Background
State Grid Ningxia is in the plateau of the northwestern part of China, where strong winds (27 m/s, 60 mph), ice and cold weather (-30°C), combined with desert heat (40°C) must be considered for the design of transmission lines.
There is a 10-mi (16-km), 330-kV circuit segment using a twin-bundle ACSR conductor JL/G1A-300/40 (slightly smaller than the ACSR Peacock), built in 2004. The rest of the 330-kV circuit has a twin-bundle ACSR conductor 2xJL/G1A-630/45 (slightly smaller than the ACSR Bittern). The 10-mi (16-km) line segment was rated for a 650-MW capacity (1364A, 70°C). By 2018, no overloading has occurred to this 10-mi (16-km) segment; however, there was no N-1 emergency capacity or ability to accommodate peak generation from renewables (about 4 GW local renewable generation in 2017). By 2020, an additional 1 GW was to be added from the local region to boost the local economy, and the power flow through the segment would reach 1016 MW, exceeding the capacity of the existing lines. The congested segment needed to be upgraded to have the same capacity as the 2xJL/G1A-630/45 circuits (2380A, 70°C, 1016 MW).
Options Evaluated
To accomplish the capacity increase without retrofitting towers and to keep the outage as short as possible (the project had to be completed before winter heating season), numerous CFCC conductors were considered due to their high current capacity, light weight, and superior sag characteristics. The options in Table 8 were considered.
Table 8. Conductor options considered
| Unit | JLRX1/F1 B-300/50 | JLRX1/F2 B-350/40 | JLRX1/F2 B-390/40 | JLRX1/F2 B-390/50 | JLRX1/F1 B-400/50 | JLRX1/LF2 B-350/40 | ||
|---|---|---|---|---|---|---|---|---|
| Area | Total | mm2 | 350.3 | 388.5 | 428.5 | 440.3 | 450.6 | 394.1 |
| Air | mm2 | 300 | 350 | 390 | 390 | 400 | 355.6 | |
| Core | mm2 | 50.3 | 38.5 | 38.5 | 50.26 | 50.6 | 38.5 | |
| Core property | RTS | MPa | 2100 | 2400 | 2400 | 2400 | 2100 | 2400 |
| OD | mm | 8 | 7 | 7 | 8 | 8 | 7 | |
| Conductor OD | mm | 21.9 | 23 | 24.15 | 24.46 | 25.9 | 23 | |
| Conductor weight | kg/km | 927.6 | 1035.1 | 1145.7 | 1167.6 | 1123.6 | 1046.6 | |
| 20°C Rdc | Ω/km | ≤0.0931 | ≤0.0798 | ≤0.0716 | ≤0.0715 | ≤0.0686 | ≤0.0783 | |
| Continuous operating temp | °C | 160 | 160 | 160 | 160 | 160 | 180 | |
| RTS | kN | ≥122.8 | ≥112.5 | 114.824 | 143.098 | ≥130.5 | ≥113.1 | |
| Max tension within sag limit | OK | OK | Exceed | Exceed | Exceed | OK | ||
The team concluded that the larger CFCC options exceeded the tension limit of the towers. The smallest conductor did not offer as much ampacity. The 23-mm sized composite conductors were selected for final consideration.
Installation Review
The 330-kV line reconductoring was completed without tower retrofitting in late 2018; the reconductored line was commissioned in early January 2019.
ACSR-type connectors were used for dead-ends (no splices were used). No training or supervision was required to install the conductor, except the initial demonstration on conductor handling. Figure 51 shows the completed line on a crowded corridor.
Figure 51. Completed 330-kV tower line
The field conditions were challenging because there were several line crossings, including one 330-kV circuit, three 110-kV circuits, numerous 10-kV circuits, and a major highway. Splicing was not permitted during installation. Several conductor segments were long (up to 5.5 km), and the conductor was pulled through 20+ sheave wheels. Preformed wires were used extensively in lieu of gripping clamps as a preference by the installation crew.