4 The Transition of China’s Power System
141
• 1000 kV Ximeng-Shandong UHV AC project (2016), with a conversion capacity
of 15 million kW;
• 1000 kV West Mongolia-South Tianjin UHV AC project (2016), with a conversion
capacity of 24 million kW;
• 1000 kV Huainan-Nanjing-Shanghai UHV AC project (2016), with a conversion
capacity of 12 million kW;
• 1000 kV Ximeng-Shengli UHV AC project (2017), with a conversion capacity of
12 million kW;
• 1000 kV Yu Heng-Weifang UHV AC transmission and transformation project
(2017), with a conversion capacity of 15 million kW.
4.3.1.4 Comparison of Two Technological Options
China’s UHV transmission network has always been characterized by a combination
of AC and DC. The replacement of UHV AC grid by UHV AC backbone network and
proper utilization of UHV AC/DC transmission for regional grids interconnection
and synergy have proved to be vital to power delivery from major energy production
bases and power transmission to remote areas (Peng et al. 2017).
Meanwhile, both technology options have their own characteristics. UHV DC
transmission technology is featured by Zhou and Zhong (2007): (1) large transmission capacity, high voltage class, narrow line corridor, suitable for high-power transmission in long distance; (2) no drop point, clear and simple architecture, and direct
transmission of power to the load center without synchronous operation between
networks; (3) equipment compromise by high-power impact on the AC system at
both ends due to DC system locking.
UHV AC transmission technology is featured by Zhou and Zhong (2007): (1) large
transmission capacity, wide coverage, minor network loss, small number of transmission corridors, and suitable for large-capacity transmission in short distance; (2)
existence of drop point, the ability of building backbone network based on actual
needs of power distribution, load position, power transmission and exchange; (3) variation of transmission power affects reactive power at the transmitting and receiving
ends, triggering chain reaction and even voltage instability.
In contrast to UHV AC, UHV DC long-distance transmission boasts low construction cost of long-distance overhead lines (as shown in Fig. 4.20) (Wen et al. 2012),
minor loss, large transmission capacity, narrow transmission corridors, easy access
to long-distance transmission, high reliability and high energy utilization (as shown
in Tables 4.10 and 4.11), etc.
With the rapid development of UHV transmission network in China, notable
changes have occurred in the running of power grids, with some regions experiencing much stronger DC than AC (Zhang and Gong 2016). Overlapping UHV
AC synchronous grids on the existing trans-regional UHV DC transmission would
produce a complex parallel of AC and DC, which is prone to new stability issues and
might incur potential security risks. Therefore, grid security and reliability should
warrant more attention.
141
• 1000 kV Ximeng-Shandong UHV AC project (2016), with a conversion capacity
of 15 million kW;
• 1000 kV West Mongolia-South Tianjin UHV AC project (2016), with a conversion
capacity of 24 million kW;
• 1000 kV Huainan-Nanjing-Shanghai UHV AC project (2016), with a conversion
capacity of 12 million kW;
• 1000 kV Ximeng-Shengli UHV AC project (2017), with a conversion capacity of
12 million kW;
• 1000 kV Yu Heng-Weifang UHV AC transmission and transformation project
(2017), with a conversion capacity of 15 million kW.
4.3.1.4 Comparison of Two Technological Options
China’s UHV transmission network has always been characterized by a combination
of AC and DC. The replacement of UHV AC grid by UHV AC backbone network and
proper utilization of UHV AC/DC transmission for regional grids interconnection
and synergy have proved to be vital to power delivery from major energy production
bases and power transmission to remote areas (Peng et al. 2017).
Meanwhile, both technology options have their own characteristics. UHV DC
transmission technology is featured by Zhou and Zhong (2007): (1) large transmission capacity, high voltage class, narrow line corridor, suitable for high-power transmission in long distance; (2) no drop point, clear and simple architecture, and direct
transmission of power to the load center without synchronous operation between
networks; (3) equipment compromise by high-power impact on the AC system at
both ends due to DC system locking.
UHV AC transmission technology is featured by Zhou and Zhong (2007): (1) large
transmission capacity, wide coverage, minor network loss, small number of transmission corridors, and suitable for large-capacity transmission in short distance; (2)
existence of drop point, the ability of building backbone network based on actual
needs of power distribution, load position, power transmission and exchange; (3) variation of transmission power affects reactive power at the transmitting and receiving
ends, triggering chain reaction and even voltage instability.
In contrast to UHV AC, UHV DC long-distance transmission boasts low construction cost of long-distance overhead lines (as shown in Fig. 4.20) (Wen et al. 2012),
minor loss, large transmission capacity, narrow transmission corridors, easy access
to long-distance transmission, high reliability and high energy utilization (as shown
in Tables 4.10 and 4.11), etc.
With the rapid development of UHV transmission network in China, notable
changes have occurred in the running of power grids, with some regions experiencing much stronger DC than AC (Zhang and Gong 2016). Overlapping UHV
AC synchronous grids on the existing trans-regional UHV DC transmission would
produce a complex parallel of AC and DC, which is prone to new stability issues and
might incur potential security risks. Therefore, grid security and reliability should
warrant more attention.