Demetrios Tziouvaras

Mathematical models for current, voltage, and coupling capacitor voltage transformers

This paper reviews a number of mathematical models used to represent the nonlinear behavior of the magnetic core of instrument transformers. Models of instrument transformers using these core representations are presented. The transient response of the instrument transformer is compared to actual test results recorded in the laboratory. The paper provides practical guidelines as to which of the physical elements of instrument transformers are important to model during transient studies and which elements could be ignored without sacrificing the accuracy of the simulation results. The electromagnetic transients program (EMTP) data files used to generate the models are also provided in the appendix to help new EMTP users model instrument transformers for evaluation of high-speed protective relaying systems.

Out-of-step protection fundamentals and advancements

Power systems are subjected to a wide range of small or larger disturbances during operating conditions. Small changes in loading conditions occur continually. The power system must adjust to these changing conditions and continue to operate satisfactorily and within the desired bounds of voltage and frequency. The power system should be designed to survive larger types of disturbances, such as faults, loss of a large generator, or line switching. Certain system disturbances may cause loss of synchronism between a generator and the rest of the utility system, or between interconnected power systems of neighboring utilities. If such a loss of synchronism occurs, it is imperative that the generator or system areas operating asynchronously are separated immediately to avoid widespread outages and equipment damage. In this paper we describe the philosophy and application fundamentals of out-of-step protection in transmission systems. We also discuss recent enhancements in the design of out-of-step tripping and blocking protection functions that improve the security and reliability of the power system. In addition, we demonstrate the out-of-step phenomena and distance relay element behavior using EMTP and Matlab simulations.

Software models for relays

This paper reviews the past and present uses of relay models. It discusses the various types of models, what information is required to build such models and the model validation process. Examples of present and possible future use of software models are given.

IEEE PSRC Report on Performance of Relaying During Wide-Area Stressed Conditions

This paper is a summary of the IEEE Power System Relaying Committee report. It describes the performance of protective relays during wide-area stressed power system conditions. First, the behavior of protection functions during dynamic operating conditions is described. Then, the lessons learned from studying recent wide area disturbances, as well as the operational history of protection performance during stressed system conditions, are analyzed. Finally, methods of implementing protective relay functions to prevent further propagation of system-wide disturbances are presented.

Protection of High-Voltage AC Cables

High-voltage underground AC cables have significantly different electrical characteristics than overhead transmission lines. The cable sheath or shield grounding method has a major impact on the zero-sequence impedance of underground cables. Understanding how the underground cable grounding method affects the series sequence impedances is very fundamental to underground cable protection. In the paper we briefly discuss the types of underground cables, their bonding and grounding methods, and the fundamental differences between overhead transmission lines and cable electrical characteristics. Finally we discuss the application of short-circuit protection for high-voltage AC cables

Controlled Switching of HVAC Circuit Breakers: Application Examples and Benefits

Controlled switching technology, that is, predefined controlled strategies for closing and/or opening each independent circuit breaker pole, is an effective way to reduce switching transients, prevent equipment failures, and improve power quality. The paper presents a tutorial on controlled switching of high-voltage ac (HVAC) circuit breakers and describes the controlled switching theory and technology that is in use today. The paper discusses the benefits of controlled switching and shares one utilitys applications and experiences with the controlled switching of shunt capacitors, shunt reactors, transformers, and lines, using modern protective relays and control devices. The paper also discusses how to select the optimum controlled switching times to reduce switching transients.

Local- and Wide-Area Network Protection Systems Improve Power System Reliability

Increasing demands on electricity supply, with the need for system economic optimization and power system growth limitations, have a significant impact on power system reliability. When the system operates in extreme conditions, load shedding, generation shedding, or system islanding must occur to prevent total system collapse. Typical causes of system collapse are voltage instability or transient angle instability. New monitoring, protection, and communications technologies allow us to implement economical local- and wide-area protection systems that minimize risk of wide-area system disruptions or total system collapse. This paper presents solutions that use programmable logic capabilities, faster communications, and synchronized phasor measurements available in meters and protective relays to prevent system disruptions

Use of synchrophasor measurements in protective relaying applications

The IEEE PSRC System Protection Subcommittee Working Group C14 has produced a report that describes practical applications of synchrophasors in protection applications. The report begins with the history of synchrophasors and then goes into issues to consider in their application. Some existing applications are described and then future applications that have been considered or are in development are described. The appendix contains applications that use synchrophasor data but are not considered protection applications. This is a summary of the complete report found on the PSRC website (http://www.pes-psrc.org click on Published Reports).

Do system impedances really affect power swings — Applying power swing protection elements without complex system studies

One of the traditional techniques for detecting power swings uses a dual-quadrilateral characteristic. It is based on the measurement of the time interval it takes the positive-sequence impedance to cross two blinders. Another technique monitors the variation of the swing center voltage approximation. This paper presents a performance comparison between applications of these two techniques in cases derived from a sample network transient simulation and in cases recorded during real operations in the field.

Protecting mutually coupled transmission lines: Challenges and solutions

This paper is a tutorial on the protection of mutually coupled transmission lines. It discusses how mutual coupling affects the polarizing quantities of ground directional elements, the reach of ground distance elements, and the accuracy of single-ended fault locating algorithms. The paper provides settings guidelines for instantaneous directional overcurrent and ground distance elements. It discusses in detail how transmission line mutual coupling causes overreaching or underreaching of ground distance elements. It also discusses the impact on these elements of grounding the mutually coupled line at both line ends during maintenance. The paper analyzes whether mutual coupling compensation offers any benefits to line protection. The ease and benefit of line current differential schemes are contrasted in the discussion. Lastly, the paper examines a case when a double-circuit transmission line is operated as a single circuit with jumpers placed across similar phases along the line. This situation typically arises when the utility company needs to free one of the bays to bring an additional line into the substation. The protection engineer needs to decide where to install jumpers to parallel the two circuits in order to avoid distance element underreaching. The paper provides an analysis of this problem and offers suggestions on how to address it.