IEEE Power & Energy Magazine - March/April 2020 - 54

networks: transmission technologies at voltage levels of 1,000 kV
for ac and ±1,000 kV for dc. In this article, the development
of UHV transmission-system technologies and projects is
detailed, with a focus on the UHV ac transmission system.
In the Strong and Smart Grid plan, the concept of a strong
grid means that UHV systems will serve as the backbone of
the national network to ensure greater reliability and stability. At the same time, the operation of UHV systems requires
addressing technical issues such as reactive power management, voltage control, and safety. The development of "smart"
control and operation technologies is a goal of UHV-system
deployment. This article describes digital real-time simulation and energy-management systems (EMS) that model,
simulate, monitor, control, and analyze the large-scale ac/dc
power grids.
So far, only a handful of countries have implemented
UHV transmission systems, and there are very few international standards to guide their development. The State Grid,
the largest utility in the world, has embarked on a project to
develop UHV ac national and international standards. Best
practices for UHV ac transmission-network deployment
and the development of UHV ac standards are presented in
this article.

UHV Grid Experiences in China
The first 1,000-kV UHV ac endeavor, the Southeast Jin-
Nanyang-Jingmen line, was launched as a pilot project in
January 2009. It was built for a capacity of 3,000 MW and
expanded to 5,000 MW on 29 December 2010 for the next
phase of the program. Construction of the Huainan-Shanghai UHV ac project began on 27 September 2011 to provide 8,000 MW of transmission capacity between Anhui
and Shanghai. In March 2015, the North Zhejiang-Fuzhou
1,000-kV UHV ac double-circuit line was commissioned,
with 6,800 MW of transmission capacity. Those projects as
well as other UHV ac transmission lines are summarized in
Table 1. All of the UHV ac lines in the list are maintained
and operated by the State Grid. Encouraged by its success,

the utility plans to build 10 more UHV ac lines as well as
UHV dc lines by 2020, raising the total UHV transmission
capacity to 450 GW.

The First UHV ac Transmission-Line Project
The first 1,000-kV UHV ac transmission project was the
Southeast Jin-Nanyang-Jingmen line. The single-circuit
transmission line (with a length of 640 km) connects the
Changzhi and Jingmen substations through the Nanyang
switching station. Each 1000-kV substation was equipped
with one 3,000-MVA UHV main transformer [consisting of
three single-phase 1,000-MVA banks (3 × 1,000 MVA)]. To
compensate for the charging capacitance, a 960-MVA reactor
(Mvar) and 720-Mvar HV shunt reactor were installed on each
side of the Changzhi-Nanyang line segment, while a 720-Mvar
and 600-Mvar HV shunt reactor were added at each side of the
Nanyang-Jingmen section. At the low-voltage side of the
Changzhi and Jingmen stations, 840 Mvar (4 × 210 Mvar) of
shunt-capacitor banks and 480 Mvar (2 × 240 Mvar) of shuntreactor banks were installed.
The Southeast Jin-Nanyang-Jingmen project demonstrated huge benefits in energy transmission, loss reduction,
and emissions mitigation. From 2009 to 2011, the UHV ac line
transmitted 27.71 TWh of electricity, with losses amounting to
only 1.7%. Of that power, 9.2 TWh was hydroelectric, which
eliminated 9 × 106 tons of carbon-dioxide emissions.

UHV Overhead Transmission-Line
Technologies
The main components of UHV overhead transmission lines
are towers and conductors. UHV towers are designed to
meet electrical, mechanical, and economic requirements.
The most commonly used tower designs for UHV ac transmission-line projects in China are guyed, single circuit selfsupporting (either the cup- or cat-head type), and double circuit. The type of tower depends on the project requirements.
1) Guyed tower: A guyed tower consumes less steel but
occupies a larger area than a self-supporting one.

table 1. The 1,000-kV UHV ac transmission-line projects.

Project

Commissioned

Circuit

Installation
Capacity (MW)

Length
(km)

Southeast Jin-Nanyang-Jingmen pilot

January 2009

1,000-kV UHV ac single circuit

3,000

640

Southeast Jin-Nanyang-Jingmen
expansion

December 2012

1,000-kV UHV ac single circuit

5,000

640

Huainan-South Shanghai

September 2013