Power System Protection -

• Analysis of Transformer Inrush Current and Comparison of Harmonic Restraint Methods in Transformer Protection - This paper will analyze factors affecting the second harmonic ratio in inrush current and describe various harmonic restraint methods and compare their performance.
• Arc Flash Mitigation Through Use Of Voltage Controlled/Voltage Restrained Overcurrent Elements - This paper investigates the use of voltage controlled/voltage restrained overcurrent elements as an arc flash mitigation technique when applied to certain industrial circuits. For additional information on this topic, see Application Note PC-ArcFlash. For details on how the BE1-50/51B-235 and 237 can help meet NESC Arc Flash requirements, see the Plug and Play Feature Flyer.
• Automatic Reclosing - Transmission Line Applications and Considerations - Topics of protection that are associated with reclosing, presented for use in applying autoreclosing to transmission circuits.
• Breaker Monitoring with Numerical Relays - This paper addresses the issues associated with Breaker Duty/Contact Wear Monitoring from the perspective of what the modern numerical protective relay can easily monitor.
• Bus Protective Relaying, Methods and Application - A review of the application of bus protective relaying, describing and comparing different. Backup protection and increasing protection security are also addressed
  For more information on mixing different ratio CTs in high impedance bus protection schemes, see Application Note PC-BUS01.
• Commissioning Numerical Relays - This paper suggests experienced-based changes to commissioning tests and revised documentation of relay settings as a method for commissioning numerical relays.
• Current Transformer Errors and Transformer Inrush as Measured by Magnetic, Optical and Other Unconventional CTs - This paper will review the errors in secondary current for these primary current conditions, provide means of determining when CTs are at risk, and show, using numerical analysis results, the output of a saturated CT. The second part will review the various types of current sensors available on the market, including conventional, hybrid, and optical sensors.
• A Derivation of Symmetrical Component Theory and Symmetrical Component Networks - This paper provides a review of some of the theory behind symmetrical component analysis and derives some of the basic calculations utilized in power system analysis for short circuit and open phase conditions. An Excel spreadsheet (ElectricCalcs_R2.xls) to perform various electric system calculations is available for download.
• Directional Overcurrent (67) Relaying Applications in the DG Environment
  This paper reviews the basics of the theory of directional overcurrent relaying as applied in modern numeric relays, and then discusses several applications of the directional overcurrent relaying in the DG environment. An Excel spreadsheet (PoleSlip_R0.xls) to model voltages, currents, and power flow during a pole slip event is available for download.
• Distributive Generation and Interconnection: Protection, Monitoring, and Interconnection Opportunities - Paralleling a distributed generation supply to an electric power system involves protection, monitoring and control of the interconnection for the mutual benefit of both parties to the interconnection. Standards exist that cover the various practices for the types of distributed energy technologies, sizes, and configurations of the interconnection.
• Effects of Distributed Generation on Utility Protection Schemes - The effects of the addition of Distributed Generation to a distribution feeder can be minimized by having digital multifunction overcurrent with voltage protection schemes previously installed as standard feeder protection.
• Fundamentals and Advances in Breaker Failure Protection - This paper will discuss backup protection in general and what issues need to be considered in deciding whether to apply dedicated breaker failure protection.
• Green Power – Wind Generated Protection and Control Considerations - Green Power projects like wind farms allow protection and control engineers to use modern technology to provide cost effective systems that were not available until the implementation of multifunction numerical devices.
• Ground Differential Protection: Revisited - This paper reviews the principles of ground differential protection within industrial power systems and discusses the use of directional overcurrent relays in this application. The use of current polarized directional ground overcurrent relays provides a novel approach in the application of ground differential protection.
• Harmonic Sharing for Effective Detection of Transformer Inrush Condition in Differential Protection Schemes - The use of harmonic sharing in transformer differential protection gives the ability to improve security for some inrush conditions, while maintaining sensitivity. 
• Intertie Requirements for DGs Connected to Radial Distribution Feeders - This paper will review some of the proposed protection requirements for Distributed Generators connected to radial distribution feeders.
• Load Shedding for Utility and Industrial Power System Reliability - Analysis of the conditions in which load shedding may be needed and review of load shed implementation strategies for when the power systems designed operating capabilities are exceeded. 
• Myths of Protecting the Distributed Resource To Electric Power System Interconnection - For the ideology of power system protection, the myths described in this paper are better described as conditional truths rather than half-truths. As you read about the myths in this paper, be alert for the assumed or not so obvious conditions that can cause one to feel there is adequate system protection when, actually, there is not.
• Negative Sequence Relaying Applications in Ungrounded and High Impedance Grounded Industrial Systems - This paper explores the use of negative sequence overcurrent sensing to detect faults at levels and speeds not achievable using conventional circuit breaker technology. It also will provide guidelines to aid in determining which systems, or where in the system, the maximum benefit can be achieved.
• Power Quality: Measurement of Sags and Interruptions - The paper will review measurement of Power Quality and review common long term outage measurements. It also will discuss the use of meters for residential and small commercial customers as the tool to track outage issues.
• Practical Experience in Commissioning Distributed Generation Installations - This paper covers the experiences of the authors during commissioning of several distributed generation projects under the auspices of Portland General Electric's Dispatchable Generation Program.
• A Practical Guide for Detecting Single-Phasing on a Three-Phase Power System - This paper is provided as reference for the loss of one or two phases of a radial three phase system and includes suggested detection and protection methods for each application. This paper has two additional downloadable resources:
• A related spreadsheet (ElectricCalcs_R30.xls) allows users to perform basic complex number calculations, sequence component conversions, and some other basic calculations associated with electric power systems, such as some very simple fault and load flow analysis
• A Mathcad (revision 7) document, Single_Phase_mc7_rev_1_1.mcd, performs some of the calculations referred to in the paper. Calculations include flux balance analysis of a 5 legged, 4 core shell form transformer, and load voltages and currents after the loss of one and two phases, using symmetrical component theory. Note: You must have Mathcad installed on your computer to utilize this file.
  See Application Note PC-95102 for additional material on the topic.
• Predicting Current Differential Relay Tripping and Targeting when Testing at Final Settings describes the issues associated with testing at final settings and gives instructions on applying an associated spreadsheet, “Transformer Differential Calculations”.
• Protective Relaying Issues in Low Voltage Systems as Addressed in the National Electric Code - This paper provides some background on low voltage (LV) design practices, as mentioned in the National Electric Code (NEC), especially for the protection engineer who normally only works in high voltage (HV) and medium voltage (MV) systems.
• Protective Relaying When Distributed Generation is Added to Your Circuit - The purpose of this paper is to highlight the advantages of having numeric multifunction protection in place when Distributed Generation (DG) is added to a radial distribution circuit.
• Reliability Considerations of Multifunction Protection - This paper evaluates the reliability of numerical multifunction protection systems against predecessor technologies. Reliability as it relates to protective relaying is defined, identifying a selected group of reliability factors that impact both predecessor and numerical multifunction technologies, discussing each factor in detail, and drawing conclusions about the overall reliability of multifunction protection.
• A Review of Ferroresonance - The basics of a ferroresonant condition are covered in this paper.
• A related spreadsheet (Ferro_R1.xls) is also downloadable. It allows users to further analyze Figure 21, "Circuit Model With Resistive Elements." from the paper.
• A Review of System Grounding Methods and Zero Sequence Current Sources - The purpose of this paper is to provide a tutorial or “refresher” on grounding methods, sources of ground current, ground current flow in the power system, and how each impacts protective relaying.
• Solutions for Unconventional Connection of Transformer Differential Current Transformers – This paper is a primer on analyzing unconventional current transformer polarity connections and how to obtain the right connection to achieve the desired direction of operation or polarity as indicated in protective relay manufacturers’ literature.
• Successful DG Projects: Design and Build Considerations - This paper covers the design and build challenges for four DG projects known as On-Site Generation Resources, including their justification based on economics, reliability considerations, and flexibility for daily operational situations.
• A Survey of Cold Load Pickup Practices - This paper discusses the concepts of cold load pickup, the causes and effects, and will investigate how CLPU generally is dealt with in protection schemes.
• Three Phase Transformer Winding Configurations and Differential Relay Compensation - This paper reviews the possible winding configuration and gives examples of the nomenclature used with them and how the various phase shifts are created. Plus, it will show how a transformer differential relay compensates for the effects of the various transformer winding configurations.
• Upgrading Intertie Protection to meet TX PU Standards
  This paper is an enhanced version of what was presented at the Texas A&M Conference. It describes the process of a wastewater facility utilizing multifunction relays as the sole means of protection, not only for the plant and its generation, but also for the utility by separating the facility system from the utility feeder in accordance with the rules of the Texas Public Utility Commission. 
  
  Upgrading Intertie Protection to Meet Texas Public Utility Commission Rules Expanded (WPRC version) - This case history points out differences between the Texas PUC rules and IEEE Standard 1547 “Interconnecting Distributed Resources with Electric Power Systems" plus the voltage operating requirements of some utilities who are members of WECC.
• Using Iop Characteristics to Troubleshoot Transformer Differential Relay Misoperation - This paper explores the issues contributing to transformer differential false trips, and suggests methods to alleviate this issue.
• Voltage Restrained Time Overcurrent Relay Principles, Coordination, and Dynamic Testing Considerations - This paper addresses the dynamic response of 51/27R relays in which the overcurrent element conforms to the dynamic characteristic defined in the ANSI C37.112 standard. The purpose of this analysis is to compare the results obtained from a proposed approximation to the exact timing results derived from a relay model and actual test.
  
  Please note that you must have Mathcad Professional Edition installed on your computer to utilize the downloadable 51V Timing Model Mathcad simulation file referenced in this paper.
• Zero Sequence Circuit of Three-legged Core Type Transformers - This paper gives the modified zero-sequence equivalent circuit for a three-legged core-type transformer. Theoretical calculation, computer simulation, and actual staged tests verify that fault current based on the modified zero sequence circuit matches the result from the simulation and actual test.
• Zero Sequence Impedance of Overhead Transmission Lines - This paper reviews the transmission line impedances, centering on zero sequence impedances, and review the work of John Carson on the topic of ground current impedances.

Power Generation

• Alternate Solutions to Replacing Aged Static Exciter Systems - This paper details the overall cost savings and improved performance from replacing only the analog portion of a static exciter system with a digital front-end controller into the existing power rectifier bridge/s.
• Application of Static Excitation Systems for Rotating Exciter Replacement - This paper discusses the static exciter system, including the power control devices, power transformer and automatic voltage regulator. Solid state fast de-excitation circuits will be discussed. Lastly, selection criteria and application considerations will be reviewed.
• Updated 3/10 Convection Cooled Bridges Offer New Solution to Old Alterrex Water-Cooled Bridges - This paper describes the actual water-cooled bridge replacement, including the testing, installation and commissioning of a convection-cooled system at the Exelon Power Mountain Creek Generating Station in Dallas, Texas.
• Coordination of Digital Excitation System Settings for Reliable Operation - This paper will address the importance of coordinating the various settings of the excitation system as well as performance checking the voltage regulator and limiter to ensure reliable operation during disturbance events.
• Designing a Voltage Regulation System - Examples of what needs to be done to put excitation system theory into practice when generator applications are in the design and proposal stages and how the application and specification dictate the design of a generator system.
• Digital Excitation System Provides Enhanced Tuning Over Analog Systems - Features in excitation control speed commissioning and offer a greater variety of tuning tools to ensure a desired performance to a specific plant.
• Easing NERC Testing with New Digital Excitation Systems - This paper discusses a portion of the North American Electric Reliability Council policy involving generator testing. The paper explains the types of tests that are required, operating modes of the excitation system, and includes a discussion of how these tests are accomplished using the commissioning tools available in today’s digital excitation systems.
• Feature Enhancements in New Digital Excitation System Speeds Performance Testing - New technology solutions built into the excitation system can ease the burden of performing required tests and provide permanent records for future analysis.
• Front End Analog Conversion to Digital Saves Cost for Upgrades of Excitation System - This paper discusses the decision factors in purchasing a 6 SCR full-wave bridge or reusing the existing 3 SCR half-wave, keeping the power potential transformer and removing the old analog electronics for a digital front end.
• Introduction to Synchronizing - An explanation of the automatic synchronizing process explores the considerations involved and looks at some synchronizing applications and provides a guide for selection of the proper synchronizer for the application.
• Parallel Operation with a Network System - Addresses the concerns of and the techniques required to successfully parallel synchronous generators to a network.
• Plant Efficiencies Benefit by Selection of Synchronous Motor - This paper will discuss the application of a synchronous motor and how the synchronous machine, with the aid of a DECS-200 intelligent excitation controller, can control power factor to reduce the plant reactive loading to the connected system.
• Power System Stability - A discussion of the various types of power system instability. It covers the effects of system impedance and excitation on stability, and reviews various types of power system stabilizers.
• Power System Stabilizer Performance with Summing Point type Var/Power Factor Controllers - Power System Stabilizer performance does not have to deteriorate during a system transient when voltage support is needed using a summing point VAR/PF control and does not require operator intervention.
• Retrofitting SCT/PPT Excitation Systems with Digital Control - This paper reviews a specific excitation system retrofit of the SCT/PPT (Saturable Current Transformer/Power Potential Transformer) Static Excitation System and the various factors involving a rehabilitation project that includes new equipment, design interface, installation, and commissioning.
• Selecting the Excitation System for the Additional Turbine Generator at the Port Wentworth Pulp Mill - This paper covers the process involved in evaluating whether or not to reuse the generator's original compound excitation system and if replaced, the type of excitation system that should be installed, Compound or Potential Bus Fed Type.
• Self-tuning of the PID Controller for a Digital Excitation Control System - This paper proposes an indirect method for self-tuning of the PID controller gains. The performance of the proposed method is evaluated with several generator sets. With self-tuned PID gains, commissioning is accomplished very quickly with excellent performance results.
• Specifying Excitation Systems for Procurement - This paper discusses considerations involved in specifying the excitation system for a project.
• Synchronous Motor Control - This paper provides a detailed discussion of the basic theory of operation and control of the synchronous motor. Typical protection also is addressed involving motor pullout and under- and overexcitation concerns.
• Tuning a PID Controller for a Digital Excitation Control System - This paper is intended to provide a better understanding of how the digital controller is tuned for optimum generator performance with two different approaches discussed.
• Understanding Power System Stability - This paper discusses the types of power system instability and the effects of system impedance and excitation. A review of various types of Power System Stabilizers also is presented.
• Voltage Regulator and Parallel Operation - This paper focuses on the control of the voltage regulator when operating generators in parallel.
• Voltage Regulator with Dual PID Controllers Enhances Power System Stability - This paper introduces a voltage regulator with two PID controllers. The fast controller is utilized with the power system stabilizer in service and the slow controller is utilized when the power system stabilizer is disabled. Transfer from one controller to the other is automatically accomplished without a bump when the power system stabilizer status signal changes.
• Voltage Versus Var/Power Factor Regulation on Synchronous Generators - When paralleled to the utility bus, synchronous generators can be controlled using either terminal voltage or var/power factor control. This paper illustrates the effect of changing system bus voltage on small generators utilizing voltage versus Var/power factor regulation.

TECHNICAL GUIDES

Generator Protection Application Guide - This guide was developed to assist in the selection of numerical multifunction and single function relays to protect a generator. The purpose of each relay is described and related to one or more power system configurations. Includes Integrated Application Examples, focusing on the BE1-CDS220, BE1-GPS100, BE1-87G, and BE1-87T, plus a list of typical Basler relays applicable to generator protection.

Transformer Protection Application Guide - This guide was prepared to assist in the selection of relays to protect power transformers. The purpose of each relay is described and related to one or more power system examples. Includes application information on the BE1-851, BE1-951, BE1-700C, BE1-700V, BE1-CDS220, BE1-CDS240, and BE1-IPS100, plus a list of typical Basler solid state relays applicable to transformer protection.