7/30/2019 IEEE Canada HRG Presentation 20110314
1/44
SystemGrounding
Impacton
reliability
and
Safety
Presentedby:
DaleepMohlaSergioPanetta
JimChannon
ScottLee
7/30/2019 IEEE Canada HRG Presentation 20110314
2/44
Agenda
SystemGroundingConsiderationsfor 600
Voltsand
less
system
TypesofSystemGroundingavailable
Prosand
Cons
of
each
Mitigationstrategies
Selectionguideline
for
mitigation
Questions
7/30/2019 IEEE Canada HRG Presentation 20110314
3/44
SystemsGroundingConsiderations
Cost?
Safety?
Reliability?
Impactof
unintended
outages?
Productionloss?
Environmental?Safety?
7/30/2019 IEEE Canada HRG Presentation 20110314
4/44
TypesofSystemGrounding
Ungrounded
SolidGrounded
ImpedanceGrounded
7/30/2019 IEEE Canada HRG Presentation 20110314
5/44
UNGROUNDED(DELTA)SYSTEM
L
O
A
D
Transformer
Secondary
Feeder(withcapacitanceto
ground)
7/30/2019 IEEE Canada HRG Presentation 20110314
6/44
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
7/30/2019 IEEE Canada HRG Presentation 20110314
7/44
Normaloperation
Intermittent
groundfault
on
phase
C
A&Bphasesare:>Linelinevoltageabove
ground
Phase
C
>ground
voltage
Intermittentfaultcurrent
Personneldanger
UNGROUNDEDSYSTEM:FAULTED
OPERATION
WITH
TRANSIENT
OVERVOLTAGE
7/30/2019 IEEE Canada HRG Presentation 20110314
8/44
UNGROUNDEDSYSTEMS:
Prosand
Cons
Pros MinimumInitialcost
Abilitytorunwith onephasefaultedtoground
Isolationof
Primary
and
Secondary
currents
(harmonics)
Initially
used
by
the
industry
to
prevent
unplanned
outages
7/30/2019 IEEE Canada HRG Presentation 20110314
9/44
UngroundedSystems
Cons
Difficult
to
detect
ground
faults
no
fault
current Runningwithagroundfault increasesstressoninsulation,
leadingtophasetophasefaults
Intermittent
fault
may
cause
transient
overvoltage
7/30/2019 IEEE Canada HRG Presentation 20110314
10/44
WyeConnected
TransformerSecondary
Feeder(withcapacitanceto
ground)
L
O
A
D
SOLIDLYGROUNDEDSYSTEM
7/30/2019 IEEE Canada HRG Presentation 20110314
11/44
SolidlyGroundingSystem
Pros
Minimumfirst
costs
Immediateisolationoffaultedsystem
Voltagestabilization
Allowsuseofneutralforsinglephaseloads
Visibledetectionoffaultedequipment Equipmentinsulatedratedforphasetogroundvoltage
7/30/2019 IEEE Canada HRG Presentation 20110314
12/44
SolidlygroundedSystems
CONS
Unplannedoutages
Voltagedipsduringfaultconditions
High
arcing
currents
through
grounding
systems Motorterminalboxcovershavebeenreported
blownaway
FireHazard
especially
in
Hazardous
(Classified)
Areas
Highrepaircostandtime
7/30/2019 IEEE Canada HRG Presentation 20110314
13/44
WyeConnected
TransformerSecondary
Feeder(with
capacitanceto
ground)
LO
A
D
NGR
RESISTANCEGROUNDEDSYSTEM
7/30/2019 IEEE Canada HRG Presentation 20110314
14/44
NGR
TransformerSecondary Feeder(withcapacitance)
LO
A
D
CurrentLimited
to
NGR
Let
Through
RESISTANCEGROUNDEDSYSTEMWITH
A
GROUND
FAULT
IF X
7/30/2019 IEEE Canada HRG Presentation 20110314
15/44
Resistance(Impedance)Grounded
SystemsPros
Reducesunplanned
outages
Transientstabilityofthesystem
Eliminates
undesired
voltage
dips
during
fault
conditions
Allowsfaultdetectionofthefaultedequipment
Minimizesarcing
fault
current
and
arc
flash
hazard
7/30/2019 IEEE Canada HRG Presentation 20110314
16/44
Resistance(Impedance)Grounded
Systems CONS
Initialinvestment
Faultdetectionandremovalrequired
SystemIntegrity
maintenance
required
Equipment insulationratedforphaseto
phasevoltages
7/30/2019 IEEE Canada HRG Presentation 20110314
17/44
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
7/30/2019 IEEE Canada HRG Presentation 20110314
18/44
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
7/30/2019 IEEE Canada HRG Presentation 20110314
19/44
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
7/30/2019 IEEE Canada HRG Presentation 20110314
20/44
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
7/30/2019 IEEE Canada HRG Presentation 20110314
21/44
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
21
7/30/2019 IEEE Canada HRG Presentation 20110314
22/44
HighResistance
Grounding
Systems
HighResistanceGrounded
Thereis
minimal
arc
flash
hazard,
as
there
is
withsolidlygroundedsystemsonthefirst
fault,
since
the
fault
current
is
normally
limitedto a verylowvalue
22
7/30/2019 IEEE Canada HRG Presentation 20110314
23/44
HighResistanceGrounding
DoesResistanceGroundingreallyreduce:
UnplannedSystemoutages?
Potentialofarcflashhazard?
Engineersanswer Itdepends
23
7/30/2019 IEEE Canada HRG Presentation 20110314
24/44
HighResistanceGrounding
Yes ifandonlyif Neutralgrounding systemIntegrityismaintained.AND
firstfaultisclearedbeforeinceptionofsecond
fault.
(Secondfaultonthesystemwillresultinaphaseto
phasefaultIFtheFIRSTFAULTISNOTCLEARED)
7/30/2019 IEEE Canada HRG Presentation 20110314
25/44
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
7/30/2019 IEEE Canada HRG Presentation 20110314
26/44
Hazard Control Measures
7/30/2019 IEEE Canada HRG Presentation 20110314
27/44
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
7/30/2019 IEEE Canada HRG Presentation 20110314
28/44
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
7/30/2019 IEEE Canada HRG Presentation 20110314
29/44
LossofGroundinHRGSystems 29
AB
CHRG
N
Sensing
Resistor
Relay
GroundFaultRelay&SensingResistor
Detects
Open
/
Short
Circuits
and
maintains
Grounding
AutomaticReductionofRisk
7/30/2019 IEEE Canada HRG Presentation 20110314
30/44
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
30
7/30/2019 IEEE Canada HRG Presentation 20110314
31/44
FAULT INDICATION USING 3 LAMPS
7/30/2019 IEEE Canada HRG Presentation 20110314
32/44
Indication of first Feeder fault
AN
LOAD 1 LOAD 2
ZSCTZSCT
M1 M2
GMMETER
GMMETER
FAULTED FEEDER INDICATION
7/30/2019 IEEE Canada HRG Presentation 20110314
33/44
- 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
7/30/2019 IEEE Canada HRG Presentation 20110314
34/44
Minimizing SecondSimultaneous
GroundFault
35
7/30/2019 IEEE Canada HRG Presentation 20110314
35/44
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
7/30/2019 IEEE Canada HRG Presentation 20110314
36/44
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
7/30/2019 IEEE Canada HRG Presentation 20110314
37/44
DSPRelay
DoubleendedUnitsubApplication
7/30/2019 IEEE Canada HRG Presentation 20110314
38/44
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)
7/30/2019 IEEE Canada HRG Presentation 20110314
39/44
MitigationStrategies
Good
Systemmaintenance
practices
Better WarningsAlarms
Procedures
PPE
BestAutomatic
Reduction
of
Risk
Elimination
EngineeringControls
7/30/2019 IEEE Canada HRG Presentation 20110314
40/44
MitigationStrategiesselection
Whichonetouse?
ItDepends Consider safety/cost/benefit Impact duetofailureinthesystem
Cansystembeshutdownimmediately?Costofshutdown?
Maintenancepractices? Environmentalconditions? Liabilityconsiderationsofdesign?
7/30/2019 IEEE Canada HRG Presentation 20110314
41/44
Riskreduction
Keystrategyin70E/CSAZ462 is risk
analysis
Risk=Frequency
X
Consequences
Use
of
HRG
reduces
the
probability
of
frequencyandthusreducestherisk
42
7/30/2019 IEEE Canada HRG Presentation 20110314
42/44
RiskAnalysis
DoesHRGreducestheincidentenergy
requiredto
be
put
on
label?
NO.Labelisbasedon3phaseboltedfault
BUT
itdoesreduceprobabilityofhighincidentenergy(80 95%)ofthetimeandcanbeutilizedinRiskAnalysis.
43
7/30/2019 IEEE Canada HRG Presentation 20110314
43/44
Questions?
Thankyouforbeinghere!!
Thanksforprovidingmewithaforumfor
preachingelectrical
safety
by
design
Daleep
Mohla
,IEEE
Fellow
,
44
mailto:[email protected]:[email protected]7/30/2019 IEEE Canada HRG Presentation 20110314
44/44
Top Related