Search

The rapid growth of wind power systems worldwide will likely see the integration of large wind farms with electrical networks that are series compensated for ensuring stable transmission of bulk power. This may potentially lead to subsynchronous-resonance (SSR) issues. Although SSR is a well-understood phenomenon that can be mitigated with flexible ac transmission system (FACTS) devices, scant information is available on the SSR problem in a series-compensated wind farm. This paper reports the potential occurrence and mitigation of SSR caused by an induction-generator (IG) effect as well as torsional interactions, in a series-compensated wind farm. SSR suppression is achieved as an additional advantage of FACTS controllers which may already be installed in the power system for achieving other objectives. In this study, a wind farm employing a self-excited induction generator is connected to the grid through a series-compensated line. A static var compensator (SVC) with a simple voltage regulator is first employed at the IG terminal in addition to the fixed shunt capacitor for dynamic reactive power support. The same SVC is shown to effectively damp SSR when equipped with an SSR damping controller. Also, a thyristor-controlled series capacitor (TCSC) that is actually installed to increase the power transfer capability of the transmission line is also shown to damp subsynchronous oscillations when provided with closed-loop current control. While both FACTS controllers--the SVC and TCSC--can effectively mitigate SSR, the performance of TCSC is shown to be superior. Extensive simulations have been carried out using EMTDC/PSCAD to validate the performance of SVC and TCSC in damping SSR. [ABSTRACT FROM AUTHOR]

This paper presents a computational approach for an offline measurement-based design of an optimal damping controller using adaptive critics for a new type of flexible ac transmission system device--the gate-controlled series capacitor (GCSC). Remote measurements are provided to the controller to damp out system modes. The optimal controller is developed based on the heuristic dynamic programming (HDP) approach. Three multilayer-perceptron neural networks are used in the design--the identifier/model network to identify the dynamics of the power system, the critic network to evaluate the performance of the damping controller, and the controller network to provide optimal damping. This measurement-based technique provides an alternative to the classical linear model-based optimal control design. The eigenvalue analysis of the closed-loop system is performed with time-domain responses using the Prony method. An analysis of the simulation results shows potential of the HDP-based optimal damping controller on a GCSC for enhancing the stability of the power system. [ABSTRACT FROM AUTHOR]

This paper investigates issues related to practical implementation of the one-quarter of cycle-based estimation method [here called delayed signal cancellation (DSC)] for online detection of positive and negative sequence components of three-phase quantities. The detection error due to non-ideal sampling frequency is calculated. Furthermore, the effect of the DSC method on estimation when harmonic components are present in the input signal is analyzed. It is shown how harmonics transfer through the DSC and how a non-ideal sampling frequency affects the estimation of the harmonics. Experimental verification of the analytical results is presented. [ABSTRACT FROM AUTHOR]

Directional relays use voltage as the polarizing quantity. When three-phase faults occur close to the relay bus, the available voltage becomes nearly zero and this creates a problem in estimation of the fault direction. The capacitor coupling voltage transformer subsidence transients add to this problem. The memory voltage used as the polarizing quantity at these situations is a compromise. This paper highlights these issues and proposes a simple solution using the power-flow direction in addition to other information. The performance of the technique is evaluated through simulation in Power System Computer Aided Design. [ABSTRACT FROM AUTHOR]

Aerial LiDAR survey is receiving wide application in transmission-line modeling due to its efficiency. The technique is particularly useful for modeling of existing lines for the purpose of thermal rating, upgrading, or vegetation management. An accurate modeling of an existing line depends largely on proper determination of the base conductor temperature, i.e. the conductor temperature at the time of the aerial light detection and ranging (LiDAR) survey. In this paper, an acceptable accuracy for the base conductor temperature is first established. Extensive parametric studies are then conducted to reveal the effects of all the potentially major factors: ambient air temperature, electrical load, solar radiation, wind, and conductor size on the base conductor temperature. As a result, recommendations are made on the proper practice of performing an aerial LiDAR survey and determining the base conductor temperature so that the resulting transmission line modeling is within an acceptable accuracy. It is demonstrated that a wide error can easily be introduced without following a proper procedure for the LiDAR survey. [ABSTRACT FROM AUTHOR]

Fault arc tests showed that the three-phase fault arc currents depend on the arrangement of electrodes at the fault site and vary stochastically. Up to now, experimental investigations have mainly been carried out for the medium-voltage switchgears, and the fault arc currents are either recognized by the experimental results or derived by the probability method. A calculation method used for the determination of the three-phase fault arc currents is introduced in this paper, which can be expressed accurately by mathematics according to the characteristics of the three-phase internal faults. [ABSTRACT FROM AUTHOR]

As a free Electromagnetic Transient (EMT) simulation program, the Alternative Transient Program (ATP) cannot simulate in batch mode. Manual operation is very boring and prone to error when thousands of faults are to be simulated. In order to automate the process, based on close observation and analysis of the operation mechanism of the ATP, the letter concludes some useful rules and develops a software package to automate the ATP-based EMT simulation. [ABSTRACT FROM AUTHOR]

This letter proposes a curve-fitting approach for modeling fluorescent lamp voltage--current characteristics based on measured lamp voltage and current. The fluorescent lamp conductance is considered as a series of piecewise cubic polynomials that describes the nonlinear voltage--current characteristic of the lamp. The proposed model has been tested with a 10-W conventional 60-Hz fluorescent lamp and a 20-W high-frequency energy-saving lamp. By comparing the measured and simulated results, it shows that the proposed model can accurately model the lamps for harmonic studies. [ABSTRACT FROM AUTHOR]