International Journal of Power and Energy Research

9

Authors: Sagarika Kumar, Subinoy Roy, Rajesh Gupta

Standard environmental tests have been developed for photovoltaic (PV) modules to assess the reliability of their performance in a short period of time. These tests generate different modes of degradation by combination of environmental stresses. There is a need to differentiate between the standard tests on the basis of severity. This helps to understand the individual and combined degradation effect occurred due to temperature and humidity stress, which is the focus of the present study. In this work, standard tests viz. humidity freeze (HF), thermal cycling (TC) and damp heat test (DH) have been performed on different batches of multi-crystalline silicon PV modules. One batch of modules was subjected to combined tests wherein the three tests were performed in succession and the other batch was separately subjected to the individual tests. Spatial characterization techniques i.e. electroluminescence (EL) and dark lock-in-thermography (DLIT) imaging were used in tandem with illuminated current voltage (I-V) analysis for detection and quantification of degradation under the standard tests. The information obtained from the comparison between the different tests, on a scale of time and severity can be helpful for preliminary investigations performed on effects of the common environmental degradation factors like high temperature, high humidity and thermal ramping. The presented findings can further aid research and development on different aspects of reliability testing on PV module performance under environmental effects.

8

Authors: Minhhung Doan, Thaison Le, Thanhtrung Dang, Jyh-tong Teng

The heat transfer characteristics of a microchannel condenser in the phase change from the vapor phase to the liquid phase depend on many factors such as the physical parameters of the working fluid, the cooling fluid, etc. In this paper, the numerical results are clearly presented for the condensation profile, the density change, and the temperature of condensed water. Based on the results in this study, a function was suggested for predicting a relationship between the temperature of condensed water and the mass flow rate of steam from 0.01 g/s to 0.1 g/s. Moreover, the results of numerical simulation are in good agreement with the experimental data. In addition, the results showed that the condensation profile is not strongly affected the gravitational force.

11

Authors: Stylianos. Sp. Pappas

Electric load forecasting is a process that has to be both fast and reliable. An accurate method of load forecasting plays the most crucial role in achieving the aforementioned properties and also is a valuable tool in overcoming a variety of economic and operational problems connected to electrical energy production and distribution. In this study real data is used and the performance of three different techniques for adaptive electric load forecasting is evaluated. The first method is a combination of the well-established multimodel partitioning filter (MMPF) implementing extended Kalman filters (EKF) with Support Vector Machines (SVM), the second is the adaptive MMPF Kalman filters (KF) model and the third one is an artificial three layer feed-forward neural network (ANN). The results indicate that all three methods are reliable, however the combination of MMPF and SVM provides a more accurate load forecasting and at the same time identifies successfully both normal periodic behavior and any unusual activity of the electric grid.

14

Authors: Hilal Mohamed Al Ghaithi, George P. Fotis, Vasiliki Vita

Hybrid energy systems can provide various benefits to an island diesel power system. This paper analyses the technical and economic viability of hybrid energy system in the Masirah Island power system in Oman. The methodology involves the use of Hybrid Optimization Model for Electric Renewable (HOMER) for the optimization of the proposed hybrid system. The simulation software package DIgSILENT is used to model and simulate the integration of the proposed hybrid system to the existing network. Different scenarios are considered in both the hybrid system optimization and the assessment of the impact of the hybrid energy system integration implemented different connection scenarios. The obtained results show that the hybrid energy system composed of diesel, photovoltaic and wind generator units is the most economically feasible option since it provides the lowest system net present cost, operating cost and cost of energy, while it also improves the voltage profile at the point of connection.

7

Authors: Christos A. Christodoulou, Vasiliki Vita, Theodoros I. Maris

The adequate protection of the distribution transformers is a critical issue, in an effort to avoid interruption of the power supply and damages of the equipment. The installation of metal oxide gapless surge arresters at the entrance of the transformers improves their lightning performance and reduces the expected annual failure rate. However, arresters can be damaged, if the discharge current that passes through them is high enough, resulting in thermal stress of the device and possible failure. The parallel connection of arresters contributes to equal current sharing, reducing their failure probability. In the current work, the parallel combination of two metal-oxide gapless surge arresters installed at the MV side of a distribution transformer is examined, considering how the voltage – current characteristic of each arrester influences the expected voltage surges at the entrance of the transformer, the current sharing between the non-linear resistors and the arresters failure probability.

12

Authors: Sadegh Jamali, Hossein Borhani-Bahabadi

With growing penetration of distributed generation (DG) in electrical distribution networks (EDNs), miscoordination between fuse and recloser is more likely. This is the result of change of direction, as well as the magnitude of the fault current in the presence of DG where fuse saving cannot be achievd with standard recloser characteristics. This paper proposes a self-adaptive relaying scheme of reclosing operation for fuse saving in EDNs with DG. The recloser is programmed with a new non-standard characteristic using only the local voltage and current magnitude measurements. The proposed relaying scheme is tested for various fault conditions in a 20 kV Iranian radial EDN containing DG units at different locations. It is shown that the proposed scheme is not affected by the presence of DG units whereas the conventional relays fail the protection coordination. The proposed characteristic maintains proper recloser-fuse coordination for all fault types and different DG conditions.

17

Authors: Muwaffaq I. Alomoush

The Bacterial Foraging (BF) is a global optimization algorithm that imitates the foraging behavior of Escherichia coli (E. coli) bacteria. Foraging habit of individuals and groups of E. coli bacteria for nutrients is modeled as a distributed optimization process. This paper applies this powerful algorithm to design an optimal controller for a single-machine-infinite-bus (SMIB) system equipped with a power system stabilizer (PSS). The main target of the optimal design is to improve the dynamic and steady-state responses when the system is subjected to sever typical disturbances. The BF-based design of the PSS will be also compared with the designs obtained by the two commonly used global optimizers; the Genetic Algorithm (GA) and Particle Swarm Optimization (PSO). Simulation results presented in the paper indicate robustness and superiority of the proposed BF algorithm to solve the design problem, where the optimal BF-based controller can significantly stabilize the system and efficiently dampen oscillations under disturbances. Results also disclose that BF has the capability to offer a much better-quality global solution with better convergence characteristics than GA and PSO. Results show that the BF-based controller has better impact on system performance in terms of damping the electromechanical oscillations of the rotor angle, rotational speed, electromagnetic torque, and terminal voltage under various disturbance conditions and its damping speed is considerably faster. The significant improvement associated with the BFbased PSS is due to the fact that the BF algorithm leads to a better global solution of the optimization problem under study.