IEEE Power & Energy Magazine - July/August 2016 - 73

Network Planning

figure 1. Maintenance being performed on the transmission line in Guizhou. (Used with permission from CSG.)

planning is carried out by provincial government energy
departments, supported by electric power design institutes,
with the participation of the grid company. Generation planning considers long-term (15 years ahead) and mid-term
horizons (five years ahead). after the planning scheme is
approved by the central government, the design and construction of power plants are carried out by each generation
company. Transmission lines that connect the power plants
with the power grid are designed and constructed by the
grid company.
Generation planning has proven to be a most economic
power plant construction scheme based on predicting load
demand and the primary energy distribution, subject to certain reliability. The main processes of generation planning
include load prediction, consideration of the current and
under-construction generation, power and energy balancing, and proving the basic input for transmission planning.
renewable resources have priority dispatch in the planning
procedures at CSG.

0.243 GW,
Other, 0.10%

network planning is also carried out by the government,
supported by grid companies and electric power design institutes. Power System Technology Guidelines of China, which
is the main guidance for power system planning, separates
the power system into the receiving-end system, power plant
connection system, and the interconnection system. Based
on technical and economic requirements of each subsystem,
the guidelines lay down a series of standards for each subsystem. By following these standards to construct the power
system, the reliability and economics of power system construction can be balanced, that is, we can meet the precondition of total investment saving and meanwhile limit the risks
of large area blackouts.

Operation Challenges of CSG
HVdc Bipolar Block
hVdc bipolar block is an issue particularly for a hybrid ac/
dc system that has paralleled ac and dc transmission lines.
once an hVdc bipolar block occurs, bulk power will be
transferred immediately to the paralleled 500-kV ac lines,
resulting in an overload and drastic voltage drop. hence, it
may induce transient instability, cascading tripping of hVac
lines, and even system blackouts.
we have to adapt a defense plan, such as generator tripping and load shedding, to maintain the system stability
after an hVdc bipolar block. The defense plan involves
many substations, for example the special protection
system (SPS) of Yun-Guang hVdc bipolar involves protection equipment in 50 substations. if one of them fails
to operate, the stability of the power system will be
destroyed. in this case, even though out-of-step protection
acts correctly, an extremely severe power outage would
occur, that is, under-frequency load shedding or undervoltage load shedding devices at the receiving-end grid
act, resulting in up to 30% of the Guangdong power load
being cut off. The security of the large-scale power system is heavily dependent on the SPS.

Simultaneous Commutation Failure
of Multi-Infeed Hvdc Systems
102.303 GW,
Hydropower, 42.10%

128.304 GW,
Thermal, 52.80%

6.804 GW,
Nuclear, 2.80%
1.701 GW,
Wind, 0.70%

3.645 GW,
Pumped Storage,
1.50%

figure 2. Installed capacity in CSG.
74

ieee power & energy magazine

Since multiple hVdc inverter stations of CSG are located
close together in the receiving grid, one single ac system
fault may trigger simultaneous commutation failures in
multi-infeed hVdc systems. if an ac fault cannot be rapidly removed, there will be a voltage reduction, together
with complex interaction between dc and ac systems after
the commutation failure, which may lead to a lack of reactive power in the power recovery, dc block, and eventually
cause blackouts.
To enhance the ability to recover from dc commutation,
fast Var compensators will be implemented in the load center near the hVdc converter. Currently, four 500-kV substations in the Guangdong power grid have been equipped
july/august 2016

Table of Contents for the Digital Edition of IEEE Power & Energy Magazine - July/August 2016