In
daily equipment inspection, various abnormal noises will be found in the
running motor, and long-term "abnormal noise operation" will
seriously threaten the safety and life of the motor. In order to eliminate the
abnormal phenomenon in time, the noise source must be identified accurately and
quickly.
1
Noise source
Generally,
motor noise sources can be divided into electromagnetic noise and mechanical
noise.
Electromagnetic
noise
The
alternating magnetic field in the air gap of the motor will cause low-frequency
noise generated by the stator, rotor and mechanical structure. Electromagnetic
noise is mainly caused by the periodically changing radial force generated by
the magnetic field in the air gap, and the non-uniform magnetic field force
will cause the stator and rotor cores to produce hysteresis contraction and
vibration. The reasons are as follows:
The
length of the stator and rotor is too different,
The
matching between the stator and rotor slots is insufficient, and the iron core
is not closely laminated.
Uneven
winding spacing
The
rotor core vibrates radially,
The
coil in the coil winding is reversed,
There
is an open branch in the parallel winding, the winding is asymmetrical or the
winding is short-circuited.
Mechanical
noise
The
friction between the stator and rotor of the motor, the unbalanced dynamic
balance, the wear of the bearing and the bearing sleeve, or the resonance of
the motor body will cause mechanical noise.
The
reasons are as follows:
The
bearing is damaged or poorly assembled. When the motor rotates, put one end of
the listening rod on the end cover of the bearing, and then put the other end
on the earlobe with your fingers to hear whether the sound of the bearing
rotates evenly. Insufficient assembly of motor bearings, wear of bearing
sleeves and looseness of bearings will cause abnormal noise in the bearings.
The
dynamic balance of the motor rotor is destroyed, the rotor is unstable or the
rotating shaft is bent, which will cause the rotor to vibrate.
The
uneven air gap between the stator and the rotor will cause mutual friction.
The
iron core is loose and the slot teeth are damaged.
Poor
bearing installation or bearing damage.
The coaxiality between the motor shaft and the load shaft is poor.
2
Noise recognition method
Power-off
method: Use the characteristics of electromagnetic noise to change with the
magnetic field strength, load current size and conversion level. After a period
of silent operation, the power supply is suddenly disconnected. After cutting
off the power, the noise will disappear immediately. This is electromagnetic
noise. After the power failure, the noise generated by the motor that continues
to run through inertia is mechanical noise.
How to
change the voltage: When the power supply voltage drops rapidly to a certain
limit, if the electromagnetic noise is the main part of the motor noise, the
change with the voltage will be large, while other noises remain basically
unchanged.
3
noise control
Reasonable
structure design: DC motors use uneven air gaps. The use of magnetic slot
wedges in AC motors can not only reduce harmonic losses and improve efficiency,
but also reduce electromagnetic noise caused by harmonic magnetic fields. The
stator winding adopts reasonable short torque.
Correctly
control the ripples, pits, roughness and radial clearance of the bearing
rolling surface.
When
the motor power has a margin, the rotor diameter can be appropriately reduced,
the air gap can be increased, and higher harmonic noise can be eliminated. The
disadvantage is that the no-load current increases and the power factor
decreases.
High
assembly accuracy: use high-quality bearings. Keep proper assembly
interference. Improve the accuracy of the rotor dynamic balance detection, and
ensure the concentricity of the motor and the load shaft during the
installation process. Ensure rotor dynamic balance
This article mainly introduces the cause analysis and
countermeasures of motor noise to improve the stability of the equipment during
operation.
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