©2007 thomas & bettstnblnx3.tnb.com/emalbum/albums/us_resource/rs_ht...¥fuse application and...
TRANSCRIPT
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©2007 Thomas & Betts
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Section 1
Introduction to the Presentation
• Introduction of T&B Hi-Tech Fuses and our
products
• Expulsion fuses vs. Current-Limiting fuses
• Hi-Tech’s fuse construction & design features
• IEEE standards & testing requirements
• Fuse Application and Coordination
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Section 2
Introduction to Hi-Tech Fuses
&
Hi-Tech’s Products
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• Established in 1984, in Hickory, NC USA
• Recently acquired by Thomas & Betts (Aug. 2006)
• Focused exclusively on high-voltage, Current-Limiting
fuse technology for power distribution system protection.
• Supplied well over 1 million fuses to the Utility Market
• Global leader in the Current-Limiting fuse market:
– Fuses sold in US, Canada, Latin America and Asia
– Leadership in IEEE/ANSI and IEC fuse standards bodies
– Award winning service levels (9 time ABB outstanding supplier of
the year award winner)
– Active product development efforts
• ISO 9001:2000 certified
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Current Product Lines
Trans-Guard OS & OS ShortyTrans-Guard OS & OS Shorty (Oil-Submersible)Backup Type Current-Limiting fuses are primarilyused with bayonet or protective (weak link) typeexpulsion fuses for "two-fuse" protection ofdistribution transformers.
Trans-Guard FX & SX (not shown)Trans-Guard FX & SX (not shown) Full-RangeCurrent-Limiting fuse provides both overload andfault protection for distribution equipment in a singlefuse body.
Trans-Guard EXT Trans-Guard EXT (External) Backup Type Current-Limiting fuses are primarily used for pole mountedtransformer or capacitor protection in series withcutout expulsion fuses.
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Fused Loadbreak Elbows
Molded CL Fuses
Molded Fuse Canisters
Current Product Lines
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Trans-Guard™ OS & OS ShortyGeneral:Oil-Submersible Backup Type Current-Limiting fuses primarily used withbayonet or protective (weak link) type expulsion fuses for "two-fuse"protection of distribution transformers.
Application:
! Pad mounted distribution
transformers
! Pole-mounted transformers
Other Brands:! Cooper ELSP
! GE OSP
Advantages:
! Highest ratings in a single fuse
body available (less paralleling)
! Shorter or smaller diameter
! Tested to applicable standards
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Trans-Guard™ OS ApplicationTrans-Guard OS fuses installed in a 3-Phase
distribution transformer
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Trans-Guard™ EXTGeneral:External Backup Type Current-Limiting fuses are primarily used for pole
mounted transformer or capacitor protection in series with cutout expulsion
fuses.
Application:
! Pole-mounted distribution
transformers
! Capacitors
Other Brands:! Cooper NX Companion
! GE ETP
! AB Chance K-mate
Advantages:
! Lowest I2t let-throughs
! Robust and durable design
! Highest ratings available
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Trans-Guard™ EXT ApplicationsFor use in high available fault current areas including:
! Pole-mounted transformers
! Overhead capacitors
! Riser pole applications
Trans-Guard EXT w ith Pole-mounted Transformer Trans-Guard EXT w ith capacitorTrans-Guard EXT w ith cutout fuse
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Trans-Guard™ FXGeneral:Full-Range Current-Limiting fuse provides both overload and fault protection
for distribution equipment in a single fuse body.
Application:
! Distribution transformers
(in dry-well canisters)
! Switchgear
(clip-mounted)
Other Brands:! Cooper NX, ELX, & X-Limiter
! Eaton CX
Advantages:
! Sealed design
! Damage Sensor
! Tested to latest standards
(includes RMAT testing)
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Trans-Guard™ FX Applications! Installed in dry-well canisters for oil filled transformer and
oil/SF6 switchgear protection.
! Clip mounted in live-front switchgear and/or dry-type
transformers
! Externally mounted on overhead distribution systems.
Trans-Guard FX in a clip mountingTrans-Guard FX with a dry-well canister
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Trans-Guard™ SXGeneral:Under-oil Full-Range Current-Limiting fuse provides both overload and fault
protection for underground cables and distribution equipment in a single fuse
body.
Application:
! Switchgear
(in wet-well canisters)
Target Market:! Utilities! Switchgear! Manufacturers! Industrial
Other Brands:! Cooper SX-Limiter & ELSG
! AB Chance SL
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Trans-Guard™ SX Applications! Installed in wet-well canisters in switchgear
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Elastimold® ProductsGeneral:Rubber encapsulated Full-Range Current-Limiting fuse provides dead-front
overload and fault protection for distribution equipment in a single fuse body.
Application:
! Underground vaults
! Dead-front transformers
& switchgear
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Section 3
Expulsion Fuses
vs.
Current-Limiting Fuses
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Two Main Types of Fuses
1) Non Current-Limiting Fuses
2) Current-Limiting (CL) Fuses
• All fuses, after melting with an overcurrent,
contain an arc that carries the current until
interruption.
• Fuses can be categorized into two main types,
depending on how they interact with relatively
high fault currents:
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1) Non Current-Limiting
(Current zero awaiting)
Does not introduce significant
resistance into the circuit after
melting. Requires natural current
zero for interruption.
Types: Expulsion fuse, vacuum fuse, sf6 fuse
(expulsion fuses are the most common)
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Common types of Expulsion FusesCommon types of Expulsion Fuses
Bayonet
Expulsion Fuse
Power Fuse
Cutout
Expulsion Fuse
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• Very effective at interrupting low fault currents
• Some types can minimize the risk of equipment failure due
to overloading
• Economical replacement
• Provide a variety of time-current curve (TCC)
characteristics
• High continuous current ratings are available
Role of Expulsion Fuses
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Expulsion Fuse Selection(Choosing Type)
Types of Bay-O-Net Fuse Available Manufacturer*
" Current Sensing (fault sensing) C, A, E
" Dual Sensing (load sensing) C, A, E
" Dual Element C, A, K
" High Ampere Overload C
*C = Cooper (RTE®), A = ABB, E = ERMCO (GE), K = Kearney
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2) Current-Limiting (Current zero shifting)
Introduces significant resistance
into the circuit after melting. At high
current, forces early current zero.
Types: Current-Limiting (CL) Fuse, Fault Limiter
(CL fuses are the most common)
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Types of Current-Limiting Fuses
Full-Range
Fuse
External Fuse
and
Oil-
Submersible
Fuse
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• Minimizes the risk of eventful/catastrophic failure of distribution equipment
by limiting the peak current and the energy let through during a fault
• Protects distribution equipment especially in areas where available fault
currents exceed interrupting capabilities of other protection devices
• Addresses concerns for potential fire hazards (e.g. grassy areas) or
safety issues associated with populated areas where expulsion gases are
not acceptable
• Enhances overall power quality by reducing “blink” time to fractions
of a cycle
• Improves coordination with source side devices (coordination up to 50kA)
• Alleviates concerns for loud noise (“bang”) during fuse operation
Role of Current-Limiting Fuses
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• Backup
• General-purpose
• Full-Range
Three classes of CL fuse:
How well Current-Limiting fuses handle low currents
divides them into three classes:
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A fuse capable of interrupting all
currents from the rated maximum
interrupting current down to the
rated minimum interrupting current.
Backup Current-Limiting Fuse
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Backup Fuse TCC
OKOK
NO
Minimum I/C Maximum - 50kARated current - IR
Current
Tim
e
1000s
.01s
Fuses cannot interrupt, or may be damaged by, currents in the red zone
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A fuse capable of interrupting all
currents from its rated maximum
interrupting current down to the current
that causes melting of the fusible
element in no less than 1 h.
General-purpose Current-Limiting Fuse
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General-Purpose TCC
OKOK
NO
Maximum - 50kA
1 Hour
Rated current - IR
Tim
e
Current
Fuses cannot interrupt, or may be damaged by, currents in the red zone
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A fuse capable of interrupting all currents from
it’s rated interrupting current down to the
minimum continuous current that causes melting
of the fusible element(s), with the fuse applied at
the rated maximum application temperature
specified by the fuse manufacturer.
Full-Range Current-Limiting Fuse
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Full-Range Fuse TCC
OK
50kAIR
1 Hour
25o o
25IR
10,000s
.010sCurrent
Tim
e
Fuse is not damaged by overloads, and can clear any current that causes it tomelt with surrounding temperatures to O
O is RMAT
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Two Important Full-Range Fuse
Concepts
1. Fuse can clear any current that melts it
(At ambient temperatures up to its RatedMaximum Application Temperature - RMAT)
2. Fuse is not damaged by overloads, up to thecurrent that causes it to melt (“self-protecting”).
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Fundamental Differences
Between
Non Current-Limiting Fuses
(Expulsion Fuses)
&
Current-Limiting Fuses
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Fundamental Differences Between Expulsion Fuses
and Current-Limiting Fuses
1. Construction
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How an expulsion fuse works:
• An expulsion fuse uses a short element
• When the element melts, a low resistancearc produces gas from the fuse liner
• An expulsion action blows the ionized gasout of the fuse
• At a current zero, if the gap is sufficientlyde-ionized, arcing ceases
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Expulsion Fuse Design
Short Fuse Element
Gas Evolving liner
Cutout fuse Bayonet fuse
Expulsion Action
Common designs
After melting, arc
produces low resistance
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How a Current-Limiting fuse works:
• A Current-Limiting fuse uses a long elemente.g. 3’ (1meter) for a 15.5kV fuse.
• When the element melts, multiple series arcsare produced.
at high fault currents:
Restrictions
initiate arcing
Long elements
are wound on an
Inert core
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Current-Limiting Fuse Design
PUNCHED ELEMENT
FILLER
At high currents,
restrictions melt
simultaneously(introducing resistance)
Continued arcing causes
the arcs to lengthen(resistance increases)
Eventually the
whole element
is consumed
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Fundamental Differences Between Expulsion Fuses
and Current-Limiting Fuses
1. Construction
2. Current Interruption
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Expulsion Fuse - Current interruption
Prospective Fault Current
Fuse Current
Current interruption
Fuse Melting Current peak
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Current-Limiting fuse - Current interruption
Prospective Fault Current
Fuse Current
Current peak
Fuse Melting
Current interruption
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Fundamental Differences Between Expulsion Fuses
and Current-Limiting Fuses
1. Construction
2. Current Interruption
3. Energy Let-through
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Current let-through
Expulsion Fuse
Current-Limiting Fuse
i2 dt (i2t)Energy
25,000A
7,000A
10,000A rms Symmetrical
Prospective Current
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What is I2t ( )?i dt2
!
i
rR
time = t
heat = i 2 R t + i 2 r t
so, i 2 t a energy
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T T
Illustration of I2t ( ) Reduction using CL Fusei dt2
!
Fault Current 5000A
rms. symmetricalFirst loop 870,000 A2-sec.
Peak current 12kA
I2t let-through by Hi-Tech 80A = 31,000 A2-sec. (<4%)
Peak current 5 kA (41%)
I
II
rms
I2t is proportional to the
volume of the “box”
t
irms
t
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Fundamental Differences Between Expulsion Fuses
and Current-Limiting Fuses
1. Construction
2. Current Interruption
3. Energy Let-through
4. Peak Current Let-through
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Peak Let-Through Curves
1K 10K 50K 100K
100K
10K
1K
Prospective Fault Current
Amps rms symmetrical
Peak C
urr
ent
Prospective
Current 10,000A
Symmetrical
7,000A
25,000A25K
2.5K
Peak current of
asymmetrical fault
Peak current of CL fuse
7K
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Fundamental Differences Between Expulsion Fuses
and Current-Limiting Fuses
1. Construction
2. Current Interruption
3. Energy Let-through
4. Peak Current Let-through
5. Sensitivity to Circuit &
Fault Conditions
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Prospective Fault Current (as a function of point on wave)
X/R >15
Voltage
The point-on-wave where fault occurs affects asymmetry
Symmetrical Current
Asymmetrical Current
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Expulsion Fuse
Operation at High Currents
Current
Voltage
MELTING
TRVExpulsion fuses are sensitive to
circuit Transient Recovery Voltage
Expulsion fuses are
sensitive to circuit X/R
(fault offset)
Fuse waits for current zero
No significant arc voltage
before current zero
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Current-Limiting Fuse
Operation at High Currents
Current
Voltage
MELTING
Significant arc voltage (result of
current-limiting action)
Significant Current-Limiting action
Current-Limiting fuses are quite
insensitive to TRV and X/R
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Expulsion FuseOperation at Low Currents
Fuse Voltage
Fuse Current
Melt
System Voltage
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Backup Current-Limiting FuseOperation at Low Currents
Voltage
Current
Melt
Current switching between multiple elements
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Fundamental Differences Between Expulsion Fuses
and Current-Limiting Fuses
1. Construction
2. Current Interruption
3. Energy Let-through
4. Peak Current Let-through
5. Sensitivity to Circuit &
Fault Conditions
6. Performance at Various
Fault Current Levels
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Expulsion Fuses
" Must wait until a current zero to interrupt
" Interruption occurs when withstand voltage
exceeds recovery voltage
Expulsion fuses cannot interrupt at high
currents because the voltage withstand never
exceeds the recovery voltage. They
therefore have a maximum interrupting
current
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Backup CL Fuse - element melting= Restriction melting
High current
Low current
Fuse does
not interrupt
current
insufficient restrictions melt
Fuse
interrupts
current
all restrictions melt
Minimum I/C
Backup CL fuses cannot interrupt currents less than their
minimum interrupting current
sufficient restrictions melt
Fuse
interrupts
current
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Section 4
Hi-Tech’s Fuse Construction
&
Design Features
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Machined
brass caps
Low current section(FX Only - includes patented Damage Sensor® ) High current
interruption element
Resin-rich filament
wound glass/epoxy body
Compacted
quartz sand
Welded element
joints
Epoxy jointSoldered electrical
connection and
sealing
Construction of a Hi-Tech Fuse
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A. Cost advantages:
! In some applications a single fuse can be used, where parallel fuses
would normally be used
! Minimize the need and extra costs associated with using parallel fuses
B. Shorter overall lengths:
! In many cases, OS Shorty fuses will be shorter or smaller in diameter
than the alternative.
C. Compliance with industry standards:
! All OS designs have been tested to
the applicable IEEE (ANSI) and IEC
standards.
OS & OS Shorty Features
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Trans-Guard™ EXT Features
A. Significant design advantages:
! EXT fuses have the lowest let-through energy (I2t) levels in theindustry minimizing the potential for distribution equipment damage.
! Durable design with machined brass end-caps and acrylic paintcoating for minimized UV degradation.
! Largest current ratings available in the industry (65K, 80K and 100K)
B. Wide industry acceptance:
! Our EXT fuses are approved and
widely used throughout the US
utility market.
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Trans-Guard™ FX Features
! All FX designs have been tested to the most current IEEE (ANSI) andIEC standards which includes short circuit testing at elevatedtemperatures (RMAT of 140°C for 2” fuses and 71°C for 3” fuses ).
A. Sealed design:
C. Commitment to compliance with industry standards:
! Ensures no gases are discharged during operation! Prevents eventful failure due to leaking dry-well canisters
B. Patented damage sensor :! Significantly reduces the risk of fuse failure should a current surge
damage the fuse elements
E. Rugged machined end caps:! Results in less distortion and secure
attachment in dry-well canisters
D. Low current element in center of fuse:! Eliminates the risk of fuse overheating in
the MCAN or other types of enclosures
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Damage Sensor®
Reason for the Damage Sensor
A concern that:
If a surge damages, but does not fully melt, a
Full-Range fuse’s (high current) ribbon
element(s), the element(s) may subsequently
melt with a current too low for the high-current
element(s) to be able to interrupt.
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FX Full-Range Fuse Damage Sensor
10000
.010current in amperes
tim
e in s
econds high
current
section
low current
section
damage
sensor
high current section low current section high current section
Damage Sensor®tin
- how it works
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Damage Sensor®e D
1. The whole of the fuse’s melting TCC is
generated in the low current section
2. A surge that could damage the ribbon
element will melt, or damage to a greater
extent, the “damage sensor”
3. If the damage sensor subsequently melts at
a low current, the low current section can
interrupt it.
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End Cap ComparisonNon Hi-Tech Design
FX Machine Design
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Blown Fuse Indication
• Note: This is not available for dry-well
canister applications
Fuse Indicator - before operation Fuse Indicator - after operation
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Trans-Guard™ SX Features
! All FX designs have been tested to the most current IEEE (ANSI) andIEC standards which includes short circuit testing at elevatedtemperatures (RMAT of 140°C for 2” fuses and 71°C for 3” fuses ).
B. Commitment to compliance with industry standards:
A. Patented damage sensor :
! Significantly reduces the risk of fuse failure should a current surgedamage the fuse elements
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Section 5
IEEE/ANSI Standards
&
Testing Requirements
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Latest Applicable IEEE/ANSI Standards
• IEEE C37.40-2003IEEE Standard Service Conditions and Definitions for High-Voltage Fuses, DistributionEnclosed Single-Pole Air Switches, Fuse Disconnecting Switches, and Accessories
• IEEE C37.41-2000IEEE Standard Design Tests for High-voltage Fuses, Distribution Enclosed Single-Pole AirSwitches, Fuse Disconnecting Switches, and Accessories
• ANSI C37.47-2000Specifications for distribution fuse disconnecting switches, fuse supports, and Current-Limiting fuses
• IEEE C37.48-1997IEEE Guide for Application, Operation, Classification, Application, and Coordination ofCurrent-Limiting Fuses with Rated Voltages 1-38kV
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Definitions1. Rated Continuous Current - a current they can
carry continuously without damage
2. Rated Maximum Voltage - the maximum voltage against
which they are capable of interrupting current
3. Rated Maximum Interrupting Current - the maximum current
they are capable of interrupting
4. Rated Minimum Interrupting Current – for a backup fuse, the
lowest current the fuse has been shown to be able to interrupt
5. Rated Maximum Application Temperature - the maximum
application temperature at which the fuse is suitable for use
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General Test RequirementsAt the Rated Maximum Interrupting Current
At current where approximate maximum arc
energy is absorbed by the fuse
At the Rated Minimum Interrupting Current for
a backup fuse or at the lowest current that can
cause melting for a Full-Range fuse
Repeating of some of the tests above at thethe Rated Maximum Application Temperature
Testing in the “take-over” region where currentinterruption transfers from the low currentelement to the high current element (Full-Range only!)
I1 Testing -
I2 Testing -
I3 Testing -
RMAT Testing -
TCC Testing -
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Section 6
Application & Coordination
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Coordination of Expulsion Fuse and
Backup CL Fuse
• Hi-Tech Fuses Application Guide FS-10
• This generally follows recommendations in
IEEE Std.C37.48TM application guide.
• Conservative recommendations.
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Interrupting Rating Low Current
operationFuse Type
Expulsion
Fuse
Backup
CL Fuse
Poor Excellent
Excellent Poor
Relative Fuse Characteristics
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• Combining a Backup Current-Limiting Fuse
with a series Expulsion Fuse
• Full-Range Fuse
Two ways to get Full-Range protection
c
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Selecting Oil-Submersible
Backup Current-Limiting Fuse
with Series Expulsion Fuse
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Coordination of Expulsion Fuse
and Backup CL Fuse:
There are two types of coordination recommended
by the IEEE (Standard C37.48).
1) Time-current Curve Crossover Coordination (TCC)
2) Match-melt Coordination
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– Transformer KVA
– Primary Voltage
– Impedance
– Expulsion Fuse
– Connection
Requirements Needed to Select Fusing
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Selecting an Expulsion Fuse
Meeting Temporary Surge Requirements
The expulsion fuse minimum melt curve should be to the right of the
following points:
INRUSH: 12 x IR at 0.1 sec.
25 x IR at 0.01 sec.
COLD LOAD PICKUP: 3 x IR at 10 SEC.
6 x IR at 1 SEC.
Where IR = transformer rated current
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1000
100
10
1
0.1
0.01 10 100 1000 10,000
Current in Amperes rms Symmetrical
!
!
!
!
Expulsion Fuse
Minimum Melting TCC
Inrush/cold load pick-up
points
!
Tim
e (
se
c)
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The fuse must be able to carry the maximum transformer load current (includingacceptable overload) without melting.
Protective “weak link”, and Current Sensing bayonet fuses are typically pickedto melt at 300% - 400% IR in 300 sec. (600 sec. for fuses rated over 100A).
Dual Sensing, Dual Element and High Ampere fuses respond significantly totransformer oil temperature. They provide transformer overload protection, andtypically allow 200% IR for 2 hours, and 160% IR for 7 hours.
Selecting an Expulsion Fuse
Overload Requirements
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Basic Principles of TCC Coordination:
1) Each fuse must protect the other in its region of
non-operation
2) Operation of the expulsion fuse must not melt or
damage the backup fuse (when there is no fault
inside the transformer)
3) Transformer overload must not damage the backup
fuse by exceeding its maximum continuous current
rating
Selecting the Backup Fuse
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Requirement 1
Min I/C CL Fuse
50kA
CL Fuse
Minimum
Melt TCC
Ti
me
Current
Max I/C Expulsion Fuse
Expulsion
Fuse Total
Clearing TCC
Region where the
expulsion fuse
cannot interrupt
Max I/C Expulsion Fuse
Expulsion
Fuse Total
Clearing TCC
Region where the
CL fuse cannot
interrupt
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Requirement 2 & 3- 25% Margin
Bolted Secondary Fault Current
CL Fuse “No-damage” Curve
100%80%
CL Fuse Minimum Melt CurveExpulsion Fuse
Total Clearing
Curve
Check
Check
Check
100% 120%
Coordination Area
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Sample Coordination Tables
@ 2.4%HTSS242125@ 3.8%HTSS2421004000353C1213200
@ 2.5%HTSS242125@ 4.1%HTSS2421004000353C1212470
@ 2.6%HTSS242125@ 4.2%HTSS2421004000353C1212000
Minimum
ImpedanceAlternativesMinimum
ImpedanceAlternativesMinimum
ImpedanceCL FuseLink Cat #
Voltage
L-L
Trans-Guard OS "Shorty" (HTSS------)
Delta Connected Transformers
500 KVA CURRENT SENSING 353C
@ 2.0%HTSS232125@ 3.8%HTSS2321004000353C1213200
@ 2.1%HTSS232125@ 4.1%HTSS2321004000353C1212470
@ 2.2%HTSS232125@ 4.2%HTSS2321004000353C1212000
Minimum
ImpedanceAlternativesMinimum
ImpedanceAlternativesMinimum
ImpedanceCL FuseLink Cat #
Voltage
L-L
Trans-Guard OS "Shorty" (HTSS------)
GRDY-GRDY Transformers - CL Fuse L-N Rated (where possible)
500 KVA CURRENT SENSING 353C
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Basic Principles of Match-melt
Coordination:1) Each fuse must protect the other in its region of
non-operation
2) Operation of the expulsion fuse must not melt or
damage the backup fuse (when there is no fault
inside the transformer).
3) Transformer overload must not damage the backup
fuse by exceeding its maximum continuous current
rating.
4) Backup fuse must always let through enough energy
to cause the expulsion fuse to melt open
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What is I2t ( )?i dt2
!
i
R
time = t
heat = i 2 R t
so, i 2 t a energy
Done by comparing I2t of fuses
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Requirement 4
2 x minimum melt I2t of the backup fuse must be greater than
or equal to the maximum melt I2t of the expulsion fuse.
Current
MELTING
Main benefit of match-melt coordination is that voltage stress is
removed from the backup fuse after interruption
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Requirement 4: How to Calculate
2 x minimum melt I2t of the backup fuse must be greater than
or equal to the maximum melt I2t of the expulsion fuse.
Minimum Melt I2t of backup fuse – Published Value
Maximum Melt I2t of expulsion fuse – Must calculate from
expulsion fuse curve
Typically done using the following equations
I.025sec x 1.2 = Imax. melt (Imax-melt )2 x .025sec = Max. Melt I2t
(From min-melt TCC)
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Fuse Voltage Rating
Single Phase Transformers:
Fuse voltage rating " maximum applied (L-N) voltage
Three Phase Transformers:
- For GndY-GndY connected transformers having
less than 50% delta connected load
Can typically use L-N rated fuses
- For all other connections (i.e. delta connections)
L-L rated fuses are typically required
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Exception
When match-melt coordination is used:
It is usually possible to use L-N rated backup fuses
and L-L rated expulsion fuses
This makes it possible to fuse delta connected
transformers having primary voltages as high
as 34.5kV
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Selecting External
Backup Current-Limiting Fuse
with Series Cutout Fuse
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• EXT’s have been rated to match-melt
coordinate with a cutout having the same rating
• This means that the backup fuse always allows
enough energy through during a fault to cause
the cutout fuse to drop open
• This removes voltage stress from the backup
fuse & provides visual indication of where the
fault occurred
Selecting a Trans-Guard™ EXT Fuse
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• Must always be coordinated with a series
connected cutout expulsion fuse
• Select Voltage Rating– Rated Maximum Voltage of the fuse must be greater than
the maximum system L-N voltage
• Select Current Rating– K rating of backup fuse must be greater than or equal to the
K rating of the cutout fuse
• Select Hardware Configuration
Selecting a Trans-Guard™ EXT Fuse
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Trans-Guard™ EXT Hardware
Standard and Offset stud Integral Eyebolt Spade
Parallel Groove Connector Loose Eyebolt Universal Adaptor
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Selecting Full-Range
Current-Limiting Fuses
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Selecting a Full-Range Fuse
Meeting Temporary Surge Requirements
The expulsion fuse minimum melt curve should be to the right of the
following points:
INRUSH: 12 x IR at 0.1 sec.
25 x IR at 0.01 sec.
COLD LOAD PICKUP: 3 x IR at 10 SEC.
6 x IR at 1 SEC.
Where IR = transformer rated current
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1000
100
10
1
0.1
0.01 10 100 1000 10,000
Current in Amperes rms Symmetrical
!
!
!
!
Full-Range CL FuseMinimum Melting TCC
Inrush/cold load pick-up
points
!
Tim
e (
se
c)
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The fuse must be able to carry the maximum transformer load current (includingacceptable overload) without melting.
Full-Range fuse are typically selected to allow between 140-200% IR or 200-300% IR.
NOTE: The Fuse’s Melting Time-Current Curve will shift to the left withincreasing oil temperature.
Selecting a Full-Range Fuse
Overload Requirements
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Derating of FX fuses
• The fuse melting characteristics move to the
left (on the TCC)
• The fuse’s continuous current to decrease
There are certain conditions that will cause:
Note that an FX fuse maximum continuous
current rating is related to its melting TCC – it
is 95% of the minimum fusing current
(The minimum fusing current is the lowest current that melts
a fuse at a particular ambient temperature, including
manufacturing tolerances)
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Derating Factors
1. Derating for the fuse being in an enclosure
(FEP)
2. Derating with an increase in Surrounding
Temperature (Ambient temperature)
There are two factors to consider:
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Derating due to use in
a Drywell Canister Submerged in Oil
Reduction of 2.0%
Example: Lowest current to melt a 30A FX fuse, in canister at 250C
IAir = 43 A ICanister = 43A x 0.98 = 42.3A
I = lowest current to melt fuse at 25o C
. ..
(From min-melt TCC)
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Derating due to
Elevated Surrounding Ambient Temperature
Reduction of 0.2 % per degree C over 250C
Example: Lowest current to melt a 30A FX fuse, in oil at 1000C
100o - 25
o = 75o 75
o x 0.2% = 15%
100% - 15% = 85% (0.85)
I25Canister = 42.3 A I100 = 42.3A x 0.85 = 36A
I q = lowest current to melt fuse at q o C
. ..
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– For single phase applications: The RatedMaximum Voltage of the fuse must begreater than the maximum system L-Nvoltage
– For three phase applications: The RatedMaximum Voltage of the fuse shouldtypically be greater than the maximumsystem L-L voltage (some exceptionsapply)
Fuse Voltage Rating
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Selecting an Elastimold Fuse
• Select Voltage Rating– For single phase applications: The Rated Maximum Voltage
of the fuse must be greater than the maximum system L-Nvoltage
– For three phase applications: The Rated Maximum Voltageof the fuse should typically be greater than the maximumsystem L-L voltage (some exceptions apply)
• Select Current Rating– Use continuous current rating
• Must consider derating due to elevatedtemperatures
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Derating due to
Elevated Surrounding Ambient Temperature
Reduction of 0.2 % per degree C over 250C
Example: Lowest current to melt a 10A Elbow fuse at 650C
65o - 25
o = 40o 40
o x 0.2% = 8%
100% - 8% = 92% (0.92)
I25 = 15 A I65 = 15A x 0.92 = 13.5A
I q = lowest current to melt fuse at q o
C . ..
(From min-melt TCC)