Ice Sleeves Research Articles

Resilience Assessment in Distribution Grids: A Complete Simulation Model

For several years, the increase of extreme meteorological events due to climate change, especially in unusual areas, has focused authorities and stakeholders attention on electric power systems’ resilience. In this context, the authors have developed a simulation model for managing the resilience of electricity distribution grids with respect to the main threats to which these infrastructures may be exposed (i.e., ice sleeves, heat waves, water bombs, floods, tree falls). The simulator identifies the more vulnerable network assets by means of probabilistic indexes, thus suggesting the best corrective actions to be implemented for resilience improvement. The fulfillment of grid constraints, i.e., loading limits for branches and voltage limits for buses, under actual operating conditions, is taken into account. Load scenarios extracted from available measurements are evaluated by means of load flow analyses in order to choose, among the best solutions identified, those compatible with the constraints. The proposed tool can assist Distribution System Operators (DSOs) in drawing up the Action Plan to improve, on one hand, the resilience of the network and, on the other hand, to remove any possible limitation for the adoption of the best solutions to ensure maximum operational continuity during extreme weather events.

Enhanced analytical model of power transmission line icing

Accidents in power transmission lines under icing conditions, in particular, those of cables, cause a great economic damage in Russia. Because of the lack of the possibility to forecast and evaluate reliably the consequences of weather conditions contributing to icing of transmisison line cables, power grid services often have to go to the place of a potential accident relying on guesswork. This leads to considerable losses of time and material resources, while the average recovery time of a damaged high voltage power transmission line is 5–10 days.For the effective prediction and timely prevention of negative consequences of icing of on power line cables, an analytical model that describes the growth of ice on the surface of the electrical cable has been developed. The model is based on a widely applicable analytical model of [1], supplemented with dependence of the growth of ice sleeve on the angle between the wind direction and the cable, and on the electric field strength of the cable.The results obtained using the new analytical model and the [1], model have been compared and show that as the angle between the wind direction and the cable decreases, the intensity of the ice growth decreases significantly. At the same time, the strength of the electric field of the cable affects negligibly the trajectory of water droplets.A conclusion is drawn about insignificance of electrical field strength of the electric cable as a factor of growth of ice deposits. It is stated that the ice thickness value obtained using the developed model can be increased under specific weather conditions and design parameters of transmission lines. The obtained model can be improved by using other physical effects that affect icing of electric cables. Further, the model can be introduced in operation of energy companies to monitor the condition of power transmission lines and to carry out anti-icing activities.

Wet snow hazard for power lines: a forecast and alert system applied in Italy

Abstract. Wet snow icing accretion on power lines is a real problem in Italy, causing failures on high and medium voltage power supplies during the cold season. The phenomenon is a process in which many large and local scale variables contribute in a complex way and not completely understood. A numerical weather forecast can be used to select areas where wet snow accretion has an high probability of occurring, but a specific accretion model must also be used to estimate the load of an ice sleeve and its hazard. All the information must be carefully selected and shown to the electric grid operator in order to warn him promptly. The authors describe a prototype of forecast and alert system, WOLF (Wet snow Overload aLert and Forecast), developed and applied in Italy. The prototype elaborates the output of a numerical weather prediction model, as temperature, precipitation, wind intensity and direction, to determine the areas of potential risk for the power lines. Then an accretion model computes the ice sleeves' load for different conductor diameters. The highest values are selected and displayed on a WEB-GIS application principally devoted to the electric operator, but also to more expert users. Some experimental field campaigns have been conducted to better parameterize the accretion model. Comparisons between real accidents and forecasted icing conditions are presented and discussed.

Numerical investigations of a new thermal de-icing method for overhead conductors based on high current impulses

The theoretical background of a thermal de-icing method for overhead bare conductors subjected to ice accumulation is presented. The proposed thermal method is based on Joule effect but uses current impulses superposed onto the AC nominal current of the conductor whose perimeter is half-covered by a semi-elliptic ice sleeve. The purpose is to study the influence of environmental parameters on the shedding time obtained. For theoretical investigations, a specific numerical model using finite elements, finite volumes and explicit finite differences was developed. Several numerical simulations were carried out in order to study the influence of characteristic environmental parameters such as air speed, air temperature and ice thickness on ice shedding time, number of required current impulses as well as temperature distribution along the ice/conductor composite. The results obtained showed that the use of current impulses allows the confinement of the Joule effect heat to the ice/conductor interface. By decreasing the current impulse duration or increasing the current impulse magnitude, a more efficient heat confinement can be obtained at the ice/conductor interface. Also, the results showed than this method is not sensitive to wind speed and that shedding time is decreased with thicker ice sleeves.

Combined Models for Glaze Ice Accretion and De-Icing of Current-Carrying Electrical Conductors

The ice storm of 1998 in northeastern North America caused much damage to the electrical installations of TransE/spl acute/nergie, the transmission provider in Que/spl acute/bec. Consequently, efforts to mitigate the effects of future ice storms have been deployed. A companion paper describes a project to deploy de-icing strategies over a region afflicted by an ice storm. It relies on a core computation that determines the current magnitudes and application times required to melt the ice off of energized conductors. This paper describes and compares the theory behind three de-icing models for transmission lines. The latter two models are new; they expand on a well-known de-icing computation by adding extra information about the ice buildup and the ice/water transition on the outer and inner surfaces of the ice sleeve, respectively.