ltcb 1 maint
TRANSCRIPT
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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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