8Littelfuse, Inc. © 2020 8
Incident Energy Contributors
▪ Arcing current depends primarily on:– Available short-circuit current
– Bus gap
– Electrode configuration
– Enclosure size
– System voltage
▪ Incident energy depends primarily on:– Calculated arcing current
– Arcing duration (function of clearing time of devices)
– Working distance
9Littelfuse, Inc. © 2020 9
Incident Energy Contributors
▪ Arcing current depends primarily on:– Available short-circuit current
– Bus gap
– Electrode configuration
– Enclosure size
– System voltage
▪ Incident energy depends primarily on:– Calculated arcing current
– Arcing duration (function of clearing time of devices)
– Working distance
11Littelfuse, Inc. © 2020 11
Only 66% of
respondents said their
facility has conducted an
arc-flash assessment
More than three quarters
of respondents have
equipment rated more
than 8 calories/cm2
12Littelfuse, Inc. © 2020 12
What Is An Arc Flash Hazard Analysis?
Mathematical methods are used to estimate the risk of injury as a result of exposure to incident energy from an arc flash.
Purpose is to identify:▪ Incident energy exposure of the worker
▪ Flash protection boundary
▪ Appropriate work distance
▪ Required calorie rating of PPE
Arc flash hazard is expressed in incident energy (cal/cm2)
Arc flash protective clothing is rated in arc thermal performance value (ATPV)
– ATPV is expressed in cal/cm2
ATPV rating of PPE must exceed calculated incident energy!
13Littelfuse, Inc. © 2020 13
Regulations and Standards
▪ OSHA 1910.132(d)(1)
– Requires employers to assess the workplace to determine if hazards are or
are likely to be present
– References NEC, NFPA 70E, and IEEE standards
▪ NFPA 70E Standard for Electrical Safety in the Workplace
▪ CSA Z462 Workplace electrical safety
– Requires an arc flash risk assessment be performed and documented
– Provides procedure for performing incident energy and risk assessment
calculations
▪ IEEE 1584 Guide for Performing Arc-Flash Hazard Calculations
– Provides procedure for performing arc flash hazard/incident energy
calculations
Z462-
18
15Littelfuse, Inc. © 2020 15
Arc-Flash Labels
▪ Labels should show voltage, incident energy value, working distance, and arc flash boundary
▪ Limited approach means a shock hazard exists within the specified boundary – qualified persons
▪ Restricted approach represents an increased shock hazard due to electric arcing combined with inadvertent movement
▪ Based on NEC Article 110.16 and NFPA 70E 130.5 (H)
17Littelfuse, Inc. © 2020 17
Recently Revised IEEE 1584 - 2018
▪ Revision based on over 1,800 actual tests
▪ Three-phase AC voltages from 208V to 15kV
▪ Three voltage-based equations: 600V, 2.7kV, 14.3kV and
interpolation used for other voltages
▪ Range of bolted fault current now dependent on voltage
▪ Range of electrode gap now dependent on voltage
18Littelfuse, Inc. © 2020 18
Recently Revised IEEE 1584 - 2018
▪ Extensive testing on five
electrode configurations
▪ Consideration of enclosure
sizes and correction factors
▪ Updated arcing current
calculations
19Littelfuse, Inc. © 2020 19
Recently Revised IEEE 1584 - 2018
▪ Guidance on 240V or less:
– Sustainable arcs are possible but
are less likely in three-phase
systems operating at 240V
nominal or less with an available
short-circuit current below 2000A
▪ System grounding no longer
considered
202020Littelfuse, Inc. © 2020 20
IEEE 1584-2018 Electrode Configuration - VCB
Vertical Conductors inside a metal Box/enclosure
212121Littelfuse, Inc. © 2020 21
IEEE 1584-2018 Electrode Configuration - VCBB
Vertical Conductors terminated in an insulating Barrier
inside a metal Box/enclosure
222222Littelfuse, Inc. © 2020 22
IEEE 1584-2018 Electrode Configuration - HCB
Horizontal Conductors inside a metal Box/enclosure
232323Littelfuse, Inc. © 2020 23
IEEE 1584-2018 Electrode Configuration - VOA
Vertical conductors in Open Air
242424Littelfuse, Inc. © 2020 24
IEEE 1584-2018 Electrode Configuration - HOA
Horizontal conductors in Open Air
25Littelfuse, Inc. © 2020 25
IEEE 1584-2002 Nine Steps for Arc-Flash Analysis
1. Collect the System and Installation Data
2. Determine the System Modes of Operation
3. Determine the Bolted Fault Currents
4. Determine the Arc Fault Currents
5. Find the Protective Device Characteristics and the duration of the arcs
6. Document the System Voltages and classes of equipment
7. Select the Working Distances
8. Determine the Incident Energy for all equipment
9. Determine the Flash-Protection Boundary for all equipment
26Littelfuse, Inc. © 2020 26
IEEE 1584-2018 Ten Steps for Arc-Flash Analysis
1. Collect the System and Installation Data
2. Determine the System Modes of Operation
3. Determine the Bolted Fault Currents
4. Determine typical gap and enclosure size based on system voltages and classes of equipment
5. Determine the equipment electrode configuration(s)
6. Determine the working distances
7. Calculate the arc current
8. Calculate the arc duration
9. Calculate the incident energy
10. Determine the Flash-Protection Boundary for all equipment
27Littelfuse, Inc. © 2020 27
IEEE 1584-2018 – Effects on Mitigation Methods
▪ HCB electrode configuration has higher energy – can be
tougher to meet performance requirements
▪ Higher arcing fault current – changes profile of how
OCPD fit in to the scheme
28Littelfuse, Inc. © 2020 28
Test Case: Comparing IEEE 1584-2002 and 1584-2018
IEEE 1584-2002 IEEE 1584-2018
Bus Name Bus kV
Prot Dev Arcing Fault (kA)
Trip/ Delay Time (sec)
Equip Type
Gap (mm)
Arc Flash Boundary
(in)
Working Distance
(in)
Incident Energy
(cal/cm2)
Prot Dev Arcing
Fault (kA)
Trip/ Delay Time (sec)
Equip Type
Busbar Config
Arc Flash Boundary
(in)
Incident Energy
(cal/cm2)
Incident Energy Percent Change
B-A-MAIN 0.208 1.54 1.539 PNL 25 52 18 6.76 1.35 2 PNL VCBB 42 5.56 -17.72%
B-CHARGER-BUS 0.48 10.93 0.0143 PNL 25 11 18 0.52 14.90 0.0134 PNL VCBB 12 0.59 12.05%
B-DS-LAB1 0.48 2.95 0.0345 PNL 25 8 18 0.31 3.27 0.0254 PNL VCBB 7 0.20 -35.20%
B-DS-LAB1-26 0.48 0.59 0.4678 PNL 25 13 18 0.73 0.49 0.6617 PNL VCBB 12 0.61 -16.65%
B-DS-LAB1-38 0.48 0.63 0.4083 PNL 25 13 18 0.68 0.53 0.5663 PNL VCBB 12 0.57 -17.03%
B-FIRE PMP 0.48 8.24 1.185 PNL 25 134 18 32.4 11.54 0.6133 PNL VCBB 86 20.2 -37.63%
B-FS-MSWBD-MAIN 0.48 9.93 0.9089 PNL 25 125 18 28.6 12.52 0.5849 PNL HCB 94 34.0 18.99%
B-FS-RTU-1 0.48 0.95 0.258 PNL 25 13 18 0.67 0.77 0.3669 PNL HCB 18 1.21 80.82%
B-FS-RTU-2 0.48 2.06 0.0096 PNL 25 3 18 0.06 1.83 0.0098 PNL HCB 5 0.08 39.76%
B-H1-07-REC 0.48 1.21 0.3985 AIR 32 15 18 0.88 0.90 0.7162 AIR HOA 24 2.07 135.89%
B-HB-07-REC 0.48 1.75 0.0277 AIR 32 5 18 0.09 1.43 0.864 AIR HOA 33 4.02 4279.64%
B-HP-1-MAIN 0.48 6.57 2 PNL 25 155 18 41.0 8.64 1.208 PNL VCBB 102 27.5 -33.07%
B-L3-01-REC 0.208 0.32 2 AIR 32 9 18 0.32 0.32 2 AIR HOA 9 0.32 0.00%
B-L3-02-REC 0.208 0.31 2 AIR 32 9 18 0.32 0.31 2 AIR HOA 9 0.32 0.00%
B-LAB2-07-REC 0.48 1.83 0.017 AIR 32 4 18 0.06 1.23 0.1631 AIR HOA 13 0.65 1002.73%
B-LB-1-MAIN 0.208 2.26 2 PNL 25 78 18 13.2 1.85 2 PNL VCBB 51 7.97 -39.75%
B-LB-2-BUS 0.208 2.25 2 PNL 25 78 18 13.2 1.84 2 PNL VCBB 51 7.92 -39.91%
B-FS-HP-MAIN 0.48 5.87 2 PNL 25 145 18 36.8 6.40 2 PNL HCB 123 59.5 61.81%
B-FS-EF-MAIN 0.48 5.87 2 PNL 25 145 18 36.8 6.40 2 PNL HCB 123 59.5 61.81%
30Littelfuse, Inc. © 2020 30
NEC 2020 Article 240.87 (Circuit Breaker)
240.87 Arc Energy Reduction
Where the highest continuous current trip setting for which the actual overcurrent device installed in a
circuit breaker is rated or can be adjusted is 1200 A or higher, 240.87(A) and (B) shall apply.
240.87(A) Documentation
Documentation shall be available to those authorized to design, install, operate, or inspect the
installation as to the location of the circuit breaker(s). Documentation shall also be provided to
demonstrate that the method chosen to reduce the clearing time is set to operate at a value below the
available arcing current.
31Littelfuse, Inc. © 2020 31
NEC 2020 Article 240.87 (Circuit Breaker)240.87(B) Method to Reduce Clearing Time
One of the following means shall be provided and shall be set to operate at less than the available arcing current:
(1) Zone-selective interlocking
(2) Differential relaying
(3) Energy-reducing maintenance switching with local status indicator
(4) Energy-reducing active arc flash mitigation system
(5) An instantaneous trip setting. Temporary adjustment of the instantaneous trip setting to achieve arc energy reduction shall not be permitted.
(6) An instantaneous override
(7) An approved equivalent means
240.87(C) Performance Testing
The arc energy reduction protection system shall be performance tested by primary current injection testing or another approved method when first installed on site. This testing shall be conducted by a qualified person(s) in accordance with the manufacturer’s instructions.
A written record of this testing shall be made and shall be available to the authority having jurisdiction.
Informational Note: Some energy reduction protection systems cannot be tested using a test process of primary current injection due to either the protection method being damaged such as with the use of fuse technology or because current is not the primary method of arc detection.
32Littelfuse, Inc. © 2020 32
NEC 2020 Article 240.67 (Fuses)
240.67 Arc Energy Reduction
Where fuses rated 1200 A or higher are installed, 240.67(A) and (B) shall apply. This requirement shall
become effective January 1, 2020.
240.67(A) Documentation
Documentation shall be available to those authorized to design, install, operate, or inspect the
installation as to the location of the fuses. Documentation shall also be provided to demonstrate that
the method chosen to reduce the clearing time is set to operate at a value below the available arcing
current.
33Littelfuse, Inc. © 2020 33
NEC 2020 Article 240.67 (Fuses)240.67(B) Method to Reduce Clearing Time
A fuse shall have a clearing time of 0.07 seconds or less at the available arcing current, or one of the following means shall be provided and shall be set to operate at less than the available arcing current:
(1) Differential relaying
(2) Energy-reducing maintenance switching with local status indicator
(3) Energy-reducing active arc flash mitigation system
(4) Current-limiting, electronically actuated fuses
(5) An approved equivalent means
240.67(C) Performance Testing
The arc energy reduction protection system shall be performance tested by primary current injection testing or another approved method when first installed on site. This testing shall be conducted by a qualified person(s) in accordance with the manufacturer’s instructions.
A written record of this testing shall be made and shall be available to the authority having jurisdiction.
Informational Note: Some energy reduction protection systems cannot be tested using a test process of primary current injection due to either the protection method being damaged such as with the use of fuse technology or because current is not the primary method of arc detection.
34Littelfuse, Inc. © 2020 34
Defining ROI and Effectiveness
Cost of
Design
Cost of
Equipment
Cost of
Downtime
Calorie
Reduction
Eliminate
Substitution
Engineering Controls
Awareness
Administrative Controls
Personal Protective Equipment
353535Littelfuse, Inc. © 2020 35
Current-limiting Fuses Reduce Time and Energy
Non Current-limiting Fuses or Circuit Breakers With Current-limiting UL Class RK5 FusesWith Current-limiting UL Class RK1 FusesWith Current-limiting UL Class J or T Fuses With Current-limiting UL Class CC/CD Fuses
Current before fault
Fault occurs
Fuse opens and
clears short circuit
Peak current which would occur without current limitation
Peak Let-Through Current
Peak Let-Through Current
Peak Let-Through Current
Peak Let-Through Current
Current limiting OCPDs reduce the total destructive heat
energy (I2t) to the circuit and its components to a small
fraction of the energy available in the system.
This is represented by the colored, shaded areas measuring
the I2t that passes thru fuse before it opens a short-circuit.
Littelfuse, Inc. © 2019 36
Reducing Arc-Flash HazardsUpgrading Fuses to Lower Incident Energies
250V Class RK5
1-600A
Cartridge: 200A
Incident Energy:
11.627 cal/cm2 @ 18 in.
PPE Category: 3
250V Class RK1
10-600A
Cartridge: 200A
Incident Energy:
3.536 cal/cm2 @ 18 in.
PPE Category: 1
Arc-Flash PPE
Category 3
Arc-Flash PPE
Category 1
TripTime @MaxFault: 0.229 sec
TripTime @MinFault: 2.900 secTripTime @MaxFault: 0.035 sec
TripTime @MinFault: 0.882 sec
37Littelfuse, Inc. © 2020 37
Substitution: Reducing Available Fault Current
• Effective way to reduce
available fault current
• Can have significant cost
100 MVA
50 MVA
50 MVA
Cost of
Design
Cost of
Equipment
Cost of
Downtime
Calorie
Reduction
$$$ $$$$ $$$ Med
Littelfuse, Inc. © 2019 38
▪ Arc-resistant switchgear requires
total replacement of existing gear
and are expensive but give higher
safety as long as the doors aren’t
open
▪ Does not mitigate the damage to
internal equipment
Cost of
Design
Cost of
Equipment
Cost of
Downtime
Calorie
Reduction
$ $$$ $$$High or
None
Substitution: Arc-Resistant Switchgear
Littelfuse, Inc. © 2019 39
▪ Zone interlock and bus differential
require higher engineering cost
▪ Requires careful time coordination
▪ Bus differential may cause problems
with selective coordination
Cost of
Design
Cost of
Equipment
Cost of
Downtime
Calorie
Reduction
$$$ $$ $$Med (Bus)
High (ZSI)
Engineering Control: ZSI or Bus Differential
Littelfuse, Inc. © 2019 40
Engineering Control: Arc-Flash Relays
▪ Easily installs into new equipment or
retrofits into existing switchgear
▪ Light measurements are independent of
inrush and other sources of temporary
overcurrent
▪ May disrupt selective coordination
▪ Self-check capabilities make maintenance
activities simple
▪ Strong incident energy reduction
Cost of
Design
Cost of
Equipment
Cost of
Downtime
Calorie
Reduction
$ $ $/$$ High
42Littelfuse, Inc. © 2020 42
Engineering Control: Arc-Flash Relays
Red LED for
Circuit-check
& Visual Diagnostics
Mounting
Holes
(front / back)32 mm
52 m
m
8 mm
Sensor
Lens
Ø3.5 mm
10 m
RxTx
PGA-LS10
Point Sensor
PGA-LS20 (8m)
PGA-LS30 (18m)
Fiber-Optic Sensors
▪ LED for visual trip
location and
sensor health
indication
▪ Built-in circuit
check
▪ Electrically
extendable (50m)
▪ Plug-in connector
The point sensor can be also be mounted
to ”see through” the back of the cabinet.
434343Littelfuse, Inc. © 2020 43
Arc-Flash Solutions for Your Customers’ Safety
PGR-8800<1 ms response
AF0500<1 ms response
AF0100<5 ms typ. response
44Littelfuse, Inc. © 2020 44
Arc-Flash Relay Application Example
Main-tie-Main
▪ Arc-flash energy can come from
either main
▪ Protection zones on an arc-flash
relay removes power from the
faulted section by tripping that
main and the tie breaker
(coupler)
▪ In the event of an arc flash in the
tie breaker cabinet, both mains
must be tripped.
45Littelfuse, Inc. © 2020 45
Active Arc-Fault Mitigation Systems
▪ IEC 60947-9-2 Active arc-fault mitigation systems – Optical-based internal arc-detection and mitigation devices (in development)
▪ IEC TS 63107 Integration of internal arc-fault mitigation systems in power switchgear and controlgear assemblies (PSC assemblies) according to IEC 61439-2– Specifies tests to verify correct integration and
operation of mitigation devices in an assembly
▪ NFPA 70E Annex 0.2.3(5)
464646Littelfuse, Inc. © 2020 46
Administrative Controls: Maintenance Mode Switch
▪ Relatively easy to adopt
▪ Effective in reducing incident
energy; however, only active
when switched on
▪ May compromise coordination
and selectivity
▪ Relies entirely on an overcurrent
event
▪ Multiple arc-flash labels usually
required which can be confusing
Cost of
Design
Cost of
Equipment
Cost of
Downtime
Calorie
Reduction
$ $$ $$ High*
4747Littelfuse, Inc. © 2020
PPE Alone
▪ Last line of defensive from dangerous
hazards
▪ Wear and Tear on expensive PPE
Cost of
Design
Cost of
Equipment
Cost of
Downtime
Calorie
Reduction
N/A $+ N/A None
4848Littelfuse, Inc. © 2020
Return on Investment Summary
Mitigation Method Cost of Design Cost of Equipment Cost of Downtime Calorie Reduction
Smaller
Transformers$$$ $$$$ $$$ Med
Zone Select
Interlock$$$ $$ $$ High
Bus Differential $$$ $$ $$ Med
Maintenance Mode
Breakers$$ $ $$ High
Arc Flash Relay $ $ $$ High
PPE N/A $+ N/A None
49Littelfuse, Inc. © 2020 49
Summary
Mitigation
Method
Cost of
Design
Cost of
Equipment
Cost of
Downtime
Calorie
Reduction
Smaller
Transformers$$$ $$$$ $$$ Med
Zone Select
Interlock$$$ $$ $$ High
Bus
Differential$$$ $$ $$ Med
Maintenance
Mode
Breakers
$$ $ $$ High
Arc Flash
Relay$ $ $$ High
PPE N/A $+ N/A None
1. Overview of an arc-flash event
2. Arc-Flash Hazard Assessments
3. IEEE 1584-2018 Updates
4. Options to Reduce Incident
Energy
5. ROI on Mitigation Methods
6. Summary