THE UNIVERSITY OF DANANG, JOURNAL OF SCIENCE AND TECHNOLOGY, NO 6(91) 2015 1 ASSESSING THE IMPACT OF DUYEN HAI THERMAL POWER SYSTEM CENTER ON THE STABILITY OF THE ELECTRICAL POWER SYSTEN OF VIETNAM Ng[.]
Trang 1THE UNIVERSITY OF DANANG, JOURNAL OF SCIENCE AND TECHNOLOGY, NO 6(91).2015 1
ASSESSING THE IMPACT OF DUYEN HAI THERMAL POWER SYSTEM CENTER ON THE STABILITY OF THE ELECTRICAL POWER SYSTEN
OF VIETNAM
Ngo Van Duong
The University of Danang; nvduong@ac.udn.vn
Abstract - Duyen Hai thermal power center has a gross installed
capacity of 4490MW, connected to the power system of Vietnam
through 220kV and 500kV voltage levels Therefore, the operating
mode of the plant has a strong influence on the stability of the power
system This paper presents the results of calculations to assess the
effects of the plant and proposes solutions to improve the Vietnam
power system stability Operating mode of the plant may alter the
stable reserve ratio of the whole system In operating process, it is
necessary to pay attention to Duyen Hai thermal power center to
generate high capacity in the peak mode of load in the Southern
region After putting the project into operation, it should be calculated
to install compensation station SVC at Phu Lam bus
Key words - Duyen Hai thermal power center; the operating mode;
voltage collapse; r egional stable operation; stability
1 Problem
The 500kV line has been put into operation since 1994
that merged power systems (PS) of 03 regions into a unified
system Since the day of being merged, the Vietnam PS has
continuously grown in additional charge, reaching an
average speed of approximately 13.85%/year In order to
meet the demand of power supply for economic
development, Vietnam Power Corporation has submitted
master plan of national power development to the
Government for approval for the period 2011-2020 and
vision to 2030 (Master Plan VII) Acordingly, the power
projects have planned for construction substantially which
will form the major power centers in the region
Transmission grid system, the transformer substations will
be built synchronously with the development of power
supplies Coal, thermal power, nuclear power and
regenerated energy are still the most important power
supplies, accounting for a relatively high proportion in the
period 2010-2020 Besides, hydropower remains unchanged
market share for the reason that hydropower has been
almost exhausted on a national scale By 2020, the gross
installed capacity of power plants in the country will be
about 75,000 MW, of which hydropower will account for
23.1%; storage hydropower for 2.4%; coal thermal power
for 48.0%; gas-fired thermal power for 6.5% (including
2.6% LNG); regenerated energy used power supply for
2.6%; nuclear power 1.3% and imported power for 3.1%
Duyen Hai thermal power center (TPC), which is the
biggest center connected to theVietnam PS, including 4
coal-fired thermal power plants 1, 2, 3 and 3 extended with a gross
installed capacity of 4490MW, was built in Duyen Hai
District, Tra Vinh Province Duyen Hai TPC was
constructed in 2010, so far it has completed the construction,
power on and put Duyen Hai 1 thermal power plant into
operation with a total capacity of 1.245MW including 2 sets
2x622, 5MW As planned, the center will be completely
constructed and put into operation by the end of 2017 [2, 3]
Duyen Hai TPC not only has large installed capacity but also is a connection with Vietnam PS through 220kV and 500kV voltage levels Therefore, operating modes of the plant has a strong influence on the stability of the PS It is necessary
to have calculation and assessment to propose solutions for improvement of operational reliability of the PS
2 Assessment of stability under voltage collapse curve and regional stable operation [4, 6, 7]
2.1 Stable reserve ratio and voltage collapse curve
Figure 1 Regional stable operation
In order to calculate the reserve ratio for the PS and build voltage collapse curve at the normal nodes for load that changes under typical script (also called natural script)
A typical scrip tis that active power and reactive power of all load node sin the system are increased simultaneously
under the same rate until the system loses stability
On that basis, a stable reserve ratio is determined by the
formula:
Kdt=P∑gh− 𝑷∑ 𝒐
P∑o
In which: P∑gh, P∑o – the gross capacity at limited mode
and originalmode
During heavy mode at typical script, consecutively calculate the mode established under the script to determine the voltage value at the buses, use this data tobuild voltage variation curve at the buses in the system According to pragmatic standards of Markovits, the stability of PS has been linked to the derivatived Q/dU, thus accessing stability uses sensitivity factor that is the inverse of this quantity Sensitivity factors are determined
in the process of parameters variability to build curve of voltage collapse (dU /dQ)
2.2 Regional stable operation
For the load nodes, in order to evaluate the ability to change capacity under stable conditions, regional stable operation in the powerplane is commonly used To build a regional stable operation, we vary capacity at load nodes in various directions until PS changes from steady state to
Trang 22 Ngo Van Duong unstable state; we will identify the points located on the limit
characteristic Connecting these points, we can divide them
into stable and unstable areas in capacity space as Figure 1
3 Connection of Duyen Hai Thermal Power Center to
Vietnam Power System [2, 3]
Duyen Hai TPC includes 3 plants: Duyen Hai 1 with
capacity of 1245MW consists of 2 sets connected to the
220kV bus, Duyen Hai 2 with capacity of 1245MW
includes 02 sets connected to the 500 kVbus, and Duyen
Hai 3 with capacity of 2000MW consists of 2 sets connected to the 500 kVbus Duyen Hai TPC is connected
to Vietnam PSin two lines: 01 two-circuit line connecting the 500kV bus of Duyen Hai TPC to the 500kV bus of My Tho 500kV substation with the length of 112.63km; 01 two-circuit line connecting 220kVbus of Duyen Hai TPC
to the 220kV bus of Tra Vinh 220kV substation Diagram
of Duyen Hai TPC connected to the 500 kVtransmission system of Vietnam PS is shown in Figure 2
Figure 2 Diagram of Duyen Hai TPC connected to the Vietnam PS
4 Calculation results to evaluate the effects of Duyen
Hai TPC to the stability of Vietnam PS
4.1 Calculation mode
Characteristic of Vietnam PS is that hydropower
accounts for 25.5%, therefore operating modes depend on
weather, while weather is different between the North and
the South In order to assess the influence of Duyen Hai
TPC on Vietnam PS, select the calculation mode
corresponding to peak times of load in the South and dry
season in the North At that time, 500kV transmission line
must transmit amounts of capacity from South to North
Considering operating mode for Duyen Hai TPC to
generate 3000MW in which, Duyen Hai 1 runs 2 sets,
Duyen Hai 2 runs 2 sets, Duyen Hai 3 runs 1 set
Conducting calculation to analyze normal operating mode
(mode 1), take the rest for Duyen Hai 3 (mode 2), and cut
one-circuit on 500kV transmission line connecting Duyen
Hai TPC to My Tho (mode 3)
4.2 Assessment of the impact according to voltage
collapse curve
In order to assess the impact of Duyen Hai TPC to
Vietnam PS, select 3 load buses of Cu Chi, Nha Be, Thot
Not and 3 power buses of Phu My, Duyen Hai, O Mon in
the southwest area for survey Calculation results allow building voltage collapse curve under the modes as Figure
3 (mode 1), Figure 4 (mode 2), and Figure 5 (mode 3)
Figure 3a Speed voltage collapse of mode 1
Figure 3b Speed voltage collapse of mode 1
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Figure 4a Speed voltage collapse of mode 2
Figure 4b Speed voltage collapse of mode 2
Figure 5a Speed voltage collapse of mode 3
Figure 5b Speed voltage collapse of mode 3
In mode 1, the system stable reserve ratio is 11%, for
load buses, voltage variation is slow but voltage collapse
occurs from the beginning and accelerates at the end of the
process of parameter variation For the power buses,
voltage of Duyen Hai bus is stable, Phu My starts to
collapse when load factor k increases by 6% and the rate of
voltage collapse rapidly increases, the voltage of O Mon
dropped early with accelerated voltage collapse when k
increases by 8%
In Mode 2, when reducing generation capacity of
Duyen Hai TPC to 1000 MW, stable reserve ratio decreases
by 9%, the rate of voltage collapse accelerates, especially
to Thot Not load bus of and O Mon power bus
In mode 3, when cutting a 500kV transmission line
connecting Duyen Hai TPC to My Tho, stable reserve ratio
decreases to 6.5%, voltage collapse curve of the load nodes
rapidly increases from the beginning Duyen Hai power bus is stable, voltage of Phu My collapses rapidly and becomes a weak bus that needs to be concerned
Through the 3 operating modes, it is shown that in the southwest area, near Duyen Hai TPC, Thot Not load bus is the weakest one (voltage collapse occurs first) which so will be chosen to survey the regional stable operation according to static stable reserve
4.3 Assessment of the impact according to regional stable operation
Through computation, build regional stable operation under static stable conditions for Thot Not load bus in 3 modes resulted in Figure 6a (mode 1), Figure 6b (mode 2), Figure 6c (mode 3)
Through survey of regional stable operation at 03 modes, we can see that when reducing generation capacity
of Duyen Hai TPC in mode 2, regional stable operation at Thot Not bus is significantly restricted, maximum of active power is reduced from 1800MW to 1000MW, and maximum of reactive power drops from 1000Mvar to 520MVar Similarly, in mode 3, regional stable operation
is also narrowed and working point approaches stable border; especially the stable border is fluctuating Thus, the
PS will lose stability if there is any significant change in capacity of 220kV grid
Figure 6a Regional stable operation of mode 1
Figure 6b Regional stable operation of mode 2
Figure 6c Regional stable operation of mode 3
Trang 44 Ngo Van Duong
5 Solutions for stability improvement for Vietnam PS
5.1 Solution for operation of Duyen Hai TPC
Through analyzing the calculation results in Section 4,
it shows that operating modes of Duyen Hai TPC have a
great influence on the stability of Vietnam PS, directly to
the power systems in the southwest area In order to
improve the stability of the system, we need to pay
attention to following situations:
- In peak mode of load in the South, it’s needed to
generatethe maximum capacity at Duyen Hai TPC
- Repair and maintenance of transmission lines
connecting Duyen Hai TPC to Vietnam PC are only
conducted on low peak time of load in the Southern Region
5.2 Solution for SVC installation [5]
Through the calculations to locate SVC installation for
power system in the Southern Region, it is found that Phu
Lam bus is a reasonable position.After installing the SVC
at Phu Lam bus and controlling to stabilize the 510kV
voltage, voltage collapse curve of theload nodes in mode 2
and mode 3 as shown in Figure 7 and regional stable
operation of Thot Not load bus as shown in Figure 8
Calculation results show that, after installing SVC,
reserve ratio has increased from 9% to 13% in mode 2 and
from 6.5% to 14% in mode 3 Through the voltage collapse
curve, it indicates that voltage at load nodes is rather stable
Voltage collapse occurred in mode 2 when load factor k
increased over 11% This situation occurred sooner in
mode 3 but increased slowly Through surveying regional
stable operation, it shows that regional stable operation is
significantly expanded after installing SVC By means of
above analysis, we can see that the installation of SVC at
Phu Lam bus has significantly enhanced stability of
Vietnam PS
Figure 7a Speed voltage collapse of mode 2
Figure 7b Speed voltage collapse of mode 3
Figure 8a Regional stable operation of mode 2
Figure 8c Regional stable operation of mode 3
6 Conclusion
Duyen Hai TPC plays an important role in supplying electricity to Vietnam Power System in general and Power System in the Southwest region in particular Operating mode of Duyen Hai TPC has a great influence on the stability of Vietnam PS; it should therefore pay attention to the system operation It is necessary to allow power plants to generate big capacity in the peak mode of load in the southern region to enhance stability of the power system In other modes, generating capacity of the plant is related to the optimal distribution problem between plants in the system Duyen Hai TPC is expected to be completed by 2017 with other plants that help to raise total power capacity in the entire system up to 60.000MW Load in the region also increases correspondingly according to the development of the economy
In order to enhance the system stability, it is necessary to install SVC compensation at Phu Lam bus and to calculate to install some other SVC stations for some other areas
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(The Board of Editors received the paper on 06/11/2015, its review was completed on 06/24/2015)