Xueshan Han

Calculation of Power Transfer Limit Considering Electro-Thermal Coupling of Overhead Transmission Line

In this paper, new formulations of the power flow and continuation power flow that allow for electro-thermal coupling in transmission lines have been proposed. The new formulations capture the overhead lines electro-thermal coupling effects by treating their series resistances as temperature dependent variables. They generate results that can differ from the results of conventional formulations markedly, particularly for problems centring on line impedances. The paper demonstrates this by applying the new formulations to the power transfer limit calculation. Generally, power transfer limits are defined either by encountering a lines thermal limit or detecting the onset of voltage collapse in the system. Studies based on 2-bus and 14-bus test systems are used to demonstrate the efficacy of the new formulations for both situations. For these studies, specific point-to-point power transfer limits are calculated with and without the lines electro-thermal coupling effects and the results are compared.

Interval Estimation for Conditional Failure Rates of Transmission Lines With Limited Samples

The estimation of the conditional failure rate (CFR) of an overhead transmission line (OTL) is essential for power system operational reliability assessment. It is hard to predict the CFR precisely, although great efforts have been made to improve the estimation accuracy. One significant difficulty is the lack of available outage samples, due to which the law of large numbers is no longer applicable and no convincing statistical result can be obtained. To address this problem, in this paper, a novel imprecise probabilistic approach is proposed to estimate the CFR of an OTL. The imprecise Dirichlet model (IDM) is applied to establish the imprecise probabilistic relation between an operational condition and the OTL failure. Then a credal network is constructed to integrate the IDM estimation results corresponding to various operational conditions and infer the CFR of the OTL. Instead of providing a single-valued estimation result, the proposed approach predicts the possible interval of the CFR in order to explicitly indicate the uncertainty of the estimation and more objectively represent the available knowledge. The proposed approach is illustrated by estimating the CFRs of two LGJ-300 transmission lines located in the same region, and it is also compared with the existing approaches by using data generated from a virtual OTL. Test results indicate that the proposed approach can obtain much tighter and more reasonable CFR intervals compared with the contrast approaches.

Dispatch Problems Due to Ramp Rate Constraints: Bottleneck Analysis and Solutions

This paper proposes a dispatch technique based on the analysis of the system ramp-up/down megawatts (MW). If a dispatch is feasible, it can be shown that the total unavailable ramp-up MW of all the slow units in any future time intervals must be less than or equal to the MW difference between the maximum system MW capacity and the load demand at the end of study intervals. Likewise, the same can be said for the total unavailable ramp-down MW of all the slow units. These two constraints can be used to guide the system away from infeasible dispatch.

Model-Free MLE Estimation for Online Rotor Angle Stability Assessment With PMU Data

Recent research has demonstrated that the rotor angle stability of a power system can be assessed by identifying the sign of the systems maximal Lyapunov exponent (MLE). A positive (negative) MLE implies unstable (stable) rotor angle dynamics. However, because the MLE may fluctuate between positive and negative values for a long time after a severe disturbance, determining the system stability is difficult when observing a positive or negative MLE without knowing its further fluctuation trend. In this paper, a new approach for online rotor angle stability assessment is proposed to address this problem. The MLE is estimated by a recursive least-squares-based method from real-time rotor angle measurements, and two critical parameters, the Theiler window, and the MLE estimation initial time step are carefully chosen to make sure that the calculated MLE curves present distinct features for different stability conditions. By using the proposed stability assessment criteria, the developed approach can provide a timely and reliable assessment of rotor angle stability. Extensive tests on the New England 39-bus system and the Northeast Power Coordinating Council 140-bus system verify the effectiveness of the proposed approach.

Study on Electricity Business Expansion and Electricity Sales Based on Seasonal Adjustment

[1] proposed a novel analysis and forecast method of electricity business expansion based on Seasonal Adjustment, we extend this work to include the effect the micro and macro aspects, respectively. From micro aspect, we introduce the concept of load factor to forecast the stable value of electricity consumption of single new consumer after the installation of new capacity of the high-voltage transformer. From macro aspects, considering the growth of business expanding is also stimulated by the growth of electricity sales, it is necessary to analyse the antecedent relationship between business expanding and electricity sales. First, forecast electricity consumption of customer group and release rules of expanding capacity, respectively. Second, contrast the degree of fitting and prediction accuracy to find out the antecedence relationship and analyse the reason. Also, it can be used as a contrast to observe the influence of customer group in different ranges on the prediction precision. Finally, Simulation results indicate that the proposed method is accurate to help determine the value of expanding capacity and electricity consumption.

A Novel Power Flow Algorithm for Hybrid AC/DC Power Grids

Abstract This study introduces a novel unified power flow algorithm for hybrid AC/DC power grids. For hybrid AC/DC power grids that incorporate voltage source converters (VSCs), the proposed algorithm uses the voltage amplitude and the phase angle of the AC bus and the voltage of the DC bus as the minimum set of state variables. The power equation of the converter is deduced by these state variables. Then, the bus-power-equilibrium (BPE) equations can be deduced based on the DC node classification and VSC converter station control modes. The Newton–Raphson method can be used to solve these BPE equations with good convergence behavior. In addition, the DC grid and converter station modeling impose no restriction on the hybrid grid topology. As a result, the Jacobian matrix in the modified equations can accurately reflect the coupling relationship between AC and DC grids and simultaneously maintain the sparse feature. The proposed unified algorithm uses the sparse technology and can solve the power flow problem for a large hybrid power grid. A simulation is implemented to illustrate the effectiveness of the proposed algorithm.