EASA’s “Recommended Practice for the Repair of Rotating Electrical Apparatus” is designated ANSI/EASA AR100 and was first approved as an American National standard in 1998. Since then it has been revised and approved four more times, in 2001, 2006, 2010, 2015 and now in 2020.
ANSI/EASA AR100 is a must-have guide to the repair of rotating electrical machines. Its purpose is to establish recommended practices in each step of the rotating electrical apparatus rewinding and rebuilding processes.
The scope of this document describes record keeping, tests, analysis and general guidelines for the repair of induction, synchronous and direct current rotating electrical apparatus. It is not intended to take the place of the customer's or the machine manufacturer's specific instructions or specifications or specific accepted and applicable industry standards or recommended practices.
This document should be supplemented by additional requirements applicable to specialized rotating electrical apparatus including, but not limited to, listed explosion-proof, dust-ignition proof, and other listed machines for hazardous locations; and specific or additional requirements for hermetic motors, hydrogen-cooled machines, submersible motors, traction motors, or Class 1E nuclear service motors.
ANSI recognizes only one standard on a topic; therefore, ANSI/EASA AR100 is the American standard for repair of rotating electrical apparatus.The Recommended Practice is an important publication to distribute both internally and to customers.
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Approval Process
The EASA Technical Services Committee (TSC) reviews the recommended practice and proposes changes; a canvass group approves and often comments on the TSC proposals. The canvass group has representation from service centers, end users, testing laboratories, government and those with a general interest. Per ANSI requirements, there must be balanced representation among the canvass group representatives. After the canvass group and the TSC find consensus agreement, the revised document is approved by the EASA Board of Directors. Following Board approval, ANSI is requested to approve the revision as an American National Standard. The entire process must be completed within five years following the previous revision.
What’s New in 2020?
The 2020 edition of AR100 contains more than 40 revisions. Here, we will focus on the more significant changes, noted in clause order, and some of the reasons for making these changes. Also noted will be links between the changes and the EASA Accreditation Program.
1.6 Terminal Leads: Added a note, “If the machine has a service factor, the terminal leads should be rated for the service factor current.” This is the practice used by many motor manufacturers. For example, if a motor had a full load current rating of 100 amps and a service factor of 1.15, the approximate service factor current would be 115 amps, and the lead wire size would be based on the 115 amp value.
1.9 Cooling System: Added a new sentence: “The locations of air baffles and any stator end winding spacers that are utilized for guiding airflow should be documented prior to any stator winding removal to allow duplication within a replacement winding.” This applies to stator rewinds and helps ensure that the cooling airflow is not reduced during the rewind process. Effective August 2021, this will be a requirement in the Accreditation Program Checklist item 3. Cooling System.
2.5.1 Rotating Elements: The sentence, “The outer diameter of the rotating element laminations should be true and concentric with the bearing journals,” has been replaced with, “The runout of the rotating element core outside diameter relative to the bearing journals should not exceed 5 percent of the average radial air gap, or 0.003” (0.08 mm), whichever is the smaller value.” The new text is independent of the number of poles in a machine and is in line with tolerances used by motor manufacturers.
3.1.2 Thermal Protectors or Sensors: The former clause 3.9 has been added for clarity. It states, “Replacement thermostats, resistance temperature detectors (RTDs), thermocouples and thermistors should be identical with or equivalent to the originaldevices in electrical and thermal characteristics and placed at the same locations in the winding. Thermal protectors or sensors should be removed or omitted only with customer consent and documented in the repair record.” The reason for moving the text of 3.9 into 3.12 was to have the topic of thermal protectors and sensors addressed in one clause. Since 3.9 was deleted, the remaining clauses of Section 3 beginning with former clause 3.10 were renumbered.
Table 4-2 Recommended Minimum Insulation Resistance Values at 40°C: This table and Table 4-1 were unnumbered in previous editions of AR100, including the 2015 edition. For clarity and editorial consistency, these two tables are now numbered. The tables that were, and remain, at the end of Section 4 were renumbered. A substantive technical change was that the minimum insulation resistance for all armatures is now IR1min = 5, which aligns with the 2013 edition of IEEE 43.
4.2.4 Form-Wound Stator Surge Tests and 4.2.5 All Other Windings Surge Tests: Two identical paragraphs have been added to each of these clauses. The first paragraph explains how a surge pattern distinguishes between a satisfactory and unsatisfactory test result. The second paragraph explains that surge test results can be influenced by multiple factors, and that analysis of surge test results is subjective.
Table 4-3 Form Coil New Winding Surge Test Voltages: This is a new table that provides surge test voltage levels for machines rated from 400 to 13800 volts in accordance with IEEE 522 and IEC 60034-15. The notes below the table provide test levels for uncured resin-rich or dry (green) VPI coils, and maintenance test levels for reconditioned windings.
4.3.1 Stator and Wound-Rotor Windings: Two notes have been added to this clause. They are: “Per CSA C392 the resistance unbalance limit for random windings should be 2% from the average, and 1% from the average for form coil windings,” and, “Some concentric windings may exceed the 2% limit.” These notes add resistance balance tolerances and provide guidance for assessing resistive unbalance with concentric windings.
4.4.1.1 New Windings: The sentence, “Immediately after rewind, when equipment is installed or assembled and a high-potential test of the entire assembly is required, it is recommended that the test voltage not exceed 80% of the original test voltage,” has been replaced with, “Immediately after rewind, when a high-potential test of the winding is required, it is recommended that the test voltage not exceed 80% of the original test voltage.” The primary reason for the change is that AR100 is a repair document, not an installation guide or standard.
Conclusion
The work of the Technical Services Committee to revise and improve AR100 is a continual process. Within a year or two, the revision process will become an active agenda item for the TSC. One of the foremost goals with AR100 is to include as many good practices as possible. Further, when it is desired or necessary to add new good practices to the Accreditation Program, AR100 is the conduit. The reason for this approach is that AR100 is the primary source document for the EASA Accreditation Program.
Since AR100 is revised periodically it is a “living document.” Changes to AR100 not only aid with the Accreditation Program, its good practices and other guidance help enable service centers to provide quality repairs that maintain or sometimes even improve rotating electrical apparatus reliability and energy efficiency.