Circuit Breakers 6k134

1 Circuit Breakers • Definition • “ Mechanical switching devices capable of making, carrying and breaking currents under normal and abnormal conditions

Circuit Breakers Requirements • Opens & closes in shortest possible time • 􀁺 Conducts rated current. • 􀁺 Withstands thermally & mechanically any short circuit. • 􀁺

Maintains its voltage to earth across open s. • 􀁺 Does not create over voltages during circuit opening • 􀁺 Easy to maintain. • 􀁺 Not very expensive.

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.

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

Circuit breakers Elements • • • •

Main 􀁺 Insulation between main s 􀁺 Interruption chamber 􀁺 Control, supervisory and auxiliary devices • 􀁺 Insulating link between control unit and main

Circuit Breakers rating – Rated normal current: to be carried without temperature rise. – Rated breaking current: – Highest current to be interrupted – rms of the peak value of the Asymmetrical current.

Circuit Breakers rating • Generally and according to voltage range, a constant is used to multiply the short circuit • current to obtain the breaking current • 􀁺 Rated MVA = sqrt(3) * Line voltage (kV) * breaking current (kA)

LT CIRCUIT BREAKER PARTS • Mechanism – Manual operation – Electrical operation

• Pole – Main s – Silver cium oxide – Arcing – Tungsten base alloy

• Arc chute

Breaker parts cont.. • Cradle for draw out – Service position – Main + control – Test position Control – Isolated position – No

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

Breaker part contd.. –Built-in-release • Magneto thermal release – Over laod – Short circuit

–Voltmetric release • Under voltage release • Shunt release – Remote operation – External relays

Main Parts of ACB

Breaker accessories –Motor –Auxiliary s- NO or NC –Terminal row –Micro switches

Mitsubishi ACB

ABB, ACB 1250 A

Heavy Industrial Breaker

Inside of ACB

Schneider Electric

Inside of the Breaker

Types of mainteance 1. preventive 2. breakdown 3. Condition based 4. Predective

INSPECTION SCHEDULE •

EVERY YEAR

1. Visual checks 2. Cleaning the insulating parts 3. Check and clean the arc chute

After short circuit clearance Or Every 5 yeas or 10000 operation

1. Dismantle the breaker  check the s  Tightening the bus bolt  clean the mechanism  replace the worn out parts

Every 5 years • Grease & oil all the bearings, ts & sliding faces • Clean the auxiliary switches • Tighten the terminals

Greasing… • No greasing is required in dust free & non corrosion atmosphere • Regrease the breaker after a cycle of 500 operations

Components to be greased 1. 2. 3. 4. 5. 6.

Rubbing surfaces in the mechanism Pins Roller assembly Pole latch spring Slotted guide Crank

Recommended grades of grease – LITHON 2 OF H.P – BALMEROL MOLY GREASE ML5

Components not be greased • • • •

All releases Main isolating s Earthing terminal Secondary isolating s

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

• 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 washers should be replaced with new • Dismantled parts should be kept in safe and dry place • New cloth to be used for cleaning the interrupter

• Do check the all fixing bolts • Test through slow operation

caution • Mechanism must be discharged before maint • Draw out the breaker • Breakers must be periodically operated

MCCB

MPCB • • • •

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

• Current Range 0.1…630 A • UL Listed for Motor Loads • Short Circuit Protection • Overload Protection • Visible Trip Indication • High Current Limiting • High Switching Capacity

• 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

MPCB

MPCB