Reasons for low efficiency of three-phase asynchronous motors

The efficiency of a three-phase asynchronous motor is directly related to the so-called five losses (core loss, stator copper loss, rotor aluminum or copper loss, mechanical loss, stray loss). Specifically, if the efficiency value is low, it may be caused by one or more of the following reasons:

(1) The core loss is large. The quality of the iron core does not meet the requirements, including: the quality of the silicon steel sheet used is poor; the length of the iron core is less than the requirements of the drawings; the effective length of the punching burr is larger; the insulation between the punching sheets is lower. When assembled, the stator core is misaligned, which is actually equivalent to a reduction in the effective length of the core.

(2) The stator copper loss is large. The reason is that the stator winding has large resistance, including poor wire quality (low copper content), small wire diameter, large number of turns, coil length exceeding the drawing requirements, poor wire connection quality, etc. This is because the stator current is large, which is caused by a small number of winding turns, a wiring error, and an inter-turn short circuit fault.

(3) The loss of aluminum or copper in the rotor is large. The reason is that the rotor winding resistance is large, including: poor aluminum quality (more impurities); smaller rotor groove area; more air holes in the cast aluminum guide bar or end ring; rotor core lamination is uneven (causing The effective cross-sectional area is reduced) and the like.

(4) Mechanical loss is large. These include: poor bearing quality; poor bearing lubrication (grease does not meet the requirements, or less or more); bearing installation quality problems (installation not in place or due to bearing chamber, end cover, machine seat processing problems) Large shaft, etc.); large fan resistance (larger fan size, more fan blades, unreasonable design shape, unreasonable air path, etc.); unexpected mechanical friction (fan and end cap, fixed rotor core) Between, between the bearing cap and the end cap, between the seal ring and the end cap or the shaft, etc.).

(5) The stray loss is large. These include: excessive aluminum between the rotor pieces due to insufficient tension of the rotor or excessive pressure during casting of the aluminum; the rotor groove slope does not meet the requirements of the drawings; the end size or shape does not meet the requirements; the rotor slot is not open The air gap size between the stator and the rotor does not meet the requirements of the drawings.