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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.

Towards the green transition of modern power systems, a massive deployment of distributed energy resources (DERs) based on renewable sources is required. These DERs are grid integrated through power electronics converters which reduce the commitment of synchronous generators and as a result, the overall inertia of the system. Maintaining the frequency stability in such low-inertia power systems is a crucial aspect for the system operators; therefore, local control schemes are integrated with conventional generators and DERs to ensure fast reaction in case of frequency disturbances so as to preserve system stability. Existing practices for maintaining the frequency stability rely on the response of a local governor controller integrated with the synchronous generators. Some new approaches introduce frequency support services by DERs, by considering the droop control and virtual inertia concept within the inverter local controller. In another approach, wide area control schemes can also be utilized to further enhance the system stability. Such a wide area control scheme is introduced in this work to coordinate the operation of DERs through 5G communication for enabling fast frequency support services. Due to the fast dynamics of a power system, a reliable and high-speed communication is particularly important for the deployment of the proposed method. Therefore, an experimental hardware in the loop setup has been developed to investigate how the communication performance can affect the stability of the power system. Moreover, a benchmarking is implemented to evaluate the frequency stability when local controllers are providing support and when the proposed wide area controller is applied under a different communication infrastructure. Experimental results demonstrate that when a reliable 5G network is used, then a significant stability improvement can be achieved by the proposed wide area controller.

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.

The decentralization of power systems and the rapid deployment of renewable energy sources (RES) has upgraded the role of the Distribution System Operator (DSO) from a passive network observer to an active system operator. This requires effective collaboration and coordination with the Transmission System Operator (TSO) to avoid any congestion issues in the distribution grid. In this paper, the local market coordination scheme is considered, where DSO has priority to procure services from distributed energy resources (DERs) in an optimization-based separate local market. In this framework, a prequalification scheme is proposed and developed to enable the participation of DERs in central markets without risking the stability of the distribution system. The proposed prequalification scheme allows the DSO to detect and manage congested lines in the distribution grid preventing decisions by the TSO that can threaten the distribution system stability. Simulation results on the IEEE 33-bus system illustrate the effectiveness of the prequalification scheme in managing potential congestions in the distribution grid that might occur by the actions of the TSO.

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 accurate transmission line parameters are important in various power system analyses, while potential uncertainty in their values affects the accuracy of control center applications and compromises the selectivity of the protection systems. The transmission line parameters are usually calculated based on manufacturers data, ignoring environmental factors (e.g. ambient temperature) which affect the accuracy of the calculated parameters. Thus, the systematic refinement of the line parameters can be very beneficial for the situational awareness of the power system operators. In this paper, the calculation of the positive sequence parameters of a transmission line of the Cyprus power system through real synchronized phasor measurements is presented. The seasonal variation of the transmission line parameters is analyzed by calculating the parameters during different periods of the year, while the impact of the instrument transformers static error is demonstrated in this real case study.

Power system operators are facing major challenges today to keep the system operating at the admissible limits. Recent blackouts demonstrated the need for a systematic study and design of a comprehensive system control strategy. Intentional controlled islanding (ICI) has been proposed as an effective corrective control action of final resort to save the system from a partial or a complete blackout. ICI limits the occurrence and consequences of blackouts by splitting the power system into a group of smaller, stable, and sustainable subsystems, also called islands. After a controlled system separation, power system operators should resynchronize and reconnect each island to restore the system. In this sense, real-time knowledge of the operating condition of the islands is required. In this paper, a real-time ICI and restoration scheme is proposed. The proposed scheme consists of an ICI algorithm that finds islanding solutions with minimal power-flow disruption while considering power system restoration constraints (e.g., blackstart availability, sufficient generation capacity, and observability), a real-time state estimator that monitors the system before and after the islanding, and a restoration process. The proposed ICI and restoration scheme is tested using the dynamic IEEE 39- and 118-bus test systems. 34 1 606 615

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Power system transmission line parameters are essential in monitoring and control applications. More specifically, the values of the transmission line parameters are used in state estimation, contingency analysis, and as settings in protection relays. However, the stored transmission line parameters in the control center database often deviate from their actual values, impacting negatively the applications of the power system control center. The use of PMU (Phasor Measurement Unit) measurements is the most convenient and simple way for refining the parameters of the transmission line; however, the contamination of the PMU measurements with noise from the instrument transformers and the communication channels could sometimes deteriorate the accuracy of the calculated parameters. In this paper, the denoising of the PMU measurements using wavelets is proposed prior to the calculation of the transmission line parameters. The proposed approach is used for calculating the transmission line parameters of the IEEE 14-bus system and the results are extensively discussed.

The accurate knowledge of the transmission line parameters can be beneficial for several monitoring and control applications accommodated in the power system control center. Actually transmission line parameters are stored in the control center databases (assuming that they are time invariant); however, the databases might be obsolete and contain erroneous parameters. This paper proposes a methodology for identifying and estimating the erroneous transmission line parameters using measurements provided by phasor measurement units (PMUs) and estimated states provided by a state estimator. The main advantage of the proposed methodology is that for the identification of the erroneous transmission lines and the estimation of the line parameters only one PMU is required for the monitoring of the transmission line (i.e., capture measurements related to the transmission line). The proposed methodology is tested in the IEEE 14- and 118-bus systems.

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.

Dynamic load models are necessary for accurate monitoring and control of the system during various events as well as for better understanding the behavior and the characteristics of the system. In this paper, a realistic approach of load modelling using real time estimated states is studied. Since Phasor Measurement Units (PMUs) are not installed yet at every bus, a linear state estimator is used to provide the state of the buses without PMUs. The overall impact of the real time estimated states and the inaccurate load model parameters are studied on the IEEE 39-bus dynamic test system. In addition, the realistic approach of load modelling is enhanced by using various load types while errors that affect the estimated states, such as line parameter errors and measurement gross errors are also considered. Furthermore, a sensitivity analysis with inaccurate load model parameters is performed to show their effect on the results of load modelling., E. Polykarpou, M. Asprou and E. Kyriakides, "Dynamic load modelling using real time estimated states," 2017 IEEE Manchester PowerTech, Manchester, 2017, pp. 1-6. doi: 10.1109/PTC.2017.7979751 © 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.

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.