August 2015
Maroeska Boots and Bieuwe Pruiksma
ENERGY
Tender Evaluation – Summary and conclusions
Occasion of the assignment
Current tendering procedures for power cable projects may be suboptimal,
ignoring certain criteria and lacking a long-term perspective, due to rather formal tendering processes. Accounting for these points might lead to different outcomes.
Therefore, ECI is looking for a simple evaluation tool to score tendering criteria in power cable projects, with the aim to assess what type of conductor is optimal.
DNV GL prepared a spreadsheet tool distinguishing relevant power cable segments and tender criteria. The tool can be used to score the segments, and the aim is to test the tool with a number of real projects. The overall scoring should result in recommended conductor types per segment.
Current
situation
Room for
improvement
The
assignment
Approach
First, the available information from relevant previous projects is summarized.
Then, general procurement policy and tender procedures with respect to power cables are discussed. This is based on available knowledge and information within DNV GL, and on the feedback of interviews conducted with DNV GL cable experts and with the procurement department of TSO and DNOs.
Subsequently, the different power cable segments, criteria and the assigned scores per segment for each criterion are described. An internal workshop with DNV GL power cable experts formed the basis for this.
Step 1:
What is
known
Step 2:
Tender info
Step 3:
Segments &
criteria
Finally, the spreadsheet tool is presented and the results are discussed.
Step 4:
Spreadsheet
Spreadsheet tool - Screenshot
Step Step 1 Step 2 Step 3
Choice
Score Relative score
Transport capacity 5 50%
Total cost of ownership -5 -50%
References 3 30%
Workability 0 0%
Reliability 0 0%
Environmental impact 1 10%
Total score 4 7%
Result per criteria
Input
Output
Introduction:
This tool can be used to see the score on tendering criteria for a certain high-level power cable segment. Both the score per criterion and the total score is presented, where the score is based on a qualitative assessment in terms of positive, neutral or negative for the use of a copper conductor compared to an aluminium conductor. The score is also expressed in relative terms (%), as per criterion a total score could be obtained in the range of -10 to +10 (because of a qualitative score in the range of -2 to +2 times a weight in the range of 1 to 5). Accordingly, the total score for copper compared to aluminium is divided by 60.
How to use this tool:
To use this tool, input is required with respect to which power cable segment is considered. Accordingly, 3 steps need to be taken (i.e. input) in order to obtain the right result (i.e. output):
- In step 1, a choice of the voltage level needs to be made: LV is ≤1kV, MV is between >1-36kV, and HV is >36-150kV - In step 2, one has to enter whether an onshore or an offshore power cable is considered
- In step 3, one can choose whether the main purpose of the power cable is transmission or distribution
Important note:
For proper functioning of the tool, please be sure to first change the input by clicking the drop-down list of step 1, then of step 2 and finally of step 3.
Evaluation tool to score criteria in power cable projects
The screenshot shows a brief
explanation, an input field
and the output.
For the segment indicated in
the input field, the output
field gives both the result
per criterion and the overall
result.
In addition, the relative
score is given, which is the
score divided by the
maximum score.
The score reflects the
performance of copper
compared to aluminium.
Results – Scores per criterion and power cable segment
Power cable segments
Voltage level HV, >36kV-150kV MV, >1-36kV LV, ≤1kV Transmission/distribution Transmission Transmission Distribution Distribution Onshore/offshore Onshore Offshore Onshore Offshore Onshore Onshore Criteria
Transport capacity
Score 1 1 1 1 1 0
Weight 4 5 3 4 3 1
Result 4 5 3 4 3 0
Total cost of ownership
Score -1 -1 -1 -2 -1 -1 Weight 5 5 5 5 5 4 Result -5 -5 -5 -10 -5 -4 References Score 0 1 0 1 0 0 Weight 2 3 1 1 1 2 Result 0 3 0 1 0 0 Workability Score 0 0 1 1 1 0 Weight 3 2 4 4 4 5 Result 0 0 4 4 4 0 Reliability Score 0 0 0 0 0 1 Weight 4 5 5 5 4 2 Result 0 0 0 0 0 2 Environmental impact Score 1 1 1 1 1 1
Main results
The significance or value of the results is not very high, since overall results per power cable segment only varies between -1.7% to +6.7% (positive sign
indicating a preference of copper over aluminium). This implies that the difference in performance between using a copper or an aluminium conductor in tendering processes is not that large.
In tendering for power cable, we expect that:
• At the LV level, the use of an aluminium conductor is beneficial compared to
copper, which is mainly due to the higher total cost of ownership for copper. This might be one of the factors explaining the increased use of aluminium
conductors at the LV segment for the larger cables (e.g. 4*150mm2).
• At the MV level, the use of a copper conductor is beneficial for onshore cables
compared to the use of an aluminium conductor. This is somewhat surprising, as more and more aluminium conductors are used in this segment.
• At the HV level, the use of a copper conductor is preferred for offshore cables,
while for the onshore cable there is no difference.
Copper performs equal or better compared to aluminium for each segment for all criteria, except for total cost of ownership. However, the weight factor contributes to the fact that the overall result (sum over criteria) per power cable segment does not differ that much (from -1 to +4, while the theoretical range is -60 to +60).
The order of most important criteria in terms of the weight factor is total cost of ownership, reliability, workability, transport capacity, references and environmental impact.
Conclusions
Given the scoring results on theoretical cases in power cable tendering
• The use of a copper conductor is slightly preferred for the power cable segments
HV offshore and for MV onshore, with about 7% and 5% respective advantage of copper above aluminium. For the MV segment this might be surprising, as more and more aluminium conductors are used in the MV onshore segment, and may require further investigation.
• For the MV offshore and HV onshore cable segment there is no difference.
• The use of an aluminium conductor is slightly preferred for the LV power cable
segment, although the difference in performance is marginal (2%). This might be one of the factors explaining the increased use of aluminium conductors at
the LV segment for the larger cables (e.g. 4*150mm2). However, the use of
copper conductors will probably remain preferred for the smaller LV cables and for public lighting. However, such specific cases has not been evaluated in this study.
Documentation on finalized real life projects could not be retrieved from the TSOs and DSOs. This would have been useful to compare and test the results of the tool for a certain power cable case.
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