Field Trials for the Empirical Characterization of the Low Voltage Grid Access Impedance From 35 kHz to 500 kHz

Abstract

The access impedance of low-voltage (LV) power networks is a major factor related to the performance of the narrow-band power line communications (NB-PLCs) and, in a wider sense, to electromagnetic compatibility (EMC) performance. Up to date, there is still a lack of knowledge about the frequency-dependent access impedance for frequencies above 9 kHz and up to 500 kHz, which is the band where the NB-PLC operates. The access impedance affects the transmission of the NB-PLC signal, and it determines the propagation of the non-intentional emissions that may disturb other electrical devices, including malfunctioning or reduced lifetime of equipment. This paper presents the results of field measurements of the LV access impedance up to 500 kHz in different scenarios, with measurement locations close to end users and near transformers. The results provide useful information to analyze the characteristics of the LV access impedance, including variation with frequency, ranges of values for different frequency bands, and analysis of specific phenomena. Moreover, the results reveal a diverse frequency-dependent behavior of the access impedance in different scenarios, depending on the grid topology, the number of end users (that is, number and type of connected loads), and the type of transformation center. Overall, the results of this paper offer a better understanding of the transmission of NB-PLC signals and EMC-related phenomena. INDEX TERMS Impedance measurement, measurement techniques, electric variables measurement, transmission line measurements, communication channels, communication networks, electromagnetic compatibility and interference.

Comparison of Measurement Methods of LV Grid Access Impedance in the Frequency Range Assigned to Nb‑Plc Technologies

“…In both cases, the signal level, the frequency and other characteristics of the injected signals was configurable. The results of this measurement campaign show a great influence of the grid topology (number and length of branches) and the number and distance of the consumer loads [28].…”

“…Second, signals above 500 kHz must be filtered out to avoid coupling of radio signals and aliasing effects. Lastly, it must provide a flat frequency response in the frequency band of interest for the wide range of typical grid impedance values (1 Ω to 50 Ω) [1, 27,28]. The characteristics and validation of this voltage probe are described in Reference [54].…”

“…Within this frequency range, the magnitude of the LV access impedance varies with frequency, from values around 1 Ohm at lower frequencies, to several tenths of Ohms at higher frequencies, and at specific frequencies where resonance effects occur [1, [27][28][29], with values of a few Ohms [1, 27,30,31]. Impedance values may also vary between rural and urban areas [27,28] due to the different grid topologies and the higher number of customer loads connected to the grid in the urban environments. For long cables and high frequencies, the line impedance is dominated by the characteristic impedance of the cable [32].…”

“…This measurement method has been used in field trials developed in Spain, in collaboration with the DSO Iberdrola, in order to characterize the access impedance of the LV grid, both in rural and urban scenarios, up to 500 kHz [28]. In particular, the system used in the field trials was prepared to inject two types of ad-hoc signals into the grid: a single frequency sweep, as described in the previous sections, and controlled NB-PLC signals according to the transmission technology used by the DSO involved in the trials.…”

Field Trials for the Characterization of Non-Intentional Emissions at Low-Voltage Grid in the Frequency Range Assigned to NB-PLC Technologies

“…In total, the measurement campaign for the characterization of NIE and grid-impedance [48] was composed of 23 measurement locations (14 in urban scenarios and 9 in rural areas), most of them in tri-phasic distribution (19 tri-phasic, 4 mono-phasic locations), with more than one measurement in some locations, in different moments, which results in more than 70 measurements. A brief description of the measured locations for the NIE characterization has been included in Table 1 and additional details can be found in [48]: The measurement campaign was developed with the collaboration of authorized staff, who was in charge of connecting the measurement system to the selected points in the LV distribution grid. The presence of NIE in the shape of tonal emissions has been previously reported in the literature.…”