Basic knowledge of motor 3

Steps for motor selection

When the motor has malfunctioning, we can prevent and troubleshoot problems in time by watching, listening, smelling, and touching to ensure the safe operation of the motor.

Look:

Observe whether there are any abnormalities during the operation of the motor. The main manifestations are the following situations.

1. When the stator winding is short-circuited, you may see smoke from the motor.

2. When the motor is severely overloaded or running under phase loss, the speed will slow down and there will be a heavier "humming" sound.

3. The motor maintenance network is operating normally, but when it suddenly stops, you will see sparks from the loose wiring; the fuse is blown or a component is stuck.

4. If the motor vibrates violently, it may be that the transmission device is jammed, the motor is not properly fixed, and the foot bolts are loose.

5. If there are discoloration, burn marks and smoke traces at the contact points and connections in the motor, it means that there may be local overheating, poor contact at the conductor connection, or burned windings, etc.

Listen:

When the motor is running normally, it should emit a uniform and light "humming" sound without noise and special sound.

If the noise is too large, including electromagnetic noise, bearing noise, ventilation noise, mechanical friction noise, etc., it may be a precursor or failure phenomenon.

1. For electromagnetic noise, if the motor makes a high, low and heavy sound, the reasons may be as follows:

(1) The air gap between the stator and the rotor is not uniform. At this time, the sound fluctuates and the interval between high and low frequencies does not change. This is caused by the bearing wearing and the discentricity between the stator and the rotor.

(2) The three-phase current is unbalanced. This is because the three-phase windings are grounded incorrectly, short-circuited, or poorly contacted. If the sound is dull, it means that the motor is seriously overloaded or running without phase.

(3) The iron core is loose. When the motor is running, the iron core fixing bolts are loosened due to vibration, which causes the iron core silicon steel sheet to loosen, causing noise.

2. For bearing noise, you should always monitor the motor when it is running.

The monitoring method is: press one end of the screwdriver against the bearing installation part and the other end close to your ear, and you can hear the sound of the bearing. If the bearing is running normally, the sound is small "sanding" continuously, and there will be no high& low sound changes and metal friction sound.

If the following sounds appear, it is abnormal:

(1) There is a "squeak" sound when the bearing is running. This is the sound of metal friction, which is generally caused by the lack of oil in the bearing. The bearing should be disassembled and added with a proper amount of grease.

(2) If there is a "chill" sound, which is the sound made when the ball rotates, it is usually caused by the drying of the grease or lack of oil, and an appropriate amount of grease can be added.

(3) If there is a "click" or "creak" sound, it is the sound produced by the irregular movement of the balls in the bearing. This is caused by the damage of the balls in the bearing or the long-term use of the motor and the drying of the grease.

3. If the transmission mechanism and the driven mechanism emit continuous rather than fluctuating high and low sounds, it can be dealt with in the following situations.

(1) Periodic "crack" sound is caused by uneven belt joints.

(2) The periodic "boom" sound is caused by the loosening between the coupling or the pulley and the shaft and the wear of the key or keyway.

(3) The uneven collision sound is caused by the impact of the blades on the fan cover.

Smell:

It is also possible to judge and prevent malfunctions by smelling the smell of the motor.

Open the junction box and sniff to check whether there is a burnt smell. If there is a special paint smell, it means that the internal temperature of the motor is too high; if there is a heavy burnt smell or burnt smell, it may be that the insulation repair net has been broken down or the winding has been burned.

If there is no smell, you need to use a megohmmeter to measure the insulation resistance between the winding and the shell below 0.5 megabytes, and you must dry it. The resistance value is zero, indicating that it has been damaged.

Touch:

Touching the temperature of some parts of the motor can also determine the cause of the fault.

To ensure safety, use the back of your hand to touch the motor housing and the surrounding parts of the bearing.

If the temperature is found to be abnormal, the reasons may be as follows:

1. Poor ventilation. If the fan falls off, the air duct is blocked, etc.

2. Overload. The current is too large and the stator windings are overheated.

3. Short circuit of stator winding turns or unbalanced three-phase current.

4. Frequent starting or braking.

5. If the temperature around the bearing is too high, the bearing may be damaged or lack of oil.

Solution:

1. Open the module cover and replace the damaged insurance, charging resistor and other components in the module.

2. Replace the damaged optical sub-board or protection diode.

3. The optical fiber is connected normally according to the label, and the optical fiber is needed replaced if it is damaged.

4. Replace the module power board.

Reported by Jessica