Adam Dysko

Enhanced Power System Stability by Coordinated PSS Design

A step-by-step coordinated design procedure for power system stabilisers (PSSs) and automatic voltage regulators (AVRs) in a strongly coupled system is described in this paper. It is shown that it is possible to separate the design of individual PSSs and separate the design of individual AVRs. Thereby, the designs of AVR and PSS devices at a given machine can be coordinated to achieve near-optimal overall power system stability performance, including oscillation stability performance and transient stability performance. The proposed coordinated PSS/AVR design procedure is established within a frequency-domain framework and serves as a most useful small-signal complement to established large-signal transient simulation studies.

An Adaptive Overcurrent Protection Scheme for Distribution Networks

Distribution networks are evolving toward the vision of smart grids, with increasing penetration of distributed generation (DG), introduction of active network management (ANM), and potentially islanded modes of operation. These changes affect fault levels and fault current paths and have been demonstrated to compromise the correct operation of the overcurrent protection system. This paper presents an adaptive overcurrent protection system which automatically amends the protection settings of all overcurrent relays in response to the impact of DG, ANM, and islanding operation. The scheme has been developed using commercially available protection devices, employs IEC61850-based communications, and has been demonstrated and tested using a hardware-in-the-loop laboratory facility. A systematic comparison of the performance of the proposed adaptive scheme alongside that of a conventional overcurrent scheme is presented. This comparison quantifies the decrease in false operations and the reduction of mean operating time that the adaptive system offers.

The Effective Role of AVR and PSS in Power Systems: Frequency Response Analysis

Two tradeoffs in the effectiveness of automatic voltage regulators (AVRs) and power system stabilizers (PSSs) are investigated together for the first time. The first is the effect of a high-gain fast response AVR on decreasing power system oscillation stability as well as increasing transient stability, and vice versa. The second is that a PSS can reduce transient stability by overriding the voltage signal to the exciter as well as increasing oscillation stability, and vice versa. In essence, the actions of the AVR and PSS devices are dynamically interlinked. A novel Bode frequency response framework for dynamic analysis of AVR and PSS performance and tradeoffs is presented. Bode frequency response also assists with the determination of suitable generator locations for PSSs and the assessment of robustness under changing power system operating conditions.

The Application of Model-Based Reasoning within a Decision Support System for Protection Engineers

This paper discusses model-based reasoning applied to power network protection system performance analysis. Appropriate modelling and reasoning methodologies are indicated, and their advantages considered. The necessity of incorporating protection system performance analysis within a decision support system (DSS), designed for electric utility protection engineers, is presented. Alarm processing and fault diagnosis are demonstrated as further requirements of the DSS for protection engineers, within which knowledge-based reasoning and model-based reasoning are combined to provide the overall functionality required.

Traveling wave-based protection scheme for inverter-dominated microgrid using mathematical morphology

Inverter-dominated microgrids impose significant challenges on the distribution network, as inverters are well known for their limited contribution to fault current, undermining the performance of traditional overcurrent protection schemes. This paper introduces a new protection scheme based on the initial current traveling wave utilizing an improved mathematical morphology (MM) technology, with simplified polarity detection and new logics introduced for meshed networks and feeders with single-end measurement. The proposed protection scheme provides ultrafast response and can be adapted to varied system operational modes, topologies, fault conditions, and load conditions. Only low-bandwidth communication is required to achieve high-speed operation and adequate discrimination level in meshed networks. Simulation in PSCAD/EMTDC verifies both the sensitivity and stability of the proposed protection scheme under different microgrid operational scenarios.

Adaptive Zone Identification for Voltage Level Control in Distribution Networks With DG

A decentralized voltage control is proposed for distributed generation (DG) units to provide short and long-term voltage support in distribution networks. Local controllable zones are used to determine the voltage control boundaries for each DG unit. The number of zones and their size depend on the number, location and size of the DG units, and can be reconfigured in real time in response to network topology changes. The performance and value of the proposed control approach are demonstrated under various operating scenarios. The study is based on the IEEE 33-bus radial distribution network implemented in DIgSILENT PowerFactory.

Adaptive protection architecture for the smart grid

Unique and varied power system conditions are already being experienced as a result of the deployment of novel control strategies and new generation and distribution related technologies driven by the smart grid. A particular challenge is related to ensuring the correct and reliable operation of protection schemes. Implementing smarter protection in the form of adaptive setting selection is one way of tackling some of the protection performance issues. However, introducing such new approaches especially to safety critical systems such as protection carries an element of risk. Furthermore, integrating new secondary systems into the substation is a complex and costly procedure. To this end, this paper proposes an adaptive protection architecture that facilitates the integration of such schemes into modern digital substations which are a staple of smart grids. Functional features of the architecture also offer powerful means of de-risking schemes and flexible implementation through self-contained modules that are suitable for reuse. An example adaptive distance protection scheme is presented and tested to demonstrate how the architecture can be implemented and to highlight the architectures novel features.

Methodology for testing loss of mains detection algorithms for microgrids and distributed generation using real-time power hardware-in-the-loop based technique

The effective integration of distributed energy resources in distribution networks demands powerful simulation and test methods in order to determine both system and component behaviour, and understand their interaction. Unexpected disconnection of a significant volume of distributed generation (DG) could have potentially serious consequences for the wider power system, and this means DG sources can no longer be treated as purely negative load. This paper proposes a method of testing loss-of-mains (LOM) detection and protection schemes for distributed energy resources (DER) using realtime power hardware-in-the-loop (RT PHIL). The approach involves connecting the generator and interface under test (e.g. motor-generator set or inverter, controlled by an RTS — Real Time Station) to a real-time simulator (in this case an RTDS — Real Time Digital Simulator) which simulates the local loads and upstream power system. This arrangement allows observation of the interaction with other controls in the network beyond the local microgrid area. These LOM detection schemes are of increasing importance because with growing penetration levels of distributed generation the network operator has less visibility and control of the connected generation. Furthermore when the generation and load in a particular network area are closely matched (e.g. a grid-connected microgrid), it becomes increasingly difficult to detect a loss of grid supply at the generator. This work builds upon the existing LOM testing methodology developed previously for the Energy Networks Association in the United Kingdom. By utilising RT PHIL and a laboratory microgrid, the testing environment has been brought to a new level of functionality where system integrity can be more rigorously and realistically evaluated.

An Optically-Interrogated Rogowski Coil for Passive, Multiplexable Current Measurement

We report on the design and implementation of a novel hybrid electro-optical sensor for the measurement of electric current. A fibre Bragg grating is utilized to passively interrogate an air-cored coil via a low-voltage piezoelectric multilayer stack. Peak Bragg reflections are strain-tuned by the Rogowski coil/piezoelectric transducer combination, allowing primary current reconstruction to be performed remotely and without active electronics at the sensor. The preliminary embodiment demonstrates long-distance, passive measurement of current for metering and protection relaying applications, and retains the fiber transducers capability for serial multiplexing.

Influence of power quality on the performance of digital protection relays

The performance of protection relays depends on many factors and needs to be carefully evaluated. One of the significant factors impacting protection system behaviour is power quality. Depending on which of the power quality parameters is distorted, the influence on the performance of digital protection relays will be different. This paper analyses the influence of power quality deterioration on digital protection relays. In the first part of the paper, the historical limitations related to electromechanical relays and the signal processing algorithms used in digital relays are outlined. In the second part, the influence of distorted waveforms on the behaviour of digital relays is analyzed. Two aspects of power quality are taken into account: harmonics and frequency variations. Additionally, several simulation examples supported by laboratory measurements are presented in order to illustrate practical implications of poor quality of power.