Miniature Circuit Breakers (MCB)

CAREER POINT UNIVERSITYCAREER POINT UNIVERSITYMAJOR ASSIGNMENTMAJOR ASSIGNMENT

Submitted By:Submitted By:Chhotray Tiyu(K12279)Chhotray Tiyu(K12279)

Guided By:Guided By:Mr. Ravindra Meena(HOD)Mr. Ravindra Meena(HOD)

Customer Training - Freddy Suhartono - April 2000 - English 2

Protect cables againstoverloads and short

circuits Let the current flow

without overheating on cables

Open and close a circuit under rated current

Protect against insulationfaults (see earth leakageprotection module)

DefinitionMain functions

Miniature circuit = switch + trip unit breaker (MCB)

Symbol

Customer Training - Freddy Suhartono - April 2000 - English 3

A mechanical system to open and close the circuit

A bimetal strip to act against overloads

A magnetic trip to act against short circuits

DefinitionA Multi 9 circuit breaker has:

Miniature circuit = switch + trip unit breaker (MCB)

Customer Training - Freddy Suhartono - April 2000 - English 4

It has standardized modular dimensions 125A 50 kA 440 V CA

DefinitionMain performances

It fits in your pocket...

Customer Training - Freddy Suhartono - April 2000 - English 5

Definition Multi 9 standard Multi 9 switchgear comes in 9 mm pitch

width

symmetricalrail

externalpartdepth

6010 maxi

3545maxi

44 maxi21.3

81

The modular design meets 2 criteria:

mounting on a 35 mmsymmetrical rail

dimensions- modules in widths of 17.5 mm + 0.5 - 0- external part = 45 mm- depth between 55 and 70 mm

Customer Training - Freddy Suhartono - April 2000 - English 6

The technologyActive parts

C60N NC100 / NC125

terminal

fixed contact

movingcontactstrip braid

magnetictrip

load side terminal

terminal

bimetral strip

strip braid

movingcontact

magnetic trip

load side terminal

strip braidbimetal strip

Customer Training - Freddy Suhartono - April 2000 - English 7

Overload protection

bimetal

tripping barbimetal

tripping bar

screwcalibration

stripbraid

NC45 NC100 / NC125

A bimetal strip is used: to protect the cable against overloadssymbol: principle of the bimetal: in a Multi 9 circuit

breaker

Customer Training - Freddy Suhartono - April 2000 - English 8

Thermal tripping curve

the "thermal" part of thetripping curve must be

inaccordance with the

standard

Overload protection

Legend:In = rated currentInd = no tripping currentId = tripping current

tripping

notripping

destructionof bimetal

accuracy

t (s)

I/InIn Ind Id

Customer Training - Freddy Suhartono - April 2000 - English 9

Overload protection

Simultaneous multi-pole tripping

Temperature derating our circuit breakers do not have temperature

compensation if the calibration temperature is different from

the ambient temperature: derating is required

Customer Training - Freddy Suhartono - April 2000 - English 10

Short-circuit protection

Short-circuit current is given as RMS or peak(Isc or Îsc)RMS = Root Mean Square in symmetrical DC(with PF = I)

Short-circuit protection must limit thermal stress in the cable in order to prevent cable damage (which may reach vaporization of the copper in some cases)

Comments slide 29

Customer Training - Freddy Suhartono - April 2000 - English 11

Short-circuit protection

"By-pass" technique for the protection of sensitive partsof the circuit breaker DCbreaking is difficult

"By-pass" technique for the protection of sensitive parts of the circuit breaker (magnetic trip)

The arc in Multi 9 circuit breakers

2 breaking techniques used by Multi 9

arcinghorn arcing

horn

NC45 NC100 / NC125

Customer Training - Freddy Suhartono - April 2000 - English 12

Short-circuit protectionMagnetic tripping curve

Our curves are instantaneous tripping curves

Legend:Ind = no tripping currentId = tripping current

destructionof the solenoid

trippingnotripping

t (s)

I/InInd Id

Customer Training - Freddy Suhartono - April 2000 - English 13

B curve 3 and 5 In protection

low short-circuit current generators

The magnetic tripping levels with high inrush current:like LV/LV transformers

C Curve 5 and 10 In control and protection of

circuits with high short-circuit currentin industrial and domestic distributions

D and K curves tripping betwen tripping: 10 to 14 In; more particulary

adopted for installations with highinrush currents like LV/LV transformers

Z curve 2.4 to 3.6 In protection against

electronic circuits

MA curve 12 In; protection only against

short-circuit and high inrush currentssuch as motors, coil

GM

Customer Training - Freddy Suhartono - April 2000 - English 14

Side panel marking:

Marking

Front panel marking:

Circuit breaker marking is governed by strict rules in accordance with the standards and decisions made by the manufacturer

Customer Training - Freddy Suhartono - April 2000 - English 15

THANK YOU