Substation Insulation Coordination Studies-Sparacino (1).pdf

8/11/2019 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.


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




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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.



(2) IEEE Std C62.221991 IEEE Guide for the Application of MetalOxide Surge Arresters for AlternatingCurrent

Systems, 1991.


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VocabularyofVoltage



PeaklinegroundVoltageRMSVoltagelineground=(Vpeak/2)

PeakVoltagelineground=VLL_rms2/3


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IllustrationofOvervoltages




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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.).




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InsulationStrength



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




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FrequencyofDifferentEvents



Transients

& Surges

Power System Control

& Dynamics

milliseconds microsecondsseconds10-20 minutes Power

Frequency


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Duty and Magnitude of applied voltage

Understanding Insulation Strength Ability to withstand applied stress






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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




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Duty and Magnitude of applied voltage

Understanding Insulation Strength Ability to withstand applied stress






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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.




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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.




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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.




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EXAMPLEAPPLICATION

STUDYFORINSULATIONCOORDINATION

LIGHTNINGSURGEANALYSIS


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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.


details of line

terminations.

XFMR Refer to Figure 3 fordetails of XFMR

terminations.


details of XFMR

terminations.

XFMR

All lengths shown in meters.


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ExampleforLine/XFMRTermination



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



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



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



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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EXAMPLEAPPLICATION


TRANSMISSIONLINESWITCHINGANALYSIS


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TransmissionLineSwitchingAnalysis



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



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



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




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StatisticalDistr.OfOvervoltagesAlong500kVLinewith

LineEndSurgeArresters



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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EXAMPLEAPPLICATION


SHUNTCAPACITORSWITCHINGANALYSIS


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ShuntCapacitorSwitchingAnalysis



ContactWearfromExcessiveInrushCurrentDuty

ExcessiveTransientOvervoltages

InducedVoltagesandCurrentsin

ControlCircuits StepandTouchPotentialsDuring

Switching


Capacitor bank is energized and

transient inrush currents flow

through capacitor bank breaker

and voltage surges propagate

into the system.

CurrentLimitingReactors


PreInsertionResistors/Inductors

SurgeArresters


ANSI/IEEEInrushCurrentLimits BasicSwitchingImpulseLevel(BSL)

BreakerCapabilityBeyondStandards

IEEEStd 80forgrounding

ApplicableCriteria

C it B k R St ik


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CapacitorBankReStrike

DuringDeEnergization



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



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.)



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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EXAMPLEAPPLICATION


SHUNTREACTORSWITCHINGANALYSIS


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ShuntReactorSwitchingAnalysis



ExcessiveInrushCurrentsfrom

Energizing

TransientandTemporaryOvervoltages

fromResonanceConditions

GenerationofHarmonics

ResonancefromParallelLines


Shunt reactor is energized and

inrush current flows through the

system and circuit breaker.


SurgeArresters

AppropriateRelaySettings

OperationalLimitations


EquipmentInsulationLevels

VoltageSag/DipCriteria

HarmonicDistortion

ApplicableCriteria


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ResonanceOvervoltages



345kVSubstation

Voltage

Measured

on

Energized

LineLineinservice

(breakersclosed

atbothends)

Lineoutofservice(breakersopenat

bothends)

345kVSubstation

345kVSubstation 345kVSubstation


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ResonanceOvervoltages



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.




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THANKYOUFORYOUATTENTION

Documents

Substation Insulation Coordination Studies-Sparacino (1).pdf