Pd Maintenance

Protective Devices Protective Devices Maintenance as it Applies to Maintenance 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, TexasTraining Institute – Dallas, TexasA DIVISION OF MEGGERA DIVISION OF MEGGER

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IntroductionIntroduction

Key component of the Flash Hazard Analysis:Key component of the Flash Hazard Analysis:– Protective device clearing time.Protective device clearing time.

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

Fuses do not have operating mechanismsFuses do not have operating mechanisms

Primary focus is maintenance issuesPrimary focus is maintenance issues

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

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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Protective relays:Protective relays:– Add approximately 3 to 4 cycles to the clearing time of Add approximately 3 to 4 cycles to the clearing time of

the medium circuit breaker.the medium circuit breaker.

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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Maintenance and testing Maintenance and testing – Accomplished in accordance with the manufacturer’s Accomplished in accordance with the manufacturer’s

instructions, orinstructions, or

– NETA NETA “Maintenance Testing Specifications for “Maintenance Testing Specifications for Electrical Power Distribution Equipment and Systems”Electrical Power Distribution Equipment and Systems” 2001 Edition. 2001 Edition.

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Molded-Case Circuit Molded-Case Circuit BreakersBreakers

Maintenance on molded-case circuit breakers is Maintenance on molded-case circuit breakers is limited to:limited to:– Proper mechanical mountingProper mechanical mounting

– Electrical connectionsElectrical connections

– Periodic manual operationPeriodic manual operation

Lighting, appliance, and power panel circuit Lighting, 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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All other MCCB’s that are UL approved:All other MCCB’s that are UL approved:– Factory-sealed to prevent access to calibrated elements.Factory-sealed to prevent access to calibrated elements.

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.

A broken seal voids the UL listing and the A broken seal voids the UL listing and the manufacturers’ warranty of the device: manufacturers’ warranty of the device: – Integrity of the device would be questionable.Integrity of the device would be questionable.

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MCCB’s, other than the riveted frame types:MCCB’s, other than the riveted frame types:– Permitted to be reconditioned and returned to the Permitted to be reconditioned and returned to the

manufacturer’s original condition. manufacturer’s original condition.

To conform to the manufacturer’s original design:To conform to the manufacturer’s original design:– Must be reconditioned according to recognized standards. Must be reconditioned according to recognized standards.

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

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Circuit breakers are often forgotten. Circuit breakers are often forgotten. Breakers supplying power for years:Breakers supplying power for years:– Several things that can go wrong. Several things that can go wrong.

Circuit breakers can fail to open due to a burned out Circuit breakers can fail to open due to a burned out trip coil, ortrip coil, or

Fail because the mechanism is frozen due to dirt, dried Fail because the mechanism is frozen due to dirt, dried lubricant, or corrosion. lubricant, or corrosion.

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Overcurrent devices can fail due to:Overcurrent devices can fail due to:– Inactivity, orInactivity, or– A burned out electronic component.A burned out electronic component.

Problems occur when a breaker fails to open Problems occur when a breaker fails to open under fault conditions.under fault conditions.– Can result in fires, damage to equipment or Can result in fires, damage to equipment or

injuries to personnel. injuries to personnel.

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A 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.

Recommendation:Recommendation:– If an MCCB has not been operated within as little If an MCCB has not been operated within as little

as six months time:as six months time: Removed from service, and Removed from service, and Manually exercised several times. Manually exercised several times.

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Manually 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 moves Ensures that the operating mechanism moves

freely freely – Does not operate the tripping mechanismDoes not operate the tripping mechanism

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Proper exercise of all breaker mechanisms:Proper exercise of all breaker mechanisms:– Remove the breaker from service and test the Remove the breaker from service and test the

overcurrent and short-circuit tripping capabilitiesovercurrent and short-circuit tripping capabilities A stiff or sticky mechanism can cause:A stiff or sticky mechanism can cause:– An unintentional time delay, and therefore An unintentional time delay, and therefore – Increase the arc/flash incident energy level.Increase the arc/flash incident energy level.

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Another consideration, addressed by OSHA:Another consideration, addressed by OSHA:1910.334(b)(2) Reclosing circuits after protective 1910.334(b)(2) Reclosing circuits after protective device operationdevice operation “After a circuit is deenergized by a “After a circuit is deenergized by a circuit protective device, the circuit may NOT be circuit protective device, the circuit may NOT be manually reenergized until it has been determined manually reenergized until it has been determined that the equipment and circuit can be safely that the equipment and circuit can be safely reenergized. The repetitive manual reclosing of reenergized. The repetitive manual reclosing of circuit breakers or reenergizing circuits through circuit breakers or reenergizing circuits through replaced fuses is prohibited.replaced fuses is prohibited.” ”

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Employee is at risk if the short circuit still Employee is at risk if the short circuit still exists. exists.

The past practice of resetting a circuit The past practice of resetting a circuit breaker one, two, or three times before breaker one, two, or three times before investigating is no longer allowed.investigating is no longer allowed.

This previous practice has caused numerous This previous practice has caused numerous burn injuries that resulted from the explosion burn injuries that resulted from the explosion of electrical equipment. of electrical equipment.

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Circuit breakers, circuits, and equipment, Circuit breakers, circuits, and equipment, must be tested and inspected by a qualified must be tested and inspected by a qualified personperson..

Melted arc chutes will not interrupt fault Melted arc chutes will not interrupt fault currents.currents.

If the breaker cannot interrupt a second If the breaker cannot interrupt a second fault, it will fail.fault, it will fail.– May destroy enclosure and create a hazard for May destroy enclosure and create a hazard for

personnel.personnel.

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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 equipment After a high level fault has occurred in equipment that is properly rated and installed, it is not always that is properly rated and installed, it is not always clear to investigating electricians what damage has clear to investigating electricians what damage has occurred inside encased equipment.”occurred inside encased equipment.”

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Low-Voltage Power Circuit Low-Voltage Power Circuit BreakersBreakers

Several studies have shown:Several studies have shown:– Circuit breakers, which were not maintained Circuit 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. Maintenance will generally consist of keeping Maintenance will generally consist of keeping

them clean and properly lubricated. them clean and properly lubricated. Frequency of maintenance will depend to Frequency of maintenance will depend to

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

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General inspection and lubrication is General inspection and lubrication is recommended at least once per year.recommended at least once per year.

Some make this recommendation after the Some make this recommendation after the first six months of service. first six months of service.

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If the breaker remains open or closed for a long If the breaker remains open or closed for a long period of timeperiod of time::– Open and close the breaker several times Open and close the breaker several times

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

Environmental conditions play a major role.Environmental conditions play a major role. More frequent inspections and maintenance may be More frequent inspections and maintenance may be

required if:required if:– Severe load conditions exist Severe load conditions exist

– Inspection reveals heavy accumulations of dirt, moisture, Inspection reveals heavy accumulations of dirt, moisture, or other foreign matter or other foreign matter

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Mechanical failure would include:Mechanical failure would include:– Unintentional time delay in the tripping operation Unintentional time delay in the tripping operation

due to:due to: Dry, dirty or corroded pivot points Dry, dirty or corroded pivot points Hardened or sticky lubricantHardened or sticky lubricant

The manufacturer’s instructions must be The manufacturer’s instructions must be followed in order to minimize the risk of any followed in order to minimize the risk of any unintentional time delay.unintentional time delay.

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Medium-Voltage Power Medium-Voltage Power Circuit BreakersCircuit Breakers

Most requirements the same as low-voltage Most requirements the same as low-voltage power circuit breakers.power circuit breakers.

Breakers should be removed from service and Breakers should be removed from service and inspected at least once per year. inspected at least once per year.

Always follow the manufacturer’s Always follow the manufacturer’s instructions.instructions.

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Protective RelaysProtective Relays Relays monitor complex power circuit Relays monitor complex power circuit

conditions, such as:conditions, such as:– Current and voltage magnitudesCurrent and voltage magnitudes– Phase angle relationshipsPhase angle relationships– Direction of power flow Direction of power flow – FrequencyFrequency

When 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 is The abnormal portion of the circuit is

deenergized via the circuit breaker deenergized via the circuit breaker

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Protective RelaysProtective Relays

The ultimate goal of protective relaying is to The ultimate goal of protective relaying is to disconnect a faulty system element as quickly disconnect a faulty system element as quickly as possible. as possible.

Sensitivity and selectivity are essential to Sensitivity and selectivity are essential to ensure that the proper circuit breakers are ensure that the proper circuit breakers are tripped at the proper speed to:tripped at the proper speed to:– Clear the fault Clear the fault – Minimize damage to equipmentMinimize damage to equipment– Reduce the hazards to personnel Reduce the hazards to personnel

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Several things may happen to prevent Several things may happen to prevent primary relaying from disconnecting a power primary relaying from disconnecting a power system fault:system fault: – Current or voltage supplies to the relays are Current 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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Each element of the system has Each element of the system has zones of zones of protectionprotection surrounding the element. surrounding the element.

A fault within the given zone should cause the A fault within the given zone should cause the tripping of all circuit breakers within that tripping of all circuit breakers within that zone and no tripping of breakers outside that zone and no tripping of breakers outside that zone. zone.

If faults occur in the overlap region, several If faults occur in the overlap region, several breakers respond and isolate the sections breakers respond and isolate the sections from the power system. from the power system.

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Voltage and current transformers play a vital Voltage 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 and Used to isolate and protect both people and

devices from high voltage and current.devices from high voltage and current. The performance of a relay is only as good as The performance of a relay is only as good as

the voltage and current transformers the voltage and current transformers connected to it. connected to it.

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Some overcurrent relays are equipped with Some overcurrent relays are equipped with an instantaneous overcurrent unit:an instantaneous overcurrent unit:– Operates when the current reaches its minimum Operates when the current reaches its minimum

pickup point.pickup point.– An instantaneous unit is a relay having no An instantaneous unit is a relay having no

intentional time delay. intentional time delay.

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Things that can go wrong:Things that can go wrong:– An open or shunted current transformerAn open or shunted current transformer– Open coilOpen coil– Dirty contacts Dirty contacts

Protective relays, like circuit breakers, Protective relays, like circuit breakers, require periodic inspection, maintenance, and require periodic inspection, maintenance, and testing to function properly. testing to function properly.

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Most manufacturers recommend that Most manufacturers recommend that periodic inspections and maintenance be periodic inspections and maintenance be performed at intervals of one to two years.performed at intervals of one to two years.

The intervals between periodic inspection and The intervals between periodic inspection and maintenance will vary:maintenance will vary:– EnvironmentEnvironment– Type of relayType of relay

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The periodic inspections, maintenance, and The 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 settings Have not deviated from the design settings

If deviations are found, the relay must be retested and If deviations are found, the relay must be retested and serviced as described in the manufacturer’s serviced as described in the manufacturer’s instructions.instructions.

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Flash Hazard AnalysisFlash Hazard Analysis

All calculations require the arc clearing time. All calculations require the arc clearing time. – Determine incident energyDetermine incident energy– Establish the flash protection boundary Establish the flash protection boundary

Clearing time is derived from the engineering Clearing time is derived from the engineering coordination studycoordination study– Based on what the protective devices are Based on what the protective devices are

supposed to do.supposed to do.

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Maintenance is a very critical part of the Maintenance is a very critical part of the flash hazard issue. flash hazard issue.

A preventive maintenance program on these A preventive maintenance program on these circuit protective devices is needed. circuit protective devices is needed.

Inadequate maintenance can cause Inadequate maintenance can cause unintentional time delays. unintentional time delays.

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Example:Example:– A low-voltage power circuit breaker had not been A 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 additional Circuit breaker could take several additional

cycles, seconds, minutes, or longer to clear a fault cycles, seconds, minutes, or longer to clear a fault condition. condition.

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Flash Hazard AnalysisFlash Hazard Analysis Flash Hazard Analysis is performed:Flash Hazard Analysis is performed:– Based on what the system is suppose to do - 5 cycles Based 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 because The worker could be seriously injured or killed because

he/she was under protected.he/she was under protected. Arc/Flash situation: 20,000-amp short-circuit, 480 Arc/Flash situation: 20,000-amp short-circuit, 480

volts, 3-inch arc gap, the worker is 18 inches from volts, 3-inch arc gap, the worker is 18 inches from the arc, with a 5 cycle clearing time for a 3-phase arc the arc, with a 5 cycle clearing time for a 3-phase arc in 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-phase arc in open-air. As a general rule of thumb, the value of arc 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 in Category 1) and by a factor of 3.4 for a multi-phase arc in a 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 to Due to a sticky mechanism the clearing time increases to 30 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 in open-air. Again, as a general rule of thumb, the value of open-air. Again, as a general rule of thumb, the value of 11.36586 would be multiplied by a factor of 2 for a single-phase 11.36586 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) and – Category 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/cm22 – Category 4). – Category 4). (The protection category is (The protection category is based 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 manufacturer’s instructions in order to according to the manufacturer’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

Proper maintenance can be performed and Proper maintenance can be performed and power systems kept in a safe, reliable power systems kept in a safe, reliable condition with the proper mixture of:condition with the proper mixture of:– Common senseCommon sense– TrainingTraining– Manufacturers’ literature and spare partsManufacturers’ literature and spare parts

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SummarySummary

Circuit breakers, if installed within their Circuit breakers, if installed within their ratings and properly maintained, should ratings and properly maintained, should operate trouble-free for many years. operate trouble-free for many years.

If operated outside of their ratings or without If operated outside of their ratings or without proper maintenance:proper maintenance:– Catastrophic failure of the power system, circuit Catastrophic failure of the power system, circuit

breaker, or switchgear can occurbreaker, or switchgear can occur– May cause serious injury or even death of May cause serious injury or even death of

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

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