Littelfuse AF0100 User guide

GENERATOR
APPLICATION
GUIDE
AF0100
ARC-FLASH
RELAY

AF0100 Arc-Flash Relay
GENERATOR APPLICATION GUIDE
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TABLE OF CONTENTS
GENERATORS.................................................................................................................................................................3
Challenges Unique to Generators .................................................................................................................................3
NEC®ARTICLE 240.87 (2017).........................................................................................................................................4
Background ...................................................................................................................................................................4
Documentation .............................................................................................................................................................4
Method to Reduce Clearing Time .................................................................................................................................4
ANSI Z10 : RISK CONTROL HIERARCHY .....................................................................................................................4
Background ..................................................................................................................................................................4
Methods........................................................................................................................................................................4
GENERATOR PROTECTION USING AF0100 ................................................................................................................5
Generator To Generator Breaker Connection................................................................................................................5
Transformer Enclosure ..................................................................................................................................................5
AF0100 CONNECTION DIAGRAM.................................................................................................................................6
SENSOR COVERAGE .....................................................................................................................................................7
EFFECT OF GENERATOR GROUNDING ON ARC-FLASH RISK .................................................................................8
Ungrounded Generator .................................................................................................................................................8
Solidly Grounded Generator..........................................................................................................................................8
Resistance-Grounded Generator ..................................................................................................................................8
ADVANTAGES OF RESISTANCE GROUNDING FOR GENERATORS.........................................................................9
BENEFITS TO ADDING ARC-FLASH RELAYS............................................................................................................10
WHY CHOOSE LITTELFUSE? ......................................................................................................................................10
APPENDIX A: SUPPORTING MATERIALS.................................................................................................................. 11
AF0100 COMMISSIONING INFORMATION ............................................................................................................... 11

AF0100 Arc-Flash Relay
GENERATOR APPLICATION GUIDE
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GENERATORS
Generators are often used to ensure continuity of energy for mission-critical applications. There are ve key reasons
generators are vulnerable to arc ash and this guide explains how to mitigate this risk.
1. The high levels of energy from the generator and low impedance (due to being near the energy source) put
the generator at risk.
2. Many mobile generators are used in cooling applications in warm, humid, and sometimes dusty geographies
where the increased conductivity of the air that’s insulating the exposed conductors can increase the risk of
an arc ash.
3. Mobile generators used in cold environments are sources of warmth that can attract rodents and small
animals that burrow into the unit and precipitate an arc ash.
4. Low zero-sequence impedance of generator windings result in arc ash on a ground fault for solidly
grounded generators.
Generators also pose an increased safety risk due to the nature of their construction. Typically, generators only
allow a narrow space for personnel to work and perform their maintenance. In many cases, arc ash calculations
limit burn time to two seconds for workers to get clear of the danger. In a generator application, the personnel
are trapped in the enclosure during an arc ash and exposed to the arc for an extended amount of time. It is
necessary for arc-ash calculations in conned spaces to increase the arc duration, resulting in even higher levels
of incident energy. The arc blast itself can thrust personnel into the walls of the enclosure with enough force to
be fatal.
Challenges Unique to Generators:
§Available space limitations
§Two sources of energy must be disconnected:
1. The generator
2. Bus connecting to parallel generators or utility
§Vibration from generator operation and transport to and from job sites
§Harsh environments with extreme heat and humidity
§Section between the generator and the generator breaker has no overcurrent protection
Generators with breakers that are rated or can be set above 1200 A (even if they are set below that point) require
a means of arc-ash mitigation. This would apply to a connected substation, switchgear, or other downstream
equipment, but could also be considered on a generator capable of producing 1200 A or more (250 kW or higher).
NEC® 240.87 (B.4) allows arc-ash relays as a cost-effective means of mitigation.
Mobile generator destroyed by arc-flash.

AF0100 Arc-Flash Relay
GENERATOR APPLICATION GUIDE
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NEC®ARTICLE 240.87 (2017)
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.
(A) Documentation. Documentation shall be available to those authorized to design, install, operate, or
inspect the installations as to the location of the circuit breaker(s).
(B) Method to Reduce Clearing Time. One of the following means shall be provided:
1) Zone-selective interlocking
2) Differential relaying
3) Energy-reducing maintenance switching with local status indicator
4) Energy-reducing active arc-ash mitigation system
5) An instantaneous trip setting that is less than the available arcing current
6) An instantaneous override that is less than the available arcing current
7) An approved equivalent means
ANSI Z10 : RISK CONTROL HIERARCHY
While PPE is often the most talked-about aspect of arc-ash risk mitigation, it is also the least effective means
of doing so. Work and research has been and is being carried out in the engineering controls area particularly to
better mitigate arc-ash risk.
ANSI / AIHA Z10 (OHS Management Standard) hierarchy, from most effective risk mitigation to least, is as follows:
1) Elimination
– Difcult to achieve
2) Substitution
– Insulated bus, smaller transformers, arc-resistant gear, current-limiting fuses
3) Engineering Controls
– Current-limiting devices (fuses, neutral-grounding-resistors), arc-ash relays,
maintenance/instantaneous trip awareness
– Labels, training, use of qualied persons
4) Administrative Controls
– No work on energized equipment, lockout-tagout
5) PPE

AF0100 Arc-Flash Relay
GENERATOR APPLICATION GUIDE
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GENERATOR PROTECTION USING AF0100
Generator to Generator Breaker Connection
While the generator breaker can protect the generator from overcurrent faults, there is often nothing protecting the
connection from the generator to the generator breaker from overcurrent or arc ash.
As a result, an arc in this connection will persist and its destructive energy will increase, being fed from other
sources connected in parallel with the generator as well as the generator itself. Eventually, the amount of energy
required may be enough to trip the generator breaker (assuming it isn’t engulfed in the arc’s plasma cloud) and the
arc will extinguish when enough material has been vaporized that the generator cannot produce enough energy to
maintain the arc, the generator is destroyed, or its fuel source consumed in the arc. Often a fault on the generator
will burn the generator to the ground.
An arc-ash relay monitoring this section of the bus can dramatically reduce the total energy released and therefore
the damage and risk to personnel. One or two point sensors are typically sufcient to monitor the busway/cables
and the breaker cabinet. In the case that an arc is detected, all sources of energy to it must be cut off. The arc-ash
relay must trip the generator breaker but also turn off the generator. The latter is usually accomplished by either
connecting to the automatic voltage regulator (AVR), an emergency stop circuit, or generator controller. Often the
voltages required to trip these two circuits are different and require isolated contacts.
The AF0100 was specically designed for generator applications, with two isolated Form-C trip outputs to cut
off all sources of energy from the arc. A 24-48 Vdc supply allows for power directly from the battery bank and
withstands voltage sags and overvoltages, and the entire relay is designed to withstand vibration. As well, a unit
health contact can be programmed for non-fail-safe so that loss of supply voltage when powering down the
batteries will not cause nuisance alarms for remote monitoring. Finally, its compact design means that it can nd a
home in any generator control panel.
Transformer Enclosure
In applications where medium voltage distribution is required, parallel generators may be connected to a step-
up transformer. It is advantageous to protect the transformer from an arc ash, particularly if there is a shunt trip
that can disconnect it from supply. In this case, one or two sensors in the enclosure monitoring the primary and
secondary connections can dramatically reduce downtime and repair cost for the transformer if an arc ash occurs.
Generator Enclosure
To other parallel generators or utility
Transformer Enclosure
Trip 1 Trip 1Trip 2
AF0100
AVR/
Control Circuit
AF0100
Sensor
Primary Side Sensor
Secondary Side Sensor
Breaker
Sensor
Generator Transformer
To application

AF0100 Arc-Flash Relay
GENERATOR APPLICATION GUIDE
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Alarm on Unit Health
Congurable to non-failsafe
to prevent alarms where
generators/battery banks are
frequently cycling on/off) in
order to avoid nuisance alarms.
PGA-LS10 Sensor
Monitors breaker
compartment on
the line side of the
generator breaker.
24 Vdc Supply
Uses the battery banks and
commonly available generator
supply voltage.
To Generator Breaker
Disconnect from bus which may include
parallel generators or the utility.
To AVR
Shut down the generator. This
could be an emergency stop or
other control circuit.
Small form factor to t in tight spaces of mobile gensets.
PC CONNECTION
TRIP OUTPUT #1 TRIP OUTPUT #2
100-240 VAC/DC
SUPPLY
24-48 VDC SUPPLY
DIGITAL INPUTS/OUTPUTS
UNIT HEALTH
AF0100 CONNECTION DIAGRAM
Generators are often the last line of defense in powering and protecting critical applications. The generator breaker
is the last line of defense protecting the generator itself: there is no protection at all between the line side of the
breaker and the generator. The AF0100 includes two Form-CTrip outputs that quickly respond to an arc ash, turning
off the generator using the AVR or other control circuits and disconnecting from the utility or parallel generators by
tripping the generator breaker. The AF0100 can be supplied directly off a battery bank and withstand the challenging
environment, vibration, and space requirements of a generator application.
TWO
ARC-FLASH
SENSOR
INPUTS

AF0100 Arc-Flash Relay
GENERATOR APPLICATION GUIDE
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SENSOR COVERAGE (Distance where a line-of-sight arc will be detected)
Light Sensor
2m
2.5m
Up to
50 m cable
Connect to Relay
180" 2-Meter Half-Sphere
Sensor Viewing Angle
Up to
50 m cables
Receiver
Black Shield
(no light detection)
Transmitter
Connect to Relay
PGA-LS20 Series
Fiber-Optic Sensor
PGA-LS10 Series
Point Sensor
Point Light Sensor
Line-of-sight light sensor detects an arc as small
as 3 kA in a 2-meter half-sphere radius.
§Visual LED indication for “Ready” or
“Tripped” state to assist with fault location
§Robust sensor design can withstand a
detected arc-ash event
§Sensor can be installed up to 50 m (164 ft)
away from relay; electrical cable can be cut
and easily re-terminated in the eld
Fiber-Optic Light Sensor
The 360° light sensor detects light throughout
the entire length of the ber. Ideal to protect
bus bars, multiple compartment installations
like motor control centers, or areas with
many obstructions.
§Visual LED indication for “Ready” or
“Tripped” state to assist with fault
location
§Durable resin ber material allows small
bending radius (>5 cm) and greater
exibility without breaking
§Ready to install from the factory, no need
to terminate in the eld or polish as with
glass ber
§Fiber sensors can be installed in locations
up to 50 m
§(164 ft) away from relay; electrical cable
can be cut and easily re-terminated in
the eld

AF0100 Arc-Flash Relay
GENERATOR APPLICATION GUIDE
8Littelfuse.com/ArcFlash© 2017 Littelfuse Products
EFFECT OF GENERATOR GROUNDING ON ARC-FLASH RISK
Ungrounded Generator
A re-striking or arcing ground fault on a generator can result in transient overvoltage, a condition where phase
voltages can be six to eight times the line-to-line voltage above ground as energy is stored in the capacitance of
the system instead of discharging through a grounding connection. This results in insulation degradation inside the
generator and can result in an explosive arc ash as the insulation fails, potentially in multiple locations.
The Littelfuse EL3100 Ground-Fault Relay can detect a grounded phase on ungrounded generators up to 600-V and
offers both indication and a relay output to alarm or trip the generator.
Solidly Grounded Generator
Generators have low zero-sequence reactance, meaning that ground-fault current on a solidly grounded generator
can exceed three-phase fault current levels. According to IEEE Std 141-1993 7.2.2, high values of ground-fault current
can destroy the magnetic core of rotating machinery. High currents also mean that ground faults (which are the most
common type of electrical fault) can result in an arc ash. Mechanical bracing in generators is also typically rated for
three-phase fault levels only, resulting in mechanical damage during a ground fault even if the fault is not arcing.
The Littelfuse SE-701 Ground-Fault Relay can monitor for a wide range of current levels and works with any 5-A or
1-A secondary as well as sensitive Littelfuse CTs for detection down to 50 mA. For applications where there is not
sufcient space for a CT, the PGR-4300 Ground-Fault Relay connects between the generator and grounding rod to
detect ground-fault currents from 100 A to 1200 A.
Resistance-Grounded Generator
High-resistance grounding eliminates arc-ash hazards on the rst ground fault and reduces burning of stator
windings during an internal generator ground fault. By adding a neutral-grounding resistor (NGR), the mechanical
damage from low zero-sequence reactance of generators is also eliminated. Even for uptime-critical generators that
might normally be ungrounded, it is permissible to continue running a generator on a ground fault so long as the
current is limited to 10 A and the generator is 4160 V or less. It is critical that the NGR is monitored using an NGR
monitor to ensure that the generator remains grounded at all times. Littelfuse recommends continuously monitored
high-resistance grounding for generators.
Use the Littelfuse SE-704 Ground-Fault Relay for high-resistance grounded generators. As well, ground-fault
protection can be combined with continuous neutral-grounding resistor monitoring using the Littelfuse SE-325 or
SE-330 NGR Monitors.

AF0100 Arc-Flash Relay
GENERATOR APPLICATION GUIDE
9Littelfuse.com/ArcFlash© 2017 Littelfuse Products
ADVANTAGES OF RESISTANCE GROUNDING FOR GENERATORS
SE-330 Series
Neutral-Grounding-Resistor Monitor
Advanced Neutral-Grounding-Resistor (NGR)
Monitor with data logging and optional
communications.
NGR Series
Neutral-Grounding-Resistor System
Monitoring-ready NGR packages that speed
deployment on site.
EL3100 Series
Ground-Fault and Phase-Voltage Indication
Ground-Fault Monitor for ungrounded generators and
phase-voltage indication for systems up to 600 volts.
NGRM-ENC Series
Neutral-Grounding-Resistor Monitor
Enclosure with SE-325 or SE-330 NGR Monitor and
optional phase voltage, metering, indication and reset.
SE-701 Series
Ground-Fault Monitor
Wide-range ground-fault relay,
especially suitable for rental units.
PGR-4300 Series
Generator Ground-Fault Relay
Generator Ground-Fault Relay for solidly
grounded generators. No CT required.
Generator ground-fault current can be higher than short-circuit current for solidly grounded generators.
High-resistance grounding can eliminate the possibility of phase-to-ground arc ash on the rst ground fault.
Continuity of service during a ground fault for applications below 5 kV and with a neutral-grounding resistor (NGR)
limiting current below 10 A.
Reduced mechanical and electrical damage resulting from high-current ground faults.
Eliminate transient overvoltages from ungrounded systems.
Multiple generators can be grounded at a single point using a zig-zag transformer.
SE-704 Series
Earth-Leakage Relay
Earth-Leakage Relay for resistance-
grounded generators.
SE-325 Series
Neutral-Grounding-Resistor Monitor
Standard NGR Monitor, ideal for systems with
let-through currents of 25-A or lower.

AF0100 Arc-Flash Relay
GENERATOR APPLICATION GUIDE
10 Littelfuse.com/ArcFlash© 2017 Littelfuse Products
BENEFITS TO ADDING ARC-FLASH RELAYS
§Minimize damage to generator sets and reduce time to repair
§Save thousands of dollars on replacement costs when unit is completely destroyed (ROI on rst arc ash
can be enough to outt a large generator eet with arc-ash relays)
§Add value to end users because their personnel are safer and outage occurrences are reduced
§Meet regulatory requirements
WHY CHOOSE LITTELFUSE?
§Right product for the right application—AF0100 is purpose-built for needs of generators
§Easily added as a retrot to existing generators or to new units
– Our unique sensor design includes cabling that can be put through tight corners with no concern of
loss of signal
– Plug and play installation approach is unmatched in industry
– Fast installation and automatic conguration minimize labor costs
§Seamless to your customer (no customer interaction required with arc-ash relay)
§We are a global partner for your global business
– Global certications
– Global distribution and fulllment, sell in various currencies
– Global support personnel/ofce locations
§Isolated outputs allow for completely separate trip circuits
§Form C contacts give exibility in connecting to any type of trip circuit, indication, etc.
Challenge Littelfuse AF0100 Benet
Available space limitations AF0100 measures 90 mm (3.5”) x 128 mm (5.0”) x 60 mm (2.4”)
Two sources of energy must be disconnected:
1. The generator
2. Bus connecting to parallel generators or utility
Two isolated Form-C Trip outputs:
1. Trip the generator breaker and disconnect from bus
2. Trip the AVR to shut down the generator
Vibration from generator operation and transport to and
from jobsites
Extensive vibration proofing to ensure quality backed by
2-year warranty
Harsh environments with extreme heat and humidity Conformally coated options available to protect circuitry from
harsh environments

AF0100 Arc-Flash Relay
GENERATOR APPLICATION GUIDE
11 Littelfuse.com/ArcFlash© 2017 Littelfuse Products
APPENDIX A: SUPPORTING MATERIALS
Littelfuse provides many supporting materials in digital format for the function and installation of the
AF0100 Arc-Flash Relay.
These can be found at: Littelfuse.com/ArcFlash
AF0100 COMMISSIONING INFORMATION
Manual
Datasheet
FAQ Booklet
Brochure
Videos
Guideform Specications
Workbook for Estimating Arc-Flash
Incident Energy Reduction
General Installation
Settings Minimum Default Max Unit Comments
Date Installed
Operator
Comment 1
Comment 2
General
System Name
Description Of This Unit AF0100 Arc-Flash Relay
Date and Time
Synchronize to PC Clock Disabled oEnabled oDisabled
Light Sensors
Common Settings
Light Immunity Lower Limit 10 10 25 klux klux
Arc Detection Time
Before Tripping
0
(Effective
0.8)
120,000 ms ms
Light Sensor 1
Sensor Status oSensor Present
oNo Sensor Detected
oSensor Missing
oSensor Tripped
Sensor Description Sensor 1
Change Configuration No Change oNo Change
oNo Sensor Expected
oSensor Expected
Light Sensor 2
Sensor Status oSensor Present
oNo Sensor Detected
oSensor Missing
oSensor Tripped
Sensor Description Sensor 2
Change Configuration No Change oNo Change
oNo Sensor Expected
oSensor Expected
Conguration of Failsafe/NFS Outputs
Trip 1 Failsafe oFailsafe oNon-Failsafe
Trip 2 Failsafe oFailsafe oNon-Failsafe
Error Failsafe oFailsafe oNon-Failsafe

Additional technical information and application data for Littelfuse protection relays, generator and engine controls, fuses and other circuit protection and
safety products can be found on Littelfuse.com. For questions, contact our Technical Support Group (800-832-3873). Specications, descriptions and illustrative
material in this literature are as accurate as known at the time of publication, but are subject to changes without notice. All data was compiled from public information
available from manufacturers’ manuals and datasheets.
© 2017 Littelfuse, Inc. Form: PF709
Rev: 1-A-030717
For more information, visit
Littelfuse.com/ArcFlash