Sukumvit Phoomvuthisarn

Optimal SVC and TCSC Placement for Minimization of Transmission Losses

Proper placement of static VAR compensator (SVC) and thyrlstor controlled series compensator (TCSC) reduces transmission losses, increases the available capacity, and improves the voltage profile. This paper presents an optimal placement of SVC and TCSC to determine SVC and TCSC locations and control parameters for minimization of transmission loss. Optimal location method utilizes the sensitivity of total real power transmission loss with respect to the control parameters of devices and multiply with new equation. The new equation of SVC is sum of reactive power flow that has relationship with bus and the new equation of TCSC is sum of real power loss that has relationship with transmission line. The method of optimal control parameters utilizes the interior point method for the minimizing real power loss. The results have been obtained on IEEE 14 bus, IEEE 30 bus, and IEEE 57 bus test system. Test result shows that both SVC and TCSC can determine optimal placement.

Hybrid ant system/priority list method for unit commitment problem with operating constraints

This paper presents a new method to solve unit commitment problem with operating constraints using a hybrid ant system/priority list method (HASP). The proposed methodology employs ant system in cooperating with the priority list method to find unit commitment solution as means of mutually combining the advantages of them in that a flexibility of the priority list method is reinforced, while AS algorithm can gain the benefit of using bias information for improving its performance during search process. The simulation results show that the proposed HASP is capable of obtaining satisfactory solution within reasonable computational time. Moreover, the proposed HASP can be extensively applied to handle the ramp rate limits and the operating reserve constraint, which are important for modern power system operation.

A solution to unit commitment problem using hybrid ant system/priority list method

This paper presents a new method to solve unit commitment problem with operating constraints using a hybrid ant system/priority list method (HASP). The proposed methodology employs ant system in cooperating with the priority list method to find unit commitment solution as means of mutually combining the advantages of them in that a flexibility of the priority list method is reinforced, while AS algorithm can gain the benefit of using bias information for improving its performance during search process. The simulation results show that the proposed HASP is capable of obtaining satisfactory solution within reasonable computational time.

Relativity Pheromone Updating Strategy in Ant Colony Optimization for Constrained Unit Commitment Problem

This paper presents a development of the enhanced ant colony optimization (EACO) based on a novel approach of the relativity pheromone updating strategy (RPUS) for solving constrained unit commitment problem which cooperates with the candidate path management module (CPMM) embedded the effective repairing heuristic module (ERHM) in reducing search space and recovering a feasible optimality region so that a high quality solution can be acquired in a very early iterative. The adoption of RPUS not only enhances the search convergence of EACO, but also provides relatively pheromone information that is suitably exploited for a good guidance of search process. The EACO algorithms have been performed on a test system up to 100 generating units with a scheduling time horizon of 24 hours. The numerical results show better economical saving in the total operating cost when compared to the previous literature results. Furthermore, the proposed EACO topology can remarkably speed up the computation time of ant colony optimization algorithms, which is favorable for a large-scale UC problem implementation.

The Line P-Q Curve for Steady-State Voltage Stability Analysis

Generally, resistances and susceptance of transmission lines are neglected in determining voltage stability limit. Differently, this paper includes such parameters to form the P-Q curve analyzed as a rotated parabola. In the region inside the line P-Q curve, a power system can operate normally, but in the outside the system operation is impossible. The line voltage collapse coefficient is determined by using the concept of the line P-Q curve. This coefficient can be used to find weak lines in the power system. It relates to the minimal distance of the P-Q boundary curve, the probability of safe load transmission and the probability of positive bus influence on load transmission. The minimal distance and the probability of safe load transmission can be determined by equations in this paper. While the probability of positive bus influence on load transmission is given from the exact post-contingency analysis with a P-V curve. The lower the values of line voltage collapse coefficient, the weaker the transmission line. The threshold of line voltage collapse is shown in this paper. The proposed method is tested on the modified IEEE 14-bus test system. The result shows that some transmission lines would be monitored carefully to prevent voltage collapse. In practice, this method can detect the weak lines. We can solve the voltage collapse problem before it occurs.

Selective self-adaptive approach to ant system for solving unit commitment problem

This paper presents a novel approach to solve the constrained unit commitment problem using Selective Self-Adaptive Ant System (SSAS) for improving search performance by automatically adapting ant populations and their transition probability parameters, which cooperates with Candidate Path Management Module (CPMM) and Effective Repairing Heuristic Module (ERHM) in reducing search space and recovering a feasible optimality region so that a high quality solution can be acquired in a very early iterative. The proposed SSAS algorithm not only enhances the convergence of search process, but also provides a suitable number of the population sharing which conducts a good guidance for trading-off between the importance of the visibility and the pheromone trail intensity. The proposed method has been performed on a test system up to 100 generating units with a scheduling time horizon of 24 hours. The numerical results show the most economical saving in the total operating cost when compared to the previous literature results. Moreover, the proposed SSAS topology can remarkably speed up the computation time of ant system algorithms, which is favorable for a large-scale unit commitment problem implementation.

Relative Velocity Updating in Parallel Particle Swarm Optimization Based Lagrangian Relaxation for Large-scale Unit Commitment Problem

This paper presents an effectiveness of combined parallel relative particle swarm optimization (PRPSO) and Lagrangian relaxation (LR) for a large-scale constrained unit commitment (UC) problem in electric power system. The proposed algorithm incorporates PRPSO with a new relative velocity updating (RVU) approach to tradeoff the solution of each slave processing unit. The parallel algorithm based on the synchronous parallel implementation is developed to consider the neighborhoods decomposition of multiple particle swarm optimizers. The proposed PRPSO divides the neighborhood into sub-neighborhood so that computational effort is reduced and UC solutions are remarkably improved. The proposed method is performed on a test system up to 100 generating units with a scheduling time horizon of 24 hours. The numerical results show an economical saving in the total operating cost when compared to the previous literature results. Moreover, the proposed PRPSO based RVU scheme can considerably speed up the computation time of a traditional PSO, which is favorable for a large-scale UC problem implementation.

Minimization of Transmission Loss with Consideration of Transformer Taps Constraint

This paper describes the solution of minimization of transmission loss with consideration of transformer taps constraint. The transformer taps are using as control variables for transmission loss minimization and maintain voltage profile when the disturbance occurs in system. When transformer taps are only used for minimization of transmission loss that has to control transformer taps close to center. Proposed methodology is to control the stages of transformer taps close to the center of transformer taps. The equation of transformer taps stages is included in the objective function and in inequality constraints. An optimal power flow problem is solved by using interior point method. The problem constraints are the power flow equation, the bound of the power system and stages of transformer taps. The performance of the method is illustrated in IEEE 14 bus, IEEE 30 bus, and IEEE 57 bus test system. Test results show that the transmission loss can be made minimum and transformer taps can be controlling close to the central tap.

Influence of Ground Potential Rise on Recloser Control Broad in Distribution Lines

This paper presents the numerical analysis method of current distribution electromagnetic fields, using grounding and soil structure analysis (CDEGS) software to interpret apparent resistances field measurement result. The steepest descent method is the function of least-square criterion which is adopted to translate and to explain the field measured result. When the ground fault occurs in any location in power system, the zero-sequence fault current will return to the power system grounded sources through the earth. They make gradient potential and ground potential rise (GPR) in the vicinity ground source. When the GPR is high, it produces shocks and makes damage to equipments. Which they have affected the stability and reliability of distribution lines during operation. So, it is essential to study and to analyze for the influence of GPR. This study has been simulated and evaluated the GPR by using CDEGS software.

The Effect of Convexity of Lightning Impulse Voltage Waveforms on Accuracy of HV Measuring Systems

This paper presents the effect of convexity of lightning impulse voltage waveforms on accuracy of HV measuring systems. The effects of different three convexities on wave front are analyzed by simulation tests with some standard waveforms. The simulation tests have two aspects. First one is consideration in frequency domain by using FFT with standard waveforms and transfer function of measuring system and second one is consideration in time domain by using time convolution method or Duhames integration method for computing waveform outputs standard testing waveforms and unit step responses of the sample measuring systems. The standard waveforms under investigations are full lightning impulse voltage waveforms, tail-chopped of lightning impulse voltage waveforms, front-chopped of lightning impulse voltage waveforms according to IEC standards 60060-2. This paper considers two samples of different types of the measuring systems. The results show that the convexity has effect on accuracy of measuring systems.