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Introduction to Protection by Fuses
Copyright Mersen ® TM_001_PROTFUSEen_001_01122 / 37
OvercurrentsThere are 2 types of overcurrents:
• Overload
• Short circuit
Copyright Mersen ® TM_001_PROTFUSEen_001_01123 / 37
Overload current
Overload current: less than 8 times or 10 times the rated current
Short-circuit current: typically more than 10 times the normal current of the system – up to 300 KA
Overcurrents
Copyright Mersen ® TM_001_PROTFUSEen_001_01124 / 37
Common causes of overloads
Overcurrents
Dust/dirt build-upforeign particles
Lack ofmaintenance
Insulationdegradationcomponent
failures
Thermaldamage
Worn partsInsufficientlubrication
Ageing ofequipment
Insufficientcapacity
excessive use
Improperuse
TransientsUndervoltageover voltage
Power quality
Metallic particleswater damage
Low-magnitudeground faults
Copyright Mersen ® TM_001_PROTFUSEen_001_01125 / 37
Bolts, screwdrivers,
other conductiveobjects
Foreignarticles
Lightningswitching
surges
Voltagespikes
Semiconductorbreakdown
Componentsfailure
Direct pathto ground
Highmagnitude
ground faults
Floodsfires
vibrations
Externalinfluences
Common causes of short-circuits
Overcurrents
Copyright Mersen ® TM_001_PROTFUSEen_001_01126 / 37
Consequences of overcurrents
Overcurrents
Loss of life,burns,
flash blindness
Injury
Continuousprocess,
steel in arc furnace,non-conforming
parts
Loss ofProcesscontrol
Thousands ofdollars or euros
per minute
Downtime
Equipmentdamage,
destruction from Magnetic
movement
Mechanicaleffect
Equipmentdamage,
destruction fromenergy arcs
Thermaleffect
Copyright Mersen ® TM_001_PROTFUSEen_001_01127 / 37
• Manufacturers are fully responsible for their components
OvercurrentsImpact of legal considerations
• OEM’s are fully responsible for their assemblies / equipment
• «Limited liability» is a thing of the past!
• Cost of settlements are growing astronomically! (personnel injury, equipment, downtime, mental anguish, punitive damages)
Copyright Mersen ® TM_001_PROTFUSEen_001_01128 / 37
Safety
• The metallic element inside the fuse melts directly upon the fault current effect without any intermediate mechanism , sensors etc ….
• The arc extinction is totally enclosed: no emission of gas, flames, arcs or melted materials
• The arc flash energy is drastically reduced when the peak current is limited by a fuse.
Maximized energy limitation =
Minimized damage & injury
Fuse advantages
Copyright Mersen ® TM_001_PROTFUSEen_001_01129 / 37
Speed / Peak let through currentComparison of protective devices
Current limiting circuit breaker
i Non-limiting circuit breaker
t
Fuse
Fuse advantages
Copyright Mersen ® TM_001_PROTFUSEen_001_011210 / 37
Breaking capacity: up to 100 000 A, 200 000 A and even 300 000 A.
Maintenance before a short-circuit: no maintenance.
Maintenance after a short-circuit: replace the blown fuse by a new one. quick and gives the insurance the equipments are still protected with exactly the same efficiency as before.
Fuse advantages
Copyright Mersen ® TM_001_PROTFUSEen_001_011211 / 37
Selectivity (or discrimination)
Fuse = minimized circuit disruption, no black out.
Future system growth
Low power consumption
Fuse advantages
Copyright Mersen ® TM_001_PROTFUSEen_001_011212 / 37
Reliability
Universal
Price
Fuse advantages
Copyright Mersen ® TM_001_PROTFUSEen_001_011213 / 37
Body
Contacts
Fuse elements
Sand
Construction of a fuse
Copyright Mersen ® TM_001_PROTFUSEen_001_011214 / 37
tp
Prearc arc tt
Fault current
0
IC
Interruption of short circuit currents
Copyright Mersen ® TM_001_PROTFUSEen_001_011215 / 37
Melted sand = fulgurite (glass-like substance)
Interruption of short circuit currents
Copyright Mersen ® TM_001_PROTFUSEen_001_011216 / 37
arc
tP
0
Prearc time = 0.1s to 4 hours
Total time
When the fuse is not designed to interrupt overloads damaged to the body may occur due to excessive temperatures reached inside the fuse before melting the fuse elements.
Interruption of overloads
Copyright Mersen ® TM_001_PROTFUSEen_001_011217 / 37
Interruption to IEC 60269 standard
IEC 60269-2Systems for use by authorized persons
(industrial application)
IEC 60269-4Systems for the
protection ofsemiconductor devices
IEC 60269-3Systems for use by unskilled persons
(household applications)
CEI 60269-3-1Section I : D & D0 (Neozed®)Section IIA : NF 6A 6,2 x 22,2 - 10A 8,4 x 22,2 16A 10,2 x 25,4 - 20A 8,4 x 31 25A 10,2 x 31 - 32A 10,2 x3 7,4
Section IIB : BS 1361Section IIC : type C (Italy)
Section III : pin-type fusesSection IV : fuses in plugs (BS 1362)
IEC 60269-4-1Examples of types: BS88, USA, DIN etc…
CEI 60269-2-1Section I : NH system
Section II : BS88
Section III: 10x38,14x51,22x58
Section IV: BS88 Offset blades
Section V : UL 248Class J & class L
IEC 60269-1Low voltage fuses
1000VAC & 1500VDC
Specific usageVoltages can goabove 1000VAC
& 1500VDC
GeneralRules
Domestic usageAs per type
and country rules
Industrial usageGeneral cables
and motorsprotection
Copyright Mersen ® TM_001_PROTFUSEen_001_011218 / 37
Interruption to IEC 60269 standard
Former type of fuses replaced by gG typegL, gF, gI, gII
Transformer protectiongTr
Semiconductor protectiongR, gS
North American general purpose time-delaygD
North American general purpose for conductor protectiongN
Motor circuit protectiongM
Full range
General purpose: mainly conductor protectiongG
Semiconductor protectionaRPartial range (back-up)
Short circuit protection of motor circuitsaM
Breaking RangeApplicationsType
Copyright Mersen ® TM_001_PROTFUSEen_001_011219 / 37
Typical IEC Curves
Copyright Mersen ® TM_001_PROTFUSEen_001_011220 / 37
High voltage : 4.16 kV, 6.6 kV, 7.2 kV etc.High voltage fuses
CompressorsFans etc.
High voltage
Low voltage gG fuse
Low voltage gG fuse Low voltage
aM fuse
UPS
High voltage generator
HV / LV transformer
HV / HVTransformer
G
Lighting
Low voltage aM fuse
ACdrive
Softstarter
DCdrive
Low voltage gG fuse
DC motorDC fuse
Semiconductor fusesURD, gRB, gRC etc.
Typical layout of a large plant
Copyright Mersen ® TM_001_PROTFUSEen_001_011221 / 37
UFUSE MAX > VCIRCUIT MAX
(1) When protecting static current & voltage converters the rated voltage UN of fuses for semiconductors often require:
1.06 UN > VCIRCUIT MAX
Fuse voltage rating selection
600600gN, gD (American ranges)
725690
550500
440400
253230
gG, gM, aM, aR(1), gR(1), gS(1)
Maximum operational voltage of the fuse UFUSE MAX (V)
Rated Voltage of the Fuse UN (V)Fuse Type
Copyright Mersen ® TM_001_PROTFUSEen_001_011222 / 37
ZNB III
ZF I1.45I
Cable protection
Copyright Mersen ® TM_001_PROTFUSEen_001_011223 / 37
i
t
I
Motor damage curve
Current-limitingFuse
Thermal relay
60 s
Motor circuit protection
Copyright Mersen ® TM_001_PROTFUSEen_001_011224 / 37
1500 RPM three phase asynchronous motor
220 V
Selected fuses: class, voltage, ranting and current rating
380 V 660 V
Motor circuit protection
Copyright Mersen ® TM_001_PROTFUSEen_001_011225 / 37
Fuse Peak Arc voltage < Reverse Voltage of the semiconductorArc voltage
Fuse minimum interrupting capacity > minimum fault current or coordination with another protection system must be checked
Minimum interrupting capacity
Fuse Breaking Capacity > largest RMS value of the short circuit current I FAULTBreaking capacity
Fuse total I2t < I2t of the semiconductor junctionor Fuse total I2t < I2t of the semiconductor case ruptureTotal I²t
I FUSE > IRMS
The calculation of the current rating of the fuse must use corrective coefficients taking into account the effect of :• ambient temperature inside the cubicle• cooling• size of cables or copper bars connected to the fuse • variations of the current (reduce the fuse life time)Coordination with a circuit breaker requires a suitable melting curve at 15 msSuch coordination may require a fuse rating higher than the rating calculated from the RMS value of the current.
Current rating
V FUSE > VLINE TO LINE and V FUSE > V FAULT
In regenerative DC drives V FAULT is higher than VLINE TO LINEFaults are not always with an AC voltage (inverters & regenerative DC drives)
Voltage rating
RequirementsFuse parameters
Power electronic protection
Copyright Mersen ® TM_001_PROTFUSEen_001_011226 / 37
VAC MAX
Fuse
Diode or thyristor
VAC MAX
Fuse
Three phase bridge with 1 semiconductor per arm
VAC MAX ≤UNUL 248
For most ratings: VAC MAX ≤ 1.06 UN
For some ratings: VAC MAX ≤ 1.10 UN
For some 690V fuses: VAC MAX ≤ 1.05 UN
IEC 60269
Fuse voltage rating UN
Copyright Mersen ® TM_001_PROTFUSEen_001_011227 / 37
Diode or thyristor
VAC MAX
Fuse
Three phase bridge with several semiconductor per arm
Copyright Mersen ® TM_001_PROTFUSEen_001_011228 / 37
Fuse voltage rating UN
UN = KAC VAC MAX with 1.25V ≤ KAC ≤ 1.70
Fuses
Fuse
Fuses
Necessary because of the DC shoot through fault
See next slide
Regenerative DC drive
Copyright Mersen ® TM_001_PROTFUSEen_001_011229 / 37
DC shoot throught fault
Regenerative DC drive
Copyright Mersen ® TM_001_PROTFUSEen_001_011230 / 37
M
Fuse
VAC MAX
Soft starters & static switches
Copyright Mersen ® TM_001_PROTFUSEen_001_011231 / 37
Inductance
CE U
+
-
Semiconductor
Fuse
Inductance
CEU
+
-
Semiconductor
Fuse
Inverters
Copyright Mersen ® TM_001_PROTFUSEen_001_011232 / 37
DC power source(Battery or rectifier or fuel cell
or photovoltaic, etc …)
N inverters feeding3-phase machines+ -
DC
ACMVDC
DCMVDC
DC
ACMVDC
AC
+
-
Multi-inverters system
Copyright Mersen ® TM_001_PROTFUSEen_001_011233 / 37
L/R = f(U) of 2000 V DC SRD fuses
DC capacities of fuses
Copyright Mersen ® TM_001_PROTFUSEen_001_011234 / 37
Typical values of L/R
1000DC motor field circuit *
40 - 100DC traction systems
20 - 60DC motor armature
< 25 main DC bus bar fed by a three phase bridge
< 10Battery
< 1Capacitor bank
L/R in msEquipement
Copyright Mersen ® TM_001_PROTFUSEen_001_011235 / 37
L / R = f(U)
Value of Ipm (minimum interrupting capacity)
Um = f(U)
Example of DC capabilities for an AC rated fuse range
Copyright Mersen ® TM_001_PROTFUSEen_001_011236 / 37
Voltage
Time constant L/R
Fault current magnitudes
Fuse definition under DC conditions
Copyright Mersen ® TM_001_PROTFUSEen_001_011237 / 37
FUS
E
Universal use of T-D fuse (ideal all-purpose fuse)
Full overcurrent protection, Fidelity of operation
Selectivity, Simplicity, Safety
Economical, Energy-limiting, Easy-to-use,Excellent protection
Conclusion: simply perfect !