An ac induction motor and generator acceptance test is a field protocol that proves a rotating machine is mechanically sound and electrically insulated before it is coupled and started. It records the machine's identification (manufacturer, model and catalog number, serial number, horsepower and kilowatt rating, rated voltage, full-load amperes, speed, phase, frequency, service factor, insulation class, frame, and equipment designation). The inspection covers condition, anchorage, alignment and grounding, the air baffles, filter media, stator winding and core, rotor, cooling fans, slip rings, brushes, and bearings, bolted-connection tightness, air-gap spacing, hand rotation of the rotor, shaft runout, the lubrication systems, the temperature detector circuits, and a thermographic survey. The electrical work covers bolted-connection resistance, insulation resistance with polarization index or dielectric absorption ratio by machine size, a dielectric withstand test on the higher-voltage machines, phase-to-phase stator resistance, optional power factor, tip-up, and surge comparison, insulated bearing insulation resistance, the surge protection devices and the motor starter under their own sections, the detector circuits, the space heater, and optional under-load vibration, bearing temperature, current signature, and partial discharge measurements. NETA ATS-2025 section 7.15.1 lists this as the standard acceptance sequence.
A motor fails in one of two ways: the insulation gives up or the mechanics do, and the acceptance test is built to see both coming. The insulation side is why insulation resistance is not a single reading here but a curve over time: the polarization index on a large machine, or the dielectric absorption ratio on a smaller one, distinguishes clean dry insulation that keeps rising from contaminated or damp insulation that plateaus immediately. Phase-to-phase stator resistance compares the three windings against each other, which is how a shorted turn or a bad connection inside the machine shows up. The mechanical side is why hand rotation, shaft runout, air-gap spacing, and alignment appear before any instrument is connected: a machine that is misaligned or has a damaged bearing will destroy itself on load no matter how good its windings are. The under-load measurements close the loop, since vibration, bearing temperature, and the current signature are the only evidence of how the machine actually behaves driving its load.
Acceptance: after installation and before the machine is placed in service, with the static tests completed uncoupled and the optional under-load measurements taken once it is running. The same form carries a maintenance service type, since insulation resistance with its index, stator resistance, and the mechanical inspection are repeated on a periodic basis, and the under-load measurements establish the trend that later readings are compared against. The insulation-resistance readings are taken with the winding temperature recorded and corrected, because the reading changes substantially with temperature, and the dielectric withstand test is run only after insulation resistance confirms the winding can take it.
With the machine de-energized, isolated, and grounded per site safety procedures, the identification data is recorded and the inspection is worked through, including the internal components, bolted connections verified with a calibrated torque wrench, air-gap spacing and alignment, hand rotation of the rotor, shaft extension runout measured while turning the shaft, the lubrication systems, and the resistance temperature detector circuits against the drawings. Bolted-connection resistance is measured phase by phase. Insulation resistance is then measured at the dc test voltage the standard's machine table assigns to the winding's rated voltage, with the winding temperature recorded: on a machine above the size threshold the test runs ten minutes and the polarization index is calculated, and on a smaller machine it runs one minute and the sixty to thirty second dielectric absorption ratio is calculated, with the one-minute value corrected to the reference temperature. On machines at the higher voltage the dielectric withstand test is applied, dc or ac by the applicable method, and phase-to-phase stator resistance is measured across the three winding pairs. Power factor, tip-up, and surge comparison are performed where they are in scope, insulated bearing insulation resistance is measured at each end, and the resistance temperature detector circuit resistances and the space heater are checked. The surge protection devices and the motor starter are tested under their own sections. With the machine running, vibration is measured at each bearing in the horizontal, vertical, and axial directions, bearing temperatures are read, and current signature analysis and partial discharge measurements are taken where they are in scope.
The machine identification (manufacturer, model and catalog number, serial number, horsepower and kilowatt rating, rated voltage, full-load amperes, speed, phase, frequency, service factor, insulation class, frame, and equipment designation); the result of each visual and mechanical item, including shaft runout, air-gap spacing, alignment, and the thermographic survey; bolted-connection resistance per phase; the machine size category, dc test voltage, winding temperature, the thirty second, one minute, and ten minute insulation-resistance readings, the temperature-corrected one-minute value, and the polarization index or dielectric absorption ratio; the dielectric withstand method, voltage, duration, and result; phase-to-phase stator resistance and the maximum deviation; power factor, tip-up, and surge comparison results where taken; the bearing insulation-resistance test voltage and the reading at each end; the surge protection device and motor starter results; the resistance temperature detector circuit readings; the space heater result; the under-load vibration amplitudes at each bearing and direction, bearing temperatures, current signature findings, and partial discharge findings; and the ambient temperature, relative humidity, test equipment with calibration due date, comments, and deficiencies.
The temperature-corrected one-minute insulation resistance must meet the minimum the standard's rotating-machinery table gives for the winding's construction and vintage, and that table also sets the dc test voltage band by winding rated voltage. The polarization index and the dielectric absorption ratio each have a published floor and a reading below it is a finding on its own, independent of the megohm value. Phase-to-phase stator resistance readings that deviate from each other beyond the published percentage are investigated. The dielectric withstand test passes if no distress or insulation failure appears during the full voltage-application time, and the surge comparison passes only if the waveforms stay nested with no distress or failure. Power-factor and dissipation-factor values are compared with the manufacturer's data or with previous results from similar machines, and the tip-up must show no significant increase. Bearing insulation resistance is judged against the manufacturer's tolerances or against similar machines. Vibration is judged against the manufacturer's published data or, in its absence, the limits in the standard's vibration table for the machine's mounting and grade, with a complete vibration analysis called for if they are exceeded. Bearing temperature detectors must read correctly, resistance temperature detector circuits must conform to the design intent and the protection device manufacturer's data, heaters must be operational, and the current signature and partial discharge findings trigger investigation at the published magnitudes. Bolt torque, air-gap spacing, alignment, and the component condition criteria all follow the manufacturer's published data or the standard's own inspection criteria. See the purchased NETA standard for every table value.
UltraDb references ASTM, ANSI, IEEE, and NETA standards descriptively, to identify the published methods its forms are built from. UltraDb and Entigy Solutions are not affiliated with, endorsed by, certified by, or licensed by NETA, ASTM, ANSI, IEEE, or Megger. Standard names and section numbers are the property of their respective organizations. Always test to the edition your contract specifies.