substation insulation coordination studies-sparacino (1).pdf
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InsulationCoordinationStudiesTheSelectionofInsulationStrength
March25,2014
AdamSparacino
MITSUBISHIELECTRICPOWERPRODUCTS,INC.
POWERSYSTEMENGINEERINGSERVICES
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DefinitionofInsulationCoordination1
Insulation Coordination (IEEE)
The selection of insulation strength consistent with expected
overvoltages to obtain an acceptable risk of failure.
The procedure for insulation coordination consists of (a)determination of the voltage stresses and (b) selection of the
insulation strength to achieve the desired probability of failure.
The voltage stresses can be reduced by the application of surge
protective devices, switching device insertion resistors and controlledclosing, shield wires, improved grounding, etc.
MITSUBISHIELECTRICPOWERPRODUCTS,INC.
POWERSYSTEMENGINEERINGSERVICES 2
(1)IEEEStd 1313.11996IEEEStandardforInsulationCoordination Definitions,Principles,andRules.
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FourBasicConsiderations
Understanding Insulation Stresses
Understanding Insulation Strength
Designing Methods for Controlling Stresses
Designing Insulation Systems
MITSUBISHIELECTRICPOWERPRODUCTS,INC.
POWERSYSTEMENGINEERINGSERVICES 3
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FourBasicConsiderations
Understanding Insulation Stresses
Understanding Insulation Strength
Designing Methods for Controlling Stresses
Designing Insulation Systems
MITSUBISHIELECTRICPOWERPRODUCTS,INC.
POWERSYSTEMENGINEERINGSERVICES 4
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DefinitionofOvervoltages
Overvoltage
Abnormal voltage between two points of a system that is greater than
the highest value appearing between the same two points under
normal service conditions.2
Overvoltages are the primary metric for measuring and
quantifying power system transients and thus insulation
stress.
MITSUBISHIELECTRICPOWERPRODUCTS,INC.
POWERSYSTEMENGINEERINGSERVICES 5
(2) IEEE Std C62.221991 IEEE Guide for the Application of MetalOxide Surge Arresters for AlternatingCurrent
Systems, 1991.
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VocabularyofVoltage
MITSUBISHIELECTRICPOWERPRODUCTS,INC.
POWERSYSTEMENGINEERINGSERVICES 6
PeaklinegroundVoltageRMSVoltagelineground=(Vpeak/2)
PeakVoltagelineground=VLL_rms2/3
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IllustrationofOvervoltages
MITSUBISHIELECTRICPOWERPRODUCTS,INC.
POWERSYSTEMENGINEERINGSERVICES 7
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FourBasicConsiderations
Understanding Insulation Stresses
Understanding Insulation Strength
Designing Methods for Controlling Stresses
Designing Insulation Systems
MITSUBISHIELECTRICPOWERPRODUCTS,INC.
POWERSYSTEMENGINEERINGSERVICES 8
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ElectricalInsulation
Insulation can be expressed as a dielectric with a function to
preserve the electrical integrity of the system.
The insulation can be internal (solid, liquid, or gaseous), which is
protected from the effects of atmospheric conditions (e.g.,transformer windings, cables, gasinsulated substations, oil circuit
breakers, etc.).
The insulation can be external (in air), which is exposed to
atmospheric conditions (e.g., bushings, bus support insulators,disconnect switches, line insulators, air itself [tower windows, phase
spacing], etc.).
MITSUBISHIELECTRICPOWERPRODUCTS,INC.
POWERSYSTEMENGINEERINGSERVICES 9
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InsulationStrength
MITSUBISHIELECTRICPOWERPRODUCTS,INC.
POWERSYSTEMENGINEERINGSERVICES 10
Source: IEEE Std 62.22-1997, IEEE Guide for the Application of Metal-Oxide Surge Arresters for AC Systems
TypicalVoltTimeCurveforInsulationWithstand
StrengthforLiquidFilledTransformers
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InsulationStrength
Example for Transformers Windings
Normal system operating voltage
345 kVLL_RMS (1.00 p.u.)
Maximum continuous operating voltage (MCOV) 362 kVLL_RMS (1.05 p.u.)
Basic switching impulse insulation level (BSL)
745/870/975 kVLN_Peak
Basic lightning impulse insulation level (BSL) 900/1050/1175 kVLN_Peak
Chopped wave withstand (CWW)
1035/1205/1350 kVLN_Peak
MITSUBISHIELECTRICPOWERPRODUCTS,INC.
POWERSYSTEMENGINEERINGSERVICES 11
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FrequencyofDifferentEvents
MITSUBISHIELECTRICPOWERPRODUCTS,INC.
POWERSYSTEMENGINEERINGSERVICES 12
Transients
& Surges
Power System Control
& Dynamics
milliseconds microsecondsseconds10-20 minutes Power
Frequency
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FourBasicConsiderations
Understanding Insulation Stresses
Duty and Magnitude of applied voltage
Understanding Insulation Strength Ability to withstand applied stress
Designing Methods for Controlling Stresses
Designing Insulation Systems
MITSUBISHIELECTRICPOWERPRODUCTS,INC.
POWERSYSTEMENGINEERINGSERVICES 13
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PotentialOvervoltageMitigation
1. Surge Arresters
Need to be sized and located properly to clip overvoltages.
2. PreInsertion Resistors/Inductors
Need to be sized according to equipment being switched (only help
during breaker operation) to prevent excessive overvoltages from
being initiated.
3. SynchronousClose/Open Control
Need to use independent pole operated (IPO) breakers and program
controller based on equipment being switched (only help during
breaker operation) to prevent excessive overvoltages from being
initiated.
4. Surge Capacitors
Need to be sized and located to slow the front of incoming surges
MITSUBISHIELECTRICPOWERPRODUCTS,INC.
POWERSYSTEMENGINEERINGSERVICES 14
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FourBasicConsiderations
Understanding Insulation Stresses
Duty and Magnitude of applied voltage
Understanding Insulation Strength Ability to withstand applied stress
Designing Methods for Controlling Stresses
Designing Insulation Systems
MITSUBISHIELECTRICPOWERPRODUCTS,INC.
POWERSYSTEMENGINEERINGSERVICES 15
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InsulationCoordinationProcess
1. Specify the equipment insulation strength, the BIL and BSL of
all equipment.
2. Specify the phaseground and phasephase clearances that
should be considered.
3. Specify the need for, location, rating, and number of surge
arresters.
MITSUBISHIELECTRICPOWERPRODUCTS,INC.
POWERSYSTEMENGINEERINGSERVICES 16
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InsulationCoordinationStudies
1. Very Fast Transients (VFT) Analysis (nanoseconds time frame)
GIS disconnected switching.
Quantify the overvoltages throughout the substation.
Primary intent of determining location and number of surge arresterswithin the substation.
2. Lightning Surge Analysis (microseconds time frame)
Quantify the overvoltages throughout the substation.
Primary intent of determining location and number of surge arresterswithin the substation.
3. Switching Overvoltage Analysis (milliseconds time frame)
Quantify the overvoltages and surge arrester energy duties associatedwith switching events and fault/clear operations.
Primary intent is to verify that transient overvoltage mitigating devices(e.g., surge arresters, preinsertion resistors, synchronous close control)are adequate to protect electrical equipment.
Capacitor, Shunt Reactor, Transformer, and Line Switching Studies.
MITSUBISHIELECTRICPOWERPRODUCTS,INC.
POWERSYSTEMENGINEERINGSERVICES 17
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InsulationCoordinationStudies(cont.)
4. Temporary Overvoltage Analysis (seconds time frame)
Quantify the overvoltages and surge arrester energy duties as produced
by faults, resonance conditions, etc.
Primary intent is to verify conditions that cause problems within thesystem and develop the necessary mitigation.
Fault/Clear, load rejection, ferroresonance studies.
5. Steady State Analysis (minutes to hours time frame)
Quantify voltage during various system configurations. Power flow/stability studies.
MITSUBISHIELECTRICPOWERPRODUCTS,INC.
POWERSYSTEMENGINEERINGSERVICES 18
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MITSUBISHIELECTRICPOWERPRODUCTS,INC.
POWERSYSTEMENGINEERINGSERVICES 19
EXAMPLEAPPLICATION
STUDYFORINSULATIONCOORDINATION
LIGHTNINGSURGEANALYSIS
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MITSUBISHIELECTRICPOWERPRODUCTS,INC.
POWERSYSTEMENGINEERINGSERVICES 20
EAST500kVBUS
WEST
500
kV
BUS
CB CB CB CB CB CB CB CB CB
DUMMYBUS(POSITIONFOR
FUTUREBREAKER)
GML00
G762W
G762E
GEB06
G752E
G752W
G3A00
B3A01
B3A00
G952E
G952W
GWB06
G962W
G962E
G972W
G972E
GLU00
G872W
BLU01
BLU00
G872E
G4A00
G772W
G772E
B4A01
B4A00
la = 30.70
lb =25.66
lc =21.76
la = 21.19
lb =20.74
lc =23.64
la = 70.62lb =76.69
lc =82.77
la = 70.15
lb =76.25
lc=82.30
la = 26.42
lb =25.51
lc =24.59
la = 23.47
lb =22.56
lc =21.64
la = 23.47
lb =22.56
lc =20.64
la = 26.42
lb =25.51lc =24.59
la,b,c = 8.323
la,b,c = 19.59
la = 12.47
lb =11.55
lc =10.64
la,b,c = 19.59
la,b,c = 8.323
la = 9.518
lb =8.603
lc =7.689
la,b,c = 8.323
la,b,c = 5.634
la,b,c = 5.634
la,b,c = 8.323
BML00
BML01
500 kV LINE500 kV LINE
Refer to Figure 2 for
details of line
terminations.
Refer to Figure 2 for
details of line
terminations.
XFMR Refer to Figure 3 fordetails of XFMR
terminations.
Refer to Figure 3 for
details of XFMR
terminations.
XFMR
All lengths shown in meters.
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ExampleforLine/XFMRTermination
MITSUBISHIELECTRICPOWERPRODUCTS,INC.
POWERSYSTEMENGINEERINGSERVICES 21
Notes
(1) Line traps only on phase A and C for 500 kV lines. In
EMTP model, phase B has a 2.53 m section ofconductor modeled in place of line trap.
550 kV GIS
To GIS
Bay #6
Line Trap1
CCVT
Gas-to-
Air
Bushing
Surge
Arrester
500 kV Line
350 MCM
Ground Lead
(38)
550 kV GIS
To GIS
Bay
Gas-to-Air
Bushing
Surge
Arrester
To Transformer
350 MCM
Ground
Lead (38)
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ApproachforEvaluationtheInsulationCoordinationof
the550kVGasInsulatedSubstation
MITSUBISHIELECTRICPOWERPRODUCTS,INC.
POWERSYSTEMENGINEERINGSERVICES 22
Step 1: A severe voltage surge was injected into the substation for various
operating configurations to screen for maximum potential overvoltages.
Step 2: The resulting overvoltages were compared to the Basic Lightning Impulse
Insulation Level (BIL) of the equipment and the protective margin1 for the
equipment was calculated.
Step 3: If overvoltages resulted in less than a 20% protective margin in the initial
screening analysis for cases with the full system in or N1 contingencies, a more
detailed analysis was performed to identify the protective margins resulting from a
reasonable upper bounds lightning surge based on the configuration of the
substation and connected transmission lines.
For the detailed analysis, specific details of the transmission lines such as conductor
characteristics, shielding design, ground resistivity, keraunic level, etc. are considered to
determine a reasonable upper bounds to place on the lightning surge impinging on the
substation.
(1) Protective Margin = [ BIL / Vmaximum_peak 1] x 100%
ScreeningAnalysis
Detailed
Analysis
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LightningSurgeIncomingFrom500kVLine
PhasetoGroundVoltageofIncomingLightningSurge
MITSUBISHIELECTRICPOWERPRODUCTS,INC.
POWERSYSTEMENGINEERINGSERVICES 23
0
1000
2000
3000
4000
0 5 10 15 20
MLFULL_halfSRC>MLSRCA(Type 1)
Voltage
(kV)
Time (us)
Peak = 3264 kV (1.2 x 2720 kV CFO)
Time-to-peak = 0.5 microseconds.
Lightning surge impinges
substation from 500 kV Line.
Lightning surge initiated at
1.0 microseconds.
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LightningSurgeIncomingFrom500kVLine
HighestPhasetoGroundVoltageObservedinGIS
MITSUBISHIELECTRICPOWERPRODUCTS,INC.
POWERSYSTEMENGINEERINGSERVICES 24
0
500
1000
1500
2000
0 5 10 15 20
MLFULLB>G752WB(Type 1)
Voltage
(kV)
Time (us)
Peak overvoltage =
1109 kV.
GIS Basic Impulse Insulation Level (BIL) = 1550 kV
Protective Margin = 40%
([1550/1109 1] x 100%)
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MITSUBISHIELECTRICPOWERPRODUCTS,INC.
POWERSYSTEMENGINEERINGSERVICES 25
EXAMPLEAPPLICATION
STUDYFORINSULATIONCOORDINATION
TRANSMISSIONLINESWITCHINGANALYSIS
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TransmissionLineSwitchingAnalysis
MITSUBISHIELECTRICPOWERPRODUCTS,INC.
POWERSYSTEMENGINEERINGSERVICES 26
ExcessiveTransientOvervoltagesand
thePossibilityofaFlashoverDuring
EnergizingorReClosing
OvervoltagesExceedingGuidelines
UsedtoDevelopLineClearances
PotentialEquipmentConcerns
Transmission line is energized
(normal energizing or re-closing).
SynchronousCloseControl
PreInsertionResistors/Inductors
SurgeArresters
ShuntReactors
PotentialMitigationTechniques
BasicSwitchingImpulseLevel(BSL) ProbabilityofFlashovers
Applicable Criteria
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StatisticalSwitchingMethodology
MITSUBISHIELECTRICPOWERPRODUCTS,INC.
POWERSYSTEMENGINEERINGSERVICES 27
Tclose
Three poles closing
centered around closing
time (Tclose)
3 = cycle 2 = 2.08 ms
Sliding cycle window for pole
closing shifted over a half cycle
timeframe using a uniform
distribution
Each pole can close at anytime
within the cycle window centered
around the closing time (Tclose) for
each energization. Random closing
times based on a normal (Gaussian)
distribution
cycle window
Source-Side Voltage
Case simulated with
200-400 energizations
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ElectroGeometricLineModel
Example345kVTransmissionLine
MITSUBISHIELECTRICPOWERPRODUCTS,INC.
POWERSYSTEMENGINEERINGSERVICES 28
14.5 14.5
27
B C A
27
54
(24atmidpoint)
78
(63atmidpoint)
Center
LineLineLength(total)=85mi
Untransposed
Groundresistivity=37Ohmm
PhaseConductor:
ACSRLapwing
2/cBundle18spacing
Outsidediameter=1.504
RDC=0.059Ohm/mi
Thick/Diam=0.375
ShieldWire:
Alumoweld7#8
Outsidediameter=0.385
RDC=2.40Ohm/mi
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StatisticalSwitchingOvervoltageStrengthCharacteristics
andSOVdensitiesoftheline
MITSUBISHIELECTRICPOWERPRODUCTS,INC.
POWERSYSTEMENGINEERINGSERVICES 29
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StatisticalDistr.OfOvervoltagesAlong500kVLinewith
LineEndSurgeArresters
MITSUBISHIELECTRICPOWERPRODUCTS,INC.
POWERSYSTEMENGINEERINGSERVICES 31
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
110%
1.00 1.50 2.00 2.50 3.00 3.50 4.00
P
robabilitytoExceed
Overvoltage(%)
PeakOvervoltage(PerUnitona500kVBase)
StatisticalDistributionofOvervoltagesAlongLine
SendingEnd
1/4
Point
1/2Point
3/4Point
RemoteEnd
ExampleCFO
Estimatedinsulation
withstandforthe
transmissionline: CFO=3.53
p.u., f/CFO =5%.
E2isthevalueinwhichthe
overvoltagesexceed2%ofthe
switchingoperations.
Highestovervoltagealongthe
line=2.21p.u.(902kV).
98%oftheovervoltagesalong
thelineare2.16p.u.(882
kV).
Statistical
distribution
based
on
thecasepeak
methodfromIEEE
Std1313.21999.
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MITSUBISHIELECTRICPOWERPRODUCTS,INC.
POWERSYSTEMENGINEERINGSERVICES 32
EXAMPLEAPPLICATION
STUDYFORINSULATIONCOORDINATION
SHUNTCAPACITORSWITCHINGANALYSIS
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ShuntCapacitorSwitchingAnalysis
MITSUBISHIELECTRICPOWERPRODUCTS,INC.
POWERSYSTEMENGINEERINGSERVICES 33
ContactWearfromExcessiveInrushCurrentDuty
ExcessiveTransientOvervoltages
InducedVoltagesandCurrentsin
ControlCircuits StepandTouchPotentialsDuring
Switching
PotentialEquipmentConcerns
Capacitor bank is energized and
transient inrush currents flow
through capacitor bank breaker
and voltage surges propagate
into the system.
CurrentLimitingReactors
SynchronousCloseControl
PreInsertionResistors/Inductors
SurgeArresters
PotentialMitigationTechniques
ANSI/IEEEInrushCurrentLimits BasicSwitchingImpulseLevel(BSL)
BreakerCapabilityBeyondStandards
IEEEStd 80forgrounding
ApplicableCriteria
C it B k R St ik
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CapacitorBankReStrike
DuringDeEnergization
MITSUBISHIELECTRICPOWERPRODUCTS,INC.
POWERSYSTEMENGINEERINGSERVICES 34
CurrentThroughSwitchingDevice VoltageonEachSideofSwitchingDevice
Currentis
interrupted
Firstrestrike
occursand
currentisre
established
Highfrequency
currentisinterrupted
Secondrestrikeoccursand
current
is
re
established
Voltageoncapacitor
banksideof
switchingdevice(DC
trappedcharge)
Voltageonsystem
sideofswitching
device
Peakovervoltage
from
1st
restrike
Peakovervoltage
from2nd restrike
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VoltageMagnification
MITSUBISHIELECTRICPOWERPRODUCTS,INC.
POWERSYSTEMENGINEERINGSERVICES 35
When a shunt capacitor bank is energized with a nearby
capacitor at a lower voltage, the potential for voltage
magnification may exist when the following condition is true:
1
1
2
2
Furthermore,whenC1>>C2,andL1
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VoltageMagnification(Cont.)
MITSUBISHIELECTRICPOWERPRODUCTS,INC.
POWERSYSTEMENGINEERINGSERVICES 36
Example 1.95 p.u. overvoltage at HV
bus when capacitor bank is switched.
Example 4.39 p.u. overvoltage at LV
bus when capacitor bank is switched.
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MITSUBISHIELECTRICPOWERPRODUCTS,INC.
POWERSYSTEMENGINEERINGSERVICES 37
EXAMPLEAPPLICATION
STUDYFORINSULATIONCOORDINATION
SHUNTREACTORSWITCHINGANALYSIS
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ShuntReactorSwitchingAnalysis
MITSUBISHIELECTRICPOWERPRODUCTS,INC.
POWERSYSTEMENGINEERINGSERVICES 38
ExcessiveInrushCurrentsfrom
Energizing
TransientandTemporaryOvervoltages
fromResonanceConditions
GenerationofHarmonics
ResonancefromParallelLines
PotentialEquipmentConcerns
Shunt reactor is energized and
inrush current flows through the
system and circuit breaker.
SynchronousCloseControl
SurgeArresters
AppropriateRelaySettings
OperationalLimitations
PotentialMitigationTechniques
EquipmentInsulationLevels
VoltageSag/DipCriteria
HarmonicDistortion
ApplicableCriteria
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ResonanceOvervoltages
MITSUBISHIELECTRICPOWERPRODUCTS,INC.
POWERSYSTEMENGINEERINGSERVICES 39
345kVSubstation
Voltage
Measured
on
Energized
LineLineinservice
(breakersclosed
atbothends)
Lineoutofservice(breakersopenat
bothends)
345kVSubstation
345kVSubstation 345kVSubstation
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ResonanceOvervoltages
MITSUBISHIELECTRICPOWERPRODUCTS,INC.
POWERSYSTEMENGINEERINGSERVICES 40
Peak overvoltage
= 2.94 p.u.
It is anticipated that the line equipment
would be capable of withstanding at
least 1.5 p.u. for 100 ms.
Line breakers open to
trip the line at 200 ms.
The shunt reactors should be tripped
within 550 ms of the line breakers
tripping to avoid excessive
overvoltages for this case.
Anticipated temporary overvoltage
(TOV) capabilit y (1.5 p.u. for 100 ms).
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Summary
Insulation Coordination is the selection of insulation strength.
Determine maximum insulation stress.
Determine the minimum insulation strength with margin taking intoaccount stress reducers (surge arresters, preinsertion resistors,
synchronous close control, etc.) that can withstand the maximumstress.
Studies help in quantifying the maximum anticipated stressand determining the rating/location of overvoltage mitigating
devices. A key component of insulation coordination is pairing the
correct strength to the correct stress.
As a rule of thumb, the shorter the time the overvoltage is applied to
the insulation the greater the magnitude of overvoltage the insulationcan withstand before failure.
MITSUBISHIELECTRICPOWERPRODUCTS,INC.
POWERSYSTEMENGINEERINGSERVICES 41
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MITSUBISHIELECTRICPOWERPRODUCTS,INC.
POWERSYSTEMENGINEERINGSERVICES 42
THANKYOUFORYOUATTENTION