Circuit Breaker - PDMaintenance

7/31/2019 Circuit Breaker - PDMaintenance

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Protective DevicesProtective Devices

Maintenance as it Applies toMaintenance as it Applies tothe Arc/Flash Hazardthe Arc/Flash Hazard

Presented byPresented by

Dennis K. Neitzel,Dennis K. Neitzel, CPECPEDirectorDirector

Training Institute Dallas, TexasTraining Institute Dallas, TexasA DIVISION OF MEGGERA DIVISION OF MEGGER


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IntroductionIntroduction

FFKey component of the Flash Hazard Analysis:Key component of the Flash Hazard Analysis:

Protective device clearing time.Protective device clearing time.

uuPrimarily circuit breakers and relays.Primarily circuit breakers and relays.

FFFuses do not have operating mechanismsFuses do not have operating mechanisms

FFPrimary focus is maintenance issuesPrimary focus is maintenance issues


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FF Molded case and low-voltage power circuit breakers:Molded case and low-voltage power circuit breakers:

Will generally clear a fault condition in 3 to 8 cycles.Will generally clear a fault condition in 3 to 8 cycles.

To be conservative a clearing time of 8 cycles should beTo be conservative a clearing time of 8 cycles should beused.used.

FF Older medium-voltage circuit breakers:Older medium-voltage circuit breakers:

Will clear a fault in around 8 cyclesWill clear a fault in around 8 cycles

Newer ones clear in 3 to 5 cycles.Newer ones clear in 3 to 5 cycles.


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FF Protective relays:Protective relays:

Add approximately 3 to 4 cycles to the clearing time ofAdd approximately 3 to 4 cycles to the clearing time of

the medium circuit breaker.the medium circuit breaker.

FF Maintenance and testing not performed:Maintenance and testing not performed:

Extended clearing times could occurExtended clearing times could occur

Unintentional time delayUnintentional time delay

Results of flash hazard analysis could be affectedResults of flash hazard analysis could be affected


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FF Maintenance and testingMaintenance and testing

Accomplished in accordance with the manufacturerAccomplished in accordance with the manufacturerss

instructions, orinstructions, or

NETANETA Maintenance Testing Specifications forMaintenance Testing Specifications for

Electrical Power Distribution Equipment and SystemsElectrical Power Distribution Equipment and Systems

2001 Edition.2001 Edition.


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Molded-Case CircuitMolded-Case Circuit

BreakersBreakersFF Maintenance on molded-case circuit breakers isMaintenance on molded-case circuit breakers is

limited to:limited to:

Proper mechanical mountingProper mechanical mounting

Electrical connectionsElectrical connections

Periodic manual operationPeriodic manual operation

FF Lighting, appliance, and power panel circuitLighting, appliance, and power panel circuit

breakersbreakers Have riveted framesHave riveted frames

Are not designed to be openedAre not designed to be opened


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BreakersBreakersFF All otherAll other MCCBMCCBss that are UL approved:that are UL approved:

Factory-sealed to prevent access to calibrated elements.Factory-sealed to prevent access to calibrated elements.

FF An unbroken seal indicates:An unbroken seal indicates: Mechanism has not been tampered withMechanism has not been tampered with

Should function as specified by UL.Should function as specified by UL.

FF A broken seal voids the UL listing and theA broken seal voids the UL listing and the

manufacturersmanufacturers warranty of the device:warranty of the device: Integrity of the device would be questionable.Integrity of the device would be questionable.


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BreakersBreakers

FF MCCBMCCBss, other than the riveted frame types:, other than the riveted frame types:

Permitted to be reconditioned and returned to thePermitted to be reconditioned and returned to themanufacturermanufacturers original condition.s original condition.

FF To conform to the manufacturerTo conform to the manufacturers original design:s original design:

Must be reconditioned according to recognized standards.Must be reconditioned according to recognized standards.

uu Professional Electrical Apparatus Recyclers League (PEARL)Professional Electrical Apparatus Recyclers League (PEARL)


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BreakersBreakers

FFCircuit breakers are often forgotten.Circuit breakers are often forgotten.

FFBreakers supplying power for years:Breakers supplying power for years: Several things that can go wrong.Several things that can go wrong.

uuCircuit breakers can fail to open due to a burned outCircuit breakers can fail to open due to a burned out

trip coil, ortrip coil, or

uuFail because the mechanism is frozen due to dirt, driedFail because the mechanism is frozen due to dirt, driedlubricant, or corrosion.lubricant, or corrosion.


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BreakersBreakersFFOvercurrent devices can fail due to:Overcurrent devices can fail due to:

Inactivity, orInactivity, or

A burned out electronic component.A burned out electronic component.

FFProblems occur when a breaker fails to openProblems occur when a breaker fails to open

under fault conditions.under fault conditions.

Can result in fires, damage to equipment orCan result in fires, damage to equipment orinjuries to personnel.injuries to personnel.


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BreakersBreakersFFA circuit breaker fails due to:A circuit breaker fails due to:

Minimum maintenance was not performed, orMinimum maintenance was not performed, or

Performed improperly.Performed improperly.

FFRecommendation:Recommendation:

If an MCCB has not been operated within as littleIf an MCCB has not been operated within as little

as six months time:as six months time:

uuRemoved from service, andRemoved from service, and

uuManually exercised several times.Manually exercised several times.


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BreakersBreakers

FFManually exercising helps:Manually exercising helps:

Keep the contacts clean due to their wiping actionKeep the contacts clean due to their wiping action

Ensures that the operating mechanism movesEnsures that the operating mechanism moves

freelyfreely

Does not operate the tripping mechanismDoes not operate the tripping mechanism


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BreakersBreakers


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BreakersBreakersFFProper exercise of all breaker mechanisms:Proper exercise of all breaker mechanisms:

Remove the breaker from service and test theRemove the breaker from service and test the

overcurrent and short-circuit tripping capabilitiesovercurrent and short-circuit tripping capabilitiesFFA stiff or sticky mechanism can cause:A stiff or sticky mechanism can cause:

An unintentional time delay, and thereforeAn unintentional time delay, and therefore

Increase the arc/flash incident energy level.Increase the arc/flash incident energy level.


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BreakersBreakersFFAnother consideration, addressed by OSHA:Another consideration, addressed by OSHA:

1910.334(b)(2) Reclosing circuits after protective1910.334(b)(2) Reclosing circuits after protective

device operationdevice operation After a circuit is deenergized by aAfter a circuit is deenergized by acircuit protective device, the circuit may NOT becircuit protective device, the circuit may NOT be

manually reenergized until it has been determinedmanually reenergized until it has been determined

that the equipment and circuit can be safelythat the equipment and circuit can be safely

reenergized. The repetitive manual reclosing ofreenergized. The repetitive manual reclosing ofcircuit breakers or reenergizing circuits throughcircuit breakers or reenergizing circuits through

replaced fuses is prohibited.replaced fuses is prohibited.


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BreakersBreakersFFEmployee is at risk if the short circuit stillEmployee is at risk if the short circuit still

exists.exists.

FFThe past practice of resetting a circuitThe past practice of resetting a circuitbreaker one, two, or three times beforebreaker one, two, or three times before

investigating is no longer allowed.investigating is no longer allowed.

FF

This previous practice has caused numerousThis previous practice has caused numerousburn injuries that resulted from the explosionburn injuries that resulted from the explosion

of electrical equipment.of electrical equipment.


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BreakersBreakersFFCircuit breakers, circuits, and equipment,Circuit breakers, circuits, and equipment,

must be tested and inspected by a qualifiedmust be tested and inspected by a qualified

personperson..FFMelted arc chutes will not interrupt faultMelted arc chutes will not interrupt fault

currents.currents.

FF

If the breaker cannot interrupt a second fault,If the breaker cannot interrupt a second fault,it will fail.it will fail.

May destroy enclosure and create a hazard forMay destroy enclosure and create a hazard for

personnel.personnel.


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BreakersBreakersFF In an EC&M article by NEMA, Jan. 1995 :In an EC&M article by NEMA, Jan. 1995 :

After a high level fault has occurred in equipmentAfter a high level fault has occurred in equipment

that is properly rated and installed, it is not alwaysthat is properly rated and installed, it is not alwaysclear to investigating electricians what damage hasclear to investigating electricians what damage has

occurred inside encased equipment.occurred inside encased equipment.


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Low-Voltage Power CircuitLow-Voltage Power Circuit

BreakersBreakersFFSeveral studies have shown:Several studies have shown:

Circuit breakers, which were not maintainedCircuit breakers, which were not maintained

within a 5-year period, have a 50% failure rate.within a 5-year period, have a 50% failure rate.FFMaintenance will generally consist of keepingMaintenance will generally consist of keeping

them clean and properly lubricated.them clean and properly lubricated.

FF

Frequency of maintenance will depend toFrequency of maintenance will depend to

some extent on cleanliness of area.some extent on cleanliness of area.


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BreakersBreakersFFGeneral inspection and lubrication isGeneral inspection and lubrication is

recommended at least once per year.recommended at least once per year.

FFSome make this recommendation after theSome make this recommendation after thefirst six months of service.first six months of service.


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BreakersBreakersFF If the breaker remains open or closed for a longIf the breaker remains open or closed for a long

period of timeperiod of time::

Open and close the breaker several timesOpen and close the breaker several times

Exercise under load conditions (hazard-remote operation)Exercise under load conditions (hazard-remote operation)

FF Environmental conditions play a major role.Environmental conditions play a major role.

FF More frequent inspections and maintenance may beMore frequent inspections and maintenance may be

required if:required if: Severe load conditions existSevere load conditions exist

Inspection reveals heavy accumulations of dirt, moisture,Inspection reveals heavy accumulations of dirt, moisture,

or other foreign matteror other foreign matter


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BreakersBreakersFFMechanical failure would include:Mechanical failure would include:

Unintentional time delay in the tripping operationUnintentional time delay in the tripping operation

due to:due to:uuDry, dirty or corroded pivot pointsDry, dirty or corroded pivot points

uuHardened or sticky lubricantHardened or sticky lubricant

FFThe manufacturerThe manufacturers instructions must bes instructions must be

followed in order to minimize the risk of anyfollowed in order to minimize the risk of anyunintentional time delay.unintentional time delay.


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BreakersBreakers


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Medium-Voltage PowerMedium-Voltage Power

Circuit BreakersCircuit BreakersFFMost requirements the same as low-voltageMost requirements the same as low-voltage

power circuit breakers.power circuit breakers.

FFBreakers should be removed from service andBreakers should be removed from service andinspected at least once per year.inspected at least once per year.

FFAlways follow the manufacturerAlways follow the manufacturerss

instructions.instructions.


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Circuit BreakersCircuit Breakers


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Circuit BreakersCircuit Breakers


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Protective RelaysProtective Relays

FFRelays monitor complex power circuitRelays monitor complex power circuitconditions, such as:conditions, such as:

Current and voltage magnitudesCurrent and voltage magnitudes

Phase angle relationshipsPhase angle relationships

Direction of power flowDirection of power flow

FrequencyFrequency

FFWhen a short circuit (or fault) is detected:When a short circuit (or fault) is detected:

Relay responds and closes its contactsRelay responds and closes its contacts

The abnormal portion of the circuit isThe abnormal portion of the circuit is

deenergized via the circuit breakerdeenergized via the circuit breaker


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FFThe ultimate goal of protective relaying is toThe ultimate goal of protective relaying is to

disconnect a faulty system element as quicklydisconnect a faulty system element as quickly

as possible.as possible.

FFSensitivity and selectivity are essential toSensitivity and selectivity are essential to

ensure that the proper circuit breakers areensure that the proper circuit breakers are

tripped at the proper speed to:tripped at the proper speed to:

Clear the faultClear the fault

Minimize damage to equipmentMinimize damage to equipment

Reduce the hazards to personnelReduce the hazards to personnel


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FFSeveral things may happen to preventSeveral things may happen to prevent

primary relaying from disconnecting a powerprimary relaying from disconnecting a power

system fault:system fault: Current or voltage supplies to the relays areCurrent or voltage supplies to the relays are

incorrect.incorrect.

DC tripping voltage supply is low or absent.DC tripping voltage supply is low or absent.

Protective relay malfunctions.Protective relay malfunctions.

Tripping circuit or breaker mechanism hangs up.Tripping circuit or breaker mechanism hangs up.


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FFEach element of the system hasEach element of the system haszones ofzones of

protectionprotectionsurrounding the element.surrounding the element.

FFA fault within the given zone should cause theA fault within the given zone should cause thetripping of all circuit breakers within thattripping of all circuit breakers within that

zone and no tripping of breakers outside thatzone and no tripping of breakers outside that

zone.zone.

FF If faults occur in the overlap region, severalIf faults occur in the overlap region, several

breakers respond and isolate the sectionsbreakers respond and isolate the sections

from the power system.from the power system.


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FFVoltage and current transformers play a vitalVoltage and current transformers play a vital

role in the power protection scheme.role in the power protection scheme.

Used to isolate and protect both people andUsed to isolate and protect both people anddevices from high voltage and current.devices from high voltage and current.

FFThe performance of a relay is only as good asThe performance of a relay is only as good as

the voltage and current transformersthe voltage and current transformers

connected to it.connected to it.


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FFSome overcurrent relays are equipped withSome overcurrent relays are equipped with

an instantaneous overcurrent unit:an instantaneous overcurrent unit:

Operates when the current reaches its minimumOperates when the current reaches its minimumpickup point.pickup point.

An instantaneous unit is a relay having noAn instantaneous unit is a relay having no

intentional time delay.intentional time delay.


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FFThings that can go wrong:Things that can go wrong:

An open or shunted current transformerAn open or shunted current transformer

Open coilOpen coil

Dirty contactsDirty contacts

FFProtective relays, like circuit breakers,Protective relays, like circuit breakers,

require periodic inspection, maintenance, andrequire periodic inspection, maintenance, and

testing to function properly.testing to function properly.


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FFMost manufacturers recommend thatMost manufacturers recommend that

periodic inspections and maintenance beperiodic inspections and maintenance be

performed at intervals of one to two years.performed at intervals of one to two years.FFThe intervals between periodic inspection andThe intervals between periodic inspection and

maintenance will vary:maintenance will vary:

EnvironmentEnvironment

Type of relayType of relay


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FFThe periodic inspections, maintenance, andThe periodic inspections, maintenance, and

testing are intended to ensure that:testing are intended to ensure that:

Protective relays are functioning properlyProtective relays are functioning properly

Have not deviated from the design settingsHave not deviated from the design settings

uu If deviations are found, the relay must be retested andIf deviations are found, the relay must be retested and

serviced as described in the manufacturerserviced as described in the manufacturerss

instructions.instructions.


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Flash Hazard AnalysisFlash Hazard Analysis

FFAll calculations require the arc clearing time.All calculations require the arc clearing time.

Determine incident energyDetermine incident energy

Establish the flash protection boundaryEstablish the flash protection boundary

FFClearing time is derived from the engineeringClearing time is derived from the engineering

coordination studycoordination study

Based on what the protective devices areBased on what the protective devices are

supposed to do.supposed to do.


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FFMaintenance is a very critical part of the flashMaintenance is a very critical part of the flash

hazard issue.hazard issue.

FFA preventive maintenance program on theseA preventive maintenance program on thesecircuit protective devices is needed.circuit protective devices is needed.

FF Inadequate maintenance can causeInadequate maintenance can cause

unintentional time delays.unintentional time delays.


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FFExample:Example:

A low-voltage power circuit breaker had not beenA low-voltage power circuit breaker had not been

operated or maintained for several yearsoperated or maintained for several years The lubrication had become sticky or hardenedThe lubrication had become sticky or hardened

Circuit breaker could take several additionalCircuit breaker could take several additional

cycles, seconds, minutes, or longer to clear a faultcycles, seconds, minutes, or longer to clear a fault

condition.condition.


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FF Flash Hazard Analysis is performed:Flash Hazard Analysis is performed:

Based on what the system is suppose to do - 5 cyclesBased on what the system is suppose to do - 5 cycles

Unintentional time delay, due to a sticky mechanismUnintentional time delay, due to a sticky mechanism

Breaker clears in 30 cyclesBreaker clears in 30 cycles

The worker could be seriously injured or killed becauseThe worker could be seriously injured or killed because

he/she was under protected.he/she was under protected.

FF Arc/Flash situation: 20,000-amp short-circuit, 480Arc/Flash situation: 20,000-amp short-circuit, 480volts, 3-inch arc gap, the worker is 18 inches fromvolts, 3-inch arc gap, the worker is 18 inches from

the arc, with a 5 cycle clearing time for a 3-phase arcthe arc, with a 5 cycle clearing time for a 3-phase arcin a box (enclosure).in a box (enclosure).

Next slide illustrates this:Next slide illustrates this:


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Calculation for 5 cyclesCalculation for 5 cycles


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Calculation with a 5 Cycle Clearing TimeCalculation with a 5 Cycle Clearing Time

This value of 1.89431 cal/cmThis value of 1.89431 cal/cm22

is based on a single-phaseis based on a single-phasearc in open-air. As a general rule of thumb, the value ofarc in open-air. As a general rule of thumb, the value of

1.89431 would be multiplied by a factor of 2 for a single-1.89431 would be multiplied by a factor of 2 for a single-

phase arc in a box (2 x 1.89431 = 3.78862 cal/cmphase arc in a box (2 x 1.89431 = 3.78862 cal/cm22

Category 1) and by a factor of 3.4 for a multi-phase arc inCategory 1) and by a factor of 3.4 for a multi-phase arc ina box (3.4 x 1.89431 = 6.440654 cal/cma box (3.4 x 1.89431 = 6.440654 cal/cm22 Category 2).Category 2).

(The protection category is based on NFPA 70E-2000,(The protection category is based on NFPA 70E-2000,

Part II, Table 3-3.9.3.)Part II, Table 3-3.9.3.)

Due to a sticky mechanism the clearing time increases toDue to a sticky mechanism the clearing time increases to30 cycles.30 cycles.

Next slide illustrates this:Next slide illustrates this:


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Calculation with a 30 Cycle Clearing TimeCalculation with a 30 Cycle Clearing Time

The value of 11.36586 cal/cmThe value of 11.36586 cal/cm22 is based on a single-phase arc inis based on a single-phase arc in

open-air. Again, as a general rule of thumb, the value ofopen-air. Again, as a general rule of thumb, the value of

11.36586 would be multiplied by a factor of 2 for a single-phase11.36586 would be multiplied by a factor of 2 for a single-phase

arc in a box (2 x 11.36586 = 22.73172 cal/cmarc in a box (2 x 11.36586 = 22.73172 cal/cm22 Category 3) andCategory 3) and

by a factor of 3.4 for a multi-phase arc in a box (3.4 x 11.36586 =by a factor of 3.4 for a multi-phase arc in a box (3.4 x 11.36586 =

38.643924 cal/cm38.643924 cal/cm

22

Category 4).Category 4). (The protection category is(The protection category isbased on NFPA 70E-2000, Part II, Table 3-3.9.3.)based on NFPA 70E-2000, Part II, Table 3-3.9.3.)

As can be seen, maintenance is extremely important to anAs can be seen, maintenance is extremely important to an

electrical safety program. Maintenance must be performedelectrical safety program. Maintenance must be performed

according to the manufactureraccording to the manufacturers instructions in order tos instructions in order to

minimize the risk of having an unintentional time delay inminimize the risk of having an unintentional time delay in

the operation of the circuit protective devices.the operation of the circuit protective devices.


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SummarySummary

FFProper maintenance can be performed andProper maintenance can be performed and

power systems kept in a safe, reliablepower systems kept in a safe, reliable

condition with the proper mixture of:condition with the proper mixture of: Common senseCommon sense

TrainingTraining

ManufacturersManufacturers literature and spare partsliterature and spare parts


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SummarySummary

FFCircuit breakers, if installed within theirCircuit breakers, if installed within their

ratings and properly maintained, shouldratings and properly maintained, should

operate trouble-free for many years.operate trouble-free for many years.FF If operated outside of their ratings or withoutIf operated outside of their ratings or without

proper maintenance:proper maintenance:

Catastrophic failure of the power system, circuitCatastrophic failure of the power system, circuit

breaker, or switchgear can occurbreaker, or switchgear can occur

May cause serious injury or even death ofMay cause serious injury or even death of

employees working in the area.employees working in the area.

Documents

Circuit Breaker - PDMaintenance