Judging the performance of the motor from no-load data
The relationship between no-load current and rated current
The nameplate of Hengli motors indicates the rated current of the motor, but what is the relationship between no-load current and rated current? This is a common problem encountered by motor users, business personnel, and distributors. The proportion of no-load current to rated current depends on the capacity, number of poles, and type of motor. The larger the capacity of a constant force motor, the fewer the number of poles, and the smaller the ratio of no-load current to rated current (referred to as the ratio). Conversely, the ratio is larger.
The relationship between no-load loss and rated power
Under normal circumstances, the ratio of no-load loss to rated power is calculated as a percentage, usually within the range of 3% -10%. For motors of the same specification, the fluctuation range of no-load motor is 5% -15%, and the fluctuation range of no-load loss is 5% -20%. The no-load current and no-load loss will affect the power factor of the motor. It is very important to control the no-load data of the motor during inspection and testing.
Analysis of the reasons for high no-load current
(1) The small outer diameter of the rotor or the large inner bore of the stator leads to an increase in air gap;
(2) The iron core slot is filed too large or there is a phenomenon of fan tension;
(3) The magnetic centerline of the stator and rotor is not aligned (the stator and rotor are not aligned);
(4) The number of turns or pitch of the coil is smaller than the design value;
(5) Repair the motor. After the iron core was baked, the oxide layer on the punching plate became thinner, resulting in an increase in magnetic flux density;
(6) The star connection is misconnected into a corner connection, which is clearly related to the correct current pattern;
(7) The number of parallel circuits exceeds the design value;
(8) Iron core aging.
The reason for the large no-load loss
(1) Poor motor assembly leads to increased mechanical losses;
(2) The bearing rotation is not flexible, or the tolerance selection for the fit between the bearing and the shaft or end cover is improper;
(3) Excessive filling of bearing grease causes motor rotation obstruction;
(4) Due to uneven iron core and filing, the iron damage increases (usually between 10-30%);
(5) Repairing the inner bore of the stator has a significant impact on iron consumption, generally ranging from 20-40%;
(6) The fan is not suitable (larger than the design or defective);
(7) The number of turns or pitch of the winding coil is small;
(8) Poor insulation treatment of the iron core and aging of the iron core;
(9) The punching sheet has burrs, which can cause a short circuit during the punching process.
During the actual testing process, it was found that for motors using sealed bearings, the mechanical losses of motors using contact bearings are greater than those using non-contact bearings, which ultimately has a significant impact on motor efficiency, especially for high-efficiency motors, which may lead to a qualitative change in efficiency performance indicators.
