Hai Bao

Impacts of TCSC and FSC on the Power-Angle

The Characteristics of FSC (Fixed Series Compensation) and TCSC (Thyristor Controlled Series Capacitor) damping power-angle oscillation and increasing the limit of power transmission were analyzed. FSC can damp the power-angle in a certain extent. Based on the linear control combined with Bang-bang control strategy, TCSC can damp power-angle effectively. In the cases of only FSC, only TCSC and their combinations, simulation results demonstrate that TCSC is more effective than FSC in damping power-angle oscillation. A conclusion is made that taking effect and cost into consideration, TCSC and FSC in a certain percentage is appropriate.

Analysis of the Energy Metering Problem in Dynamic Environment

The traditional electric power metering theory is a kind of no-error metering theory in sinusoidal steady-state circuit. However, the applying condition is too rigor, and the engineering environment is hard to fulfil, the application premise should be extended to dynamic. Ideal linear elements are adopted to build a first-order dynamic circuit. And the analytic expressions of the capacitor cumulative electric energy in the charging process are derived theoretically. It points out that the cumulative electric energy of capacitor in dynamic circuit is a nonzero value. This fully demonstrates that the energy metering principle brings error when it is used in dynamic environment.

The Influence of Time Truncation on Phase Angle Measurement Principle

Real-time accurate voltage phase angle measurement data has a very important significance to monitor and analyze the power system, and phase angle measurement principle of Fourier transform plays an important role in the theoretical calculations and engineering applications. The dynamic sinusoidal voltage signal contains two parts of the sinusoidal steady-state component and decaying DC component, and the decaying DC component having a continuous spectrum, at the frequency corresponding to the sinusoidal steady-state component must have a non-zero value, making dynamic signal phase than steady signal phase has one extra deviation angle. Considering Fourier transform method and theory of engineering application are different, this paper only considered the application conditions of time truncation, analyzes continuous Fourier transform under a real eigenvalue and a pair of conjugate complex roots condition, then compared with the theoretical calculation, for the two case of limited time integration and theoretical calculation condition, the phase angle difference and influencing factors are given.

Analysis of Input Phase for PLL in Dynamic Environment

In dynamic operating environment, it is one of key issues in the research field of electric energy metering that the accuracy of synchronous sampling signal based on phase locked technology. Because operating environment changes from steady state to dynamic, analytical description of PLL input signal becomes an urgent problem to be solved. In this paper, dynamic signal is analyzed mathematically by using zero-crossing detection theory, its phase expression is obtained, then mathematical equivalent conversion is made based on operation characteristics of PLL, its phase input equation is obtained, finally the correctness of the input equation is verified by Fourier transform method. This study lays the foundation for error analysis of electric energy metering system under dynamic condition.

An on Line Method of the Steady-State Data Acquisition

Steady-state power flow calculation belongs to power system steady-state analysis, and the data used in calculation should be steady-state data. However, the existing SCADA system hasnt distinguished the transient data from the steady-state data. The real-time measured data reflect the dynamic electric power system. It is the right reason for not all of the real-time measured power can be used for power flow calculation. In another word, it causes the matching problem between measured data and power flow calculations. Based on the current situation of information collection system, the characteristics of the measured data had been analyzed in this paper. And an effective acquisition method for steady-state measured data is proposed on the theoretical basis of the law of large numbers. It uses the average value of the measured data that in the same load state to approximate the steady-state true value in one period. And the steady-state data can be used in power flow calculation. The simulation results show that the method proposed in this paper ensures the accuracy and reliability of power flow calculation.

The Fast Estimation of the Electromechanical Oscillation Frequency

Analyzing stability of power system mainly relates to the model of machine, which can be simulated by two order and damping coefficient D (D represents mechanical damping and electrical damping), but there is no standard which can illustrate how much the damping coefficient D is. Usually power flow, excitation system, PSS and prime mover system affect the total damping largely, but have little impact on the electromechanical oscillation frequency. Firstly the paper theoretically proves the correctness of calculating electromechanical inherent frequency with system matrix. Secondly considering the damping ration characteristic of power system, the feasibility of estimating the electromechanical oscillation frequency with electromechanical inherent frequency is analyzed. With different models, the simulation results demonstrate that the electromechanical oscillation damping is affected very largely, but the frequency is affected little, which proves the effectiveness of the system matrix analysis method.

The Analysis of Rogowski Coil Transfer Characteristics in the Composite Frequency Environment

This article uses the method of frequency characteristic to analysis transfer characteristics of Rogowski coil. In the case of the composite frequency signal, Rogowski coil transfer ratio is the function of frequency, that is the transfer ratio varies with the frequency, which makes the signal of the secondary side not restore to the primary side. The simulation results prove the conclusion. In view of the situation, this paper presents an ideal transfer ratio, which provides the reference standard for correcting the frequency characteristics of the Rogowski coil integrating circuit.

The Effect of the Accuracy of Reactive Power Measurement on Transmission Node Cost

Power flow calculation is the fundamental of cost analysis of transmission node. In traditional methods, the rationality of the cost analysis is of more concern than the accuracy of the power flow calculation’s results. This paper starts from the reactive data that being used for power flow calculation, expatiate that the method of present reactive power data measurement is inaccurate and explains why it is inaccurate. What reactive power would do to node cost analysis and why it could do so are analyzed considering cost analysis of transmission node. At last, an example of IEEE 9 is used. And it is proved that the fluctuation of reactive power will affect the power distribution of the whole network, as a result affect the generators’ sale of electricity income to loads greatly.

A New Method for Online Steady-State Power Flow Calculation in Electric Power System

Owing to the given variables are measurable in online power flow calculation, the electrical variables of higher measuring accuracy should be chosen for calculation. Currently the theory of reactive power is deficient and several methods for reactive power measurement are briefly introduced in this paper. The inaccuracy of those methods is pointed out by the relevant references in non-sinusoidal conditions. The measuring accuracy of Active power directly obtained by voltage and current is the same as that of voltage and current. For increasing the accuracy of online power flow calculation, a method substituting voltage magnitude for reactive power is proposed in this paper. The new method eliminates the effects resulted from inaccurate reactive power measurement. The simulation results on software MATPOWER verify the correctness and rationality of the new method.

Error Analysis of Wide Area Measurement Based Measurement Power Flow

Measurement take place of calculation is an advantage of wide area measurement based measurement power flow, but its accuracy needs to be explored. This paper points out the measurement power flow’s data dose not conform to the actual power flow’s data on condition of phase angle measurement exist error. Through the analysis of example we can see that the deviation of active power will reach 15% when phase angle exist 0.1°error, its accuracy is worse than DC power flow in engineering calculation .This paper suggest using the phase angle value which was measured as initial value in power flow calculation, it will reduce the error’s impact on power flow calculation.