Introduction (This introduction is not part of IEEE Std 421.5-2005.IEEE Recommended Practice for Excitation System Models for Power System Stability Studies.) Excitation system models suitable for use in large-scale system stability studies are presented in this recommended practice.With these models,most of the excitation systems currently in widespread use on large,system-connected synchronous machines in North America can be represented. In 1968,models for the systems in use at that time were presented by the Excitation System Subcommittee and were widely used by the industry.Improved models that reflected advances in equipment and better modeling practices were developed and published in the IEEE Transactions on Power Apparatus and Systems in 1981.These models included representation of more recently developed systems and some of the supplementary excitation control features commonly used with them.In 1992,the 1981 models were updated and presented in the form of recommended practice IEEE Std 421.5-1992.In 2005,this document was further revised to add information on reactive differential compensation,excitation limiters,power factor and var controllers,and new models incorporating proportional,integral,and differential (PID) control. The model structures presented are intended to facilitate the use of field test data as a means of obtaining model parameters.The models are,however,reduced order models and do not represent all of the control loops on any particular system.The models are valid for frequency deviations of +5%from rated frequency and oscillation frequencies up to 3 Hz.These models would not normally be adequate for use in studies of subsynchronous resonance or other shaft torsional interaction problems.Delayed protective and control features that may come into play in long-term dynamic performance studies are not represented.A sample set of data for each of the models,for at least one particular application,is provided. Notice to users Errata Errata,if any,for this and all other standards can be accessed at the following URL:http:// standards.ieee.org/reading/ieee/updates/errata/index.html.Users are encouraged to check this URL for errata periodically. Interpretations Current interpretations can be accessed at the following URL:http://standards.ieee.org/reading/ieee/interp/ index.html. Patents Attention is called to the possibility that implementation of this standard may require use of subject matter covered by patent rights.By publication of this standard,no position is taken with respect to the existence or validity of any patent rights in connection therewith.The IEEE shall not be responsible for identifying patents or patent applications for which a license may be required to implement an IEEE standard or for conducting inquiries into the legal validity or scope of those patents that are brought to its attention. Copyright 2006 IEEE.All rights reserved.iv Copyright © 2006 IEEE. All rights reserved. Introduction Excitation system models suitable for use in large-scale system stability studies are presented in this recommended practice. With these models, most of the excitation systems currently in widespread use on large, system-connected synchronous machines in North America can be represented. In 1968, models for the systems in use at that time were presented by the Excitation System Subcommittee and were widely used by the industry. Improved models that reflected advances in equipment and better modeling practices were developed and published in the IEEE Transactions on Power Apparatus and Systems in 1981. These models included representation of more recently developed systems and some of the supplementary excitation control features commonly used with them. In 1992, the 1981 models were updated and presented in the form of recommended practice IEEE Std 421.5-1992. In 2005, this document was further revised to add information on reactive differential compensation, excitation limiters, power factor and var controllers, and new models incorporating proportional, integral, and differential (PID) control. The model structures presented are intended to facilitate the use of field test data as a means of obtaining model parameters. The models are, however, reduced order models and do not represent all of the control loops on any particular system. The models are valid for frequency deviations of ±5% from rated frequency and oscillation frequencies up to 3 Hz. These models would not normally be adequate for use in studies of subsynchronous resonance or other shaft torsional interaction problems. Delayed protective and control features that may come into play in long-term dynamic performance studies are not represented. A sample set of data for each of the models, for at least one particular application, is provided. Notice to users Errata Errata, if any, for this and all other standards can be accessed at the following URL: http:// standards.ieee.org/reading/ieee/updates/errata/index.html. Users are encouraged to check this URL for errata periodically. Interpretations Current interpretations can be accessed at the following URL: http://standards.ieee.org/reading/ieee/interp/ index.html. Patents Attention is called to the possibility that implementation of this standard may require use of subject matter covered by patent rights. By publication of this standard, no position is taken with respect to the existence or validity of any patent rights in connection therewith. The IEEE shall not be responsible for identifying patents or patent applications for which a license may be required to implement an IEEE standard or for conducting inquiries into the legal validity or scope of those patents that are brought to its attention. (This introduction is not part of IEEE Std 421.5-2005, IEEE Recommended Practice for Excitation System Models for Power System Stability Studies.)