Search

Accurate fault locating on transmission lines is of great value to power transmission asset owners and operators. Fault locating as a discipline dates back to the 1940s. Visual inspection methods evolved from road patrols in the past, to air patrols today, and, more recently, to trials with unmanned aerial vehicles. Fault locating using electrical measurements evolved from simple electromechanical devices to microprocessor-based systems integrated with geospatial data.

Transformers experience magnetizing inrush that creates an operating current in the transformer differential protection. Early transformer differential relays had to address the limits of analog technology. Analog filter circuits could extract the second-and fourth-harmonic components of the differential current, and these were used as a surrogate measure for determining if the operating current was due to inrush. Today, we can design algorithms that distinguish directly between inrush characteristics and fault current characteristics. By using the new time-domain algorithms, we can improve sensitivity and speed of transformer differential protection. We can also maintain protection security for transformers built using improved core steels.

This paper reviews technical, safety, and economical merits of adaptive autoreclosing based on fault location calculated in real time. These applications include preventing reclosing for faults on cable sections of hybrid lines comprising overhead and cable sections, faults located close to large generating stations, faults on line sections crossing densely populated areas or fire-prone terrain, or faults on line sections near airports that receive small airplanes. The paper explains principles of fault locating based on traveling waves and introduces an adaptive autoreclosing control logic to allow or cancel reclosing based on the location of the fault. The paper includes examples that explain and illustrate these principles. The paper also describes several methods of using operational data — internal and external faults as well as switching events — to further improve the fault-locating accuracy of a commissioned fault locator.

This paper explains the asymmetrical short-circuit interrupting current rating for high-voltage circuit breakers. The paper teaches how the decaying dc component in the asymmetrical fault current affects the breaker, and it explains how the X/R ratio and the relay operating time affect the asymmetrical current breaker rating. The paper briefly introduces, and illustrates with field cases, several ultra-high-speed protection principles that can operate in just a few milliseconds. The paper then explains how to derate a breaker for the relay operating time that is shorter than the standard reference value of 0.5 cycle. The paper calculates the “rating loss” due to fast tripping and suggests that applying customary margins when selecting breakers may be sufficient to mitigate the effect of ultra-high-speed relays without the need to replace breakers.

We look back at the history of distance protection, explain the first principles, and discuss why our industry settled on designs we know and appreciate today. We look at why, after a century of refinements, a typical distance element still uses heavily filtered voltages and currents and operates on the order of one power cycle. In the second part of the paper, we explain the principles of time-domain distance protection based on incremental quantities, and operating by processing samples of voltages and currents without band-pass filtering to retrieve phasors. We discuss various choices for a time-domain distance element and present test results and field cases of an implementation with operating times of just a few milliseconds. In the third part of the paper, we discuss the feasibility of a distance element based on traveling waves and operating even faster.

This paper describes a single-ended traveling-wave-based fault-locating method that works with currents only. Unlike current transformers, coupling-capacitor voltage transformers do not have a frequency bandwidth that is wide enough to allow measuring of voltage traveling waves for this application. The key to a robust single-ended traveling-wave fault-locating method is to correctly identify reflections from the fault point. For this purpose, the method uses additional information, such as the impedance-based fault location and reflections from the remote terminal and external network elements. This paper presents the single-ended traveling-wave-based fault-locating method in detail and explains how to perform fault locating manually using ultra-high-resolution fault records from any recording device. This paper also presents laboratory test results as well as field cases in which line crews found the actual faults.

Ultra-high-speed line protection is becoming a reality today, giving the industry a way to trip line faults in a few milliseconds. One relay described in this paper that uses time-domain principles incorporates incremental-quantity (TD32) and traveling-wave (TW32) directional elements in a communications-assisted tripping scheme, incremental-quantity distance element (TD21), and traveling-wave differential element (TW87). This paper introduces these time-domain line protection elements, shares key details of their implementation in hardware, and illustrates their operation using real-world faults and digital simulations. By comparing the performance of the time-domain line protection elements with the traditional phasor-based elements of the in-service relays that captured the fault records, we demonstrate the performance of the time-domain line protection elements.

This paper analyzes the performance of current transformers (CTs) under the presence of geomagnetically induced currents (GICs). Our intent is to qualify the impact of GICs on CT performance in the context of protection security and dependability. The paper proposes a simple method to analyze the GIC problem and applies it to explain and quantify the impact of GICs on CTs. The paper uses carefully selected simulation tools, as well as laboratory tests on a physical CT to derive and support our key findings. We summarize our conclusions as follows: GIC impact is negligible in steady states during load conditions or faults but is significant in the first few milliseconds of a fault. As such, the GIC impact is very similar to the impact of the CT remanent flux on the performance of CTs during fault conditions. This impact is significant but short-lived. The component of CT saturation caused by high remanent flux or a preexisting GIC disappears very quickly.

This paper addresses the subject of reducing outage durations and autorestoration applications within the distribution substation. Employment of intelligent electronic devices (IEDs) can aid in the reduction of the fault duration time, and also it enhances the protection, control, and monitoring at the distribution level. Further, communication among these IEDs can provide faster autorestoration, remote data analysis, event recording, etc. Many recent issues related to distribution substation protection are discussed and techniques to address these issues using current technologies are proposed.

This paper summarizes the IEEE C37.234–2009 Guide for Protective Relay Applications to Power System Buses. In the Guide, concepts of power bus protection are discussed. Consideration is given to availability and location of breakers, current transformers, and disconnectors as well as bus switching scenarios, and their impact on the selection and application of bus protection. A number of bus protection schemes are presented; their adequacy, complexity, strengths and limitations with respect to a variety of bus arrangements are discussed; specific application guidelines are provided for a variety of situations. Breaker failure protection is discussed as pertaining to bus protection. Means of securing bus protection schemes against corrupted relay input signals are also included.

Synchronized phasor measurements are becoming an important element of wide area measurement systems used in advanced power system monitoring, protection, and control applications. The recently issued revised standard C37.118 for synchrophasors has facilitated interoperability of phasor measurement units (PMUs) from different manufacturers. This standard defines performance for compliance when the input signals are in steady state. The performance of PMUs under transient conditions is not considered by the standard at this time, although clearly PMUs will be subjected to inputs under transient conditions. This paper is an attempt to provide the authors' views on how one may approach the question of standardizing PMU response under transient conditions.

IEEE Standard 1344-1995 [1] on measurement of synchronized phasors of power system currents and voltages has been revised and published as IEEE Standard C37.118-2005 [2]. This paper has been prepared by the IEEE Working Group who developed the revised version. The purpose of the paper is to acquaint the power engineering community of the availability and content of this new standard, highlight some of the key differences between the old and new versions, and introduce several applications of this powerful technology.

Breaker failure (BF) protection provides backup for circuit breakers (CBs) and associated control wiring. Traditionally, CBs are not duplicated, but monitored by BF relays when ordered to trip. Upon a failure of a breaker to interrupt the current, the BF relay opens adjacent breakers to isolate the problem. The total trip time under a BF condition is often tightly fit into the critical fault clearance time as determined by system stability. With narrow stability limits in today's power systems, coordination margins for the operation of BF functions are becoming scarce. This imposes a requirement for the fast reset time of BF protection. In its first part, this paper presents a novel algorithm for numerical current-based BF function with a fast 0.5-cycle reset time even under severe subsidence current. In the second part, the paper addressed the problem of fast and secure recognition of binary inputs for both BF initiation and BF detection based on the auxiliary breaker contacts. This novel algorithm works with analog representation of binary signals and provides security under induced transients, battery ground faults, and other interfering events.

The classical two-parameter Fourier algorithm for computing synchrophasors is appropriate when the underlying voltage and current waveforms are sinusoids with constant amplitude and phase angle and with a frequency equal to the assumed value. Synchrophasor measurements, however, are applied in power systems to track dynamic conditions where, by definition, currents and voltages, though resembling sine-waves, exhibit changes in their magnitudes and vectorial positions. This paper presents a novel algorithm for estimating synchrophasors under such dynamic conditions. In contrast to the classical Fourier algorithm, our model is a complex Taylor expansion, yielding several parameters in the model to be estimated. Four- and six-parameter models are presented corresponding to first and second order Taylor expansions. This paper derives a compensation method for canceling the error in the classical Fourier algorithm that arises under dynamic conditions, shows comparative simulation and test results and describes an efficient implementation. Application of the error cancellation method to other phasor algorithms and extending the technique to higher order Taylor expansions, are discussed. Implementation of synchrophasor measurements on protection and control intelligent electronic devices (IEDs) is discussed, and solutions are presented that allow for secure integration.

This paper explains the principles of negative-sequence differential (87Q) protection, its basis for excellent sensitivity and speed, and the need for securing it with external fault detectors to deal with the saturation of current transformers. The paper reviews applications of 87Q elements to lines and transformers. It explains why 87Q elements cannot be used for turn-to-turn fault protection in shunt reactors and stators of generators and motors. The paper presents applications of negative-sequence directional elements for turn-to-turn fault protection in reactors and stators. Finally, it derives two new protection principles based on negative sequence for generator turn-to-turn fault protection.

Today's relays are predominantly based on phasors, and as such, they incur a delay associated with the full-cycle observation window required for accurate phasor estimation. Considerable improvement in speed is possible by using information in the transients of voltages and currents. We review a number of protection techniques, including directional elements, direct tripping underreaching elements, and differential elements that significantly speed up line protection.

This paper presents a new adaptive phasor estimation algorithm for digital protective relaying. The algorithm is completely immune to an exponentially decaying dc component regardless of its initial magnitude and time constant. The algorithm is primarily intended for current signals and improves both magnitude and impedance measurements. The new technique is based on the recursive full-period Fourier filter with a separate adaptive function allowing for thorough rejection of the dc signal component. The comparative analysis of the algorithm, both analytical and by simulation, is included. The presented algorithm outperforms known measuring techniques including the digital mimic filtering broadly used in today's relays.

This paper presents a new first zone algorithm for distance protection of series compensated lines. The algorithm detects faults with the reach of 75-85% of the line length by measuring two distinctive impedances, using three adequate regions on the impedance plane and applying appropriate logic functions. The algorithm estimates instantaneous values of the voltage drop across the series capacitors online, and compensates for this signal when calculating the impedance valid for faults behind the series capacitors. The other impedance (without compensation) is calculated for faults in front of the series capacitors. An explicit selecting procedure for the two impedances is not required since the presented relaying method asserts directly the fault within or outside the first zone. The algorithm is presented in detail and extensively tested using the EMTP model of a 400 kV 300 km transmission line. The enclosed results demonstrate high speed, dependability and security of the new algorithm.

This paper presents a new fuzzy logic controller (FLC) for on-load tap change control for distribution transformers. The model of a transformer with its tap changing mechanism is given first. Next, the FLC is presented in detail. The proposed algorithm is optimized from the numerical point of view and proved to be implementable on contemporary programmable logic controllers (PLCs). Simulation results are included that compare the proposed control algorithm with the classical inverse-time controller and prove the efficiency of the new solution.

This paper presents new digital measuring algorithms for generator and transformer protection. Two methods are proposed to make the estimation of amplitudes of the fundamental frequency component and the higher harmonics immune to frequency deviations. The first method is based on the software re-sampling of the physical data window and on the simultaneous iterative estimation of the frequency. The second algorithm employs the amplitude estimator having unique frequency response in the entire frequency spectrum and enables direct compensation for the frequency deviations. Also a new Volts/Hertz inverse-time algorithm is proposed which does not call for the direct measure of frequency. It relies on the second method and uses the amplitude estimator having the gain close to the inverse of the frequency; therefore, it acts as a direct amplitude-to-frequency estimator. The proposed algorithms were analyzed analytically and tested using EMTP simulations.

This paper presents the digital algorithm for on-line dynamic compensation of the secondary voltage of a capacitive voltage transformer (CVT). The adopted CVT model together with the assumed simplifications is given first. Next, the compensating algorithm based on digital inversion of the CVT transfer function is derived. Frequency domain analysis and quantitative evaluation of the compensation follow. The ATP-EMTP simulations are included that show the improvement of the measurement of protective criteria quantities as a result of dynamic compensation of a CVT.

This paper reviews the protection requirements for generators during periods of off-nominal frequency operation. It investigates the behavior of instrument transformers during these periods as well as the impact of frequency on the accuracy of protection operating quantities. Traditional methods for frequency tracking and compensation are reviewed. A novel approach, which provides excellent performance for very significant frequency deviations and can accommodate multiple frequency islands, is presented.

Transmission power lines can feed distribution networks or either serve loads or interconnect generation directly via tapped transformers. In some utilities, as many as three to five taps may be used on some lines. As a part of the bulk electric system, tapped transmission lines must be protected with instantaneous fault-clearing times and proper selectivity and sensitivity. This paper reviews various approaches to protecting tapped lines, including pilot protection schemes with distance and zero- and negative-sequence directional elements, time-overcurrent elements, line current differential schemes, and stepped distance backup. In addition, this paper discusses protection applications for in-line transformers where a transmission line terminates on a transformer and a single protection zone includes both the line and the transformer.

This paper addresses the security of transformer differential protection with low levels of second harmonic during magnetizing inrush conditions. The paper explains the phenomenon of ultrasaturation causing the second harmonic to drop below the traditional 15 to 20 percent setting levels and points to possible causes of and conditions for ultrasaturation. A number of field cases are presented and discussed in addition to the engineering analysis of the problem. The paper outlines several simple solutions to address the security problem while minimizing the adverse impact on dependability. Further, the paper presents a new method for inrush detection that considerably improves security without diminishing dependability. Finally, a method to accelerate operation of transformer differential protection is presented.

Faults on overhead transmission lines cause transients that travel at the speed of light and propagate along the power line as traveling waves (TWs). This paper provides an overview of TWs and TW fault locators. It explains the physics, reviews the theory of TWs, explains the foundations of various types of TW fault locators, and provides an in-depth discussion on a number of TW fault locating implementation challenges. Finally, it discusses integration of TW fault locating in microprocessor-based relays and presents Bonneville Power Administration's (BPA's) field experience using these relays.

Faults on overhead power lines cause transients that travel at the speed of light and propagate along the line as traveling waves (TWs). This paper presents a new algorithm for TW fault locating suitable for implementation in line current differential relays. The paper presents the new algorithm in detail, including filtering, phase and mode selection, time stamping, and compensation for dispersion. The paper includes a number of actual field cases from a 161 kV transmission line at Bonneville Power Administration.

In the paper the fuzzy logic based multi-criteria protective relay for a three-phase power transformer is presented. Twelve criteria used to stabilize the relay are introduced and integrated by means of multi-objective decision-making methods. The introduced protection scheme contains several internal functions and coefficients which are subject to off-line pre-installation self-setting. Three unique procedures are delivered for self-adjusting the relay, and thus, making it self-organized. The results of testing show significant gains in both sensitivity and selectivity of the self-organized relay compared with traditional approaches.

This paper presents a new digital impedance measuring technique for transmission lines that combines symmetrical components and the complex differential equation of an equivalent fault loop circuit. The phase voltages and currents at the relaying point are transformed into symmetrical components using Fourier filters of short window length. Depending on fault type, an appropriate fault loop circuit is formed, signals of which are the appropriate symmetrical components, while a parameter of which is the positive sequence impedance being a geometrical measure of the distance from the relaying point to a fault. The impedance, however, is measured very fast by on-line solving the complex differential equation originated for this fault loop circuit. Consequently, this approach combines frequency domain estimation of symmetrical components (accurate filtration) and time domain measurement of positive sequence impedance (high speed response). The presented method suits well the protection of parallel lines against high-resistance faults occurring very close to the far end of a line. A new method is proposed for detecting high-resistance faults and deciding which line out of two parallel lines actually suffers a fault. The included EMTP test results demonstrate the efficiency of the proposed relaying algorithm.

It is common knowledge that the line current differential protection principle is not susceptible to unusual system conditions. This is true and straightforward regarding protection security but is not immediately obvious when considering dependability of protection. As a result of dismissing the impact of unusual system conditions, the effect of series compensation, power swings, and inverter-based short-circuit current sources on line current differential protection is not well understood. This paper briefly touches on protection security but focuses on the dependability of line current differential protection under a number of specific system conditions, including series compensation, power swings and off-nominal frequency, and inverter-based sources. This paper reviews the impact of each of the mentioned conditions and provides illustrations using simulations.

The globally used COMTRADE standard was initially developed by IEEE and later adopted by IEC. The first IEEE version was published in 1991 and was later revised in 1999. The IEC version was adopted in 2001. The 2013 revision of the COMTRADE standard is an IEEE/IEC Dual Logo standard planned for publication during the first quarter of 2013. The main motivations for the current revisions are: 1) to remove restrictions that were only relevant for computing technologies of the 1990s and 2) to satisfy the requirement of universal time information in COMTRADE files. The second need was identified during the 2003 Northeast Blackout analysis to time synchronize data from different substations. The working group has also addressed other issues, including the availability of a single file. Industry users feel very strongly about this need to easily exchange and manage COMTRADE files, and the working group's recommendations address these concerns.

This paper presents a digital relay scheme for the primary protection of power transformers. A multi-criteria algorithm is developed based on fuzzy sets for the decision making part of the scheme. The cost of wrong decision-making and the amount of information inflow are used along with several standard criteria to improve the reliability of the protection. It is shown that the proposed scheme, if properly tuned, can enhance the sensitivity and selectivity of the digital relay and mitigate problems associated with conventional relay schemes. >

Testing line current differential (87L) schemes is more complicated than testing directional comparison schemes. The latter exchange simple on/off (permission or block) signals that can be conveniently checked at the output of a given relay and conveniently forced at the input to a given relay in the scheme. Line current differential schemes exchange synchronized current values that cannot be easily intercepted or forced at the 87L communications port of the relay. Moreover, the communications channel is an integral part of the 87L scheme, and its characteristic can impact some fundamental aspects of the scheme, such as sensitivity and speed. Therefore, it is preferable that the actual channel be in use when testing the scheme. Line current differential schemes that apply external time sources for synchronization need to be tested with time sources as well. Often, 87L schemes are tested with multiple crews dispatched to two or more line terminals using either test sets synchronized via the Global Positioning System or other methods of controlling the relationship and timing between current sources at the line terminals. This paper presents several approaches to testing 87L schemes. These approaches include verification of relay hardware, firmware and settings, channel performance, and, if used, external time sources. The paper also describes features of line current differential relays and multiplexers to aid testing.

This paper discusses merits, advantages, and disadvantages of integrating breaker failure (BF) protection with zone protection relays (ZPRs). In this context, the paper considers cost savings, security and dependability, simplicity, the danger of human errors when testing bus configurations, overall relaying philosophy, and reliability of applied protection devices. Several ways of integrating BF protection are proposed, allowing different tradeoffs between the mentioned factors. This paper also reviews methods to improve the security of BF protection.

The IEEE/PSRC Substation Protection Subcommittee Working Group (WG) K5 on Ancillary Protective and Control Functions Common to Multiple Protective Relays have produced a document that addresses the considerations in applying the ancillary protection, control and monitoring functions that are commonly available in multiple relays and the integration of these functions into the overall protection system. Modern protection schemes are designed with fully integrated protection, control and monitoring functions to accommodate the implementation of many different design requirements. These functions can be used to achieve reliable protection and control solutions. Implementing these designs can be an exhilarating and very satisfying challenge to the engineer's imagination. This summary paper addresses subjects related to specific protection and control topics with application examples which were covered in the special PSRC publication.

This paper considers the sensitivity of essential line protection elements: ground distance and ground directional overcurrent elements applied as time-coordinated functions or in pilot-assisted protection schemes and line current differential schemes. Factors discussed include fault resistance, line unbalance and charging currents, impact of in-line reactors, system short-circuit capacity, load encroachment and swings, sequential tripping and weak feed terminals, steady-state and transient errors of instrument transformers, impact of current transformers (CTs) in dual-breaker line terminals, and single-pole-open conditions. Protection element design improvements and application principles enhancing sensitivity are included.

Distance and directional overcurrent protection can provide 100 percent coverage of transmission or subtransmission feeders through the use of teleprotection (communications-assisted tripping) schemes. We briefly review in this paper various types of teleprotection schemes and then present principles to successfully apply a directional comparison blocking scheme (DCB). We amplify these principles by examining the reasons why incorrect tripping occurred on feeders using DCB schemes in five field cases. Further, we alert readers to the conundrum of using DCB schemes in emerging electricity markets — dependability of protection versus less security of supply. We propose that protection engineers can apply the advantages of digital communications systems, functionality of numerical relays, and increased electricity network infrastructure to intelligently design line protection systems with high dependability and high security.

This paper concerns the justification of the use of pilot protection on transmission lines.

Line current differential protection creates challenges for relay design and application. From a design perspective, the distributed nature of the line current differential system imposes limits on the amount of data that can be exchanged between the system terminals and calls for data alignment schemes to enable the differential protection principle. From the application perspective, line current differential schemes are concerned with CT saturation, particularly in dual-breaker applications; in-zone reactors and line-charging current; in-line and tapped transformers; sensitivity to high-resistive faults; single-pole tripping; security on channel impairments; application to lines with more than three terminals; and so on. This paper reviews technical solutions to the line current differential design and application, addressing the common design constraints and utility-driven application needs. The paper is a tutorial in this challenging area where protection principles and applications mix with communications and signal processing.

This paper reviews principles of protection against internal short circuits in transformers of various constructions. Transformer fundamentals are reviewed as pertaining to protection. In particular, the electromagnetic circuit of a transformer is reviewed that links the terminal currents, winding currents, fluxes, and ampere-turns (ATs) in a set of balance equations for a given transformer. These balance equations are used to explain the sensitivity of protection to various types of transformer faults. The paper shows that the classical transformer differential compensation rules have roots in the first principles — they reflect the AT balance of the protected transformer. The rule of building transformer differential protection equations following the AT balance is used in this paper to derive differential equations for autotransformers; power zig-zag, Scott-T, and Le-Blanc transformers; and phase shifters. The restricted earth fault (REF) and negative-sequence transformer differential (87TQ) functions are explained as a means to detect ground faults near the neutral and turn-to-turn faults, respectively.

Modern electric power protection, monitoring, and control systems rely on the availability of high-accuracy time. Precise time enables technologies like synchrophasors, IEC 61850 Process Bus, and highly accurate, wide-area power system event reporting. Today, high-accuracy time is generally provided by Global Positioning System (GPS) clocks. However, if GPS is the only source of accurate time, it becomes the single point of failure in systems that rely on precise time. GPS may become unreliable due to solar activity, intentional or unintentional jamming, or the U.S. Department of Defense (DoD) modifying GPS accuracy or turning off the satellite system. (5 pages)