Introduction to Protection by Fusesep-es.mersen.com/fileadmin/catalog/Multimedia-Premium/TM_001... · Title: Microsoft PowerPoint - TM_001_PROTFUSEen_001_0112.ppt Author: cmou Created

Introduction to Protection by Fuses

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OvercurrentsThere are 2 types of overcurrents:

• Overload

• Short circuit


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


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


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


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


• 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)


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


Speed / Peak let through currentComparison of protective devices

Current limiting circuit breaker

i Non-limiting circuit breaker

t

Fuse

Fuse advantages


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


Selectivity (or discrimination)

Fuse = minimized circuit disruption, no black out.

Future system growth

Low power consumption

Fuse advantages


Reliability

Universal

Price

Fuse advantages


Body

Contacts

Fuse elements

Sand

Construction of a fuse


tp

Prearc arc tt

Fault current

0

IC

Interruption of short circuit currents


Melted sand = fulgurite (glass-like substance)

Interruption of short circuit currents


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


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


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


Typical IEC Curves


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


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


ZNB III

ZF I1.45I

Cable protection


i

t

I

Motor damage curve

Current-limitingFuse

Thermal relay

60 s

Motor circuit protection


1500 RPM three phase asynchronous motor

220 V

Selected fuses: class, voltage, ranting and current rating

380 V 660 V

Motor circuit protection


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


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


Diode or thyristor

VAC MAX

Fuse

Three phase bridge with several semiconductor per arm


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


DC shoot throught fault

Regenerative DC drive


M

Fuse

VAC MAX

Soft starters & static switches


Inductance

CE U

+

-

Semiconductor

Fuse

Inductance

CEU

+

-

Semiconductor

Fuse

Inverters


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


L/R = f(U) of 2000 V DC SRD fuses

DC capacities of fuses


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


L / R = f(U)

Value of Ipm (minimum interrupting capacity)

Um = f(U)

Example of DC capabilities for an AC rated fuse range


Voltage

Time constant L/R

Fault current magnitudes

Fuse definition under DC conditions


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 !

Documents

Introduction to Protection by Fusesep-es.mersen.com/fileadmin/catalog/Multimedia-Premium/TM_001... · Title: Microsoft PowerPoint - TM_001_PROTFUSEen_001_0112.ppt Author: cmou Created