AR100 Revisions 2020

Update includes notes, additions, numbered tables

AR100 is a document considered “essential” by many EASA members. Since its first issuance in 1998, the booklet has been revised a number of times (it is required by ANSI to be revised at least every 5 years), all of which are worth analyzing.

EASA’s “Recommended Practice for the Repair of Rotating Electrical Apparatus”, as it is formally known, is what is called a “living document” due to its revision procedures. Let’s take a look (with help from EASA) at the most recent revisions in 2020, which were released last month.

What’s New in 2020?
The 2020 edition of AR100 contains more than 40 revisions. EASA has a very thorough rundown of some of the more significant changes, noted in clause order, and some of the reasons for making these changes. Also noted in the analysis are links between the changes and the EASA Accreditation Program. View the EASA summary, with full explanations of each new note, alteration, or addition, in its entirety here. This link also includes EASA’s summary and conclusion.

Also, download the full revised document here.

EASA’s summary notes the following changes and corresponding sections of AR100:

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.”

 1.9 Cooling System: Added a new sentence: “The locations of air baffles and any stator end winding spacers (Figure 1) that are utilized for guiding airflow should be documented prior to any stator winding removal to allow duplication within a replacement winding.”

2.5.1 Rotating Elements: The sentence, “The outer diameter of the rotating element laminations should be true and concentric with the bearing journals to within 0.001” (0.025 mm) for two-pole and 0.005” (0.013 mm) for other machines,” 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.”

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.”

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.


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.

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. 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.”

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