SVL Selection

7/23/2019 SVL Selection

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n ergroun

S stem


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The Underground System

HV Underground Systems

Lower Loss Designs are in demand Longer Lines and Longer Unit Lengths are in demand

Higher Reliability is Always in demand

A Need for Better Insulation

A Need for Better Protection of the

raphic

A need for Optimized ArresterSelection

So

uthwireG


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High Voltage Cable

Phase Conductor

Primary Insulation

Metallic Sheath

Jacketaphic

SouthwireG

r

raphic

So

uthwireG


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The High Voltage

Phase Arrester

a e erm na on

Sheath Voltage Limiter

Tower Ground


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Protection of HV Cables with single

requires two types of Arresters

an ar a on ass rres er pro ec s

the primary insulation from failure.

A Sheath Voltage Limiter (low MCOV

distribution arrester without disconnector)

is used to protect the jacket of the cable

ur ng surge even s on eprimary conductor.


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Underground Cable Run

LinkBox

s ys em as on nuousCross Bonding of the Sheathwith no Trans osition of theconductors in the Link Boxes


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Underground Cable Run

Cross Bonding and Tranpositioning are

LinkBox

techniques used to reduce steady state loses dueto currents induced onto the shield and circulated

.


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Link Box

SVL, Crossover

con uc ors aninterrupter

nsu a on


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ea o age

Limiter


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Sheath Voltage Limiter. yp ca y a s r u on ass rres er

but can be a Station Class

2. Low MCOV ratings 3-22kV typicallyCourtesy of Tridelta

Tride

lta

applied

3. Metal Oxide Varistors (MOV) are the

onl t e of arrester used in this

Courtesyof

application.

4. Polymer housed arresters are only

.


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Typical SVL Characteristics

Tridelta

Courtesy

of


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Typical TOV data for SVL

Tridelta HC SVL


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Link box for 345kV system

Link Box Data1.Typically water tight

2. Must have same BIL rating as

cable interrupts

.

maintenance check

4.Offer option to cross bond theGeneralCable

sheathsCourtesy

of


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z ng e

eaVolta eLimiter


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SelectingtheOptimum SVLSVLorDistributionArresterArresterLocation ArresterTypes1

2

eters

A

rrester

Select ArresterACRatingSystemVoltagesandNeutral

Configuration

ArresterMCOV

andTOV

Capability

3Todaysem

Para

Paramet

ec arg no ro ec on, , , FOW,LPL,SPL

CheckEnergyHandlingLightningIntensityTLD,HighCurrent

ShortDuration

Ca abilit

4

Focus

Syst rs

Energy

CheckFailureModeSystemFaultCurrentAvailabilityandPostBIL

ArresterShortCircuit

Capabilityand

DisconnectorOperation

5

SelectandCheckMountingInstallationParametersClearances,Cantilever

SeparationDistance,Lead

Length

ArresterCreep,Strike,

MarginofProtectionRe

check

ArresterIsSelected


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Selecting the SVL MCOV Rating

Step 1: Determine Sheath voltage during a fault

Example (Single Point Bonding with SVL at open end)

Sheath voltage on a flat configured 1000kcmil, 1000m cablewith 25kA (17.5kA rms) system fault using ATP transient

30[kA]

6000

(green)

Fault Current

-15

0 -1000

Current(red)

heathVoltage

Sheath VoltageMaximum Sheath

(file SVL_Fault_Analysis.pl4; x-var t) c:FAULT - v:S-OPNA0 10 20 30 40 50[ms]-30 -8000

Fau

lt S

Voltageduring 17.5kA rms

fault is 3800 V rms

Sheath diameter 90mm

Conductor center to center distance 450mm


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Hand calculation of d d = 90mm

Sheath1. Determine physical dimensions

S/d=240/90=5of cable construction

2. Calculate S/d

1. S = Center to center cable spacing

S

. = ame er o s ea

3. Using Figure 1 of IEEE 575

determine the sheath voltage

radient for this confi uration at

1000 amps.


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Hand calculation of Induced Voltage on Sheath

Step 3

Sheath voltage gradient from

Figure 1 is 200v/km/1000A

Step 4 Determine the voltage for

the length of cable and fault

current level

Max V = L x Vg x I

Where

L = length o f cable section in km

V = Sheath Volta e Gradient

I = Ampli tude of fault current in kA

Max V = 1 x 200 x 17.5

Max V = 3400V rms


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Alternative to Using the IEEE 575 Graph

The general equation for the log linear

curves is:

Where

E is the Sheath Voltage gradient in V/km/kA

S is center to center distance between cables

d is diameter of sheath

E = 75 x (S/d).466

For outer conductors of flat layout

E = 107 x (S/d).369


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Hand calculation of Induced Voltage on Sheath

Select the SVL that has MCOV onerating above the Max rms sheath

voltage for maximum fault for the

witha

4.8kV

MCOV

.

Ifthecablelengthwasthecorrect choice


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Current in SVL on a 1 and 2km cable run60

0 10 20 30 40 50ms-40

10

[uA] 30uA SVL

current on1km line

.

(file SVL_Fault_Analysis.pl4; x-var t) c: -SVL1B c: -SVL1A c: -SVL1C

0

300

600[A] 550A SVL

current on2km line

(file svl_fault_analysis_with_wrong_svl.pl4; x-var t) c: -SVL1B c: -SVL1A c: -SVL1C0 10 20 30 40 50[ms]

-600

-300

50 400

4.8kV MCOV on 2km l ine

-10

10

30

0

100

200

300

cycle and about 50 C per half cyc le

(file svl_fault_analysis_with_wrong_svl.pl4; x-var t) c: -SVL1B c: -SVL1A c: -SVL1C t:JOULES t:TEMP4.8kV MCOV on 2km line


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Checking Energy Handling

If the SVL is chosen correctly, it will not adsorb

.

However it will during a

switching surgeAnd during a lightning

surge


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SVL Switching Surge Analysis

Large Switching Surge on Primary Conductor

- With a MJ energy dissipation o the primary arresters 5kJ kV M V

0.8

1.2[MJ ]

(file svl_switching_analysis.pl4; x-var t) e:X0002A- e:X0002C-14.0 14.5 15.0 15.5 16.0 16.5 17.0[ms]

0.0

0.4

- . -

- This energy absorption level is only 25% of a heavy duty

distr ibution arrester capability

1000

2000

3000

4000

5000

10

20

(file SVL_Switching_Analysis.pl4; x-var t) t:JOULES t:TEMP14.0 14.5 15.0 15.5 16.0 16.5 17.0[ms]0 0


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SVL Lightning Surge Analysis

115kA Lightning Surge on Primary Conductore ser o e rres er a es an e sees

80

100

120[kA]

-20

0

20

40

60

Riser Pole at 100kASVL 15kA

15kA through a 4.8kV SVL is not an issue. It appears that as

(file SVL_Lightning_Analysis.pl4; x-var t) c:X0002A- c:SVL1A - c:XX0025-X0003A0.270 0.285 0.300 0.315 0.330 0.345 0.360[ms]

long as there is a riser pole arrester, the SVL current will notbe significant.


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Margin of Protection AnalysisVolta e on Sheath at O en end without SVL Max = 260kV

0

150

300

[kV]

(file SVL_Lightning_Analysis.pl4; x-var t) v:S-OPNA

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6[ms]-300

-150

13

20[kV]

Voltage on Sheath at Open end with 4.8kV SVL Max = 16.4kV

0.0 0.5 1.0 1.5 2.0 2.5 3.0[ms]-15

-8

-1



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Margin of Protection AnalysisVoltage on Sheath at Open end with 8.0kV SVL Max = 27kV @15kA

0

15

30

[kV]


0.0 0.4 0.8 1.2 1.6 2.0[ms]-30

-15

Voltage on Sheath at Open end with 9.6kV SVL Max = 32kV @15kA

40 16

5

[kV]

4

10

(file SVL_Lightning_Analysis.pl4; x-var t) v:S-OPNA c:SVL1A -0.0 0.5 1.0 1.5 2.0 2.5 3.0[ms]

-30 -2


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Margin of Protection Analysis[ MP =( (BIL/V10kA)-1) *100 ]

ArresterMCOV

10kADischarge

230kV SheathInterrupt to 230kVMarginof 345kV SheathInterrupt to

Gnd BIL

345kV

MarginofRating

Vo tage

kV

PerIEEE575

kV

Protect on

%

PerIEEE575

kV

Protect on

%

4.8 18 40 120% 60 233%

8 28 40 42% 60 140%

9.6 34 40 17.6% 60 76%

Based on this table, it would be unwise to use any arrester with an

MCOV greater than 8kV mcov on a 230kV circuit. IEEE C62.22

recommends no more than 15% on most insulation.


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ummary

O8


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Summary

Protection of HV Cables with single

requires two types of Arresters

an ar a on ass rres er pro ec s

the primary insulation from failure.

A Sheath Voltage Limiter (low MCOV

distribution arrester without disconnector)

is used to protect the jacket of the cable

ur ng surge even s on e

primary conductor.

O8


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Summary

When Selecting the MCOV Rating

HV Station Class Arrester

The system line to ground voltage and TOVdetermine the MCOV rating.


The voltage induced on the sheath from afault in the phase conductor primarily

determines the MCOV rating o the SVL


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Summary

When Selecting the MCOV rating


In all cases, the station class arrester willprovide adequate insulation protection.


For longer segments of cable the AC ratingmay need to be closely checked and

optimized arther on 230kV lines, but inmost other cases, the Margin of Protectionis not an issue once the AC rating is


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Summary

When Selecting the Energy


Use Station Class arrester for mostapplications.


For most cases a standard distributionclass arrester will work.

SVL Selection

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