Stray voltages have always been a power quality concern to utility companies and customers. The long-term exposure to sufficient stray voltage can be harmful to human being's and animals' health. The stray voltage in the low voltage network is generally related to the load unbalance, grounding condition and network structure. Through analytical study and detailed system simulations, this paper makes a sensitivity study on how serious these factors affect the stray voltage in low voltage networks. Therefore some recommendations can be formulated to prevent the excessive stray voltage. On the other hand, this paper also provides guidance on how to identify the cause of excessive stray voltage incidence if it is detected.

The development of renewable energy can effectively reduce CO 2 emission and fossil fuel dependency. The costs for manufacturing and installation of wind generators can be reduced by using superconducting technology. Superconducting wind generators can be built smaller and lighter due to higher power density and efficiency. Semi-superconducting generators with superconducting field windings have relatively better technical and more feasible. This paper presents conceptual design of the field winding for a 12 MW offshore superconducting wind generator, based on general design specifications for this size of wind turbines. Different wires, cooling methods and coil sizes are analysed by finite element method (FEM) and compared. Finally, a structural design is also proposed.

This paper presents a probabilistic harmonic simulation method to study the power quality impact of electric vehicles (EV). The proposed method takes into account the random operating characteristics of the vehicles, such as random charging time, charging duration and vehicle locations. A multi- phase model of the primary and secondary systems is used to represent the study system. Extensive case studies have been conducted using the method and the measured EV data. The results reveal that the current versions of plug-in hybrid EVs have no significant harmonic impact on power systems. However, the Level 1 charger can increase the neutral to earth voltage at homes which could lead to increased stray voltage incidents.

To avoid self excitation and over voltage of generator during black start is one of the key factors for a successful start up.Based on the research of self excitation principle and judging method,a simple self excitation judging criterion has been adapted to analysis and calculates if the self excitation occurred in Liangjiang Power Station air 220kV Jiangdun line.A black start up simulation model has been established and the transient progress of black start up simulation has been carried out by Mat lab.The dynamic progress of black start up has been simulated in detail.

The proliferation of power-electronic-based residential loads has resulted in significant harmonic distortion in the voltages and currents of residential distribution systems. There is an urgent need for techniques that can determine the collective harmonic impact of these modern residential loads. These techniques can be used, for example, to predict the harmonic effects of mass adoption of compact fluorescent lights. In response to the need, this paper proposes a bottom-up, probabilistic harmonic assessment technique for residential feeders. The method models the random harmonic injections of residential loads by simulating their random operating states. This is performed by determining the switching-on probability of a residential load based on the load research results. The result is a randomly varying harmonic equivalent circuit representing a residential house. By combining multiple residential houses supplied with a service transformer, a probabilistic model for service transformers is also derived. Measurement results have confirmed the validity of the proposed technique. The proposed model is ideally suited for studying the consequences of consumer behavior or regulatory policy changes.