This paper aims at characterizing and improving the metrological performances of Current (CT) and Voltage Instrument Transformers (VT) in harmonic measurements in power system. A theoretical analysis is carried out to demonstrate that, due to the iron core non linearity, CT and VT output signal is distorted even when the input signal is a pure sinusoidal. Starting from this analysis, a new method for CT and VT characterization and compensation is proposed. In a first step, they are characterized in sinusoidal conditions and the harmonic phasors of the distorted output are measured; in the second step, these phasors are used to compensate the harmonic phasors measured in normal operating conditions, which are typically distorted. The proposed characterization and compensation techniques are called SINDICOMP (SINusoidal characterization for DIstortion COMPensation). Several experimental tests, using high accuracy calibration setups, have been performed to verify the proposed methods. The experimental results showed that the SINDICOMP technique assures a significant improvement of CT and VT metrological performances in harmonic measurements.

The electrical arc occurring in the sliding con-1 tact between the supply contact line and the current collector 2 (pantograph) of an electrical locomotive is a fast transient 3 phenomenon able to degrade progressively the line-to-pantograph 4 contact quality and, consequently, the continuity of operation.

Nowadays, the interest in low-cost and increasingly accurate Phasor Measurement Units (PMUs) for active distribution systems is steadily growing. In this paper, an algorithm for synchrophasor, fundamental frequency and ROCOF estimation tailored for processing platforms with limited computational resources is described and characterized extensively in terms of both accuracy and processing time. The proposed solution harnesses the main advantages of two state-of-the-art algorithms, i.e. the Interpolated Discrete Fourier Transform (IpDFT) and the Taylor-Fourier Transform (TFT). Such algorithms are combined and implemented in a computationally-efficient manner to reduce processing time as much as possible, while ensuring good accuracy in the main testing conditions specified in the IEEE Standard C37.118.1-2011 and its Amendment C37.118.1a-2014. Estimation accuracy has been evaluated not only through simulations, but also experimentally. The good consistency between simulationbased and experimental results provides clear evidence that the uncertainty contributions due to transducers, acquisition and synchronization systems can be reasonably kept under control. The processing times of the algorithm, implemented on an embedded platform suitable for PMU prototyping, are compliant with the mandatory reporting rates of Class M PMUs.

The increasing interest in the use in medium and high voltage networks as well as in the low voltage ones of nonconventional low power instrument measurement transformers entails the availability of dedicated calibration set-up, equipped with flexible and accurate measurement systems. The paper presents a measurement system for the calibration of both inductive and low power voltage and current transformers, which includes a low cost and digital acquisition and measurement equipment. It is based on a portable data acquisition system composed of various current and voltage data acquisition boards. The proposed system can be used for the calibration of transducers with analog output from DC up to tens of kilohertz and allows the comparison of signals of different kind and order of magnitude.

A setup for the measurement of the frequency\ud response of voltage measurement transformers under actual\ud waveform conditions is presented. It is based on a two-step\ud procedure that makes use of high voltage gas insulated capacitors\ud and a digital bridge. It allows calibrations using distorted\ud waveforms, with a fundamental tone at medium voltage level\ud and superimposed harmonics up to 20% and 15 kHz. Combined\ud standard uncertainty in the measurement of the voltage transformer\ud (VT) error is estimated at 200 µV/V for the ratio error\ud and 300 µrad for the phase displacement up to 10 kHz. First\ud applications to the measurement of the frequency response of VTs\ud with different rated primary voltages up to 50 kV are presented