Mechanical fault inspection

(1) Bearing wear

Baijian of the motor itself has strict requirements for the front and rear bearings, and the quality of the bearings directly affects the working condition of the motor itself. If the motor is in operation during inspection, one end of the screwdriver can be used to touch the bearing cover, and the ear should be tightly pressed against the handle of the screwdriver. Listen carefully for any abnormal sounds such as noise or vibration during bearing operation. If the sound is abnormal, it can be determined that the bearing is damaged. Stop the motor operation and open the motor for inspection. Check the damage of the fixed frame between the bearing small ring and the large ring, whether the bearing is stuck or damaged, whether the motor end cover is properly matched with the bearing, and whether there is any play. If play is found, use a chisel to make some marks on the shaft or use a milling machine to roll on the motor shaft before assembling the bearing. Then check the oil shortage of the bearings, whether the bearings are assembled in place, whether the concentricity of the assembly is good, and whether the motor end cover is assembled in place

(2) Friction between stator and rotor

First, rotate the motor rotor by hand, carefully listen for any friction sounds, or gently touch the motor shaft and surrounding parts with your hand to feel any friction.

. Alternatively, the motor can be disassembled to observe if there are any signs of friction on the surface of the stator core, and then observe if there are any signs of friction on the rotor. The cause of friction can be determined based on the location of the friction marks on the rotor core. The main reasons are: the end cover is not in the appropriate position, the bearing is damaged, the shaft is rubbing against the bearing, there are impurities sandwiched between the rotor and stator, the silicon steel sheets are misaligned and strung out, and the motor's rotating magnetic field is mutated

Inspection of motor stator winding

(1) Inspection of motor winding grounding

① Use a megohmmeter to find the motor grounding point. If the motor winding is grounded, the first step is to identify which group of the three windings of the motor is grounded, or which two groups are grounded. Firstly, remove the connecting wires of the three-phase winding, and then use a 500V megohmmeter to test the phase to phase insulation of the three-phase winding. If the insulation between the three-phase windings is good, then perform a ground to ground test. The detection method is to connect one end of the megohmmeter to the output wire of the three-phase winding, and the other end touches the nameplate of the motor's metal shell or the non rusty metal shell of the motor. In order to further identify which winding is grounded, it is necessary to separate the bridge wires between each winding in the coil winding and gradually search ② Use a light bulb to find the grounding point of the motor. In rural areas, sometimes the electrical instruments are not complete. Connect the 220V AC power directly in series with a light bulb and connect it to one end of the motor casing and motor winding (pay attention to connecting the zero line to the motor casing and avoiding personnel touching the live parts). If a certain phase in the three-phase winding is touched and the light bulb lights up in time, it indicates that there is a grounding fault point in that phase winding. The specific location of the grounding point can be found according to the previous method ③ Use a voltage tester to find the grounding point of the motor. This method can directly observe the location of the grounding point. If the grounding point is inside the motor slot, the approximate location of the grounding point can be determined based on the "creaking" sound generated by the voltage withstand test. Then, the slot wedge inside the slot is removed and the voltage withstand test is repeated until the specific location of the grounding point is identified. When applying this method, attention should be paid to personal safety during voltage withstand, and personnel and equipment should maintain a certain safe distance to prevent electric shock

(2) Inspection of motor winding short circuit fault

Short circuit of motor winding can cause damage to surrounding insulation and discoloration.

. If there is a phase to phase short circuit, it can be measured with a megohmmeter. The consequences of this type of fault are more serious, and there are signs of burning in the short circuit area visible from the surface The detection method for inter turn short circuits in motor windings is to use a short circuit detector to detect them. Connect the short circuit reconnaissance device to a 220V AC power supply, and then align the iron core opening with the slot where the inspected winding is located. At this time, the short circuit reconnaissance device and a part of the stator form a small "transformer". The winding of the short circuit reconnaissance device itself is composed of the primary winding of the transformer, while the tested motor winding is the secondary winding of the transformer. The iron core of the short circuit reconnaissance device and a part of the stator iron core form the magnetic circuit of the transformer. When a 220V AC power supply is connected, the detected stator winding will generate induced electromotive force. If there are short circuit turns, there will be current passing through the short circuit turns, reflecting that the primary current of the short circuit detector is also higher than usual. At the same time, it will cause a magnetic field to be generated in the iron core around the motor stator winding. At this time, a thin iron sheet is placed at the slot, and the magnetic flux generated by the short circuit coil will form a circuit through the iron sheet, Attracting the iron sheet onto the iron core and generating vibration can determine the location of the inter turn short circuit point of the motor