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Inverter-Based Resources (IBRs) are challenging traditional line protection systems, that have been designed and developed over the years considering the fault characteristics of synchronous generator dominated power systems. The response of IBRs under faults is mainly driven by the inverter control design that can vary across different manufacturers. This study focuses in assessing the performance of negative and zero sequence voltage polarized ground directional elements in a Medium Voltage (MV) distribution grid with increased penetration of Photovoltaic (PV) systems. A system has been developed, modelling a part of a distribution grid and utilizing detailed Electro Magnetic Transient (EMT) models to emulate the behavior of IBRs. The design of the substation protection scheme includes an 11 kV blocking scheme employing ground directional elements. The system is simulated in a real time environment and Hardware In the Loop (HIL) tests are performed with actual protection relays utilizing the industry standard IEC 61850 protocol for the communications. The performance of the blocking scheme is examined under different configuration scenarios, with the results indicating that under certain conditions, with heavy IBR fault contributions, the protection scheme is impacted negatively.

The fast deployment of the Phasor Measurement Units (PMUs), especially in the transmission level of the power systems, enables the development of wide area monitoring, protection and control (WAMPC) applications that enhance the situational awareness of the power system operator as well as the stability of the power system. Such applications are dependent on the communication network that supports the transfer of the PMU measurements to a central monitoring application or to a local protection application (situated in a substation). It is therefore of paramount importance to ensure the transfer of measurements with the least delay, while at the same time to ensure the integrity of the PMU measurements. In this work, the impact of using a wireless communication network for transferring the PMU measurements to the WAMPC applications is examined and the advantage of the 5G communication network over 4G and 3G in such real-time monitoring and control applications is demonstrated.

This deliverable aimsto elicit the necessary regulatory, technological and IT requirements for scaling up TSO-DSO-large consumers coordination models with a view to providing near real time scalable coordination among market and network operation.

The most widely used method for monitoring Low Voltage Distribution Grids (LVDGs) is the three phase Weighted Least Squares (WLS) State Estimation (SE), which was initially developed for Medium Voltage Distribution Grids (MVDGs). This methodology is implicitly applied in LVDGs with an assumption that the neutral conductor represents a zero potential across the whole system. However, this assumption is often not valid for LVDGs as the consumers loads are highly asymmetrical and the neutral conductor is usually grounded only at the MV-LV transformer substation. Therefore, if this method is applied for the monitoring of LVDGs it may deteriorate the performance of the WLS SE leading to inaccurate results. In this paper, an investigation is initially conducted in order to evaluate the performance of the conventional WLS SE methodology when applied for the monitoring of LVDGs. The results of this study indicate that the performance of this methodology is not consistent and is highly affected by the operating conditions of the LVDG. In view of these results, a new methodology is proposed and developed that takes into consideration the effect of the neutral conductor and as a result an outstanding performance is achieved compared to the conventional methodology.

Various factors which can occur in the power system can potentially have a negative impact on the damping performance of a wide area controller, in case they are not properly considered. Such factors might be the measurement uncertainty of Phasor Measurement Units (PMUs), line parameters error, topology changes, and measurement delays of PMUs due to the communication network. Therefore, it is important to identify which factors are capable of affecting the wide area control (WAC) damping capabilities, in order to find ways to compensate their effect. In this paper, a case study is performed, where each factor is separately considered when a line is tripped and reclosed. The results indicate that data delays and topology changes are the factors which deteriorate the performance of the WAC. The simulations are based on the IEEE 39-bus dynamic test system., © 2017 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works. L. Zacharia, M. Asprou and E. Kyriakides, "Investigation of the Factors Influencing Wide Area Control," in IEEE PES General Meeting, Chicago, 2017.

Includes bibliographical references (p. 131-140). Number of sources in the bibliography: 94 Thesis (Ph. D.) -- University of Cyprus, Faculty of Engineering, Department of Electrical and Computer Engineering, 2015. The University of Cyprus Library holds the printed form of the thesis. Η εφαρμογή της τεχνολογίας συγχρονισμένων μετρήσεων (ΤΣΜ) συνέβαλε στην έναρξη μιας νέας εποχής για τις εφαρμογές που είναι υπεύθυνες για την παρακολούθηση και τον έλεγχο των συστημάτων ηλεκτρικής ισχύος. Συγκεκριμένα, η συσκευή μέτρησης φασιθετών (ΣΜΦ), που αποτελεί βασικό στοιχείο της ΤΣΜ είναι σε θέση να παρέχει σε πραγματικό χρόνο, υψηλής ακρίβειας μετρήσεις φασιθετών τάσης και ρεύματος. Αυτά τα χαρακτηριστικά μπορούν να εφαρμοστούν σε υπάρχοντα εργαλεία του κέντρου ελέγχου με σκοπό την βελτίωση της απόδοσης τους. Η πιο φυσική εφαρμογή της ΤΣΜ είναι ο εκτιμητής κατάστασης, ο οποίος αποτελεί τον ακρογωνιαίο λίθο του κέντρου ελέγχου, παρέχοντας σημαντικές πληροφορίες σχετικά με την κατάσταση λειτουργίας του συστήματος ηλεκτρικής ενέργειας. Δεν θα ήταν υπερβολή να παρομοιάσουμε τον εκτιμητή κατάστασης, σαν τα "μάτια" των διαχειριστών του συστήματος ηλεκτρικής ισχύος. Λόγω της σημασίας του εκτιμητή κατάστασης, οι προσδοκίες για αυτό το εργαλείο είναι μεγάλες, γι’ αυτό και υπάρχει μια συνεχής προσπάθεια για τη βελτίωση της ακρίβειας, της αξιοπιστίας, της ευρωστίας, και της απόδοσης του. Σε αυτή την εργασία, τα χαρακτηριστικά της ΤΣΜ χρησιμοποιούνται για τη βελτίωση της ακρίβεια και της λειτουργίας του εκτιμητή κατάστασης σε πραγματικό χρόνο. Πιο συγκεκριμένα, σε αυτή τη διατριβή προτείνεται ένας υβριδικός εκτιμητής κατάστασης, ο οποίος ενσωματώνει τόσο συμβατικές όσο και μετρήσεις από ΣΜΦ στο ίδιο διάνυσμα μετρήσεων, παρέχοντας εξαιρετικά ακριβή εκτίμηση της κατάστασης του συστήματος ηλεκτρικής ισχύος. Ο προτεινόμενος εκτιμητής κατάστασης αντιμετωπίζει αποτελεσματικά τα προβλήματα σύγκλισης που προκαλούνται από την παρουσία των μετρήσεων των φασιθετών του ρεύματος με τη μετατροπή τους σε ψευδομετρήσεις ροής ισχύος. Η ακρίβεια και η ευρωστία του υβριδικού εκτιμητή κατάστασης μπορεί να υποβαθμιστεί με την παρουσία μετασχηματιστών μέτρησης χαμηλής ακρίβειας στην αλυσίδα μέτρησης μιας ΣΜΦ. Ως εκ τούτου, η ακρίβεια και η ευρωστία του προτεινόμενου υβριδικού εκτιμητή κατάστασης βελτιώνεται περαιτέρω μέσω της ανάπτυξης μιας νέας μεθοδολογίας για στάθμιση των μετρήσεων, λαμβάνοντας υπόψη τόσο την αβεβαιότητα των συσκευών μέτρησης όσο και των μετασχηματιστών μέτρησης. Επιπλέον, σε αυτή τη διατριβή προτείνεται η ανάπτυξη ενός εκτιμητή κατάστασης δύο σταδίων που παρακολουθεί τη μεταβατική κατάσταση του συστήματος ηλεκτρικής ισχύος κατά τη διάρκεια ενός σφάλματος. Ο προτεινόμενος δυναμικός εκτιμητής κατάστασης δεν απαιτεί πλήρη παρατηρησιμότητα του συστήματος ηλεκτρικής ισχύος από ΣΜΦ. Αυτό το χαρακτηριστικό καθιστά τον προτεινόμενο δυναμικό εκτιμητή κατάστασης προσαρμόσιμο στην τωρινή εγκατάσταση των ΣΜΦ στα συστήματα ηλεκτρικής ισχύος. The advent of the Synchronized Measurement Technology (SMT) has set the beginning of a new era in the power system monitoring and control applications. In particular, the Phasor Measurement Unit (PMU) which is the key-element of the SMT is able to provide time stamped voltage and current phasor measurements in high fidelity and at a real-time reporting rate. These features can certainly be applied to existing control center applications for improving their performance. The natural application of the SMT is the state estimator, which constitutes the cornerstone of the control center, providing essential information about the operating condition of the power system. It is no exaggeration to characterize the state estimation tool as the “eyes” of the power system operators. The significance of the state estimator imposes major expectations for this tool and there is an ongoing effort to improve its accuracy, reliability, robustness, and performance. In this thesis, the SMT features are used in state estimation tool for improving the contemporary state estimation in terms of its accuracy and real time response. More specifically, a hybrid state estimation scheme is proposed that incorporates both conventional and PMU measurements in the same measurement vector and provides highly accurate estimations of the power system states. The proposed state estimation scheme addresses effectively the convergence problems caused by the presence of current phasor measurements by transforming the respective current phasor measurements to pseudo flow measurements. The accuracy and robustness of the hybrid state estimator might degrade in the presence of poor accuracy instrument transformers in the measurement chain of the PMUs. Therefore, the accuracy and robustness of the proposed hybrid state estimator is further enhanced through the development of a novel weighting scheme for the measurements used, considering both measurement devices and instrument transformers uncertainties. Further, the issue of monitoring the power system states in real time is considered in this dissertation by developing a two-stage state estimator that tracks the transients of the power system states during fault conditions. The proposed dynamic state estimator does not require a fully observable power system by PMUs; this feature makes the proposed dynamic state estimation scheme adaptable to the current deployment of the PMUs in the power system.

Electric power systems (EPS) evolved over years from local independent entities towards large interconnected networks monitored and controlled by sophisticated ICT technologies, and which, eventually will be transformed into Smart Grids where also distributed energy sources, storage, electric vehicles and appliances will be active components of the system. Thus, the scale of complexity involved in present and future power systems architectures is significantly greater than in the past. This paper aims to discuss the interdependency between electric power and communication systems under the system of systems concept. The nature and scale of interdependency between these two critical systems is then further analyzed using an example of disturbance on communications and observing the cascading effects on the power system's monitoring process. Specifically, the impact on the state estimation accuracy is investigated, as a result of a communication node failure, which is responsible for transferring Phasor Measurement Unit (PMU) data to the control center.

The Cyprus power system is undergoing vast changes due to the increasing penetration of renewable energy sources. The isolated nature of the system makes it more vulnerable to large frequency deviations. As a consequence, frequency control becomes challenging especially in the case of large disturbances. To keep the system in admissible frequency limits and avoid brownouts or even system blackout, it is important to have a detailed and accurate model of the system to improve monitoring and control, and enhance the situational awareness of the system operators. One important component of the system to be modelled is the system load. Although this is not a straightforward task, the significance of load modelling can be underlined by the fact that the system response is affected by the type of the system loads. In this sense, the type of the load in combination with the increased penetration of dispersed renewable energy sources can significantly affect the system frequency response to generation loss events. In this paper, the importance of accurate load modelling and the associated effect to the response of the Cyprus power system is examined. The system frequency response to generation loss events for multiple scenarios is investigated. Various load compositions are examined, while PV generation is also considered in order to simulate realistic system conditions. Furthermore, two cases of different plant mix are also examined.

Power systems are experiencing major changes in their structure and operation that make them more complex in nature. Further, the ever-increasing electricity demand along with the high penetration of renewable energy sources push the power systems to work closer to the system limits. In this sense, there is a need for accurate analysis for assessing the power system operating condition. Since the loads are a source of uncertainty in the power system analysis, in this work an extended investigation of the effect of the inaccurate load composition on the frequency response of the system is performed. The composite load model is used to represent the loads on the IEEE 39-bus dynamic test system in which a protection scheme was added, including a high penetration of renewable energy sources is assumed in order to have a more realistic representation of the current power system case. The aim of this work is to underline the importance of the accurate load composition for contingency analysis and system planning.

Low voltage distribution grids (LVDGs) are evolving from their traditional passive behavior into highly active systems. Their secure and reliable operation will require effective control schemes which in return require reliable and accurate monitoring systems. Most of the related existing works rely on the three-phase Weighted Least Squares (WLS) state estimation method which is used mainly on Medium Voltage Distribution Grids (MVDGs). However due to different characteristics between MVDGs and LVDGs this method may not be suitable for monitoring LVDGs. This paper investigates the performance of the WLS state estimator on a radial low voltage test feeder and due to the random nature of the measurement errors, the analysis is conducted in a Monte Carlo fashion. The investigation indicates that a significant error is imposed in the monitoring of the LVDG which is related to the loading conditions and the asymmetric operation of the distribution grid.&nbsp