Protective Device Maintenance - Cooper · PDF fileMolded-Case Circuit Breakers FMaintenance on...

Protective DevicesProtective DevicesMaintenance as it Applies toMaintenance as it Applies to

the Arc/Flash Hazardthe Arc/Flash Hazard

Presented byPresented by

Dennis K. Neitzel, Dennis K. Neitzel, CPECPE

DirectorDirector

Training Institute – Dallas, Texas Training Institute – Dallas, TexasA DIVISION OF MEGGERA DIVISION OF MEGGER

22

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 be

used.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 manufacturer’’ss

instructions, orinstructions, or–– NETA NETA ““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 CircuitBreakersBreakers

FF Maintenance on molded-case circuit breakers isMaintenance on molded-case circuit breakers islimited 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 circuitbreakersbreakers–– Have riveted framesHave riveted frames–– Are not designed to be openedAre not designed to be opened

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FF All other All other MCCBMCCB’’ss 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 themanufacturersmanufacturers’’ 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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FF MCCBMCCB’’ss, 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 the

manufacturermanufacturer’’s original condition.s original condition.

FF To conform to the manufacturerTo conform to the manufacturer’’s 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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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, oruuFail because the mechanism is frozen due to dirt, driedFail because the mechanism is frozen due to dirt, dried

lubricant, or corrosion.lubricant, or corrosion.

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FFOvercurrent 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 openunder fault conditions.under fault conditions.–– Can result in fires, damage to equipment orCan result in fires, damage to equipment or

injuries to personnel.injuries to personnel.

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FFA 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, anduuManually exercised several times.Manually exercised several times.

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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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FFProper 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 capabilities

FFA 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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FFAnother consideration, addressed by OSHA:Another consideration, addressed by OSHA:1910.334(b)(2) Reclosing circuits after protective1910.334(b)(2) Reclosing circuits after protectivedevice 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 bemanually reenergized until it has been determinedmanually reenergized until it has been determinedthat the equipment and circuit can be safelythat the equipment and circuit can be safelyreenergized. The repetitive manual reclosing ofreenergized. The repetitive manual reclosing ofcircuit breakers or reenergizing circuits throughcircuit breakers or reenergizing circuits throughreplaced fuses is prohibited.replaced fuses is prohibited.””

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FFEmployee is at risk if the short circuit stillEmployee is at risk if the short circuit stillexists.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 beforeinvestigating is no longer allowed.investigating is no longer allowed.

FFThis previous practice has caused numerousThis previous practice has caused numerousburn injuries that resulted from the explosionburn injuries that resulted from the explosionof electrical equipment.of electrical equipment.

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FFCircuit breakers, circuits, and equipment,Circuit breakers, circuits, and equipment,must be tested and inspected by a qualifiedmust be tested and inspected by a qualifiedpersonperson..

FFMelted arc chutes will not interrupt faultMelted arc chutes will not interrupt faultcurrents.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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FF 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 equipmentthat 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 hasoccurred inside encased equipment.occurred inside encased equipment.””

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Low-Voltage Power CircuitLow-Voltage Power CircuitBreakersBreakers

FFSeveral 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 keepingthem clean and properly lubricated.them clean and properly lubricated.

FFFrequency of maintenance will depend toFrequency of maintenance will depend tosome extent on cleanliness of area.some extent on cleanliness of area.

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FFGeneral inspection and lubrication isGeneral inspection and lubrication isrecommended 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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FF If the breaker remains open or closed for a longIf the breaker remains open or closed for a longperiod 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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FFMechanical 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 pointsuuHardened or sticky lubricantHardened or sticky lubricant

FFThe manufacturerThe manufacturer’’s instructions must bes instructions must befollowed 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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Medium-Voltage PowerMedium-Voltage PowerCircuit BreakersCircuit Breakers

FFMost requirements the same as low-voltageMost requirements the same as low-voltagepower 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 manufacturer’’ssinstructions.instructions.

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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 todisconnect a faulty system element as quicklydisconnect a faulty system element as quicklyas possible.as possible.

FFSensitivity and selectivity are essential toSensitivity and selectivity are essential toensure that the proper circuit breakers areensure that the proper circuit breakers aretripped 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 preventprimary relaying from disconnecting a powerprimary relaying from disconnecting a powersystem 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 has Each element of the system has zones ofzones ofprotectionprotection surrounding 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 thatzone and no tripping of breakers outside thatzone and no tripping of breakers outside thatzone.zone.

FF If faults occur in the overlap region, severalIf faults occur in the overlap region, severalbreakers respond and isolate the sectionsbreakers respond and isolate the sectionsfrom the power system.from the power system.

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FFVoltage and current transformers play a vitalVoltage and current transformers play a vitalrole 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 and

devices 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 asthe voltage and current transformersthe voltage and current transformersconnected to it.connected to it.

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FFSome overcurrent relays are equipped withSome overcurrent relays are equipped withan instantaneous overcurrent unit:an instantaneous overcurrent unit:–– Operates when the current reaches its minimumOperates when the current reaches its minimum

pickup 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, andtesting to function properly.testing to function properly.

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FFMost manufacturers recommend thatMost manufacturers recommend thatperiodic inspections and maintenance beperiodic inspections and maintenance beperformed 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 andmaintenance will vary:maintenance will vary:–– EnvironmentEnvironment–– Type of relayType of relay

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FFThe periodic inspections, maintenance, andThe periodic inspections, maintenance, andtesting 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 andserviced as described in the manufacturerserviced as described in the manufacturer’’ssinstructions.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 engineeringcoordination 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 flashhazard 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 causeunintentional 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 faultcondition.condition.

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Flash Hazard AnalysisFlash Hazard AnalysisFF 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 fromthe 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-phase is 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 of1.89431 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 for 30 cyclesCalculation for 30 cycles

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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 in is based on a single-phase arc inopen-air. Again, as a general rule of thumb, the value ofopen-air. Again, as a general rule of thumb, the value of11.36586 would be multiplied by a factor of 2 for a single-phase11.36586 would be multiplied by a factor of 2 for a single-phasearc in a box (2 x 11.36586 = 22.73172 cal/cmarc in a box (2 x 11.36586 = 22.73172 cal/cm22 –– Category 3) and Category 3) andby 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/cm22 –– 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 an As can be seen, maintenance is extremely important to an electrical safety program. Maintenance must be performed electrical safety program. Maintenance must be performed according to the manufactureraccording to the manufacturer’’s instructions in order to s instructions in order to minimize the risk of having an unintentional time delay in minimize 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 andpower systems kept in a safe, reliablepower systems kept in a safe, reliablecondition with the proper mixture of:condition with the proper mixture of:–– Common senseCommon sense–– TrainingTraining–– ManufacturersManufacturers’’ literature and spare parts literature and spare parts

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SummarySummary

FFCircuit breakers, if installed within theirCircuit breakers, if installed within theirratings and properly maintained, shouldratings and properly maintained, shouldoperate 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 withoutproper 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.

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