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[.]
THE UNIVERSITY OF DANANG, JOURNAL OF SCIENCE AND TECHNOLOGY, NO 6(91).2015 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 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 Assessment of stability under voltage collapse curve and regional stable operation [4, 6, 7] 2.1 Stable reserve ratio and voltage collapse curve Key words - Duyen Hai thermal power center; the operating mode; voltage collapse; regional stable operation; stability 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 coalfired thermal power plants 1, 2, and 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 thermal power plant into operation with a total capacity of 1.245MW including sets 2x622, 5MW As planned, the center will be completely constructed and put into operation by the end of 2017 [2, 3] Figure 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 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 Connection of Duyen Hai Thermal Power Center to Vietnam Power System [2, 3] Duyen Hai TPC includes plants: Duyen Hai with capacity of 1245MW consists of sets connected to the 220kV bus, Duyen Hai with capacity of 1245MW includes 02 sets connected to the 500 kVbus, and Duyen Hai with capacity of 2000MW consists of 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 Figure Diagram of Duyen Hai TPC connected to the Vietnam PS 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 runs sets, Duyen Hai runs sets, Duyen Hai runs set Conducting calculation to analyze normal operating mode (mode 1), take the rest for Duyen Hai (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 load buses of Cu Chi, Nha Be, Thot Not and 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 (mode 1), Figure (mode 2), and Figure (mode 3) Figure 3a Speed voltage collapse of mode Figure 3b Speed voltage collapse of mode THE UNIVERSITY OF DANANG, JOURNAL OF SCIENCE AND TECHNOLOGY, NO 6(91).2015 Figure 4a Speed voltage collapse of mode Figure 4b Speed voltage collapse of mode 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 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 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 5a Speed voltage collapse of mode Figure 6a Regional stable operation of mode Figure 5b Speed voltage collapse of mode 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 Figure 6b Regional stable operation of mode Figure 6c Regional stable operation of mode Ngo Van Duong 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 and mode as shown in Figure and regional stable operation of Thot Not load bus as shown in Figure Calculation results show that, after installing SVC, reserve ratio has increased from 9% to 13% in mode and from 6.5% to 14% in mode Through the voltage collapse curve, it indicates that voltage at load nodes is rather stable Voltage collapse occurred in mode when load factor k increased over 11% This situation occurred sooner in mode 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 8a Regional stable operation of mode Figure 8c Regional stable operation of mode 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 REFERENCES Figure 7a Speed voltage collapse of mode Figure 7b Speed voltage collapse of mode [1] Viện Năng lượng, Quy hoạch phát triển điện lực quốc gia giai đoạn 2011-2020 có xét đến năm 2030, 2012 [2] Quyết định số 110/2007/QĐ-TTg ngày 18/7/2007 của Thủ tướng Chính phủ phê duyệt Quy hoạch phát triển điện lực quốc gia giai đoạn 2006-2015 có xét đến năm 2025 [3] Quyết định số: 1135/QĐ-BCT ngày 17/10/2007 của Bộ Công thương về phê duyệt Quy hoạch tổng thế Trung tâm Điện lực Duyên Hải – Trà Vinh [4] Lã Văn Út (2011), Phân tích điều khiển ổn định hệ thống điện, Nhà xuất bản Khoa học và Kỹ thuật, Hà Nội [5] Narain G Hingorani, Laszlo Gyugyi (2000), Understanding FACTS, Concepts of Flexible AC Transmission Systems, TheInstitution of Electrical and Electronics Engineers, Inc, New York [6] P Kundur (1994), Power System Stability and Control, McGrawHill, New York [7] C W Taylor (1994), Power System Voltage Stability, McGraw-Hill, New York (The Board of Editors received the paper on 06/11/2015, its review was completed on 06/24/2015) ... Connection of Duyen Hai Thermal Power Center to Vietnam Power System [2, 3] Duyen Hai TPC includes plants: Duyen Hai with capacity of 1245MW consists of sets connected to the 220kV bus, Duyen Hai. .. 220kV substation Diagram of Duyen Hai TPC connected to the 500 kVtransmission system of Vietnam PS is shown in Figure Figure Diagram of Duyen Hai TPC connected to the Vietnam PS Calculation results... 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