Operational Problems and Chalenges in Power System of Vietnam (Part III of III)

Ngày cập nhật: 30/11/2011
Ngo Son Hai, Nguyen The Huu, National Load Dispatch Centre of Vietnam

III. CHALLENGES TO THE OPERATION OF VIETNAMES POWER SYSTEM IN THE NEAR FUTURE

A.    Limiting the fault current

Existing regulations, the Gird Code [3], set the maximum allowable fault currents for the corresponding 500kV/220kV/110kV voltage levels are 40kA/40kA/31.5kA, respectively. At the moment, NLDC’s calculation shows that the fault currents at 220kV centre and near large generation sources have passed the limit of 40kA. Various solutions have been proposed in section II.C but only temporary.

The true challenges for the operation of the power system are exposed when the quantity of generators grow very quick with the total installed capacity almost doubles by the end of 2015. Preliminary calculation shows that the fault current at most of 500kV, 220kV busbars at load centres in Hanoi, Haiphong, Ho Chi Minh City, Dong nai and other generation centres such as Quang Ninh, O Mon, My Tho are all higher than the allowed current. A simultaneous comprehensive solution of both planning and operating to limit the fault current on the transmission network is urgently required for securing the operation. A number of these solutions are as follows:

(1)    The planning solution: the transmission grid in large urban areas is 500kV ring circuit, each 500kV substation supply 2 to 4 220kV substations, 220kV network has ring configuration but operate as an open circuit. The method can be applied to city centres, which are heavily loaded areas, such as Hanoi, Hai Phong, Ho Chi Minh City, Dong Nai and surrounding areas.

(2)    Imposing standard inductance values for step-up transformers within a sufficient range, together with supplementing Superconducting Fault Current Limiter that can be applied in a number of distribution or transmission areas to reduce the fault currents.

(3)    Considering mandatory requirements for key locations that need circuit breakers with higher rated current. 

B.    Operating standards of a power system with interconections with other nations

In the future, the cooperation and power exchange among neighboring countries are certain. The connection shall bring benefits similar to those of unifying regional sub-systems within a nation. Besides, this is also an opportunity to develop an inter-country power market (possibly among countries in the Indochina peninsula or even Asean countries). However, interconnection with outside system may create new challenges to the operating process. The first and foremost is the setting of technical standards (applying to connecting equipments, operating modes, fault responses, etc.). Between two electrically interconnected nations, there is usually a negotiation process to standardize all technical requirements. But for interconnections among more than two countries, there is a need for the establishment of a common system of technical standards for the whole area, at least for the parameters required during operation.

The idea of promoting interconnection between China southern grid and Vietnamese grid through HVDC at 500kV has been raised for few years. By using HVDC, Vietnam hopes to thoroughly resolve the current issue of operating separate systems. At the same time, the power exchange with the neighboring country will become safer.

Collaboration among system operators is also a key problem. It includes from dispatching authority and communicating languages. From previous experiences, since the current power trading is usually carried out in one direction, meaning one side is always the buyer – the other side is always the seller, the operation is fairly simple and the communicating language is the language of the selling partner. However, the progressing level of integration and more interconnections necessitate a more definite set of rules of collaboration among system operators. The communicating language should be English, since it is the most popular language in the area.

C.    System operation in accordance with market-based rules

Decision 26/2006/QD – TTg of the Prime Minister defines the three developing phases of a competitive power market [2]. The period of 2005 – 2014 employs the model of a competitive generation single buyer market. The period of 2015 – 2022 will be the competitive wholesaling phase and after 2022 is will be a retailing market. Figure 5 shows the roadmap for establishment and development of the electricity market in Vietnam. However, from the system operator’s perspective, the transition from a centralized system to a deregulated system itself carries certain difficulties.


Fig. 5. Roadmap for electricity market development in Vietnam
(Source: Decision No. 26/2006/QD-TTg dated January 26, issued by the Prime Minister, approving the development phases and establishing requirements of a power market in Vietnam)


First of all, the load dispatch completely depends on the bids, which do not follow a preplanned schedule. This might cause overload, bottle-neck or local over-voltage, under-voltage at certain buses. The operator has to perform analysis of system security and reliability with extra measures to prevent such problems.

Secondly, the market payments based on metered values demands an accurate metering system as well as a high level of transparency and fairness.

Thirdly, the tight supply at the moment and the fact that many power plants are not used to the bid-based operation, the bids of participants will usually orients towards the high end of the bid caps. Consequently, it affects the economic target of the system.

Finally, previous experiences in constructing and operating power markets at some areas around the world (the Nordic countries [6], Singapore, New Zealand) have shown that the investment from non-government sector mostly goes into the generation sector, the investment for the transmission system usually depend on state companies (usually the Power Transmission Companies), resulting in pressures on the transmission network, which in general cause various problems in the actual operation. This condition can be resolved if the government can construct a reasonable transmission tariff, enough for reinvesting in the transmission system or encourages non-government sectors to invest in transmission system (the case of Australia [7]).

IV.    CONCLUSION

In this paper, operational problems in power system of Vietnam are presented. Many difficulties in operation has been identified since the introduction of the 500kV extra high voltage, in which three most critical ones are described in this paper that include stabilities, voltage regulation and high fault current. In the new environment of globalization and liberalization of the electricity industry, there are challenges that the operators have to face up to.

According to the Master Plan [4] regarding power sector development during the period of 2011 – 2015, the sum of the produced energy and the imported energy approximates to about 194 – 210 billion kWh by 2015, which is twice the current demand. Vietnam will also keep developing the EHV 500kV network. The total length of newly constructed lines is expected to be equal to the current length; the capacity of transformers will be 1.7 times that of the existing total capacity. Recognizing these challenges, NLDC has defined the operating strategies for the operation the power system including:

(1) Applying the State-of-the-art automation technology for power system operation such as a new SCADA/EMS (hardware, software, database, and telecommunication) to support the system and market operation.
(2)  Staff training in specialized fields and foreign language for system analysis engineers, system operators as well as market operators.
(3)  Constructing standard rules and procedures in operating system and market to comply with the laws, available capacity and actual ability (of the power system).
(4)  Cooperating with domestic and international research centres and specialists, applying technical solutions to increase the reliability and stability of the transmission system such as installing new automatic systems including direct load control, fault recording on 500kV network, recognizing and suppressing outage spreading systems, etc.
(5)  Strengthening the research of new issues in power system operation for short-term and mid-term periods such as direct current, hybrid AC/DC, reactive power control, effects of nuclear power plants to the grid, pumped storage hydro power plants, etc.



REFERENCES

[1]    National Load Dispatch Centre, Annual Operating Summary 2010 and appendices.
[2]    Decision No. 26/2006/QD-TTg dated January 26, 2006 issued by the Prime Minister of the Socialist Republic of Vietnam, approving the development phases and establishing requirements of a power market in Vietnam.
[3]    Decision No. 12/2010/TT-BCT dated April 15, 2010 issued by the Minister of Ministry of Industry and Trade, approving the Grid Code.
[4]    Decision No. 1208/2011/QD-TTg dated July 21, 2011 issued by the Prime Minister of Vietnam approving the Master plan of Vietnam power developments for the period of 2011 – 2020, taking into accounts year 2030.
[5]    Dantri Online, http://dantri.com/vn/c76/x76-494482/khoi-dong-thi-truong-phat-dien-canh-tranh.htm
[6]    Grid Investments from a Nordic Perspective – Nordic Energy Regulators recommendations, https://www.nordicenergyregulators.org/.../Nordic_grid_conclusions.pdf
[7]    ACCC (Australian Competition & Consumer Commission) - State of the Energy market 2009 – Chapter 5, Figure 5.2, Page 128.

BIOGRAPHIES



Ngo Son Hai was born in Quang Ninh, Vietnam, in 1968. He received the B.E. degree in power electrical engineering from Hanoi University of Technology, Hanoi, Vietnam, in 1991, and the MEngSc degree in power electrical engineering from University of New South Wales, Sydney, Australia, in 1999, and the EMBA degree from Asian Institute of Technology, Bangkok, Thailand, in 2008.
In 1991, he joined the Dispatching Department of Hanoi Power Company, as a dispatcher. Since 1994, he has been with the National Load Dispatch Centre (NLDC), Hanoi, Vietnam where he was an Power System Operator in 1994, became a Deputy Manager of Dispatching Department in 1997, and a Manager of Dispatching Department in 2001, a Manager of Economic Operation Department in 2005, became a Deputy Director of NLDC in 2006, and a Director of NLDC in 2011. His experiences include power transmission network operation, power system operation planning, power generation scheduling and dispatching in the large system, power market operation.



Nguyen The Huu was born in Vietnam, in 1979. He studied electrical engineering at Hanoi University of Technology in Vietnam, graduating with with a B.E. degree in 2001. He joined the National Load Dispatch Centre (NLDC), Hanoi, Vietnam in 2001 and working as power system analysis engineer. From May 2011, Huu became deputy manager of Power System Analysis and Planing Department, NLDC. His special field of interest include electric power systems operation and planing, power market operation.

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