Vadodara institute of engineering,kotambi NAME:NAFISKHANPATHAN(13ELEE181) BARIYA VIPUL(13ELEE182) PATEL AMIT(13ELEE180) BRANCH:EE-2 PPT OF EEE

Miniature circuit breaker(mcb)

Miniature Circuit Breakers (MCB) Multi 9

Protect cables against overloads and short circuits Let the current flow without overheating on cables Open and close a circuit under rated current Protect against insulation faults (see earth leakage protection module) Definition Main functions Miniature circuit = switch + trip unit breaker (MCB)  Symbol

A mechanical system to open and close the circuit A bimetal strip to act against overloads A magnetic trip to act against short circuits Definition A Multi 9 circuit breaker has: Miniature circuit = switch + trip unit breaker (MCB) 

It has standardized modular dimensions   125A   50 kA   440 V CA Definition Main performances It fits in your pocket... 

Definition Multi 9 standard  Multi 9 switchgear comes in 9 mm pitch  width symmetrical rail external part depth 6010 maxi maxi 44 maxi The modular design meets 2 criteria:  mounting on a 35 mm symmetrical rail  dimensions - modules in widths of 17.5 mm external part = 45 mm - depth between 55 and 70 mm

The technology Active parts C60N NC100 / NC125 terminal fixed contact moving contact strip braid magnetic trip load side terminal terminal bimetral strip strip braid moving contact magnetic trip load side terminal strip braid bimetal strip 

Overload protection bimetal tripping bar bimetal tripping bar screw calibration strip braid NC45 NC100 / NC125 A bimetal strip is used:  to protect the cable against overloads  symbol: principle of the bimetal: in a Multi 9 circuit breaker 

Thermal tripping curve the "thermal" part of the tripping curve must be in accordance with the standard Overload protection Legend: In = rated current Ind = no tripping current Id = tripping current  tripping no tripping destruction of bimetal accuracy t (s) I/InInIndId

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

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

Short-circuit protection "By-pass" technique for the protection of sensitive parts of the circuit breaker DC breaking 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  arcing horn arcing horn NC45NC100 / NC125

Short-circuit protection Magnetic tripping curve Our curves are instantaneous tripping curves  Legend: Ind = no tripping current Id = tripping current destruction of the solenoid tripping no tripping t (s) I/InIndId

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 current in industrial and domestic distributions D and K curves tripping betwen  tripping: 10 to 14 In; more particulary adopted for installations with high inrush 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 currents such as motors, coil  G M

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 

Choosing a circuit breaker In conclusion A Multi 9 circuit breaker is determined by:  rating  breaking capacity  number of poles  voltage  tripping curve  standard  frequency  type of load 

Auxiliaries: C60  SD: alarm switch  MX + OF: shunt trip  MN: undervoltage release The information is transmitted via a mechanical link C60/NC100 and NC125 auxiliaries are not compatible  54 mm maxi 4 types of auxiliaries for our Multi 9 circuit breakers  OF: indication switch MX+OF OF SD C60 44/3 MN 51/3 52/3 54/3 53/3

Auxiliaries: NC100 - NC125 The information is transmitted via a mechanical link C60/NC100 and NC125 auxiliaries are not compatible  NC100H MX+OF or Vigi MN or OF SD 33/334/3 35/3 36/3 27/3  SD: alarm switch  MX + OF: shunt trip  MN: undervoltage release 4 types of auxiliaries for our Multi 9 circuit breakers  OF: indication switch

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