Download - 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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The Underground System
High Voltage Cable
Phase Conductor
Primary Insulation
Metallic Sheath
Jacketaphic
SouthwireG
r
raphic
So
uthwireG
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The Underground System
The High Voltage
Phase Arrester
a e erm na on
Sheath Voltage Limiter
Tower Ground
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The Underground System
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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The Underground System
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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The Underground System
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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The Underground System
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
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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Selecting the SVL MCOV Rating
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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Selecting the SVL MCOV Rating
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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Selecting the SVL MCOV Rating
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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Selecting the SVL MCOV Rating
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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Selecting the SVL MCOV Rating
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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SVL Lightning Surge Analysis
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
(file SVL_Lightning_Analysis.pl4; x-var t) v:S-OPNA
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SVL Lightning Surge Analysis
Margin of Protection AnalysisVoltage on Sheath at Open end with 8.0kV SVL Max = 27kV @15kA
0
15
30
[kV]
(file SVL_Lightning_Analysis.pl4; x-var t) v:S-OPNA
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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SVL Lightning Surge Analysis
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.
Sheath Voltage Limiter
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
HV Station Class Arrester
In all cases, the station class arrester willprovide adequate insulation protection.
Sheath Voltage Limiter
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
HV Station Class Arrester
Use Station Class arrester for mostapplications.
Sheath Voltage Limiter
For most cases a standard distributionclass arrester will work.