Equivalent Ice Thickness Research Articles

Research on equivalent ice thickness monitoring model of overhead transmission lines based on representative span

Research on equivalent ice thickness monitoring model of overhead transmission lines based on representative span

Experimental study on ice monitoring method for 10 kV transmission line with tangent tower in alpine landform

AbstractIce monitoring methods were applied for 110 kV and above transmission lines with tangent towers. However, the change in the vertical span is not considered, and a significant difference lies in the tower‐conductor structure of 10 kV transmission lines. For this reason, a proposal is made about the ice monitoring method for the 10 kV transmission line with tangent tower in alpine landform, which includes the ice monitoring system based on pressure measurement and corresponding equivalent ice thickness calculating methods. Different methods calculate the vertical span under different height difference coefficients. A finite element simulation model and a simulated ice load experiment system are established based on real conductors and insulators. Experiments and simulations under four simulated terrains are conducted within 2.5–20 mm ice thickness range. The comparison is made between this method and the method without considering the change in vertical span. The results show that the two methods are consistent and the relative errors are lower than ±4% in simulation and ±10% in experiment when the height difference coefficient is 0. When it is not 0, the relative errors of this method fall between +0.38% and +6.78% in simulation and −6.40% to +6.60% in experiment, while the relative errors of the method without considering the change in vertical span ranges between −11.13% and −20.23% in simulation and −11.65% to −23.20% in experiment.

Automatic Calculation of Graphic Area Change Rate for Icing Overhead Power Line Insulators Based on Bounding Box Automatic Matching and GrabCut Contour Automatic Segmentation

Image monitoring of icing insulators is valuable for ice-disaster risk management of overhead power lines. This paper proposes an automatic calculation method of graphic area change rate for icing insulators to address laborious manual viewing, computational complexity, poor generalization, weak interpretability, and label data demand of existing approaches. The method automatically identifies insulators in monitoring images by the trained YOLOv5 model, matches the ice-free and test images taken by the same terminal at the same angle utilizing intersection over union of identified bounding boxes, and segments them using an improved GrabCut algorithm. In the segmentation maps, insulator string contours before and after icing are automatically detected to compute the graphic area change rate. The graphic area change rate of insulators in 815 images monitored by 22 terminals from December 2017 to February 2018 is automatically calculated, which is separately data-fused with the tension monitoring value and equivalent ice thickness collected closest to the image acquisition time to obtain the 22 terminals' time series correlations. The correlations approximately follow normal distributions with mathematical expectations of 0.70 and 0.68 and reach 0.95 and 0.94 for high-quality image samples, respectively, verifying the effectiveness. The method enables real-time evaluation of insulators' icing degrees.

Icing detection method of 500 kV overhead ground wire with tangent tower under special terrain based on vertical tension measurement technology

The operation reliability of the power grid and the stability of social production are seriously threatened by the icing of the overhead line. The equivalent ice thickness (EIT) is to convert different densities and shapes of ice into the uniform annular ice with density of 0.9 g/cm3. Although many methods for calculating EIT of transmission line conductors have been proposed, there are lack an effective monitoring method of EIT for 500 kV ground wire with tangent tower under the special terrain where “the virtual lowest point” of the ground wire appears in the condition of large height difference. Therefore, a calculation method of EIT for 500 kV ground wire with tangent tower under the special terrain based on vertical tension measurement technology is proposed. That is the iterative method is used to preset different EITs. Then the calculated vertical tension under the preset values are solved by the established ground wire state equation and vertical tension equation. The EIT can be obtained when the calculated vertical tension is equal to the measured vertical tension. The comparison between the artificial observed EIT and the calculated EIT is carried out for two practical cases of 500 kV ground wire in the mountainous area of southern China. The results show that the absolute error is less than 2 mm, which verify the two values are in strong agreement. The corresponding finite element simulation models are established. A comparative study between the simulated EIT and the calculated EIT is carried out. The results show that the relative error is less than ±10% under severe icing from 10 mm to 30 mm and the absolute error is less than 1 mm under mild icing of 5 mm, which verify the two values are highly consistent. Finally, the application effect of this method in practical cases is analyzed.

Detection Method for Equivalent Ice Thickness of 500-kV Overhead Lines Based on Axial Tension Measurement and Its Application

Overhead line icing may threaten the operational stability of power grid. In this paper, a detection method for equivalent ice thickness of 500 kV overhead lines based on axial tension measurement was proposed. Firstly, according to the tension of insulator string when the transmission lines are not covered with ice, the horizontal distance from the lowest point of the transmission line to the tower on the side where the tension sensor is installed is calculated. Secondly, the state equation of the transmission line in the whole tension section is established. Then, the state equation is solved by iterative method. The initial ice thickness is taken as 0 mm. The ice thickness when the iteration value of tension <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">F</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">i</sub> is equal to the measured value of tension <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">F</i> is taken as the equivalent ice thickness of transmission lines. The actual cases of single span transmission line and multi-span transmission line were used for verification and application effect analysis of the proposed method. The results show that the detected results of this method were consistent with the artificial ice observation values of typical 500 kV single span and multi-span transmission line cases. The accuracy of the proposed method can be further verified through finite element simulation analysis. The variation trends of the detected ice thickness is consistent with the icing conditions created by the meteorological factors during the same period, and can be verified by the icing photos captured on site.

Calculation model and experimental verification of equivalent ice thickness on overhead lines with tangent tower considering ice and wind loads

Overhead line icing will seriously affect the safety of power grid. Accurately predicting the ice thickness on power lines is a persistent research problem. Accurate prediction is essential for the anti-icing/de-icing measures of power grid and prevention of serious ice accidents. Based on fluid mechanics theory, a simulation model for the aerodynamic characteristics of the typical icing section of conductor is established. The influence of wind attack angle, wind speed, ice thickness and section shape on the aerodynamic parameters (lift and drag coefficients) is analysed. Combined mechanics principle and conductors icing characteristics, a calculation model of equivalent ice thickness on transmission lines with a tangent tower is developed. The tension and inclination angle of insulator suspension point to tangent tower, as well as the ice and wind load characteristics are considered. Based on the field data from the State Field Scientific Observation and Research Station of Xuefeng Mountain Energy Equipment Security of Chongqing University, it is verified that the results of proposed model strongly agree with the actual measurements. The model can meet the requirements of the engineering applications, with the deviation of all the results less than 10%. The theoretical reference for the design, construction, operation and maintenance of anti-icing and mitigation with power infrastructure can be provided.

Equivalent ice thickness in ship ice transit simulations: overview of existing definitions and proposition of an improved one

ABSTRACTSeveral definitions of equivalent ice thickness for simplification of complex ice cover are found in the literature. However, their systematic analysis is currently absent. Therefore, this paper reviews different definitions and validates them against a high-fidelity ice transit simulator, determining the most accurate one, with an average error of 16% for one analysed ship, and 10.5% for the other. Furthermore, capability of equivalent ice thickness to predict ship besetting in ice is tested, accurately predicting this event in 88% of the cases. Moreover, sensitivity analysis to the parameters not included in the traditional definitions is conducted, and it is found that only the thickness of ridge consolidated layer has significant impact. Finally, traditional concept based on equivalent ice volume is extended, and a concept of equivalent-performance ice thickness is developed, outperforming the traditional approach by reducing the average error to 4.6% for one ship, and to 3.2% for the other.

Assessment of Transmission Line Icing State Based on Multi-Sensor Information Fusion

Due to considerations limited for the current monitoring techniques and computational models and other reasons,the accuracy rate of line icing condition assessment is not high. Transmission line icing are affected by many factors, having greater relevance with micro-meteorological parameters. To improve the assessment accuracy of transmission line icing condition,multi-sensor information fusion method are put forward for a comprehensive assessment to Line icing state, based on online monitoring system,considering the equivalent ice thickness of monitoring system, micro-meteorological parameters and duration of ice cover.BP neural network convergence line icing membership value, the output state is cing probability. Then ,the probability of the state of uncertainty output line integrated assessmen through Fuzzy Reasoning

Predictive Model for Equivalent Ice Thickness Load on Overhead Transmission Lines Based on Measured Insulator String Deviations

Transmission-line icing presents a serious threat to the safe operation of power systems. Therefore, the icing condition of overhead transmission lines must be accurately calculated for online monitoring and prewarning systems. Based on the icing data obtained at Xuefeng Mountain Natural Icing Stations (XMNIS), the cross-sectional shape of glaze icing on conductors was studied, and the correction coefficient of the actual nonuniform ice was proposed to provide an accurate and convenient method for field icing measurement. In addition, by analyzing the characteristics of the tension and tilt of the insulator string at the iced tangent tower, a new mechanical calculation model considering the ice and wind loads was established. One-month field observations and experiments were conducted in XMNIS, and it is shown that the calculation results have good agreement with experiment results, which suggests that the model can be used for ice thickness calculation and online monitoring on transmission lines.

Sea-ice management and its impact on the design of offshore structures

Abstract A methodology for including ice-management in a structural reliability analysis is presented. The approach mainly focuses on how icebreakers or offshore installation disconnection capabilities may alter ice-load distributions and thereby reduce the probability of failure. To demonstrate the approach, a moored symmetrical structure in the central Barents Sea was considered. Realistic ice data from a probabilistic ice-drift simulator was used as a basis and ice loads were calculated in hourly time steps for a 1000-year period. The load calculations were based on the transformation of all developing ice conditions into a standardized equivalent ice thickness. Furthermore, empirical formulations for ice resistance on icebreaking vessels were combined with “max-to-mean ratios” from physical tank-model tests to estimate peak loads. The demonstration reveals a need for more relevant ice-load models that are valid both for managed as well as unmanaged ice. The methodology used for the calculation of ice equivalency and ice loads significantly underestimates the loads from severe ice features (compared to approaches recommended in ISO 19906). In a severe ice environment, it was found that the icebreaker's ability to reduce ice loads was insufficient to reduce the most extreme (abnormal) loads. The ability to disconnect moorings and risers and escape the site prior to abnormal ice events will ensure that the ice loads are within an acceptable range, conditional that the disconnection capabilities are sufficiently reliable. A fault-tree analysis including failure probabilities in ice-management operations and/or disconnection operations is considered useful for estimating the frequency of specified accidents.

The effect of density variations during rime growth on overhead transmission line conductors

Known density relationships, which are functions of the variables and parameters controlling rime-ice accretion on circular cylinders, are incorporated in a heat and mass transfer rime-icing model, to give predictions for the iceload and equivalent ice thickness during the evolution of the ice surface. Whereas predictions for ice thickness and ice shape are found to depend on the choice of density relationship, predictions for the transient iceload are in satisfactory agreement. A recommendation is made for adopting a density relationship which can be readily used to predict iceloads on overhead line conductors, having finite span and finite torsional stiffness.

Statistical properties of sea ice surface topography in the Baltic Sea

The results from helicopter-borne laser profiling of the ice surface in the Baltic Sea for March 1988 are presented. The laser was a PRAM III system with a measurement frequency of 1–4 kHz, a footprint of approximately 20 cm at a flight elevation of 100 m and a single-shot vertical resolution of 12.5 cm. The laser profiles were calibrated to remove aircraft motion and averaged to 1-m intervals which combined to produce an elevation accuracy of 1.8 cm. A total of 51 profiles with varying lengths from 6 to 24 km, in all 662 km, are analysed. The data were stratified into 5 groups representing different ice fields. The standard deviation of the surface elevations ranged from 7 to 14 cm. The spectrum of surface roughness displayed a red noise form (slope about − 1.5) through the wave-lengths 4 to 100 m. Ice ridges were identified using the Rayleigh criterion with a cutoff height of 40 cm. The mean ridge height ranged from 52 to 59 cm, the standard deviation 12 to 20 cm, and the maximum ridge height sampled was 197 cm. The number of ridges was 1.4 to 9.5 km −1 for 4 of the groups and up to 17.4 km −1 in one group representing an intense shear zone. Ridge heights were exponentially distributed whereas the log-normal distribution provided the best fit for the ridge spacings. Mean ridge height and ridge density were not strongly correlated. The amount of ridged ice was estimated to account for 1 to 18 cm of equivalent ice thickness while based on a crude extrapolation method rubble fields summed up to 2 to 10 cm. Deformed ice constituted 15 to 40% of the total ice volume. DOI: 10.1034/j.1600-0870.1993.t01-1-00004.x