Online Estimation of Cable Harmonic Impedance in Low-Voltage Distribution Systems

Abstract

Incorrect values of cable harmonic impedance can lead to wrong conclusions when assessing an impact of current distortion on the power network. A theoretical derivation of resistance and reactance for harmonic frequencies is not sufficient as it neglects operating conditions of cables as well as their configuration and actual installation pattern. In this paper, a noninvasive procedure for estimating parameters of the low-voltage cable is proposed. On contrary to invasive methods, the proposed technique does not require any external sources of harmonic excitation, and consequently, it does not introduce additional disturbances to the system. A disconnection of the cable is not required as the procedure meant to be performed online. The methodology employs natural variations of harmonic currents and voltages; however, the impedance angle is preserved due to the utilization of synchronized measurement samples. The developed signal processing algorithm provides noise reduction capabilities and smoothing of the output in presence of fluctuating harmonics. In addition, an attention is given to the metrological characterization of the measurement system and evaluation of uncertainty of impedance values. The results of the laboratory experiment indicate that for selective harmonics the variations of impedance estimates are no more than 10 m , which is in the range of calculated uncertainty values. The practical applicability of the method is discussed together with its limitations.

An approach to the impedance modelling of low-voltage cables in digital twins

“…Primitive impedance matrices or series impedances form the foundation for modelling distribution networks. Unbalance analysis or harmonic inspection, as well as simulations of the impact RES generates on distribution networks [19,[24][25][26][27] necessitate accurate modelling of the lines in order to produce accurate results. While calculating the primitive impedance matrix, geometrical parameters are important.…”

Application of computational methods for harmonic state estimation of power system networks

“…Topology evaluation networks were investigated in [15], which are defined as strategic sites for meter connections, and measured values used to calculate the rest of the variable state (X series and Y shunt). In [16,17], the topology approach was introduced and used to achieve harmonic state estimation (HSE), which is conducted by assuming that the current measured by a power quality meter is connected to a bus and can change the PQ meter location depending on the number of sections linked to the corresponding bus. However, the assumptions in this approach are not pragmatic owing to the limited number of channels for most power quality meters.…”