Instrument transformers (ITs) play a key role in electrical power systems, facilitating the accurate monitoring and measurement of electrical quantities. They are essential for measurement, protection, and metering in transmission and distribution grids and accurately reducing the grid voltage and current for low-voltage input instrumentation. With the increase in renewable energy sources, electronic converters, and electric vehicles connected to power grids, ITs now face challenging distorted conditions that differ from the nominal ones. The study presented in this paper is a collaborative work between national metrology institutes and universities that analyzes IT performance in measuring distorted voltages and currents in medium-voltage grids under realistic conditions. Both current and voltage measuring transformers are examined, considering influence quantities like the temperature, mechanical vibration, burden, adjacent phases, and proximity effects. The study provides detailed insights into measurement setups and procedures, and it quantifies potential errors arising from IT behavior in measuring distorted signals in the presence of the various considered influence quantities and their combinations. The main findings reveal that the temperature has the most evident impact on the inductive voltage transformer performance, as well as the burden, causing significant changes in ratio error and phase displacement at the lower temperatures. As for low-power ITs, establishing a priori the effects of adjacent phases and proximity on the frequency responses of low-power ITs is a complex matter, because of their different characteristics and construction solutions.

The paper presents and evaluates three advanced methods for the characterization of the low-voltage (LV) grid access impedance for the frequency range assigned to Narrow Band-Power Line Communications (NB-PLC): 9 kHz to 500 kHz. This study responds to the recent demand from both regulatory bodies and Distribution System Operators about the need for accurate and validated methods for this frequency band, due to the limited knowledge of the impedance values in the electrical grid and their influence on NB-PLC transmission channels. In this paper, the results of a collaborative work to develop different proposals to overcome the challenges for the proper characterization of the frequency and time-varying grid impedance, from different theoretical approaches, are presented. The methods are compared in a controlled and isolated scenario: the impedance characterization of passive filters. Then, the results are validated two-fold: first, against theoretical simulations, based on the schematics provided by the manufacturer, and second, against the measurement results of a precision impedance meter, used as a reference of accuracy. The results demonstrate a high degree of precision of the three proposals to characterize the access impedance of the LV grid.

The standard flickermeter (voltage flickermeter) algorithm commonly used for the evaluation of flicker severity in current electromagnetic compatibility standards originates from the 1980 s. It was developed to mimic irritation of an average human observer by flickering incandescent lamp as a reference light source and optimized to voltage fluctuations caused by arc furnaces. However, the algorithm is questionable as the situation in the grid changed since the 1980 s; many modern devices are being connected to the grid, creating voltage distortion patterns which are not properly recognized by the voltage flickermeter. In addition, incandescent lamps have been largely replaced by discharge lamps and later by LEDs. Transitioning the algorithm from incandescent lamp light to LED light requires detailed revision of every part of the algorithm. This paper is concerned with verifying the frequency weighting function of the average human observer which is one of the bases of the voltage flickermeter, as well as of the derived light flickermeter. Flicker sensitivity of 34 human observers is measured with two different light sources (LED warm and neutral white, incandescent lamp) and compared with the frequency weighting function used in the current specification of the flickermeters in standards. Finally, an optimization of the weighting function is proposed based on the findings.

Quantifying harmonic contribution of customer installations to the voltage distortion in the network is still one of the main challenges of utilities with respect to power quality, particularly when integrating large number of renewable energy sources. This paper discusses different aspect of evaluating the low-order harmonic emission of a 100 kW photovoltaic (PV) installation consisting of 16 single-phase inverters. Based on field measurements of one week the harmonic currents of the installation are analyzed with respect to different operating conditions. The measured harmonic currents are compared with emission values provided by the manufacturer as well as emission limits specified in standards. Finally, different methods for the determination of the contribution of the PV installation to the voltage distortion in the network are compared.

Flicker is a subjective perception of instability of artificial light sources, which can be, under certain conditions, induced in a human observer by temporal light modulation (TLM). As such, it is addressed by the CIE as a phenomenon related to lighting, but also by the International Electrotechnical Commission (IEC) as a phenomenon related to light sources that are supplied by electricity and whose properties are eventually governed by electronic circuits. However, each organisation uses not only slightly different definitions of what flicker is, but also of the visibility/perceptibility threshold of flicker in terms of TLM properties. This paper aims to compare these definitions. To this end, a data set of threshold measurements with human observers performed via QUEST procedure is evaluated according to each definition. Resulting thresholds are then compared in order to determine whether both definitions of threshold are equivalent (i.e., yield the same threshold).