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1

Circuit Breakers Definition Mechanical switching devices capable of

making, carrying and breaking currentsunder normal and abnormal conditions

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Circuit Breakers Requirements

Opens & closes in shortest possible time Conducts rated current.

Withstands thermally & mechanically anyshort circuit.

Maintains its voltage to earth across opencontacts.

Does not create over voltages during circuitopening

Easy to maintain. Not very expensive.

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Particulars of a Circuit Breaker

Medium for arc extinction. Rated line voltage. Rated breaking current. Type of construction e.g outdoor,

indoor. Etc Type of operating mechanism Total breaking time.

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Frequency of LTCB maint.depends upon.

1. Service condition 2. Frequency of operation

3.Tripping of fault 4. Relative humidity

5. Presence of dust 6. Reactive gases

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Circuit breakers Elements

Main Contact Insulation between main contacts Interruption chamber Control, supervisory and auxiliary

devices Insulating link between control unit and

main contact

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Circuit Breakers rating

Rated normal current: to be carried withouttemperature rise.

Rated breaking current: Highest current to be interrupted rms of the peak value of the Asymmetrical

current.

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Circuit Breakers rating

Generally and according to voltage range, aconstant is used to multiply the short circuit

current to obtain the breaking current Rated MVA = sqrt(3) * Line voltage

(kV) * breaking current (kA)

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LT CIRCUIT BREAKER PARTS

Mechanism Manual operation Electrical operation

Pole Main contacts Silver cadmium oxide

Arcing contact Tungsten base alloy Arc chute

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Breaker parts cont.. Cradle for draw out

Service position Main contact + control contact Test position - Control contact Isolated position No contact

Control box Closing and trip push botton Operating handle On Off indicator

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Breaker part contd..

Built-in-release Magneto thermal release Over laod

Short circuit Voltmetric release

Under voltage release Shunt release

Remote operation External relays

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Main Parts of ACB

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Breaker accessories

Motor Auxiliary contacts- NO or NC Terminal row Micro switches

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Mitsubishi ACB

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ABB, ACB 1250 A

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Heavy Industrial Breaker

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Inside of ACB

http://en.wikipedia.org/wiki/File:Circuitbreaker.jpg

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Schneider Electric

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Inside of the Breaker

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Types of mainteance

1. preventive

2. breakdown3. Condition based

4. Predective

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INSPECTION SCHEDULE

EVERY YEAR

1. Visual checks

2. Cleaning the insulating parts

3. Check and clean the arc chute

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After short circuit clearanceOr

Every 5 yeas or 10000 operation

1. Dismantle the breaker check the contacts

Tightening the bus bolt clean the mechanism replace the worn out parts

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Greasing

No greasing is required in dust free& non corrosion atmosphere

Regrease the breaker after a cycleof 500 operations

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Components to be greased

1. Rubbing surfaces in the mechanism2. Pins

3. Roller assembly

4. Pole latch spring

5. Slotted guide6. Crank

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Recommended grades of

grease

LITHON 2 OF H.P BALMEROL MOLY GREASE

ML5

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Components not be greased

All releases

Main isolating contacts Earthing terminal Secondary isolating contacts

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Important points for general

maintenance Isolation of circuit breaker from power & control

supply

Discharging of spring Observe all the instruction Understand the procedure of breaker operation

Do not use force Replace the cover and wire mesh after the inspection

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Oiling /greasing after cleaning only Use always proper tools Spit pins, lock washers, spring washers

should be replaced with new All the gaskets, o-rings & rubber washersshould be replaced with new

Dismantled parts should be kept in safe anddry place New cloth to be used for cleaning the

interrupter

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Do check the all fixing bolts Test through slow operation

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caution

Mechanism must be dischargedbefore maint

Draw out the breaker Breakers must be periodically

operated

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MCCB

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MPCB

Protection against over current

Protection against short circuit Protection against earth fault Protection against single phasing

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Current Range 0.1630 A

UL Listed for Motor Loads

Short Circuit Protection

Overload Protection

Visible Trip Indication High Current Limiting

High Switching Capacity

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Key Specifications/Special Features: Rated current: 0.1-0.16, 0.16-0.25, 0.25-0.4,

0.4-0.63, 0.63-1, 1-1.6, 1.6-2.5, 2.5-4, 4-6.3,6-10, 9-14, 13-18, 17-23, 20-25, 24-32A

Rated voltage: up to 660

Frequency: 50/60Hz

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MPCB

http://epub1.rockwellautomation.com/images/web-proof-small/GL/36209.jpg

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MPCB

http://powerli.manufacturer.globalsources.com/si/6008828230287/LargeImage/50-60Hz-Motor-Protection/product_id-1007805288/action-GetProduct.htm

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