Preface: This is the first edition of CSA C391, Testing of three-phase synchronous machines during refurbishment. CSA acknowledges that the development of this Standard was made possible, in part, by the financial support of BC Hydro, Canadian Electrical Association, Efficiency Nova Scotia, Hydro Québec, Manitoba Hydro, Natural Resources Canada (NRCan), Ontario Power Authority and Saskatchewan Power. Introduction: This comprehensive Standard provides guidance to electric machine service centres to assist in verifying that the refurbishing process has maintained or enhanced the synchronous machine efficiency. It is also intended to provide a reliable evaluation of any changes to the condition of a machine, with respect to its efficiency, that could have resulted from its failure. It is not mandatory that all of the tests presented in this Standard be performed on every machine that is refurbished by the service centre. The application of these tests will depend on the type of work performed and the need to confirm that no change in efficiency has occurred as a result of damage to the machine and its repair. It is acknowledged that the machine efficiency could be depreciated by the damage caused during the motor operation or failure mode. In cases where the test results exceed the prescribed pass/fail criteria, it is not the intent of this Standard to require that the machine be removed from service nor scrapped. However, the test results might assist in future repair/replace decisions and future energy conservation planning. The prescribed tests and pass/fail criteria are well known and employed throughout the machine service centre industry in North America. Clause 2 provides reference materials that may be accessed for further details on the various tests prescribed by this Standard. It should be pointed out that there are many additional tests and inspection procedures employed when refurbishing machines that are not part of this Standard because they are not directly related to the motor efficiency. Some of the more common ones are available in the materials referenced in Clause 12. Not all of these prescribed tests can or should be administered on every machine that is to be refurbished. It is the responsibility of the machine service centre to determine which inspection and tests options are applicable. Load testing is not required by this Standard because such equipment is not readily available throughout the machine service industry. In some cases it will not be practical to run the machine because of the lack of components. Scope: 1.1 This Standard covers three-phase, alternating current, salient pole synchronous machines 150 kW and up, 200 through 13,800 volts, 60 and 50 Hertz and will assist in verifying the machine efficiency has been maintained. Note: This Standard can be useful and applied with discretion to products outside the scope of this Standard. 1.2 Large 2-pole and 4-pole solid cylindrical rotor machines, typically used as generators for utility and large industrial applications, are excluded from this Standard. Note: See Annex E for information on generators. 1.3 In this Standard, "shall" is used to express a requirement, i.e., a provision that the user is obliged to satisfy in order to comply with the standard; "should" is used to express a recommendation or that which is advised but not required; and "may" is used to express an option or that which is permissible within the limits of the standard. Notes accompanying clauses do not include requirements or alternative requirements; the purpose of a note accompanying a clause is to separate from the text explanatory or informative material. Notes to tables and figures are considered part of the table or figure and may be written as requirements. Annexes are designated normative (mandatory) or informative (non-mandatory) to define their application.