Vadodara institute of engineering kotambi NAME NAFISKHANPATHAN13 ELEE

Vadodara institute of engineering, kotambi NAME: NAFISKHANPATHAN(13 ELEE 181) BARIYA VIPUL(13 ELEE 182) PATEL AMIT(13 ELEE 180) BRANCH: EE-2 PPT OF EEE

Miniature circuit breaker(mcb)

Miniature Circuit Breakers (MCB) Multi 9

Definition Main functions n Protect cables against overloads and short circuits n Let the current flow without overheating on cables n Open and close a circuit under rated current n Protect against insulation faults (see earth leakage protection module) n Symbol Miniature circuit = switch + trip unit breaker (MCB) 4

Definition A Multi 9 circuit breaker has: n A mechanical system to open and close the circuit n A bimetal strip to act against overloads n A magnetic trip to act against short circuits Miniature circuit = switch + trip unit breaker (MCB) 4

Definition Main performances n It has standardized modular dimensions o £ 125 A o £ 50 k. A o £ 440 V CA It fits in your pocket. . . 4

Definition n The modular design meets 2 criteria: o mounting on a 35 mm symmetrical rail o dimensions - modules in widths of 17. 5 mm + 0. 5 - 0 - external part = 45 mm - depth between 55 and 70 mm n Multi 9 standard o Multi 9 switchgear comes in 9 mm pitch 4 44 maxi 21. 3 81 45 maxi width symmetrical rail depth external part 10 maxi 35 60

The technology Active parts C 60 N NC 100 / NC 125 terminal bimetral strip fixed contact strip braid moving contact magnetic trip load side terminal magnetic trip strip braid bimetal strip load side terminal 4

Overload protection n A bimetal strip is used: o to protect the cable against overloads o symbol: n principle of the bimetal: in a Multi 9 circuit breaker 4 NC 45 NC 100 / NC 125 bimetal tripping bar bimetal screw calibration strip braid

Overload protection n Thermal tripping curve n the "thermal" part of the tripping curve must be in accordance with the standard t (s) tripping no tripping destruction of bimetal accuracy Legend: In = rated current Ind = no tripping current Id = tripping current 4 In Ind Id I/In

Overload protection n Temperature derating o our circuit breakers do not have temperature compensation o if the calibration temperature is different from the ambient temperature: derating is required Simultaneous multi-pole tripping 4

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 The arc in Multi 9 circuit breakers NC 45 NC 100 / NC 125 arcing horn "By-pass" technique for the protection of sensitive parts of the circuit breaker DC breaking is difficult arcing horn "By-pass" technique for the protection of sensitive parts of the circuit breaker (magnetic trip) 2 breaking techniques used by Multi 9 4

Short-circuit protection Magnetic tripping curve t (s) destruction of the solenoid tripping no tripping Legend: Ind = no tripping current Id = tripping current Ind Id I/In Our curves are instantaneous tripping curves 4

The magnetic tripping levels with high inrush current: like LV/LV transformers n C Curve o 5 and 10 In control and protection of circuits with high short-circuit current in industrial and domestic distributions n D and K curves tripping betwen o tripping: 10 to 14 In; more particulary adopted for installations with high inrush currents like LV/LV transformers n B curve o 3 and 5 In protection low short-circuit current generators G n Z curve o 2. 4 to 3. 6 In protection against electronic circuits n MA curve o 12 In; protection only against short-circuit and high inrush currents such as motors, coil 4 M

Marking n Front panel marking: n Side panel marking: Circuit breaker marking is governed by strict rules in accordance with the standards and decisions made by the manufacturer 4

Choosing a circuit breaker In conclusion n A Multi 9 circuit breaker is determined by: o rating o breaking capacity o number of poles o voltage o tripping curve o standard o frequency o type of load 4

Auxiliaries: C 60 o SD: alarm switch o MX + OF: shunt trip o MN: undervoltage release n 4 types of auxiliaries for our Multi 9 circuit breakers o OF: indication switch SD MX+OF MN C 60 51/3 52/3 54/3 53/3 44/3 OF 54 mm maxi The information is transmitted via a mechanical link C 60/NC 100 and NC 125 auxiliaries are not compatible 4

Auxiliaries: NC 100 - NC 125 n 4 types of auxiliaries for our o SD: alarm switch o MX + OF: shunt trip o MN: undervoltage release MN or MX+OF or Vigi 27/3 35/3 NC 100 H SD 34/3 33/3 OF 36/3 Multi 9 circuit breakers o OF: indication switch The information is transmitted via a mechanical link C 60/NC 100 and NC 125 auxiliaries are not compatible 4

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