Foreword?(This Foreword is not a part of IEEE Std 434-1973@ IEEE Guide for Functional Evaluation of Insulation Systems for Large High-Voltage Machines).The Rotating Machinery-Insulation Subcommittee@ Power Engineering Society@ IEEE@ has been actively developing functional testing guides during the past two decades for rotating machines under the authorization of IEEE Std 1-1969@ General Principles for Temperature Limits in the Rating of Electric Equipment. In 1965@ the working group assigned to develop a test procedure for machines rated at 50 to 2000 hp and below 6600 V completed their task. After more than a decade of work by two working groups@ a revised test procedure was issued in December@ 1966 as IEEE Std 275-1966@ Test Procedure for Evaluation of Systems of Insulating Materials for AC Electric Machinery Employing Form-Wound Preinsulated Stator Coils.It has become the custom at these working group meetings to devote a short time to the consideration of functional test procedures for larger machines than those included within the scope of IEEE Std 275-1966 . With the discharge of the old working group@ a new task force was established at the February@ 1965 meeting of the Rotating Machinery Insulation Subcommittee. Its charter was: "To review available means of functional evaluation of insulation for large@ high-voltage machines@ and report on the feasibility of standardizing test procedures for this purpose." This report was favorable and was accepted at the February@ 1966 meeting of the Insulation Subcommittee. At the same time@ the task force was reconstituted as a regular working group to prepare a suitable guide for the functional testing of this class of machines.Over the past six years@ five drafts of the new guide have been prepared and the final version successfully balloted through the Insulation Subcommittee@ the Rotating Machinery Committee@ and the Standards Committee of IEEE with no negative votes or unresolved comments.There was considerable doubt in 1965 that an IEEE standard could be written for insulation functional evaluation of large@ high-voltage machines. Many thought the effort was premature and that ten years or more would be spent by working groups before a useful@ acceptable document could be written.It is recognized that this standard does not describe all of the functional tests currently in use by manufacturers of large@ high-voltage rotating machines@ and that these additional tests may be essential to a complete evaluation and classification of a new insulation system. The tests described in the guide are@ however@ in widespread use and are generally performed prior to the newer@ more complex and less generally used model tests which have recently been described in technical papers. A period of experience with this guide and the continued rapid development of new test methods will enable a revised edition to be developed within a few years.Active participants in the present document will continue their IEC roles in Technical Committee 63 (Insulation Systems) and Technical Committee 2 (Rotating Machines) by transmitting IEEE viewpoints to these international organizations.The membership of the Working Group is:E.A. Boulter @ ChairV.S. McFarlin @ SecretaryJ. C. BottsJ. M. BrownA. W. W. CameronE. M. FortM. M. FrommJ. L. KuehlthauP. LonsethC.V. MaughanJ.A. OliverP. RichardsonC.C. SargeantE.S. YatesScope?The tests outlined in this guide are applicable to the insulation systems used in coils of generators@ motors@ and synchronous condensers operating at 6600 V and above.The basic ingredient of these insulation systems is usually mica combined with reinforcing@ bonding@ and impregnating materials. This guide is based on the experience of the industry with micaceous systems; any evaluation of nonmicaceous systems should@ however@ consider the requirements of this guide.