# Multi-Point Time-Synchronized Waveform Recording for the Analysis of Wide-Area Harmonic Propagation
## 1 Introduction  
Harmonic emission evaluation has been known as complex problem for many decades. Fluctuating nature of harmonics, high level of diversity and additional implications which appear with interconnection of Renewable Generation (RG) require improvement of the existing assessment and measurement methods. The problem is determination of the origin of harmonic distortion in the case when multiple sources of harmonics are connected to the network. The system-wide studies of harmonic propagation phenomena and emission assessment present challenges for researchers and engineers. In essence, the broad term 'propagation' includes several specific harmonic-related mechanisms among which are:  
* Harmonic interaction
* Phase angle diversity and cancellation
* Harmonic attenuation
* Impact of system and load impedance  
Given the dynamic nature of the mentioned processes an appropriate solution for investigation of harmonic propagation in specific parts of the power grid would be the application of multi-point distributed measurement system synchronized to a precision clock with high accuracy. Such ameasurement system configuration will allow the study of the harmonic response of a system to the current injection from diverse loads at different points of the electrical network. For power system analysis (not specifically PQ) synchronized measurements have already been proposed as a method for resolving several engineering tasks such as stability assessment, fault location, distribution state estimation, and event detection [1; 2; 3]. For these purposes, PMU-based infrastructure proved to be an efficient solution. Synchronized phasors reported by each PMU must comply with synchronization accuracy requirement of not worse than \(\pm 31.7\)\(\upmu\)s which is satisfactory for most of the applications sought by power system engineers. On the other hand, as authors of [4] have shown in their laboratory experiment, much stricter time synchronization requirement of not worse than \(\pm 1\)\(\upmu\)s has to be imposed when a fundamental goal is to process harmonic spectral components. Given the sub-microsecond time synchronization accuracy, the authors of [5] investigated the feasibility of assigning harmonic responsibilities based on data provided by distributed measurement system installed in small test bench power network. In [6], a methodology for calculating synchronized harmonic phasors was proposed. This methodology aimed to accurately resolve harmonic phase angles while reallocating samples between two subsequent PPS edges. This allows considerations to be taken with regard to deviations in fundamental frequency. Some studies investigated methodologies on determining individual harmonic current contributions. In [7], the authors reported results of an experiment involving synchronized measurements at large industrial plant facilities. Furthermore, in [8], by utilizing GPS synchronized PQ recorders installed as part of a real high voltage (HV) network, the authors investigated the phenomena of dynamic interaction of harmonic sources with special attention given to the grid code compliance. Large-scale harmonic measurements with provision of time-synchronized instruments were reported in [9]. The experiment was performed in a distribution system characterized by high penetration of RG. Values of harmonic amplitudes and intersite phase angles have been recorded and interpretation of results has been provided in comparison with the outcome of computer modeling. It is worth noting that PQ measurement techniques based on synchronized sampling are currently being developed not only for distortion-related issues but also for other PQ events, for instance dips, swells, and interruptions. An example of such a study was presented in [10] with a focus on offshore wind farms [4]. As current state-of-the-art shows that new measurement methods are vital for resolving challenges which are brought by the operation of modern power systems.