System Vision Investigation
Grid Vision
(Technical Feasibility)
330/400 kV Transmission Line Upgrade Study
Analysis of costs and Practicality of upgrading two existing
220 kV lines to 330 kV Operation
Ref: SVI 104.03.04 030825 R1
August 2003
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Version History
Version
Date
Nature of Amendment
Issue 1
25 Aug 03
Distribution List
Person
Position
Copy #
Chandra Kumble
Project Director System Vision Investigation
1
Graham Marriott
Project Manager System Vision Investigation
2
Mohamed Zavahir
Technical Manager System Vision Investigation
3
Ranjith de Silva
Transmission Line Design Leader
4
Prahlad Tilwalli
Technical Manager System Configuration
5
Signoff
Person
Position
Signature
Date
Prepared by:
Ranjith de Silva
Transmission Line
Design Leader
Reviewed by:
Technical Manager
Mohamed Zavahir
Technical Feasibility
Grid Vision
Endorsed by:
Project Manager System
Graham Marriott
Vision
Approved by:
Project Director System
Chandra Kumble
Vision
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Table of Contents
1.
Executive Summary
2.
Purpose
3.
Introduction
4.
Scope of Investigation
5.
Summary of Findings from PLS Study
6.
Limitations of Investigation
7.
Sensitivity Analysis
8.
Comments on conversion of SFD-TMN A and HLY-TMN A Lines to
330 kV
9.
Conclusions
Appendix A – References
Appendix B - Scope of work provided to Power Line Solutions
Appendix C – Conductor Details and new 330/400 kV Tower Weights
Appendix D – PLS Report on 330/400 kV Line Upgrade Study
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1.
Executive Summary
A high level investigation based on the preliminary design criteria has shown
that the cost of converting the ROX-ISL A and OTA-WKM A 220 kV lines for
330 kV operation is about 75% of a new line cost, if continuos and unrestricted
outages can be obtained to build.
However, planning studies indicates that outages will be possible only around 1
a.m. to 6 a.m. during summer months even as early as 2005 and becomes even
more restrictive in the subsequent years.
When practicality and provision for minimising outages are taken into account,
the cost of conversion varies between 107% and 112% of new line costs. .
Therefore the conversion of the above two lines to 330 kV operation is not
considered to be a viable or a practical option.
The conversion of SFD-TMN A and HLY-TMN A 220 kV double circuit line
to 330 kV double circuit is neither feasible nor economic.
2.
Purpose
To present the findings of the high level investigation conducted on the
practicality of converting existing 220 kV lines for 330 kV operation.
This report is based on a very high level preliminary engineering work
completed on two core grid lines namely, ROX-ISL A (ISL-LIV section) and
OTA-WKM A lines. Overview comments on the practicality of converting
SFD-HLY A line to 330 kV double circuit are also included.
3.
Introduction
As part of the Grid Vision investigations, a high level analysis of converting
some of the existing 220 kV circuits to 330 kV was undertaken. In addition, the
options of building new 330 and 400 kV single and double circuit lines are also
being investigated.
Teshmont Consultants have carried out a Pre-feasibility study of converting
some of the existing 220 kV lines (Ref. 2). The preliminary results indicated
that it may be possible to convert to 330 kV and that the cost of the upgrade
varies from 35 to 80% without allowing for practicality issues.
In order to assess the practicality of conversion as well as to narrow down the
costs,
Power line Solutions (PLS) NZ Ltd was engaged to complete a high
level quantitative analysis of the practicality of conversion and to derive
associated costs, based on preliminary design information provided by
Transpower.
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The references used in this report are provided in Appendix A.
A copy of the PLS report is included in Appendix C.
4.
Scope of Investigation
Phase 1 of the System Vision Project includes the investigation of technical
feasibility of conversion of three critical transmission lines, namely ROX-ISL A
(LIV-ISL section), OTA-WKM A and HLY-SFD A lines, to 330 kV operation.
However,
PLS brief included only ROX-ISL A and OTA-WKM A lines.
The scope for PLS included
:
Ø Practicality of upgrading existing structures for 330 kV operation
Ø Outage requirements for strengthening works and for installing new
conductors
Ø Work methods to reduce outage durations
Ø live-line maintenance constraints on existing structures
Ø order of magnitude cost estimates for conversion options
Ø Comparative costs for new 330 and 400 kV lines.
A detailed scope is provided in Appendix B.
Transpower provided the following information as input to PLS investigation.
- Extent of structural modifications and height increases required on the
towers for conversion of 220 kV single cct towers to 330 kV (for ISL-LIV
section of ROX-ISL A and OTA-WKM A lines)
- Approximate weights of tower steel required for strengthening existing
220 kV towers for 330 kV operation
- Average tower weights for new 330 and 400 kV lines.
- Comments from Field Services and Network support on various
practicality aspects of conversion options.
Reports from the preliminary feasibility engineering assessment by Teshmont
Consultants were also made available to PLS prior to this work.
Tower weights for new lines were estimated from outline drawings based on
spacing and clearance requirements to comply with the preliminary design
criteria formulated by the Technology and Engineering (T&E) Group and
conductor selection completed by Meritec.
Appendix C provides details of conductor configurations and weights of new
330/400 kV Towers used in the analysis.
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5.
Summary Findings from PLS Study
Main findings from the PLS study are:
Ø Conversion of the two lines for 330 kV operation is feasible
Ø Cost of conversion to 330 kV with continuos and unrestricted outages is
about 75% of a new line cost with equivalent transfer capability.
Ø If outages are to be minimised using temporary bypass lines, then the
conversion cost becomes approximately 107 to 112 % of new line costs
Ø Bare hand live maintenance is not feasible on converted lines compared to
new build lines.
The cost of achieving bare hand capability on new lines is only marginally
higher. Therefore if the costs were adjusted to remove this facility from new
lines, it is not expected to alter the cost relativity to any significant level.
Alternatively to include barehand capability on converted lines would mean
major modifications to the tower superstructure.
Table 1 highlights the order of magnitude cost estimates and estimated outage
periods required for line construction. The overall durations of construction,
however, will depend on the availability of outage windows. This could span a
few years depending on the options taken and on availability of outage
windows.
Table 1 - Summary of Overall Estimated Costs and Outages
Optio
Cost
Outages
Line
n Ref
Description
$M
Days
#
1
Conversion to 330 kV using outages for
71
129
wiring
ROX
2A
Conversion to 330 kV using bypasses and
99
89
ISL
outages to connect and disconnect
A
2B
Conversion to 330 kV using bypasses & live
99
15
(ISL-
work to connect and disconnect bypasses
LIV)
3
New 330 kV single circuit line parallel to the
93
2
existing line
1
Conversion to 330 kV using outages for
54
106
wiring
2A
Conversion to 330 kV using bypasses and
82
74
OTA
outages to connect and disconnect
WK
2B
Conversion to 330 kV using bypasses & live
82
12
M A
work to connect and disconnect bypasses
3
New 330 kV single circuit line parallel to the
73
2
existing line
Note – (1) above figures do not include cost of easements, land
acquisition, RMA compliance costs or outage related costs, but
includes design and project management costs
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(2) Cost of dismantling existing lines, which may happen with option 3
are not included in the costs. These will be considered separately in the
overall economic analysis.
The PLS report has been reviewed internally by Field Services and Network
Support.
5.1 General
It should be recognised that within the accuracy of estimates (30%) the
conversion costs are in the same order of magnitude as the new line costs, with
out the cost of outages.
Estimated costs from PLS are based on budgetary prices of main materials.
Estimates of erection rates are based on productivity levels in Australia and
New Zealand. Preliminary inquiries indicate that the tower steel supply rate
could vary as much as 100% depending on the country of origin. This can
amount to a variation of upto about 20% in the total installed costs given in the
PLS report.
There are also some intangible aspects associated with the different options that
cannot be easily quantified. These aspects are compared in Table 2.
Table 2 - Comparison of modified and new 330 kV single circuit lines.
Item
Modified existing line
New 330 kV SC Line
Tower Strength
Barely
meets
current Adequately meets current
design Criteria
design criteria
Reliability
Acceptable
High
Tower Condition
Need to repaint every 10-
Structural integrity will
20 years to maintain
be maintained for at least
structural integrity
60 yrs+ without painting.
Foundations
2/3rds new concrete
All new concrete
1/3rd grillages converted
to concrete
Conductor
New twin Moose
New twin Moose
Insulation
New composite
New composite
Earthwires
1 OPGW and 1 A/C Steel
1 OPGW and 1 A/C Steel
Live Work Constraints
Hot stick access only
Full bare hand access
Ongoing Maintenance
Average
Below average
Costs
Avoided Future
Moderate
High
Maintenance
It must be noted that the converted towers do not have provision for bare hand
maintenance work. A proper comparison can only be made if this can be
quantified. The maintenance costs during the first 30 to 40 years will normally
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be limited to replacing insulators from flashover incidents. These will be very
rare and not predictable. Alternatively provision for bare hand capability on
converted towers will result in major modifications to towers.
5.2 Option 1 – Conversion with total outages
Option 1 requires 129 and 106 days of continuos outages for ISL-LIV and
OTA-WKM A lines respectively. It is extremely unlikely that long outages can
be obtained for the reasons given below.
Indications from load duration curves for the Canterbury region are that it is
only feasible to have the outages during the period 1 a.m. to 6 a.m. in summer
months, even as early as the year 2005 (ref 4, Appendix A). A similar situation
exists in the Central North Island region
The outage period can be significantly reduced (from 129/106 to 2 days) with
new line construction
Therefore Option 1 cannot be considered as a viable or practical option.
5.3 Option 2A – Conversion with temporary bypass lines
Option 2A also requires 89 and 74 days of outages for ISL-LIV and OTA-
WKM A respectively. The costs for this option are 7 to 12% higher than that for
a new line and
therefore unlikely to become a preferred option.
5.4 Option 2B - Conversion with temporary bypass lines and live
connection/disconnection of bypasses
Option 2B requires 15 and 12 days of outages for ROX-ISL A and OTA-WKM
A respectively and have been based on the assumption of being able to connect
and disconnect bypasses using live line techniques. As these techniques have
not been used so far in New Zealand, they may need significant development
and trialing prior to implementation.
However, as for option 2A, due to higher
costs this option is not favoured.
5.5 Option 3 – New Line Construction
Out of the viable options, the new line cost is 7 to 12% cheaper than the
conversion options with bypasses. In addition the new line will be fully
compliant and will have reduced maintenance costs.
Accordingly it is
considered to be the preferred option for 330 kV.
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6. Limitations of the Investigation
The investigation has the following limitations
Ø
Tower strengthening requirements for conversion to 330 kV
Only the predominant tower type (standard suspension) was analysed on both
lines. Tower strengthening requirements for other tower types have been
extrapolated. It is possible that the extent of strengthening and therefore the extra
steel weights could vary when subjected to detailed designs. Therefore, if more
tower steel is required for strengthening, then additional costs will occur for
conversion to 330 kV making it more costly.
Ø
Tower crossarm lengths on existing single circuit towers
The crossarm lengths were found to be adequate for 330 kV based on tower
outline drawings produced earlier by Teshmont. It appears that the insulator
lengths used by Teshmont were shorter compared to data received from Maclean
Power Systems (MPS) in USA.( MPS is a regular supplier of insulators and
fittings to Transpower). The maximum allowable swing angles with the existing
towers will be limited to about 47 deg in comparison to 65 deg used on new
tower designs. Tower strengthening weights will increase significantly if longer
arms have to be provided. This is not considered to be a major deficiency.
However, this will impact negatively on 330 kV conversion option.
Ø
Conductor selection was based on preliminary deign criteria
Design criteria with regard to allowable RFI and EMFs is yet to be finalised.
These parameters can influence the conductor sizes, phase spacings and tower
heights and hence changes to these limits will change the overall costs. This will
apply to both new and converted lines.
Ø
Tower steel supply rate
This rate can vary within wide limits depending on the origin. A budgetary price
from the only Australian supplier is still awaited and in the meantime a median
price has been used. The impact on the overall cost is about 20% of the change in
the steel price.
Ø
Tower height increases to meet EMF requirements for conversion option
The tower height increases for 330 kV were based on a cursory examination of
limited ALS data available and existing profile drawings. Existing profile
drawings sometimes do not reflect the actual site conditions due to changes in land
use and design/construction errors. Once again this will have a negative impact on
the conversion option.
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Ø
New Line costs
New line costs are constructed from estimated material quantities and unit prices
for materials and erection rates. In the absence of any preliminary line design
work, the tower quantities for new lines were based on tower for tower
replacement of existing lines. Economic line designs may be possible on green
field line routes.
These costs exclude easement, land, RMA compliance costs as well as any
dismantling costs of existing lines that the new lines replace.
7. Sensitivity Analysis
A sensitivity analysis is carried out in the next section to establish the influence
on the overall analysis.
7.1 Increase in Crossarm lengths
This is based on needing additional 0.6 T of steel per tower to allow for swing
angles upto 65 ο (the limit on converted towers without arm extension is 47 ο )
Table 3 – Extended outer phase crosarms- ROX-ISL A
Option
Description
Base
Revised
Cost
Cost
Estimate
$ m
$ m
1
Modify Existing line with 100%
70.7
74.8
Outages
2A
Modify Existing with Bypasses &
99.1
103.1
Outages
2B
Modify Existing with Bypasses &
99.3
103.4
Live Work Outages
3
New 330 kV Single Circuit
92.7
92.7
The increase in total costs is about 6%, which is within the accuracy of the
estimates.
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7.2 Tower Steel Supply Rate
Table below shows the sensitivity of tower steel supply rate changing by
±20%.
Table 4 – Tower Steel Supply rate - ROX-ISL A
Option
Description
Base
Revised Costs
Cost
$ m
Estimate
$ m
-20%
+20%
1
Modify Existing line with 100%
70.7
70.6
70.9
Outages
2A
Modify Existing with Bypasses &
99.1
98.9
99.2
Outages
2B
Modify Existing with Bypasses &
99.3
99.2
99.5
Live Work Outages
3
New 330 kV Single Circuit
92.7
87.9
97.5
As expected the variation for option 1, 2A and 2B are minimal as these options
use only small quantities of imported tower steel (mainly for totally replaced
towers). For option 3, the overall costs changes by about 5%.
It is very unlikely that the price of steel will increase when exposed to
competitive tendering. Most probably the price will be lower which makes the
new line build more attractive.
The sensitivity analysis shows that option 3 remains attractive even if the
tower steel price increases by 20%.
7.3 Variation in the extent of Strengthening
This is probably the single item that could vary within wide limits, as the
weights have been estimated based on a very high level analysis. It is unlikely
that the estimated strengthening steel to be lower. The table below shows the
sensitivity based on the assumed weights increasing by 10% and 30 %. The
analysis clearly demonstrates how the relativity can change with even a
moderate increase in the extent of strengthening. It is possible that increases in
excess of 30% to be needed when subjected to detailed structural analysis.
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Table 5 – Tower Strengthening Steel - ROX-ISL A
Option
Description
Base Cost
Revised
Revised
Estimate
Cost-
Cost-
$ m
Weights up
Weights up
by 10%
by 30%
$ m
$ m
1
Modify Existing line
70.7
72.4
75.7
with 100% Outages
2A
Modify Existing with
99.1
100.7
104.1
Bypasses & Outages
2B
Modify Existing with
99.3
101.0
104.3
Bypasses & Live Work
Outages
3
New 330 kV Single
92.7
92.7
92.7
Circuit
For 10% to 30% variations in tower steel weight, the overall costs increase by
about 2% and 7% respectively.
However, as the new line build is not subjected to this variation, option 3
becomes more attractive.
7.4 General Comment on Sensitivity Analysis
The sensitivity of most of the aspects on estimated costs vary between 2 and
7%, which is within the accuracy of the estimates. However, the single item that
can significantly affect the relativity between conversion and new build options
is the extent of strengthening of existing towers. This will have a major
influence on the cost of the conversion options but not on the new build option.
Even though the sensitivity analyses has been done only for ROX-ISL A line,
similar comparisons can be drawn for OTA-WKM A line as well.
Depending on the extent of variations in the individual items, it is possible for
the conversion costs with total outages to exceed that of new line costs.
8. Conversion of SFD-TMN A and HLY-TMN A lines to 330 kV
These two lines form part of the 220 kV double circuit line from Stratford to
Huntly commissioned during 1987-1988. The lines were designed and built for
carrying single Zebra conductors per phase with a designed maximum operating
temperature of 120 ο C.
A major part of SFD-TMN section runs through extremely rugged terrain,
which presented several challenges during construction. Most tower sites are
perched on very narrow edged ridge tops
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As 330 kV operation requires heavier conductors and larger electrical
clearances, the conversion of these lines to 330 kV double circuit require major
alterations to the upper part of the tower body. A high level comparison of the
tower design loads for the most common tower types with loadings that would
be imposed even with twin Zebra conductors indicate excessive overloading.
The extent of overloading is illustrated in table 6.
Table 6 – Comparison of Tower Design Loads
Transverse Load
Vertical Load
Tower Type
Tower
Site specific for
Tower
Site
Design
2xZebra
Design
specific for
2xZebra
kN
kN
kN
kN
C806 Type 0
11.7
23.7 (202%)
21.6
13.2
C806 Type 1
11.7
31.4 (268%)
32.4
16.9
A high level check was also done on the loading of main members below the
waist. This indicates approximately 135% loading for Type 0 and 120% for
Type 1, confirming that significant strengthening would be required even to
install twin Zebra conductors.
To comply with RFI and Noise limits, double circuit 330 kV requires triple
conductors with diameters bigger than 30 mm (existing conductor is single
Zebra with a diameter of 28.6 mm) per phase. The overloading levels in table 6
indicate that practically the whole tower would need to be replaced for
upgrading the lines to 330 kV double circuit.
Some parts of the line runs through very rugged terrain with towers located on
very narrow ridge tops. The use of existing easement on such sections will be
difficult if not impossible.
From this high level analysis it appears that the conversion of SFD-TMN A and
HLY-TMN A line for 330 kV double circuit is neither feasible nor economic.
9. Conclusions
Based on this high level investigation on practicality aspects and costs, it is
concluded that for ROX-ISL A and OTA-WKM A lines:
• Option 1 (conversion with full outages) is not worth pursuing due to
inevitable system constraints and the outage requirements being not
practical and its inability to provide bare hand live line maintenance
capability.
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• Option 3 (new line construction) is preferred to Option 2A or 2B
(conversion with bypasses) as this option is about 4 to 7% cheaper than
options 2A or 2B.
• In the event that any of the conversion options (1, 2A or 2B) become a
preferred option after an overall economic analysis, then it is considered
essential to revisit the cost estimates with a more detailed engineering
analysis to ensure that the relativity of costs between various options remain
unchanged.
The conversion of SFD-TMN A and HLY-TMN A line for double circuit 330
kV operation is neither feasible nor economic. It may be feasible to convert this
line to 330 kV single circuit line, but this option has not been fully investigated
as the thermal capacity will be lower than that for the existing 220
configuration.
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APPENDIX A
References
1. Transpower Draft Standard - Design and Performance Criteria for 330 and
400 kV Transmission lines – Revision 1, 7 July 2003
2. Teshmont Consultants Preliminary Investigations Summary Report – March
2003
3. Conductor Selection Report -Rev 2 , July 2003, Meritec LTD
4. Internal Memo on Load curve for Canterbury Region and North dated 8 Aug
2003 – Carmen Yip to Mohamed Zavahir
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APPENDIX B
SCOPE OF WORK PROVIDED TO POWER LINE SOLUTIONS
As part of a high level assessment of the impact on the above issues, Transpower has
completed a preliminary structural analysis on one representative tower type (standard
suspension) on each of the following lines.
(a) ROX-ISL A
(b) OTA-WKM A
The structural analysis has identified the structural components that need to be
modified for 330 kV operation. The combined weights of these components have also
been estimated. On some locations it may be necessary to raise the towers by about 2
to 3.0 m and erect the modified tower on new foundations to meet the required ground
clearances.
The 330 kV conversion also requires the conductors to be replaced with new duplex
conductors of at least 33 mm in diameter and new 330 kV insulators. ACSR
BUNTING has been used in the structural analysis. (Tower out line drawings showing
the modifications is attached).
Please investigate and report on the constructibilty, outage durations and rough order
costs (erection only) for completing the following activities on each section of the
above lines.
1. Strengthen and modifying the tower with out any body extensions
2. Strengthen and modifying the tower with a 3 m body extension and erecting on
new foundations adjacent to existing one.
3. Re-insulating and installing new conductors on approximately 10 km section on
terrain representative of the line. It may be assumed that the line section consist of
all standards suspensions and two strain towers. All strain towers can be assumed
to be replaced with new towers and foundations. Costs should be assessed for two
scenarios: building with outages as required for various activities and building
with a temporary by pass line constructed to minimise outage durations.
4. The cost of building a new line of the same length and number of structures as in
(3), adjacent to the existing line. Tower weights can be assumed to be similar to
the existing ones.
5. Order of magnitude costs for any modifications required on existing structures to
provide live line maintenance facility.
400 kV Line Costs
Please provide material and erection costs new 400 kV single and double circuit lines
based on overseas utility experiences with recently installed lines customised for New
Zealand situation.
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APPENDIX C
Preliminary Conductor Selection and Conductor Configurations used in the
Analysis
Nominal
Circuit
Conductor and
Conductor
Voltage
Configuration
Configuration
Diameter
(kV)
(mm)
Single Circuit
Duplex Moose
31.77
330
Double Circuit
Triplex Cardinal
30.38
Single Circuit
Duplex Chukar
40.68
400
Double Circuit
Quad Goat
25.97
Tower Weights used in the Analysis for new 330/400 kV Towers
Nominal
Circuit
Tower Type
Tower
Voltage kV
Configuration
Weight
(Tonne)
Suspension
10
Single Circuit
Angle
18
330
Strain
22
Suspension
14
Double Circuit
Angle
22
Strain
30
Suspension
12
Single Circuit
Angle
20
400
Strain
25
Suspension
16
Double Circuit
Angle
25
Strain
35
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APPENDIX D
PLS Report on 330/400 kV Line
Upgrade Study
Version: Final
22 August 2003
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