PGR-8800
Arc-Flash Relay
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Arc Faults: Costly and Dangerous
Dangers
 Fires
 Burns
 Injury
 Death
Costs
 Collateral
damage
 Equipment
replacement
 Downtime
 Labour
2
Types of Electrical Hazards
 Electric Shock - trauma caused by the passage
of electric current through the body.
 Arc-Flash – an unexpected sudden release of
intense heat and light energy produced by
electricity traveling through air, usually caused by
accidental contact between live conductors.
 Arc-Blast - a pressure wave created by heating,
melting, vaporization, and expansion of
conducting material and surrounding air during
an Arc-Flash.
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Arc-Flash Hazards
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Arc Flash: The Difference Time Makes
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Arc Flash: Up to 4x Brighter Than the Sun
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Arc Blast: A 700 MPH Pressure Wave
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Arc Flash: Caught on Film
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Arc Flash: Fire Hazard After Flash
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Initiators of these faults

IEEE Std 493-1997 (Gold Book) Recommended
Practice for the Design of Reliable Industrial and
Commercial Power Systems
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Development of an Arc Fault
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Large voltage difference between two conductors
Separated by air gap, high resistance
Voltage reaches breakdown point, rapid release of energy across gap
Shortest distance from bus bar corner to bolt corner
At breakdown, the air gap impedance is reduced to almost zero.
Energy limited only by system resistance, air gap impedance
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Lifespan of an Arc Fault
1
4
2
5
3
6
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Effects of an Arc Fault
NFPA 70E Hazard Risk
NFPA Levels required to reduce
probability of second-degree burn to
50%. Does not cover danger from
explosion, gases, noise, etc.
0
0.5 0.6
1.8
2.5
6.0
Distance (m)
Time = 0.5 seconds, Fault Current = 60 kA
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What Determins Arc-Flash Severity?
 Available energy
– kVA of transformer, generator, etc.
 Arc Characteristics
– Arc gap, distance from arc, impedance
 Fault Current
– System impedance
– Available fault current
– Arc current typically 38% of available
“bolted” fault current
Image from OSHA Office of Training & Education
 Time
– Clearing time
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Reducing Arc-Flash Hazard:
System Design (Available Energy)
Designing the system to use smaller
transformers in place of a giant one will
reduce the available energy.
10 MVA
20 MVA
10 MVA
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Reducing Arc-Flash Hazard:
Arc Resistant Switchgear
Arc-resistant switchgear attempts to
contain the arc within the gear and
vent the arc energy away from
workers.
These systems require total
replacement of existing gear and
are expensive but give higher
safety as long as the doors
aren’t open.
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Reducing Arc-Flash Hazard:
Fault Current (Resistance Grounding)
rsystem
rsystem
rfault
rfault
RNGR
Resistance grounding limits
the fault current and can
eliminate phase-ground arcs
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Reducing Arc-Flash Hazard:
Ground Fault Escalation
A phase-ground arc flash is a risk on solidly grounded systems.
This fault can quickly escalate to a phase-phase fault…
… or a three-phase fault
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Reducing Arc-Flash Hazard:
NGR in a Three-Phase Fault
The reverse of this scenario shows how a three-phase fault can be limited by
resistance grounding as well.
The three-phase fault escalates to include
ground, but the current from each phase
to ground is limited by the NGR.
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Three-Phase Fault:
High-Resistance Grounded System
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Three-Phase Fault:
Solidly Grounded System
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Reducing Arc-Flash Hazard:
Time (Fuses)
Current limiting overcurrent protective devices reduce the total destructive heat energy
(I2t) to the circuit and it’s components to a small fraction of the energy available in the
system. This is represented by the colored, shaded areas above.
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Lifespan of an Arc Fault
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The PGR-8800 Arc-Flash Relay
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Simple Installation, Setup and Maintenance
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Reliable Operation with Built-in Redundancies
Redundant Internal Trip Path
• 2 internal trip paths for added reliability—if the microprocessor trip path fails, the backup
analog trip path will seamlessly take over, sending a notification to operators
• Backup analog trip path ensures fast protection while energizing the system when
hazard risk is higher
Health Monitoring
• Continuously monitors connection to trip coil to ensure path is intact
• LED local indication of sensors’ “Ready” or “Tripped” status
• Sensors are durable enough to withstand a detected arc-flash event
Reliable Light Detection
• Two types of light sensors (point and fiber-optic) for different applications
• Adjustable light-level and wide-angle detection add flexibility
• Durable and flexible sensor design eliminates breakage and re-work
Eliminate Nuisance Tripping
• Avoid nuisance tripping with current-supervised arc-flash trips
• Phase Current Transformers for overcurrent detection
• Two user-defined definite-time overcurrent protection levels and times
Optional Upstream Tripping
• Ability to trip upstream device if the local breaker fails to clear the fault
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Arc Flash Relay – Features

Local CB trip
–

Upstream CB Trip
–
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Breaker failure protection
Light Detection
–
–

1 ms reaction time
Point sensors
Fiber optic sensor
Over-current validation
–
–
Phase CTs (3) with 5A sec
Two definite-time set points
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Dual inputs for switches and PLCs
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Local USB interface
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No drivers or software required
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Event logging
Scalability
–

Up to (4) for larger systems
TIA-485 Modbus
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PGR-8800 Sensor Coverage
(Distance where a line-of-sight arc will be detected)
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PGR-8800 Sensor Features
 LED for visual trip
location and
sensor health
indication
 Built-in circuit
check
The point sensor can be also be mounted
to ”see through” the back of the cabinet.
10 m
Ø3.5 mm
8 mm
Sensor
Lens
Tx
Red LED for
Circuit-check
& Visual Diagnostics
52 mm
 Electrically
extendable (50m)
Rx
 Plug-in connector
32 mm
PGA-LS10
Point Sensor
Mounting
Holes
(front / back)
PGA-LS20 /
PGA-LS25
Fiber Sensor
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PGR-8800
Specifications

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Arc fault detection < 1 ms
-25ºC to +70ºC operating range
120-240 Vac/Vdc Supply
12-48 Vdc Supply
10k-40k lux Sensitivity
Form C contacts
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PGR-8800
Functions & Features
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Current-Supervised Optical Protection
 Prevent nuisance trips
Overcurrent protection
 Two definite-time set points
6 fiber-optic or point-sensor inputs
Operate stand-alone with front sensor
Link up to 4 modules (24 sensors/CB)
Dual inputs for switches and PLCs
Event logging
Fail-safe operation
 Fully redundant trip path
Local USB interface
 No drivers or software required
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PGR-8800 Wiring Diagram
To next PGR-8800 or Modbus network
Positive Bus
Negative Bus
100-240
Vac/Vdc
12-48 Vdc
+
-
Inputs
Outputs
Online Service Tripped
Trip Voltage
24 - 600 VDC
24 - 440 VAC
Battery (24 VDC)
L1 L2 L3
GND
Trip
Coil
USB
5A CTs
PC with
Microsoft Windows®
Three-phase
Overcurrent
Protection
Config, log &
firmware upgrade
Up to 6 Point or Fiber Optic Sensors
with built-in circuit-check
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Important Features:
Fail-Safe Operation
Redundant, solid-state trip
path ensures fast operation
even on boot-up.
Can trip an upstream
circuit breaker if local
breaker fails to trip.
Trip coil voltage
monitored constantly.
Sensors and cable
continuity are verified
constantly.
Tx
Rx
Option to add CTs to
prevent nuisance trips
from bright light.
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Circuit Breaker Failure Protection:
What it is
1. Arc-Flash detected
2. PGR-8800 sends
signal to local breaker
3. Local breaker
malfunctions
4. PGR-8800 detects
malfunction and sends
signal to upstream
breaker
5. Arc fault cleared
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Circuit Breaker Failure Protection:
How it works
Detecting Failure
• Current sensors still reading
current?
• Auxiliary contact still closed?
• Expected trip time expired?
Sending Upstream Trip
• Programmable outputs
• TRIPPED
• SERVICE
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Multi-Unit Installation Example
LINK
Switchboard
Supply
2
L1 L2 L3
Trip
Electrical cables
Sensors Detecting Arc
Fiber-Optic Sensor
Point Sensors
System can be expanded with up to four PGR-8800 Modules
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PGR-8800 Applications
Switchgear
Substations, switchgear, and MCCs are common
locations for an arc-flash event.
Show here is an installation of the PGR-8800,
monitoring switchgear in an underground
mine in Australia.
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PGR-8800 Applications
Transformer / Substation
This substation in Chile has a PGR-8800
installed to monitor the transformer and
quickly disconnect the transformer supply
if an arc-flash is detected.
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PGR-8800 Applications
Wind Turbines
Wind turbines are beginning to standardize on Arc-Flash Detection systems like the
PGR-8800 for the reasons shown above. The Arc-Flash relay cannot prevent an arc flash,
but it can limit the damage so that the installation can be more easily repaired.
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PGR-8800 Applications
Wind Turbines
Transformer secondary
3 x 22 kV
Transformer primary
3 x 690 V
Air-cooled transformers are sensitive to contaminants,
affecting the resistance of the air gap between electrical
connections (phases, bolted connections etc.)
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PGR-8800 Applications
Drawout Circuit Breakers
Drawout circuit breakers can be
monitored by installing one point
sensor on each side of the barrier
such that the view is not obstructed
when the breaker is being racked in
or out.
Fiber-Optic Sensor
Alternatively, fiber-optic cable can be
installed to monitor each side of the
barrier through multiple sections as
shown below and right.
8m
Point Sensor
ABOVE: An example of point sensor and fiberoptic sensor location on a drawout breaker with
shielding on either side and insufficient clearance
above.
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Case Study: PGR-8800 Saves
Plant from Catastrophic Damage
•
Facility had a 480 V switchgear fed from 3500 kVA
transformer, resulting in a Hazard Risk Category 4 (HRC)
•
•
•
•
PGR-8800 Arc-Flash Relay was retrofitted in 3 hours AND reduced HRC to HRC 2
Less than a week after installation, the plant experienced an arc-flash incident
An arc started in the cables inside the switchgear and tracked up to the bus
All 6 sensors reacted to the immense light and the PGR-8800 sent a signal
to the CB in less than 1ms
 The damage was limited and the repair work was less than $6,000;
The plant was back in operation in less than 24 hours
The plant estimates the damage would
have been between $800,000 to $1,000,000
This printed Case Study is now available at: Littelfuse.com/ArcFlash
Also available in: Chinese, German, Spanish, Portuguese
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Arc Flash Relay – Reference
Materials
Catalog sheet
A list of Arc Flash
Related Frequently
asked questions from
our customers
Brochure
Workbook: Calculate
your facility Incident
Energy Reduction
Application Guide
White Paper: Key
Considerations for
Selecting an Arc
Flash relay
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