Georgios N. Korres

Open-source IEC 61850 software is widely used in smart-grid research, but it has mostly been validated against software-emulated servers. This paper integrates OpenPLC61850, an open-source programmable logic controller (PLC) featuring an integrated Manufacturing Message Specification (MMS) client, with the Siemens SIPROTEC 5 distance (7SX85) and backup overcurrent (7SJ82) relays of a 150 kV transmission-line bay. The client runs in a virtual machine on the station bus and is engineered through a reproducible two-stage workflow that combines offline tagging of Substation Configuration Language (SCL) files with online data-set and report engineering. Seven interoperability gaps were identified and resolved, among them a firmware-specific suffix in report names, data-set granularity, double-point decoding, device-side switching authority and setting-group control through the Setting Group Control Block, which SCL-based tools do not expose. The client was extended with select-before-operate breaker control and remote setting-group switching. Protocol traces and secondary injection with an OMICRON CMC 356 test set showed that, for both relays, an identical fault trips the relay in one setting group and not in the other, with the appropriate group selected by the PLC, while the operation times agree with the manufacturer’s specifications. The results establish a reproducible path for using open-source clients with commercial protection devices.

This paper presents the newly installed digital substation infrastructure of the Protec-tion, Automation and Control Laboratory (PAC Lab), a dedicated subsection of the Power Systems Laboratory (PSL) of the National Technical University of Athens (NTUA). The infrastructure replicates the secondary equipment of a 150 kV substation of the Hellenic transmission system and, at its present stage, comprises two fully equipped transmission line bays from different vendors, a Siemens and an ABB substation/bay, operable as bays of the same or of two different substations. The bays integrate commercial protection and control Intelligent Electronic Devices (IEDs), IEC 61850 station buses over fiber optics, local SCADA systems, a substation gateway providing the interface toward a (theoretical) control center via IEC 60870-5-101, and state-of-the-art secondary injection test equipment. Beyond its educational role illustrated by a set of hands-on demonstration cases spanning secondary injection trip testing, closed-loop system-based testing and synchrophasor streaming the substation infrastructure supports secure remote experimentation by remote users (diploma, master and PhD candidates), research on innovative protection techniques, Hardware-in-the-Loop (HIL) studies in interconnection with the Real-Time Digital Simulator (RTDS) facility of the NTUA PSL, cybersecurity research in the Operational Technology (OT) networks of IEC 61850 substations, and multi-vendor interoperability testing.

The development of the global positioning system in conjunction with information and communication technology has resulted in the development of modern power systems, known as smart grids, which automatically permit the monitoring of energy flow as well as the response to any change in the supply or demand of energy. In order to accomplish these goals, the vector of measurements used in conventional state estimation has been expanded to include synchronized phasor measurements provided by accurate measuring devices known as phasor measurement units (PMUs). This study presents practical empirical methods for optimal PMU placement, which seek the minimum number of PMUs to be installed and their corresponding locations. The data pertaining to the power system topology and the interconnections of buses are recorded in appropriate matrices, which are organized according to the number of branches directly connected to each bus and the probability that each bus could serve as candidate for PMU installation. The effectiveness of the proposed methods is verified on different IEEE test systems in the presence or absence of zero injections (ZIs).

Optimal measurement selection for distribution state system estimation (DSSE) has been on a key research focus for efficient grid monitoring, given the increasingly active nature of distribution grids. Lately, the integration of synchrophasor techology, the reduction of pseudo-measurements that compromise DSSE performance, and the consideration of uncertainties (topology changes, DER penetration, load growth), are the most interesting directions to follow. This paper tackles these challenges by utilizing semidefinite programming (SDP) to develop a robust optimization framework for optimal planning of metering unit installations, concentrating on synchrophasors. The objective is to ensure concrete grid observability and quality DSSE while accommodating various uncertainties. To achieve this, the study employs the SDP-formulated A-, E- and M- optimal experiment designs under budget constraints, alongside a new SDP-based model for selecting minimal measurement sets subject to accuracy criteria. The proposed approach is tested on the IEEE 33-node test feeder and the 95-node UK distribution grid, demonstrating its ability to deliver optimal measurement configurations that enhance DSSE performance, improve economic efficiency, reduce reliance on pseudo-measurements, and remain robust to diverse grid uncertainties.

This paper presents a multi-stage forecasting-aided state estimation (FASE) framework with equality constraints, utilizing the extended Kalman filter (EKF) to independently process supervisory control and data acquisition (SCADA) and phasor measurement unit (PMU) data. The conventional SCADA-based state estimator remains unaltered and is augmented with synchronized PMU data and a priori state information derived from the EKF. An estimation fusion technique leveraging real-time PMU measurements is developed to enhance the accuracy of the FASE forecasting model. To address measurement asynchronization and random delays, the modified Bryson-Frazier (MBF) fixed-interval smoothing algorithm is applied, combining current state information with a series of prior FASE solutions to optimally infer the system states. Extensive numerical simulations on the IEEE 14-, 118-, and 300 -bus benchmark systems demonstrate the efficacy and practical applicability of the proposed method.

The dynamic monitoring and control of modern power systems require synchronized time-stamped electrical measurements to estimate the voltage and current phasors, as well as frequency and rate of change of frequency (ROCOF), under normal and abnormal conditions. Phasor measurement units (PMUs) are designed to perform this task by providing accurate, high speed measurement data to the phasor data concentrator (PDC), while the time stamping is provided by a global positioning system (GPS) at the coordinated universal time (UTC). However, the cost of these devices remains high due to their complex infrastructure, thus low-cost PMU design is needed without sacrificing their accuracy and reliability. This paper presents a complete development of a low-cost laboratory PMU, based on phase-locked loop (PLL) concept, employing the third order generalized integrator (TOGI) PLL for the estimation of the positive sequence of the voltage and current phasors, synchronized with the UTC time given by a GPS module.

This paper proposes an equality-constrained hybrid state estimation algorithm that processes data from the supervisory control and data acquisition (SCADA) and wide area monitoring systems. The devised method is founded upon the widely accepted weighted least squares approach and is viable in single- and multi-stage architectures. The main advantage of this method is found in its non-intrusive implementation, that is, keeping the core functions of conventional state estimation software intact in the energy management system, while improving the quality of the conventional SCADA-based estimators. Following a detailed description of the derivation of the proposed approach and its alternative formulations, numerical simulations on the IEEE 14-, 118-, and 300-bus benchmark systems are conducted to assess its performance. The proposed estimation scheme is found to outperform similar methods found in recent literature with respect to various performance metrics.

The dynamic monitoring, control, and protection of modern power systems in real time require time-stamped electrical measurements to accurately estimate the bus voltage phasors using the state estimation function under normal and abnormal conditions. These measurements can be acquired by time-synchronized devices, known as phasor measurement units (PMUs). PMUs can measure bus voltage and branch current phasors of a three-phase network, as well as the frequency and the rate of change of frequency (ROCOF), with high speed, accuracy and time stamping provided by global positioning system (GPS) at the coordinated universal time (UTC). Various phasor estimation algorithms have been proposed in the literature, while most of them are concentrated in the discrete Fourier transform (DFT) algorithm, where an integer number of samples multiple of the nominal frequency is required for the computations. In cases where the frequency of the power grid deviates from its nominal value, the raw application of the DFT approach can lead to large errors during phasor estimation. Another approach of the phasor estimation is based on the phase-locked loop (PLL) techniques, widely used in grid tie inverters. PLL techniques can track dynamically (continuous time) the estimated frequency to the time-variant frequency of the power grid. A brief introduction to the basic concepts of the synchrophasor definition is provided, while the main DFT methods for synchrophasor estimation according to recent literature are mentioned. PLL-based PMU techniques are reviewed for both steady-state and dynamic conditions according to IEEE standards. In conclusion, the performance of PLL-based PMU algorithms presented in this literature review is discussed.

State estimation (SE) is an essential tool of energy management systems (EMS), providing power system operators with an overall grasp of the actual power system operating conditions and aiding them in sustaining reliable and secure operation of the grid. In modern transmission sectors, two main measurement systems are deployed, namely the supervisory control and data acquisition (SCADA) and the wide area monitoring systems (WAMS). The multiple advantages of augmenting conventional SCADA-based SE algorithms with synchrophasor measurements from WAMS are already well-established; thus, an abundance of different methodologies has been reported in the field of hybrid SE (HSE). Under this premise, this paper provides a thorough literature review of novel HSE methods in transmission systems and proposes a classification based on the scope and mathematical modeling of each method. Following a brief introduction to the concept of SE based on WAMS and SCADA measurements, an insight into the main challenges emerging in HSE implementations is provided. Various HSE methods which overcome these challenges are reviewed, for both static and dynamic SE implementations. In conclusion, the research trends in the area of HSE are summarized, and the main findings of this literature review are discussed.