The Un Un de derg rgro roun und d Sys yste tem m HV Unde nd ergro rg roun und d Systems ys tems •
Lower Los s Design Design s are in demand demand
•
Longe Long er Lines and and Long er Unit Unit Lengths are in demand demand
•
Higher Reliabilit Reliabilit y is i s Always in demand demand
• A Need f o r B ett et t er Ins In s u l ati at i o n • A Need f o r B ett et t er Pro Pr o t ect ec t i o n o f t h e • A need n eed f o r Opt Op t i m i zed Ar A r r est es t er Selection
c i h p a r G e r i w h t u o S
The Un Un de derg rgro roun und d Sys yste tem m Hi g h Vo l t ag e Ca Cab l e Phase Condu on duct ctor or Prima rim ary Insula nsu latio tion n Metallic Sheath c i h p a r G e r i w h t u o S
Jacket c i h p a r G e r i w h t u o S
The Underground System The High Voltage Phase Arrester a e erm na on
Sheath Voltage Limiter Tower Ground
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 fro m 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 conduct or.
The Underground System Underground Cable Run
Link Box
s ys em as on nuous Cross Bonding of the Sheath with no Trans osition of the conductors in the Link Boxes
The Underground System Underground Cable Run
Link Box
Cross Bonding and Tranpositioning are techniques used to reduce steady state loses due to currents induced onto the shield and circulated .
The Underground System Link Box
SVL, Crossover con uc ors an interrupter nsu a on
ea o age Limiter
Sheath Voltage Limiter Sheath Voltage Limiter . yp ca y a s r u on ass but can be a Station Class Courtesy of Tridelta
a t l e d i r T f o y s e t r u o C
rres er
2. Low MCOV ratings 3-22kV typically applied 3. Metal Oxide Varistors (MOV) are the onl t e of arrester used in this application. 4. Polymer housed arresters are only .
Typical SVL Characteristics
a t l e d i r T f o y s e t r u o C
Typical TOV data for SVL Tridelta HC SVL
Link box for 345kV system Link Box Data 1.Typically water tight 2. Must have same BIL rating as cable interrupts
e l b a C l a r e n e G f o y s e t r u o C
. maintenance check 4.Offer option to cross bond the sheaths
z ng e ea Volta e Limiter
Selecting the Optimum SVL 1 SVL or Distribution Arrester
Arrester Location
Arrester Types
2 s r e t e
System Voltages and Neutral Configuration
Today’s , , , a r Focus a
P Lightning Intensity m e t sEnergy y S System Fault Current Availability and Post BIL Installation Parameters Clearances, Cantilever Separation Distance, Lead Length
Select Arrester AC Rating
Arrester MCOV and TOV Capability
3
ec
arg n o
ro ec on
FOW, LPL, SPL
Check Energy Handling
TLD, High Current Short Duration Ca abilit
Check Failure Mode
Arrester Short Circuit Capability and Disconnector Operation
4
5
Select and Check Mounting
Arrester Is Selected
A r r e s t e r P a r a m e t r s
Arrester Creep, Strike, Margin of Protection Re‐ check
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 cable with 25kA (17.5kA rms) system fault using ATP transient
30 [kA] ) d e r ( t n e r r u C t l u a F
6000
Fault Current
0
-1000
Sheath Voltage
-15 -30
0
10
(file SVL_Fault_Analysis.pl4; x-var t) c:FAULT -
20 v:S-OPNA
30
Maximu m Sheath Voltage 40 [ms]
50
-8000
during 17.5kA rms fault is 3800 V rms
•Sheath diameter 90mm •Conductor center to center distance 450mm
Using Figure 1 of IEEE 575 determine the sheath voltage radient for this confi uration at 1000 amps.
S
Selecting the SVL MCOV Rating Hand calculation of Induced Voltage on Sheath Step 3 Sheath voltage gradient fro m Figur e 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 sectio n 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
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 conduc tors of fl at layout E = 107 x (S/d) .369
Selecting the SVL MCOV Rating Hand calculation of Induced Voltage on Sheath Select t he SVL th at has MCOV one rating abov e the Max rms sh eath voltage for m aximum fault for t he .
with a 4.8kV MCOV
If the cable length was the correct choice
Selecting the SVL MCOV Rating Current in SVL on a 1 and 2km cable run .
-10 s vl_fault_analysis_with_wrong_svl.pl4; x-var t) c: 4.8kV MCOV on(file 2km lin e
0 -SVL1B
c:
-SVL1A
c:
-SVL1C
t:JOULES
t:TEMP
Checking Energy Handling If the SVL is chosen correctly, it will not adsorb . However it will during a switching surge
And during a lightning surge
SVL Switching Surge Analysis Large Switching Surge on Primary Conductor - With a MJ energy dissipation o the primary arresters 5kJ kV M 1.2 [MJ] 0.8 0.4 0.0 14.0
345kV Sheath 230kV Sheath 10kA 230kV Interrupt to Discharge Interrupt to Margin of Gnd BIL Vo tage Protect on Per IEEE 575 Per IEEE 575 kV % kV kV
345kV Margin of 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 th is 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.
ummary
O8
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 fro m 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 conduct or.
Summary When Selecting the MCOV Rating
HV Station Class Arrester The system line to ground voltage and TOV determine the MCOV rating. Sheath Voltage Limiter The voltage induced on the sheath from a fault in the phase conductor primarily determines the M V rating o the VL
Summary When Selecting the MCOV rating
HV Station Class Arrester In all cases, the station class arrester will provide adequate insulation protection. Sheath Voltage Limiter For longer segments of cable the AC rating may need to be closely checked and optimized arther on kV lines, but in most other cases, the Margin of Protection is not an issue once the AC rating is
