International Journal of Power and Energy Research

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.