Electrical Circuit Protection

7/28/2019 Electrical Circuit Protection

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Electrical Circuit Protection

By

Saman Rajapakse Assistant Manager-Technical Training

Rotax Ltd


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Electrical circuit protection

Circuit Breakers

Over Current andShort Circuit

Protection

Earth FaultProtection

Miniature Circuit

Breakers (MCB)

Air circuit breaker

(ACB)

RESIDUAL CURRENTCIRCUIT

BREAKER(RCCB)

Earth Fault Relay

(EFR )

Molded case circuitbreaker (MCCB)

Earth leakage relayELR

Surge protectiondevices


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Protection Types ( )

Over Current( )

Short Circuit ( )

Earth Leakage( )


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Circuit protection devices

A circuit protection device has three maincomponents ( )

Sensing to sense the line current, leakage currentetc( )

Measure - to measure the current and decideweather the same is above/below the set point( /

)

Action - to trip the circuit if the current is abovethe set point

( )


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Over Current and Short Circuit

Miniature Circuit Breaker (MCB)( )

Molded Case Circuit Breaker (MCCB)( )

Air Circuit Breaker (ACB)( )


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Earth Leakage

Residual Current Circuit Breaker (RCCB) ( )

Earth Leakage Relay( )

Earth Fault Relay( )


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Miniature Circuit Breakers (MCBs)

Comply with IEC 60947-2 or IEC 60898

Fixed Thermal / Magnetic Releases ( , /

)

Rated Current up to 125 Amps ( 125 )

Breaking Capacity ( ) up to 10 kA (IEC 60898) or 15 kA (IEC 60947-2)

Up to 4 Pole ( ) Versions

Tripping Characteristic Curves ( ) - B/C/D

Specifications


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Miniature circuit breakers (continued )

Specifications . . .IEC 60947-2

Low voltage switch gear and control gear circuitbreakers

IEC 60898

Circuit breakers for over current protection for household and similar installations


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Miniature circuit breakers (continued)

Specifications

Thermal over load ( )

Bi metal construction ( )

Inverse time characteristics ( )

Magnetic short circuit ( )

Main circuit current excites the coil of an electromagnet ( )


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Miniature circuit breakers(continued)

Specifications .

Preferred current ratings ( )

6, 10, 16, 20, 25, 32, 40, 50, 63,80, 100, 125 amperes

Some mcb current rating can be identified by its togglecolour (

)

Eg; F&G AUSTRIA6(green),10(red),25(yellow),40(black),63(orange)


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Miniature circuit breakers(continued)

Specifications .

Breaking capasity ( )to 10ka as per IEC60898

Suitable for domestic and medium size commercial applications( / )

Breaking capasity above 10 ka as per IEC 60947-2

Suitable for large commercial applications ( )


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Miniature circuit breaker

Magnetic short circuit release

Bi metallic thermalrelease

Arcchute

toggle

contacts


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Specifications .

No; of poles (e.g; single, two, three, three pole +N, four)

when No; of poles increases toggles are interconnected by abridging bar ( )

Three pole +N version no over load/short circuit protection for

neutral ( )

Four pole version overload/short circuit protection for threephases +neutral ( )


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Miniature circuit breakers

1 pole 1p& n2 pole

3 pole

3p & n4 pole


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Specifications . Tripping characteristics

Type B 3-5 times rated current and suitable for lighting loads( )

Type C 5-10 times rated current and suitable for motor loads( )

Type D 10-20 times rated current and suitable for x-ray units,welding plants ( / )


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Miniature circuit breakers

B curve

C curve

D curve

Thermalregion

Magneticregion


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MINIATURE CIRCUIT BREAKER

MAKE & MODEL

THERMAL CURVETYPE C

BREAKINGCAPASITYIN AMPS

RATEDCURRENT IN

AMPS

RATEDVOLTAGE

RELEVENTSTANDARD


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Molded case circuit breakers Breaking Capacity up to 100 Ka

Utilization category ( )type A or type B

Front/rear connections ( /

Isolation marking

( )-


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Molded case circuit breaker

Thermal Release sense the over load condition ( )

Magnetic release sense the short circuit condition (

)

Rated Current up to 2500 Amps

Breaking Capacity up to 100 kA

Rated insulation voltage ( ) (U i) 690 v ac

Rated impulse withstand voltage ( )(Uimp) 8000 volts


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Molded case circuit breakers (continued)

Specifications Thermal/magnetic releasesFixed thermal/magnetic

Adjustable thermal(.63-1 times of ratedcurrent)/fixed magnetic

Fixed thermal/ adjustable magnetic(6-12 times of rated current)

Adjustable thermal/magnetic

0.63

0.8

1.0


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Molded case circuit breaker

Thermalregion

Magneticregion

Thermaladjustment(.63-1 of In)

Magnetic adjustment

(5-10 times of In)


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Molded case circuit breaker (continued)

Specifications Rated current expressed as frame size/thermalrelease current

Frame size ratings ( AF )100,125,160,250,400,630,800,1250,1600,2000amperes

Thermal release current ratings ( AT )10,15,20,30,40,50,60,75,100,125,160,250,400,630,800,1000,1250,1600,2000 amps


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Molded case circuit breaker (continued )

Specifications Breaking capacity expressed as two values

Rated ultimate short circuit breaking capacity(I cu ) up to 100 Ka at 400 volts ac

Rated service short circuit breaking capacity

(I cs ) up to 75 kA at 400 volts ac

Ics =% of Icu (eg; 25,50,75,100 %)


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Molded case circuit breakers(continued)

Specifications Utilization category type A designed for current discriminationonly

Utilization category type B ,designed for current and timediscrimination

Short time withstand current ( Icw) available for only type B mccb


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Specifications . Type of connections

Front connected (most popular type)

Rear connected (for bus bars)

Plug in ( special applications)


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Specifications Externally mounted accessories

Handles panel /breaker mounted

Motor operator

Mechanical interlocks

Extended bars for terminals

Inter pole barriers


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Molded case circuit breaker (continued)

Motor operator

Thermal o / l and s/crelease

Extended bars


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Specifications .

Internally mounted accessories

Shunt trip coil

Under voltage trip coil

Auxiliary switches

Alarm switch


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MOLDED CASE CIRCUIT BREAKERS (INTERNALLYMOUNTED ACCESSORIES)


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Air circuit breakers (continued)

Specifications , Rated current -800,1250,1600,2000,2500,3200,4000,5000,6300 amps

Over current release (OCR) for general feeder protection andgenerator protection

Rated current of OCR 200,400,800,1250,1600,2000,2500,3200amps


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Position switchterminal

Close/openCounter

ON OFF indicator

Over current release (OCR)

OFF button

Breaker Fixingbolt

Key-lock location

Draw-out position padlock

Control circuit terminal

Auxiliary switch terminal

Draw-out chassis

Spring charge indicator

Spring charging handle

Close

button

Draw-out handleinsertion hole

Draw-out positionindicator

Air circuit breaker


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Main circuit terminal

Draw-out maincontactFixed contact

Moving contact

Measurement CT

Power CT

Draw-out arm

Control circuitterminal

Charging motor

Closing coil

Closing spring

Arc chamber

Operating mechanism

Mold cover

air circuit breaker (internal structure)


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Air circuit breakers (continued )

Specifications .

Breaking capasity I cu up to 220 kA at 440 volts ac

Breaking capasity I cs up to 100 kA at 440 volts ac


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Horizontalterminal

Verticalterminals

Front connection

Air circuit breaker

(Main circuit terminals)

Rear connection

Up to 1600 amps asstandard

2000 amp and above asstandard

Specify when ordering


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Air circuit breakers (continued)

Specfications . Mounting type fixed or draw out

Fixed no maintenance possible

Draw out maintenance and inspection/replacement of contacts possible

Terminals -vertical (standard version) or horizontalor front connected


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Air circuit breakers (continued )

Specifications Spring charging operation manual or motor operator

Charging the closing spring

Closing the ACB

Opening the ACB

Mechanical interlocks


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Air circuit breaker (Mechanical

Interlock)Horizontal type Vertical typeStainless steel wire

Rod


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Residual Current Circuit Breakers (RCCBs)

Rated Current up to 100 Amps

Sensitivity 30/100/300 mA

Application Types A , AC and B

Tripping Delay Type S and G

Comply with IEC 61008 standard

Specifications


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Residual current circuit breakers (continued)

Specifications . Two types of technologies

Voltage dependent- electronic type-supply voltage dependent

Voltage independent- electro mechanical type- supply voltageindependent


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VOLTAGE DEPENDENT RCCB VOLTAGE INDEPENDENT RCCB

ELECTRONICAMPLIFIER

POWER SUPPLY TOELECTRONICS

CORE BALANCE TRANSFORMER


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Specifications .. Rated tripping (residual) current -10,30,100,300,500 Ma

Personal shock protection max; value

30mA

Fire protection max; value 300 mA


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Specifications Type of residual current (sensitivity)

Type AC full wave ac residual current detection

Type A -full wave ac +pulsating dc residual currents

Type B -full wave ac +pulsating dc +pure dc residualcurrents


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Specifications

Type of applications

Type AC - for domestic /commercial use

Type A - for computer network use

Type B - for variable speed drive circuit use


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Specifications

Operating time category for rated residual current

Type G (instantaneous) - max; response time = 300Ms

Type) S (delayed)- min/max; response time= 130-500 mS


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Earth Leakage Relay

Sensitivity up to 30 Amps

Trip Time Delay up to 3 Secs

Zero Current Transformer Sensing

Specifications


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3-pole or 4-pole

Earth leakage relay (continued )

Zero currenttransformer

Earthleakage

relay


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Earth leakage relays (continued)

Specifications Sensitivity setting -30-750 mA,1- 30 amps

Time delay setting-inst; 50-500ms,1-3s leakage indicaters-10%-80%

Trip contact and 50% pre fault contact

Zero CT 40-120 mm inner dia; selectable


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Earth Fault Relay

Microprocessor based type

Low /high set earth fault setting

Adjustable Trip Time Delay for low/high setting

Sensing Using Current Transformers

C;T; Secondary current 5 amps

04 no current transformers required for a 3p & n system

Specifications


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Earth fault relay


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Surge protection devices

Different types of voltage surges

voltage Surges due to Direct lightning hits

Protected by lightning arresters/ finials

voltage surges due to Indirect lightning hits and switching

Protected by surge protection devices


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Two different technologies

Metal oxide varisters shows low resistance to high voltages

Gas discharge tube - discharges the high voltages to earththrough an air gap inside a glass envelope


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Metal oxide varisters

Type 1 (type B) -for out door use eg; over head distribution lines

Type 2 ( type B ) for incomer main distribution switchgear

Type 3 (type C) -for the protection of electrical appliances eg;

Type 4 (type D) for the protection of delicate electronicequipment


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surge protection levels


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Thank You


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Electrical Circuit Protection

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