Advanced Materials Research Vols. 732-733

Abstract: This paper presents impacts of distributed generators (DGs) such as synchronous-based DG and inverter-based DG on voltage sag analysis in distribution systems. Voltage sag analysis is assessed through area of vulnerability (AOV), number of sags frequency (NSF) and voltage sag index (SARFI). Single line-to-ground and three-phase faults are investigated. Size and location of DG are carried out by using Particle Swarm Optimization algorithm (PSO) in order to minimize losses and number of sag frequency. Roy Billinton Test System (RBTS) Bus 2 is used for simulation cases. Results show that the distribution system with DG installed improves voltage sag performance compared with the system without DG installed.

Abstract: Mid-term stability assessment is an important work to support power system operation in a province power grid of China every year. The stability assessment method and process was introduced in this paper. As an example, the stability of Jiangxi province power system was evaluated in the following two years. Weak area and weak transmission line were found out in each power supply area. Prevention and control measures were proposed. According to problems among the assessment process and using the state monitoring data, an approach was discussed to increase the assessment result accuracy. The analysis conclusion provides the reference to the safe and stable operation of Jiangxi power system.

Abstract: The most widely adopted methodology for the analysis of power system small signal stability relies on the approach in the frequency domain, i.e. to linearize the system equation to obtain a linear model as well as the system matrix of which the eigenvalues can be calculated to determine the system stability. However, we often have high order of system matrix and thus it will be undesirable to calculate and analyze all the system eigenvalues. This paper is to explore the problem of small signal stability for power system and the main purpose is to find out the worst-damped mode of system eigenvalues and thus to alleviate the effort for computing and analyzing all the system eigenvalues. The developed algorithm is to be tested on a sample power system to validate the feasibility of the proposed new eigenvalue calculation method.

Abstract: The decomposition scale value is usually given by experience while the wavelet analysis method is used for daily load forecasting. Directed to the influence of decomposition scale, the paper constructed a level-termination function as SNR and put forward a constraint conditions according the accuracy requirement to solve out the optimal decomposition level. Then followed the load data which was decomposed into high and low frequency component, built up different models for different level series and sum up the forecasting result. The accuracy assessment index shows the effectiveness of the whole method and prediction thought.

Abstract: This paper proposed a fast protection and control scheme of feeder automation (FA) for the modern distribution grid. The smart terminal unit (STU) is installed at each switchgear of the feeder, and STU has a directional over-current component. The adjacent STUs are connected each other by the optic fibre network, and ultimately they are all connected to the central station of FA. STU detects the local current and the status of breaker in real time, meanwhile exchanges the information with adjacent STUs. Through analyzing the information, STU can make a correct identification for a faulted section. Therefore, the faulted section can be isolated and power supply of non-faulted section can also be restored rapidly. Case analysis illustrates that the proposed fast protection and control scheme is valid and feasible.

Abstract: Low frequency oscillations (LFO) reflect the damping and the stability of a power system and is essentially non-stationary. The LFO is a composite response of various oscillation modes and of which the frequency may be changing with time; thus, direct analysis of such time-domain responses is difficult. The main purpose of this paper is to apply the method of empirical mode decomposition (EMD) to the study of power system stability. First the method of EMD is to expand the time-domain responses under study into multiple intrinsic mode functions (IMFs). Then the 2D time-frequency information inherent in the response under study is obtained using the wavelet transform. The 2D time-frequency graph is further expanded into a 3D time-frequency-energy graph. Information from the 3D time-frequency graph is analyzed to determine those generators that have higher extent of oscillation involvement during the occurrence of LFO in the power system. The results from comparative analysis show that, at specific frequencies from LFOs, higher extent of oscillation involvement will reveal a greater factor of involvement in the frequency domain behavior.

Abstract: Reasonable dispatching strategies are important to guarantee secure and reliable operation of power system. Now the operators use real-time data and their experience to dispatch the system, but the huge data system brings much inconvenience to operators. In this paper, the risk theory is introduced into dispatching operation quantitative assessment, and a real-time dispatching operation risk analysis method is proposed. Fault tree is used to simulate dispatching operation process and comprehensively analyze the system risk in both under-successful and failure state of the operation. Risk indices are given to quantitatively reflect the risk level of each operation step based on local information, such as voltage out-of-limit risk, line overload risk, load curtailment risk, so that the operators can clearly recognize the risk and risk sources in each operation step and take corresponding pre-control measures. Finally, the effectiveness and practicability of proposed method is validated by an IEEE RTS test system.

Abstract: HVDC technology is more and more common in practical projects, of which reliability will affect the whole power system. As different evaluation methods, FTA and FD method had their own advantages and disadvantages, this paper combined FTA method with FD method. Firstly FTA method was used to get basic parameters of each subsystem, then combined each subsystem to a whole equivalent model with FD method. What's more, different capacities of AC filters were also under consideration. Finally, an actual example was given to demonstrate validity of the method that this paper proposed. Compared with Zusim software, the result is more accurate.

Abstract: With the minimization of the annual operation cost as the objective function while meeting constraint conditions of the node voltage and the branch power factor, this article proposes a practical Reactive Power Programming method for regional power distribution network. The problem of reactive compensation planning capacity turns into the problem of constrained quadratic programming. Then the problem is solved by MATLAB Optimization Toolbox. The actual engineering examples show that the method is simple, fast, efficient, and has practical values in engineering.

Abstract: Load forecasting technology is an important guarantee of the safe and steady operation in power system. Based on the analyzing and designing the network structure of GRNN, this paper sets an appropriate smoothing parameter and proposes a strategy for load forecasting under considering the weather factors. A short-term load forecasting model with the factors of temperature, humidity, wind speed, barometric pressure and rainfall is established. And the model can achieve the expected result after a complete test. Finally, comparing with the forecast model based on BP neural network, GRNN method shows the great superiority in power load forecasting.