cracking the code for arc-flash mitigation

11

Cracking the Code for

Arc-Flash Mitigation

March 12, 2021

22Littelfuse, Inc. © 2020

Cracking the Code for Arc-Flash Mitigation

Mark Pollock, P.Eng.Global Product Manager, Protection Relays

Industrial Business Unit

Littelfuse, Inc.

3Littelfuse, Inc. © 2020 3

Electrical Safety is Everyone’s Responsibility


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

Arc-Flash Events


The Breakdown of an Arc-Flash Event


Estimated $2.5 - $3.0 Million Damage


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

Arc-Flash Hazard

Assessments


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


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!


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


Regulations and Standards


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)

IEEE 1584-2018

Updates


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



▪ Extensive testing on five

electrode configurations

▪ Consideration of enclosure

sizes and correction factors

▪ Updated arcing current

calculations



▪ 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


IEEE 1584-2018 Electrode Configuration - VCB

Vertical Conductors inside a metal Box/enclosure


IEEE 1584-2018 Electrode Configuration - VCBB

Vertical Conductors terminated in an insulating Barrier

inside a metal Box/enclosure


IEEE 1584-2018 Electrode Configuration - HCB

Horizontal Conductors inside a metal Box/enclosure


IEEE 1584-2018 Electrode Configuration - VOA

Vertical conductors in Open Air


IEEE 1584-2018 Electrode Configuration - HOA

Horizontal conductors in Open Air


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


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


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


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%

Incident Energy

Mitigation


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.


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.


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.


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.


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


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




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


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


▪ 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


▪ 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


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



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.


Arc-Flash Solutions for Your Customers’ Safety

PGR-8800<1 ms response

AF0500<1 ms response

AF0100<5 ms typ. response


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.


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)


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*


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


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


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


Thank You

Mark Pollock, P.Eng.

Email: [email protected]

mailto:[email protected]

cracking the code for arc-flash mitigation

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