IEEE Canada HRG Presentation 20110314

7/30/2019 IEEE Canada HRG Presentation 20110314

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SystemGrounding

Impacton

reliability

and

Safety

Presentedby:

DaleepMohlaSergioPanetta

JimChannon

ScottLee


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Agenda

SystemGroundingConsiderationsfor 600

Voltsand

less

system

TypesofSystemGroundingavailable

Prosand

Cons

of

each

Mitigationstrategies

Selectionguideline

for

mitigation

Questions


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SystemsGroundingConsiderations

Cost?

Safety?

Reliability?

Impactof

unintended

outages?

Productionloss?

Environmental?Safety?


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TypesofSystemGrounding

Ungrounded

SolidGrounded

ImpedanceGrounded


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UNGROUNDED(DELTA)SYSTEM

L

O

A

D

Transformer

Secondary

Feeder(withcapacitanceto

ground)


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Normaloperation Ground

fault

on

phase

C

Neutralpointestablished

bydistributedcapacitance

Phase

C

at

ground

potential

Nofaultcurrent

(noreturnpathtosource)

Allphases

are

at

linetoneutralvoltage

aboveground(eg:347V) A&Bphasesareatlinelinevoltage

aboveground

(eg:600V)

UNGROUNDED SYSTEM:NORMAL

OPERATION

&

FAULTED

OPERATION


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Normaloperation

Intermittent

groundfault

on

phase

C

A&Bphasesare:>Linelinevoltageabove

ground

Phase

C

>ground

voltage

Intermittentfaultcurrent

Personneldanger

UNGROUNDEDSYSTEM:FAULTED

OPERATION

WITH

TRANSIENT

OVERVOLTAGE


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UNGROUNDEDSYSTEMS:

Prosand

Cons

Pros MinimumInitialcost

Abilitytorunwith onephasefaultedtoground

Isolationof

Primary

and

Secondary

currents

(harmonics)

Initially

used

by

the

industry

to

prevent

unplanned

outages


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UngroundedSystems

Cons

Difficult

to

detect

ground

faults

no

fault

current Runningwithagroundfault increasesstressoninsulation,

leadingtophasetophasefaults

Intermittent

fault

may

cause

transient

overvoltage


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WyeConnected

TransformerSecondary

Feeder(withcapacitanceto

ground)

L

O

A

D

SOLIDLYGROUNDEDSYSTEM


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SolidlyGroundingSystem

Pros

Minimumfirst

costs

Immediateisolationoffaultedsystem

Voltagestabilization

Allowsuseofneutralforsinglephaseloads

Visibledetectionoffaultedequipment Equipmentinsulatedratedforphasetogroundvoltage


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SolidlygroundedSystems

CONS

Unplannedoutages

Voltagedipsduringfaultconditions

High

arcing

currents

through

grounding

systems Motorterminalboxcovershavebeenreported

blownaway

FireHazard

especially

in

Hazardous

(Classified)

Areas

Highrepaircostandtime


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WyeConnected

TransformerSecondary

Feeder(with

capacitanceto

ground)

LO

A

D

NGR

RESISTANCEGROUNDEDSYSTEM


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NGR

TransformerSecondary Feeder(withcapacitance)

LO

A

D

CurrentLimited

to

NGR

Let

Through

RESISTANCEGROUNDEDSYSTEMWITH

A

GROUND

FAULT

IF X


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Resistance(Impedance)Grounded

SystemsPros

Reducesunplanned

outages

Transientstabilityofthesystem

Eliminates

undesired

voltage

dips

during

fault

conditions

Allowsfaultdetectionofthefaultedequipment

Minimizesarcing

fault

current

and

arc

flash

hazard


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Resistance(Impedance)Grounded

Systems CONS

Initialinvestment

Faultdetectionandremovalrequired

SystemIntegrity

maintenance

required

Equipment insulationratedforphaseto

phasevoltages


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ProtectionorPrevention:

Whichis

more

effective?

Seatbelts,Airbags,*Accidentavoidance? *alarmandautomatic responsewhencloseto

anothercar) NFPA70E/CSAZ462 primarilyaddressprotectionofpersonneltominimizepersonnelinjury duetoelectrical

hazards

:Shock

and

Arc

Flash

by

removing

power withsomesoftsuggestiononreductionofhazards

Engineeringcontrols minimizethepotentialofelectrical

incidents

SafetyBydesignminimizesinjurypotential. RoleofHighResistanceGrounding?

17


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GroundFaults

Therehasbeendocumentationovertheyears

indicatingthat

between

80%

and

95%

of

all

electricalfaultsinitiateasgroundfaults. By

limitingthegroundfaultcurrenttoasmall

magnitude,agreat

majority

of

all

phase

to

phasearcingfaultscanbeeliminated.

Informalnumbers

are

that

less

than

1%

of

the

faultsareinitiallystartasthreephasefaults

(jumpers

left

installed,

snakes

etc)18


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120.3 FPN No. 3:

high-resistancegrounding of low-

voltage and 5 kV(nominal) systems, are techniques

available to reducethe hazard of the

system

PowerSystemGrounding

MitigationElectricShockandArcFlashEnergy ATotalSystemApproachforPersonnelandEquipmentProtection IEEE IASPCIC2010


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4.3.1.1 Note (3)

high-resistancegrounding of low-

voltage and 5 kV(nominal) systems, are techniquesavailable to reducethe hazard of the

system

PowerSystemGrounding

MitigationElectricShockandArcFlashEnergy ATotalSystemApproachforPersonnelandEquipmentProtection IEEE IASPCIC2010


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70E 130.5

InformationalNoteNo.3:Theoccurrenceofarcingfault insideanenclosureproducesavarietyofphysicalphenomena

Forexample,

the

arc

energy

resulting

from

an

arc

developed

in

the

airwillcauseasuddenpressureincreaseandlocalizedoverheating.

Equipmentanddesignpracticesareavailabletominimize theenergylevelsandthenumberofatriskproceduresthat

requirean

employee

to

be

exposed

to

high

level

energy

sources.Provendesignssuchasarcresistantswitchgear,

remoteracking(insertionorremoval),remoteopeningand

closing

of

switching

devices,

high

resistance

grounding

of lowvoltageand5kV(nominal)systems,currentlimitation, andspecificationofcoveredbuswithinequipmentare

techniquesavailabletoreducethehazardofthesystem

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HighResistance

Grounding

Systems

HighResistanceGrounded

Thereis

minimal

arc

flash

hazard,

as

there

is

withsolidlygroundedsystemsonthefirst

fault,

since

the

fault

current

is

normally

limitedto a verylowvalue

22


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HighResistanceGrounding

DoesResistanceGroundingreallyreduce:

UnplannedSystemoutages?

Potentialofarcflashhazard?

Engineersanswer Itdepends

23


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HighResistanceGrounding

Yes ifandonlyif Neutralgrounding systemIntegrityismaintained.AND

firstfaultisclearedbeforeinceptionofsecond

fault.

(Secondfaultonthesystemwillresultinaphaseto

phasefaultIFtheFIRSTFAULTISNOTCLEARED)


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25

Possible LossofNeutralPath

OpenorShortedNeutralPathtoGround

Resistor

Failure

Loose

Connection

BrokenWire

Broken or

Grounded Wire

Corrosion

Excerpt from a technical paper presented at2009 IEEE IAS Electrical Safety Workshop


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Hazard Control Measures


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Hazard Control Measuresoutlined in ANSI Z10

Elimination Substitution Engineering

Controls

Warnings Administrative

Controls

PPE

Addressed in NFPA 70E

Addressed in70E Tables

Prevention Protection

An effective electrical safety program incorporates all control measures


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LossofGroundinHRGSystems 28

A B

C

N N

HRGC

BA A B

CHRG

N

HRGC

Open Circuit:

Desired fault currentcannot flow.

Ungrounded System.

Open Circuit:

Desired fault currentcannot flow.

Grounded thru highinductive transformer.

Resonance System.

Short Circuit:

Undesired fault currentcan flow.

Place CT close to N,>costs (elevated N).

Solidly GroundedSystem.

WarningofRisk


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LossofGroundinHRGSystems 29

AB

CHRG

N

Sensing

Resistor

Relay

GroundFaultRelay&SensingResistor

Detects

Open

/

Short

Circuits

and

maintains

Grounding

AutomaticReductionofRisk


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AvoidingSecondGroundFault

Toreducearcflashhazard,itiscriticaltoreducethe

possibility

of

two

faults

at

the

same

time.How?

Warning

of

risk Eithermakesuremaintenancepeopleremovethegroundfaultimmediately

Automaticreduction

of

risk

Providesensing equipmenttoprioritizefeedersto

avoidsecond

simultaneous

ground

fault

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FAULT INDICATION USING 3 LAMPS


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Indication of first Feeder fault

AN

LOAD 1 LOAD 2

ZSCTZSCT

M1 M2

GMMETER

GMMETER

FAULTED FEEDER INDICATION


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- Alarm on first fault

Trip on second fault Cannot prioritize essential feeders

Difficult to locate fault(s)

R R R

R2.5A

PICKUP

100A

PICKUP

100A

PICKUP

100A

PICKUP

5A NGR

MGFRrelays


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Minimizing SecondSimultaneous

GroundFault

35


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Faulted Feeder First Fault Alarm Faulted PhaseIndication

Second Fault Trip Selective Inst. Feeder Tripping Ground Current as % of Let

Through

DDAI

DDR2

NGR

ALARM

FM1 FM2 FM3 FM4CM

DSP MKII


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Combined DSA/DSP Identifies individual faulted load and Phase Second Fault Protection Backup

DDR2SWGR

DDR2DSA

ALARM

ALARM

CM FM1 FM2 FM3 FM4

CM FM1

DSP MKII

TRIPS


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DSPRelay

DoubleendedUnitsubApplication


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Parallel

Generators

GENERATORS 600V

600V

DDR2-6

DSA

15-20A, 3P

100 kAIC

5A, 347V Neutral

Grounding Resistor

G G G G

ToBMS

ToBMS

TYPICAL PARALLEL GENERATOR HIGH RESISTANCE GROUNDING SCHEME

Zero Sequence Current Sensors

(one per feeder; one per generator)

Optional

Pulsing Resistor

5A, 600V

Zig-Zag Grounding

Transformer

2 - #16AWG, 24Vdc

for pulsing control

See Notes 1 and 2.

Notes:

1. NGR/Zig-Zag assembly with pulsing resistor, IPC Part Number: OHMNI-6PM-5-ZZ

2. NGR/Zig-Zag assembly without pulsing resistor, IPC Part Number: NTR600-5-ZZ

DS-PM2

OptionalDS-PM2 Pulsing Card

AWG#8 as per

CEC 10-1108(3)


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MitigationStrategies

Good

Systemmaintenance

practices

Better WarningsAlarms

Procedures

PPE

BestAutomatic

Reduction

of

Risk

Elimination

EngineeringControls


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MitigationStrategiesselection

Whichonetouse?

ItDepends Consider safety/cost/benefit Impact duetofailureinthesystem

Cansystembeshutdownimmediately?Costofshutdown?

Maintenancepractices? Environmentalconditions? Liabilityconsiderationsofdesign?


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Riskreduction

Keystrategyin70E/CSAZ462 is risk

analysis

Risk=Frequency

X

Consequences

Use

of

HRG

reduces

the

probability

of

frequencyandthusreducestherisk

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RiskAnalysis

DoesHRGreducestheincidentenergy

requiredto

be

put

on

label?

NO.Labelisbasedon3phaseboltedfault

BUT

itdoesreduceprobabilityofhighincidentenergy(80 95%)ofthetimeandcanbeutilizedinRiskAnalysis.

43


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Questions?

Thankyouforbeinghere!!

Thanksforprovidingmewithaforumfor

preachingelectrical

safety

by

design

Daleep

Mohla

,IEEE

Fellow

,

P.E [email protected]

44
mailto:[email protected]:[email protected]


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IEEE Canada HRG Presentation 20110314

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