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Autonomous power systems with a single power station and a high-voltage (HV) network may be susceptible to overvoltage instability, especially during light-load conditions. Moreover, in low inertia systems, considerable frequency excursions may be observed after disturbances. To deal with voltage and frequency stability problems in such isolated power systems, several measures should be taken, such as rules for adequate automatic voltage control of the synchronous generators and load-tap-changers (LTCs), and/or adequate design of actions applied during emergency system conditions such as reactors switching, and redesigning underfrequency load shedding taking into account overvoltage problems. The effectiveness of the proposed countermeasures against overvoltage instability in autonomous power systems is illustrated in this paper. In 2016, the autonomous power system of the Greek island of Rhodes experienced similar voltage/frequency problems leading to a blackout. This event has been accurately reconstructed in this paper. The application of the suggested countermeasures during the simulation of the 2016 blackout event in Rhodes, further highlighted the effectiveness of these measures, providing a guideline for similar cases. [ABSTRACT FROM AUTHOR]

This paper investigates the Multilevel Current Source Converter (MCSC) STATCOM. It proposes a new method of modulation. The new modulation method produces less THD and di/dt at the terminals of the MCSC STATCOM when compared to the widely used Phase-Shifted Carrier SPWM (PSC-SPWM). To ensure the inductors' currents remain balanced, a Current Balancing Algorithm (CBA) is presented. The CBA does not require any controls. It relies on assigning optimum switching states to each CSC module in real-time. In addition, two control strategies are presented in this paper. The first one assumes the STATCOM to be a SISO. Therefore, it only requires one PI controller. However, the gains for the controller must be changed if the STATCOM was to transition from capacitive mode to inductive mode, or vice versa. The second control strategy overcomes this problem by implementing a TITO integral state feedback controller. The contributions of this paper are validated via simulation and experimental results. [ABSTRACT FROM AUTHOR]

This paper presents a new solution method that combines state-space and nodal analysis for the simulation of electrical systems. The presented flexible clustering of state-space-described electrical subsystems into a nodal method offers several advantages for the efficient solution of switched networks, nonlinear functions, and for interfacing with nodal model equations. This paper extends the concept of discrete companion branch equivalent of the nodal approach to state-space described systems and enables natural coupling between them. The presented solution method is simultaneous and enables benefitting from the advantages of two different modeling approaches normally exclusive from one another. [ABSTRACT FROM AUTHOR]

This paper proposes the performance study of the rotary power-flow controller (RPFC) operating in a two-line transmission corridor. Part I presented the RPFC model and its implementation in SPSIMatlab. This paper presents the simulation results of the RPFC operating in the corridor during the postcontingency period, when one of the two lines is out of service. From the RPFC model and the RPFC control system, derived in part I, this paper first determines the model of the electrical corridor equipped with the RPFC, and then implements the entire model, including the RPFC control system, in the SPS/Matlab. The obtained results provide the behavior of the RPFC as well as that of the corridor during the postcontingency period. This paper analyzes, among other parameters, the influence of the RPST number of poles on the RPFC performances. Finally, the utilization of the RPFC, associated with the shunt capacitive compensation, allows restoring the postcontingency power-flow conditions to be equal to those of the precontingency period. [ABSTRACT FROM AUTHOR]

This paper proposes to introduce additional constraints in the directional overcurrent relay coordination problem to tackle the sympathy trips. This paper attempts to tackle the sympathy trips in which other relay(s) in the system operate(s) earlier in the designated primary relay. The solution to this problem requires the inclusion of some additional constraints, making the coordination problem too complex. This paper proposes to solve the problem in two phases. In the first phase, the problem is solved by a normal coordination procedure and sympathy trips are identified. In the second phase, the proposed additional constraints are imposed only for the sympathy trips identified in the first phase. For the second phase, three approaches for including additional constraints were investigated. This paper includes results of the proposed algorithm for the IEEE 30-bus system. The results amply suggest that one of the three approaches of including additional constraints successfully tackled the problem of sympathy trip. [ABSTRACT FROM AUTHOR]

In this paper, investigations are carried out to explore the impact of a midpoint static synchronous compensator (STATCOM) on the coordination between the generator distance phase backup protection (function 21) and the generator capability curves. The results of these investigations have shown that the midpoint STATCOM has an adverse effect on such coordination. Such an impact varies according to the fault type, the fault location, and the generator loading. This paper proposes the use of the support vector machines' classification technique for generator phase backup protection to enhance the coordination between such protection and generator capability curves in the presence of a midpoint STATCOM. The dynamic simulations of a test benchmark have been conducted by using the PSCAD/EMTDC software. [ABSTRACT FROM AUTHOR]

This paper presents the control system based on the so-called repetitive control for a five-level flying-capacitor dynamic voltage restorer (DVR). This DVR multilevel topology is suitable for medium-voltage applications and operated by the control scheme developed in this paper. It is able to mitigate power-quality disturbances, such as voltage sags, harmonic voltages, and voltage imbalances simultaneously within a bandwidth. The control structure has been divided into three subsystems; the first one improves the transient response of the filter used to eliminate the modulation high-frequency harmonics, the second one deals with the load voltage; and the third is charged with maintaining balanced voltages in the flying capacitors. The well-developed graphical facilities available in PSCADIEMTDC are used to carry out all modelling aspects of the repetitive controller and test system. Simulation results show that the control approach performs very effectively and yields excellent voltage regulation. [ABSTRACT FROM AUTHOR]

Power-quality voltage and current transient waveform data have been explored rather extensively as the primary input data in predictive maintenance, automatic root-cause analysis, and evaluating system performance to indicate potential problems. Unfortunately, very few efforts have been directed toward making use of the voluminous steady-state data collected alongside waveform data. Therefore, this paper proposes to use steady-state data, particularly, rms voltage data to detect abnormal trend behavior that may be indicative of a problem. Specifically, this paper develops a statistical analysis algorithm based on the well-known statistical process control methods for assessing feeder voltage regulation performance. The assessment results can be used to indicate potential regulator problems as well. The efficacy of the method is demonstrated by applications to two sets of actual rms voltage data. [ABSTRACT FROM AUTHOR]

Delayed signal cancellation is one of the methods used to separate the negative- and positive-sequence components in unbalanced 3\phi systems. In this letter, a DSC methodology with fast convergence time is proposed and it is shown that an improved separation of the positive and negative sequences is feasible. Experimental results are presented to demonstrate the performance of the proposed methodology. [ABSTRACT FROM AUTHOR]

Automation can significantly enhance substation reliability by speeding up service restoration. Although much research works has been done in reliability assessment of substation control systems, there are still several aspects that need to be considered in automated substation reliability evaluation. The impacts of automation system on substation reliability indices have not been comprehensively covered in the literature so far. This paper aims at presenting a comprehensive technique to quantitatively assess the reliability of the automated substations. The technique is based on the event tree methodology and the concepts of conditional probability technique. A step by step evaluation procedure is presented using a typical substation automation architecture known as simple star. The proposed technique is applied to some conventional substation configurations to examine the effectiveness of the technique and also to examine the level of reliability improvement achieved by automation. Furthermore, different sensitivity analyses have been carried out for both automatic switching action and a specific automated substation. The proposed strategy is easy to implement and suitable to analyze for an automated substation reliability with arbitrary automation architectures. Also, automated substation reliability assessment tools can be developed in detail, and can be catered to the specific needs of substation design. [ABSTRACT FROM AUTHOR]

In this paper, load compensation using multilevel inverter-based distribution static compensator (DSTATCOM) is presented. The DSTATCOM is connected to a three-phase four-wire (3p4w) distribution system. Two different multilevel inverter topologies are used to realize the DSTATCOM. They are diode-clamped multilevel inverter (DCMLI) and flying capacitor multilevel inverter (FCMLI). A compensating technique has been derived, which uses the state feedback control to the multilevel inverters-based DSTATCOMs. A switching strategy for the multi-level inverters that ensures utilization of all output voltage states of the inverter for efficient tracking of references has been proposed. The schemes of dc-link capacitor volthge control for DCMLI and flying capacitor voltage control for FCMLI have been discussed. Comparative studies of performances of the two DSTATCOM topologies are performed. The simulation studies are performed using PSCAD/EMTDC to validate the efficacy of the proposed control scheme. [ABSTRACT FROM AUTHOR]

This paper proposes a control strategy for a VSC-HVDC for improving the quality of power supply to industrial plants. The new idea of this control strategy is to give high priority to keep up the ac voltage and slightly decrease the frequency during disturbances. The motivation for choosing this strategy is that the sensitive processing industries are much more sensitive to voltage drops as compared with frequency deviations. In order to test this control strategy, the dynamic performance of a VSC-HVDC supplied industrial plant is investigated during sudden load disturbances, balanced and unbalanced faults from the grid. Simulation results obtained using PSCAD/EMTDC show that with the use of the proposed control strategy, the system can ride through disturbances such as motor starting and faults by slightly decreasing the frequency. The current limit of the VSC-HVDC converters has a significant influence on the dynamics of the system. An increase of the current limit significantly improves the power quality of the system. The comparison of the behavior between a pure ac supplied industrial plant and a VSC-HVDC supplied industrial plant clearly shows the capability of the VSC-HVDC to mitigate voltage dips during faults. [ABSTRACT FROM AUTHOR]

This letter presents a semidefinite programming model for passivity enforcement of frequency-dependent network equivalents. This model has some advantages over the existing quadratic programming model. Numerical tests show the validity of the proposed model. [ABSTRACT FROM PUBLISHER]

This paper presents a modified adaptive Kalman filter for sensorless current control of a three-phase inverter-based distributed generation system. Measurement and digital signal processor delays have been compensated by using a modified Kalman filter. The control variable states can be estimated one sample in advance with a reduced number of sensors. Two current control loops with the steepest descent adaptive control for grid voltage estimation have been employed to boost robustness. Stability and dynamic performance have been examined for different state variables using root locus. Simulation and experimental results validate the proposed control approach. [ABSTRACT FROM AUTHOR]

The paper investigates three different ways of using the transfer function method for detecting mechanical winding displacements in power transformers. The most reliable approach is time-based comparison, which requires finger print data from a previous measurement. Such information is, however, usually not available. For multilegged transformers without zigzag-connected windings the results of separately tested legs can be used as mutual references (construction-based comparison). A third approach is to compare the transfer functions with those obtained from an identically constructed transformer (type-based comparison). However, for a transformer with given nominal specification data, the winding design may over time undergo changes which causes changes to the transfer function. It is proposed to solve this problem by calculating tolerance bands using transfer functions from a big group of the same-type transformers. A novel statistical algorithm for this purpose is presented. The approach is demonstrated for a set of 28 specified identically 200-MVA power transformers. [ABSTRACT FROM AUTHOR]

Explores the application of array-based logic to substation control system for switch interlocking. Building primitives; Incorporation of primitives into system rule-bases; System testing using the complete system rule-base; Design support; System verification; Control units.

A smart-metering system is a system that meters electricity, gas, and water consumption and manages their supply by controlling measuring devices remotely. Power-line communication (PLC) does not require a separate communication line and can be easily installed by utilizing power-line infrastructure. PLC also allows users to easily connect measuring devices to the PLC network by plugging the power cord into an electrical outlet. Therefore, a smart-metering system over PLC has been considered as one of the most appropriate technologies for meter reading and automatic control, which are essential in realization of a smart grid. We propose a secure smart-metering protocol including: 1) key materials generation and provisioning to devices without exposure; 2) initialization to authenticate devices in the network and share keys between devices before exchanging data, (3) secure transmission of meter-reading data, and 4) revocation management to handle discarded devices from the network. Especially, our protocol provides strong authentication of devices and data: It prevents a single point of failure by adopting secret sharing through multiple certificate authorities. It also reduces the risk of denial-of-service attacks on the server by hop-by-hop authentication for data transmitted from terminal nodes to the server. [ABSTRACT FROM AUTHOR]