China Power Network Research Articles

Transmission adaptability planning considering cluster correlation of wind farms

Wind farm cluster penetration and its long-distance delivery have become the important form of wind power accommodation of power network in China. For the adaptability of power network planning to the output volatility of clustering wind farms, three steps are studied as follows. Initially, the output uncertainty model of clustering wind farms based on Auto Regression Integrated Moving Average (ARIMA)-Generalized Autoregression Conditional Heteroscedasticity (GARCH)-Pair Copula is put forward to analyze the intermittency, fluctuation and clustering wind power correlation. Secondly, Full Cost (FC) theory is introduced to account social expense brought by grid-connected clustering wind farms from four aspects of static cost, dynamic cost, environmental cost and inter-generational cost. Meanwhile, available wind power transmission capacity is defined to reflect wind power accommodation based on transmission margin. Finally, the adaptive efficiency index is proposed by the ratio of available wind power transmission capacity to FC. The transmission adaptability planning model considering cluster correlation of wind farms is built with the objective function of the adaptive efficiency index. Taking the actual regional power grid as an example, the results show that the planning scheme considering the optimal adaptive efficiency index of clustering wind farms can be better adapted to the future power network environment.

Study on External Power Receiving Planning of Receiving-end Grid in AC/DC Hybrid Background

Based on the practical experience of power grid planning, the general characteristics and main problems of the receiving-end grid are summarized, and the ideas and methods of external power receiving planning are put forward. Combined with the current situation, the pattern of power supply and demands of a typical recipient power network in China, this paper analysed the reasonable scale of power receiving, the proportion of AC/DC power transmitted and the infeed AC/DC terminal location for long-term development, and conducts comprehensive technical and economic comparisons among various feasible external power receiving schemes to form a recommended scheme

Practical short‐term voltage stability index based on voltage curves: definition, verification and case studies

Short-term voltage stability (SVS) is a serious issue in modern power systems. In China, the East China Power Network is especially vulnerable to short-term voltage instability due to its increasing dependence on electrical power from external through high-voltage direct current (HVDC) transmission lines. To study the SVS, a criterion/index is first required to evaluate the SVS of power systems. However, the currently used practical criteria cannot effectively evaluate the influence of controlling strategies (such as regulating dynamic VAR reservation) of power systems. Therefore, a practical and continuous SVS index (SVSI) based on voltage curves is proposed in this study. The proposed SVSI can quantify the extent of SVS in power systems, thus can be used in the optimisation target of preventive control for improving the SVS of power systems. Moreover, the SVSI consists of three components, and each component reflects a feature of the voltage curve in terms of SVS. The SVSI is essentially a model-free method for assessing the SVS of power systems, so it is robust. Three verifying cases and one application case are presented to show the validity of the SVSI and the feasibility of the SVSI in practical applications.

Efficiency evaluation of hydropower station operation: A case study of Longyangxia station in the Yellow River, China

Hydropower plays a major role in the Chinese electricity generation industry. It is of significant importance to perform efficiency evaluation of the economic operation in a power station, which can help promote better water resources management and create more benefits for power network. Therefore, the main goal of this study is to establish a set of evaluation indexes and investigate the evaluation method to assess the economic operation in a power station. Based on the operation chart, three evaluation indexes including the Relative Water Consumption Rate (RC), the Relative Hydropower Utilization Rate (RU), and the Relative Hydropower Utilization Increasing Rate (RI) were proposed. The Longyangxia power station, as the biggest peak regulation source in the Northwest Power Network in China and the largest reservoir in the Yellow River Basin, was selected to perform an efficiency evaluation of economic operation. The result showed that the economic operation of this power station was not reasonable with RC > 1, RU < 1 and RI < 0. And the rationality of the evaluation result was illustrated through analyzing the actual operation situation of the Longyangxia reservoir.

Application of MMC‐UPFC in the 500 kV power grid of Suzhou

To solve the problem regarding the power supply capacity improving and ultra-high-voltage direct current (UHVDC) power assumption of 500 kV Suzhou power network in China, research on the feasibility for application of a unified power flow controller (UPFC) in 500 kV southern power grid of Suzhou is carried out. Furthermore, the scheme of the UPFC integrated and its topology structure is given, and the capacity of the UPFC is determined by system calculation. The principle for the selection of key parameters for the main equipment in the UPFC project is discussed. The effect on the power flow and voltage regulation of 500 kV Suzhou power grid is verified by simulation, which indicates that the regulating by UPFC can eliminate the overload of key transmission section as line tripped, under the heavy load condition in winter. During summer under heavy load conditions, it is beneficial to decrease the capacity of load shedding as the UHVDC bipolar is blocked. In addition, the reactive power control of the UPFC can provide the dynamic voltage support for the power grid, which reduces the probability and the time duration of the commutation failure of the UHVDC.

Calculation of geomagnetically induced currents reactive power loss disturbance in China&amp;rsquo;s UHV power grid considering the influence of 500 kV power grid

Geomagnetically induced currents (GIC) in power systems which are generated during magnetic storms, increased reactive power consumption in transformers, it is necessary for geomagnetic storms disaster prevention in power system to calculate GIC-Q increment and recognize voltage changes of substation nodes under simultaneity and proruption of massive GIC-Q loss disturbance in whole power grid. A method combines U - I curve and transformers’ reactive loss coefficient parameter K is proposed to calculate transformers’ GIC-Q increment, based on the GIC data of 1000 kV UHV power network in China, and considering the influence of 500 kV transformers’ GIC-Q loss on 1000 kV power grid, we used the Newton method to calculate voltage fluctuation of 1000 and 500 kV power grid under GIC-Q disturbance. At last, the impact of the simultaneity of massive GIC-Q loss on the 1000 and 500 kV grid is analyzed, we investigated the mutual influence between these two power grids under all circumstances. The results show that 1000 kV Fuzhou substation has a maximum voltage fluctuation that drops by 74.48 kV, whose voltage deviation compared with normal shows a decrease of 7.13%, which beyonds the regulation that the operating voltage deviation should not exceed ±5%. And whether the suddenly voltage drop of 74.48 kV can lead to the reduction of SVC devices reactive power output, and the simultaneity of massive GIC-Q loss as well as the suddenly reduction effect of SVC reactive power output need to be further researched.

GIC due to storm sudden commencement in low‐latitude high‐voltage power network in China: Observation and simulation

AbstractThe impact of geomagnetically induced currents (GICs) on the power networks at middle and low latitudes has attracted attention in recent years with the increase of large‐scale power networks. In this study, we report the GIC monitored at two low‐latitude 500 kV substations of China during the large storm of 17 March 2015. The GIC due to the storm sudden commencement (SSC) was much higher than that during the storm main phase. This phenomenon is more likely to happen at low‐latitude locations, highlighting the importance of SSC in inducing GIC in low‐latitude power networks. Furthermore, we ran a global MHD model to simulate the GIC during this SSC event by using the solar wind observation as input. The model results reproduced the main features of the GIC. The study also indicated that the eastward component of the geoelectric field is dominant for low‐latitude locations during the SSC events. Further, topology and electrical parameters of the power grids make significant differences in the GIC levels.

A Modified Optimization Model for the Location Selection of Distribution Transformer Used in Rural Power Network

The rural power networks play a very important role in the power network in China. The rural networks built in the old days are usually not standardized, and therefore, a lot of problems emerged these days. Such as, most of the transmission line is aged, the insulation ability of the transmission line degraded, the household voltage is relatively low, the distribution network line loss is very high, and so on. As the rural power network mainly distributes in the hilly and mountainous land, the altitude of the load points has an important impact to the location of distribution transformer. Meanwhile, because of the existence of the sag, the length of the transmission line is not a straight-line distance. Therefore, this paper modified the traditional optimization model used in the location of distribution transformer, introduced the line correction coefficient (α) which was connected with the sag, improved the line distance computational formula according to the altitude of the load points, and put forward the modified optimization model which is called M-TLOM. Then, an optimized location system of distribution transformer (DTLOS 1.0) based on the Visual Basic 6.0 was developed. The instance analysis indicated that, the modified model could reduce the loss of distribution network.

An Adaptive Protection Method for Power System under Wide Area Networks

The grid structure and its operation mood are becoming more complicated with the expansion of China Power Network which have higher requirement for security protection for relay protection network. This article proposes adaptive setting of switch positioner and line fault under wide area networks. Adaptive setting of switch positioner in system operation mode can effectively extend the protection scope of zone 2 impedance relay on the premise of protecting the cooperative relationship which has a better sensibility than traditional setting value of zone 2 impedance relay. Adaptive setting of line fault has high level of adaptation in system operation mode and sensitivity in each adjacent line which has lager protection scope than that of the traditional setting value and switch positioner.

Wavelet-Based ARMA Model Application in Power Network

The theoretical properties of the ARMA model and the modeling process, then, the Shanghai power network and Shenzhen power network in China were established ARMA model and wavelet-based ARMA model fitting, prediction, and finally, to fit forecast The results were compared. It can be seen, combined with relatively good forecasting effect after wavelet.

Crack Growth Prediction of the Steam Turbine Generator Shaft

The power network in China is encountering great changes and large-scale network is increasingly implemented for long distance power transmission as well as various kinds of power electronic devices, which bring in the risk of the torsional vibration of the turbine generator shafts, may cause the fatigue damage and cracks in the product life cycle. The paper analyzed the failed coupling of some 600MW steam turbine generator and calculated the local stress of the assembly under torsional load caused by the network disturbance. Then the crack propagation was analyzed with the predicted crack initiation position and crack propagation routine. The assembled coupling contains shaft, coupling and keys with interferences between the parts. Therefore the contact analysis was included. Extended Finite Element Method (X-FEM) is used to calculate the crack propagation and that the mesh needs not to be regenerated with the crack propagation, which is beneficial for engineering applications.

Application of the injection modeling approach to power flow analysis for systems with unified power flow controller

This paper proposes an improved injection modeling approach for power flow analysis of unified power flow controller (UPFC) embedded power systems. With the UPFC injection models, an equivalent network without UPFCs can be obtained easily according to four basic scheduled control objectives of UPFCs. For the equivalent network, conventional techniques such as Newton–Raphson method and even commercial software can be directly employed for power flow solutions of original systems with UPFCs. Hence, it inherits all advantages of conventional techniques both in convergence and in speed. With the power flow solution, control parameters of each UPFC are then evaluated using the equations derived in this paper. Case studies on the IEEE 14-bus system and on North China power network are given to indicate that the approach is reliable and efficient.

Practical implementation of the SCADA+AGC/ED system of the Hunan power pool in the central China power network

To accomplish the dispatching automation of the Hunan Power Pool (HPP), a supervisory control and data acquisition and automatic generation control/economic dispatch (SCADA+AGC/ED) system supplied by Systems Control in the USA was imported by the Hunan Power Dispatch Control Center. In December 1990 the practical implementation acceptance test for the new system was completed. The new system is the first system completed to use closed loop control of AGC in the power pools of China. This paper reviews the background of developing the new system, and describes implementation schemes and operation tests of AGC. At the same time, the Constant Net Interchange (CNI) mode of AGC in the HPP is also discussed in detail, and finally the economic benefits and the improved operation quality after AGC is in operation are described.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Practical implementation of the SCADA+AGC/ED system of the hunan power pool in the central China power network

Practical implementation of the SCADA+AGC/ED system of the hunan power pool in the central China power network