An approach to dynamic line rating state estimation at thermal steady state using direct and indirect measurements

Abstract

Dynamic line rating has emerged as a solution for reducing congestion in overhead lines, allowing the optimization of power systems assets. This technique is based on direct and/or indirect monitoring of conductor temperature. Different devices and methods have been developed to sense conductor temperature in critical spans. In this work, an algorithm based on WLS is proposed to estimate temperature in all ruling spans of an overhead line. This algorithm uses indirect measurements -i.e. weather reports and/or downscaling nowcasting models as inputs as well as direct measurements of mechanical tension, sag and/or conductor temperature. The algorithm has been tested using typical atmospheric conditions in Iceland along with an overhead line's real design, showing robustness, efficiency and the ability to minimize error in measurements.

Conductor Temperature Estimation and Prediction at Thermal Transient State in Dynamic Line Rating Application

“…Equivalent values of sag and tension were computed using the values of T S -Theor. and measurement functions [19]. Then, direct measurements were simulated with the Matlab R function randn, adding values of normal random errors with mean zero and equivalent standard deviation to the sag, tension and temperature.…”

“…Thus, normal random errors with mean zero were added to current intensity (|i km |) with σ = 5/3 [A], to ambient temperature (T a ) with σ = 1/3 [K], and to wind attack angle (δ) with σ = 12.5/3 [ • ]. These standard deviations were taken from [19]. Table III shows the average RMSe and the average computing time to run Algorithm 1.…”

“…The expressions used for computing the partial derivatives of matrices F, L, H, M can be found in [19]. Finally, the proposed EKF for DLR estimation is shown in algorithm 1.…”

“…To implement the EKF, it is provided that the set of critical stringing sections are monitored by DLR hardware and their atmospheric conditions are known. The motivation to propose this algorithm is that currently used methods to minimize errors in the estimation of temperature in OHLs [17], [18], [19] are probably not the best choice for on-line dynamic state estimation during thermal transients. With the EKF, estimation and prediction of both states and parameters of nonlinear dynamic systems is reached [20].…”

Distributed vs. spot temperature measurements in dynamic rating of overhead power lines

“…An accurate knowledge of the electric grid state is crucial for operating the line as efficiently as possible and one of the most important grid parameters to be measured and controlled is the temperature of the overhead conductors due to their relation with the maximum allowable sag of the line and its thermal limit [4]. This paper presents the results of real-time monitoring of an overhead power line using a distributed temperature sensing system (DTS) [5,6] and compares these results with spot temperature measurements in order to estimate the loss of accuracy of having less thermal information.…”