An effective controlled islanding method for power grid through a sequence of optimization problems

Controlled islanding is an important approach to prevent instability in power grids. In this paper, a novel approach is proposed for power system separation, which consists of two steps: 1) Finding multiple islanding scenarios, 2) Choosing the best option to reach the most desirable island. In the first step, different islanding solutions are determined by a proposed hierarchical clustering method. In this algorithm, which is based on minimum active power flow disruption objective function, the generator coherency constraints are considered in the clustering process. In the second step, the best separation scenario can be chosen based on an arbitrary objective function. Particularly, in this paper, the amount of load shedding and the voltage profile deviation after separation are considered as the final criteria to select the best solution among available options. In so doing, the degree of load importance is also taken into account. The proposed two-step method is applied on the IEEE 9-bus test system and also it is evaluated on the IEEE 39-bus grid. The simulation results on the IEEE 39-bus grid and the comparative analysis with a state-of-the-art method confirm that the final islanding solution is more optimized based on the secondary criteria, which cannot be concerned in the existing approaches. Moreover, the proposed method is computationally efficient and can be employed in the real-scale power grids.<br/

Conventional diverting techniques and novel fibr-assisted self-diverting system in carbonate reservoir acidizing with successful case studies

Conventional diverting techniques may not be useful, and the use of the advanced and well-documented diverting technique is needed to overcome the complexity and heterogeneity of carbonate reservoirs. Nowadays, there have been a lot of materials and techniques utilized for acid diversion. This paper aimed to consider various utilization of fiber-assisted self as the diverting system in acidifying carbonate reservoirs. One of the main reasons for its ability to overcome uncertainty is that the fiber itself is an inherent property, allowing for an automatic diversion adjustment downhole. When a media with infinite permeability, such as a perforation tunnel or natural fracture, is filled and bridged with a material of finite permeability such as degradable fiber, this creates a temporary skin to injectivity in that zone. This is a powerful concept, as it is a way, despite uncertainty from a lack of logging data or uncertainty in the data itself, of dampening the reservoir’s natural permeability contrast. It does not rely on petrophysical certainty to design a successful treatment

ANN-DEA Approach of Corporate Diversification and Efficiency in Bursa Malaysia

There is little consensus on the corporate diversification-efficiency relationship in the diversification literature. According to the corporate diversification, firms have a tendency to get more market share with diversifying in the local segment or in the international market. Theoretically, a contradictory exists between the profitable strategy and the value reducing strategy in the diversification strategy. In this paper, we measure firm’s efficiency by applying Data Envelopment Analysis (DEA) in manufacturing firms listed in Bursa Malaysia for five years. Meanwhile, a feed forward multilayer perceptron neural network is applied to model the mapping function between the input and output data to the efficiency score. Back propagation (BP) learning algorithm is applied to update network’s weights through minimizing the cost function, and the best topology of the network is conducted. The result of this study shows that there is a negative relationship between total product diversification and efficiency, and international diversification has a non-linear effect on the efficiency

Discriminating cloud to ground lightning flashes based on wavelet analysis of electric field signals

Lightning discharges produce electromagnetic radiation in a wide frequency range, but its propagation in a certain frequency range are usually used by lightning detection networks. Investigation of lightning activities in time-frequency domain can be obtained by using the wavelet transform. This study proposes a new approach using the discrete wavelet transform (DWT) algorithm to classify the detected lightning strikes. The measuring station would capture lightning electric field in 500 ms time scale and then utilizes a wavelet based recognizer algorithm to duly differentiate the cloud to ground flash from other cloud activities. Wavelet transform allows the expansion of transient events into a small number of coefficients. A total of 200 lightning flashes were randomly selected among the captured lightning discharges in South of Malaysia in one year. Initially, the cloud to ground and other cloud activities were manually analysed and discriminated. Then, these lightning flashes were analysed using different mother wavelets such as Haar, symmlet, Coiflet, and Daubechies by means of MATLAB program. Haar mother wavelet gives the best result for CG decomposition analysis. A total of 24 decomposition layers were chosen and the energy level of each layer was calculated to obtain the correlation between energy fluctuation and type of signal. The investigations reveal that the CG discharges have higher energy in 17th to 20th layers compared to the rest. However, the opposite results were obtained for the case of other cloud activities. To increase the accuracy of the wavelet transform approach algorithm, another filter was added to the algorithm flowchart. The proposed CG discrimination algorithm successfully classified 92% of the randomly selected flashes

Combined backscatter and transmission method for nuclear density gauge

Nowadays, the use of nuclear density gauges, due to the ability to work in harsh industrial environments, is very common. In this study, to reduce error related to the ρ of continuous measuring density, the combination of backscatter and transmission are used simultaneously. For this reason, a 137Cs source for Compton scattering dominance and two detectors are simulated by MCNP4C code for measuring the density of 3 materials. Important advantages of this combined radiometric gauge are diminished influence of μ and therefore improving linear regression