Project Description
The design capacity of the existing transmission lines varied between 60 and 100 MVA. Due to local constraints, new rights of way and new transmission line construction were not possible. City Power’s plan identified key network upgrade projects that had to be carried out to avoid network overloading.
Options Considered
City Power determined that, for the future, it would establish a 200-MVA capacity limit for existing lines to ensure adequate transmission capacity throughout the transmission network. This required a twofold increase in the capacity of the current transmission assets throughout the network. To achieve a doubling of capacity on the existing transmission network, the following options were considered:
- Increasing conductor tension on the existing transmission lines
- Increasing the conductor size on the existing transmission lines
- Installing new structures with a larger conductor
- Increasing the system voltage from 88 kV to 132 kV
- Installing a new high-temperature conductor on existing towers, while deenergized
- Installing a new high-temperature conductor on existing towers, while energized
- Installing a high-voltage underground cable system
Justification for HTC Selection
Various advanced conductors were reviewed. Based on the options evaluated (shown previously), the most technically and financially viable solution was to reconductor the existing ACSR UPAS (300-mm2 nominal Al area), Wolf (155-mm2 nominal Al area), and Goat (300-mm2 nominal Al area) ACSR-sized conductor lines with Lisbon (325-mm2 nominal Al area) HVCRC produced by Mercury Cable and Energy, Inc., and stranded by Hindusthan Urban Infrastructure Ltd.
Factors in the selection of HVCRC included the ability to operate at up to 180°C during peak loading conditions without clearance encroachments. This reconductor option also used the existing lattice support towers.
The HVCRC carbon composite core provides support for the aluminum conductor strands as the temperature increases under heavy loading (Figure 44). Accordingly, high-temperature compression accessories were used to ensure proper installation and operation. Although the connectors for the HVCRC are a new design, the connectors use conventional compression technology. There was no need for any special tooling or installation procedures other than taking care to diligently perform all required procedures with care and consistency. Figure 45 shows the installation of these connectors, and Table 6 shows a summary of options and issues surrounding them.
Figure 44. Mercury Cable HVCRC
Figure 45. Double compression dead-end connectors being installed
| Summary of Options | Resulting Issues Surrounding the Available Options |
|---|---|
| Reconductor with a larger diameter conductor or increasing the tension on existing conductors. | Towers were designed in the 1930s, erected in the 1950s. Considering current towers’ condition, they would not be able to handle additional loading with existing span lengths. |
| Reconductor existing towers with high-temperature conductors (deenergized line work). | Extended outages required. Not possible due to network loading. |
| Reconductor existing towers using HVCRC (high-voltage composite reinforced conductor). | Expensive compared to the conventional way of reconductoring. |
| Rebuild lines and install new towers with a larger diameter ACSR conductor. | Extended outages required. Not possible due to network loading. Towers to be changed. |
| Increase the system voltage from 88 kV to 132 kV. | Towers, power transformers, and related switchgear required replacing. Very expensive. |
| Install new high-voltage underground cable systems. | Very expensive option compared to all of the preceding options. |
Installation Review
Mercury Cable provided installation training and supervision, and the installation of the HVCRC and accessories was performed by Edison Power Group. As a result of the project, power delivery over the existing right of way and infrastructure was effectively doubled by replacing the existing ACSR conductors with the HTLS HVCRC.