Method A – Direct Test Method for Efficiency
Method A is also commonly referred to as the input-output method, as during the test, two data necessary for calculating the efficiency can be directly obtained, namely the input power and the output power. When a specified load is applied to the test motor, and it operates until the temperature stabilizes or for the specified period of time (in the latter case, the difference between the temperature reached by the test motor winding and the actual temperature stability should not exceed 5K), the load is adjusted within the range of 1.5 to 0.25 times the rated power, and two working characteristic curves are measured when the load decreases and increases. At least 6 readings should be taken for each curve, and each reading includes: three-phase line voltage (should be maintained at the rated value), three-phase line current, input power, speed, output torque, and if possible, output power should also be recorded. Finally, the power supply is cut off and the motor is stopped. The DC resistance of the stator winding is measured within the specified time. Otherwise, an extrapolation correction should be made according to the relevant regulations for calculating the thermal resistance after the thermal test.
When conditions permit, the method of using live measurement (superposition method) or pre-installing thermocouples or copper (platinum) thermistors as temperature sensors in the windings to obtain the temperature or resistance of each stator winding point should be adopted as the priority. During the test, the ambient temperature should also be recorded.
Post time: Dec-19-2025