Abstract
This paper proposes a methodology for determining the optimal bidding strategy of a retailer who supplies electricity to end-users in the short-term electricity market. The aim is to minimize the cost of purchasing energy in the sequence of trading opportunities that provide the day-ahead and intraday markets. Agenetic algorithm has been designed to optimize the parameters that define the best purchasing strategy. The proposed methodology has been tested using real data from the Spanish day-ahead and intraday markets over a period of two years with a significant cost reduction with respect to trading solely in the day-ahead market.

Abstract
This paper proposes an optimization model based on a centralized dispatch to analyze the impact of plug-in electric vehicles (PEV) penetration on the Spanish electricity demand and price. Different charging strategies, from the plug-and-charge strategy to the smartest vehicle-to-grid (V2G) capabilities, have been simulated and compared with the non PEV scenario, under different penetration values. Traditional generation resources have been represented with technical aspects such as ramps and minimum loads. Hydraulic resources management is also partially supported but limited to weekly management. Distribution network constraints and how they could limit the contribution of PEV to the grid services have been neglected. The model considers both load and reserve requirements to evaluate the PEV contribution to energy production or consumption, but also to secondary reserve regulation. Interesting results comparing the different simulation scenarios are discussed in the case examples. © 2012 IEEE.

Abstract
Modeling competition in the future European Electricity Market (EEM) suggests considering new perspectives of leadership between the participant generators. EEM models should then be able to represent the possible existence of leaders and followers, and Conjectural Stackelberg equilibriums could be a powerful approach to do so. These asymmetric equilibriums can represent several types of competitive advantages among the market participants, though existing literature approaches generally assume single-leader-follower games. In addition, the complexity of the resolution methodologies sometimes compromises their applicability, especially if large-scale problems have to be solved. In this paper, a multi-leader-follower conjectural Stackelberg equilibrium model is presented. A simple convex quadratic optimization problem is proposed for its resolution, and the conditions for the equilibrium existence are discussed. A case study is presented to validate the model, and to analyze how market competition changes with the number of leaders or followers. The main conclusion is that if leadership spreads and Stackelberg models are used for its representation, regulatory policies should be oriented to increase the number of followers. However, there exists a maximum number of followers for which Stackelberg equilibriums does not exist, suggesting a deeper analysis for these cases to understand that matter and to decide the possible use of other market models. © 2012 IEEE.

Abstract
High penetration of renewable energies presents a new challenge for conventional power system. Such penetration of renewables resulted in renewed interest in load modeling which may include small renewable generation as a portion of loads. A new CIGRE working group was established to provide guidance with respect to load modeling of new types of load including renewables using measurement data and historical data. This paper summarizes major results of the work of this WG after two years' activities. Although the deliverables are not fully completed, beneficial recommendations of the load modelling such as selection of load model structure, picking up suitable data, proper approach for deriving load model parameters, requirement of measurement data, etc. are introduced in this paper identifying clearly advantage and disadvantage of various load modelling approaches.

Abstract
Conventional second harmonic current restriction approach is an adopted method which has been implemented to transformer differential protection schemes. Because of unreliable nature of this approach in discrimination between inrush current, internal faults and external faults and due to the saturation of current transformers, we present new features of the differential protection scheme. This helps to determine the feasibility and applicability of the proposed approach in differential protective scheme for power transformer. The Current Transformer Saturation (CTS) phenomenon issue and its revelation is one of the most significant problems in power system protection particularly in the differential protection. In this paper, the saturation phenomenon and its effects on the differential protection are analyzed. Prevalent algorithms in digital signal processing which are implemented in power system cannot correctly recognize this phenomenon. Mal-operation of differential protection relay takes place when saturation in CT is appeared. This paper presents a Third-Difference Algorithm (TDA) for CTS recognition. In order to make comparison between the presented approach and prevalent digital protective algorithm, an identical case study is simulated. Simulation results also show that the TDA is both satisfactory and consistent with expectation. © Indian Society for Education and Environment (iSee).

Abstract
This paper presents descriptive equations on the voltage breakdown in ultra-quick circuit breakers (UQCB). In this paper, main breakdown characteristics of UQCB's are presented. Gaseous breakdown in the sub-nanosecond regime is of interest for fast pulsed power switching, short pulse electromagnetics, and for plasma limiters to protect devices from high power microwave radiation. In order to study pulsed gas breakdown initiation dynamics, a sub-nanosecond voltage pulse is simulated by Electro-Magnetic Transient Program (EMTP). © Indian Society for Education and Environment (iSee).