Counting machines are common in thirteen questions
Counting machines are common in thirteen questions
Motor in the production and life play a very important role, its importance is increasingly recognized by the people and attention to the motor in the event of failure will seriously affect our production and life, the following inventory of the machine often appear several major problems , To help practitioners in the event of failure of the motor, make early decisions, troubleshooting, reduce losses and the same.
1, why does the motor generate shaft current?
The shaft of the motor --- the bearing block --- the current in the base circuit is called the shaft current.
Shaft current causes:
(1) magnetic field asymmetry;
(2) there is a harmonic in the supply current;
(3) manufacturing, installation is not good, due to rotor eccentric air gap caused by uneven;
(4) detachable stator core between the two semicircular gap;
(5) The number of chips in the fan-shaped stator core is not suitable.
harm:
So that the motor bearing surface or ball erosion, the shape of microporous, so that the bearing performance deterioration, friction loss and heat increased, resulting in bearing burned.
Prevention:
(1) to eliminate pulsating flux and power supply harmonics (such as the inverter output side of the installation of AC reactor);
(2) motor design, the sliding bearing bearing and base insulation, rolling bearing outer and end cover insulation.
2, why the general motor can not be used for highland areas?
Altitude has an adverse effect on the motor temperature rise, the motor corona (high voltage motor) and the DC motor commutation. Should pay attention to the following three aspects:
(1) high altitude, the greater the motor temperature rise, the smaller the output power. But when the temperature rises with altitude and reduce enough to compensate the impact of altitude on the temperature rise, the rated output power of the motor can be unchanged;
(2) high-voltage motor used in the plateau to take anti-corona measures;
(3) altitude of the DC motor commutation disadvantage, pay attention to the choice of carbon brush material.
3, why should not light motor running?
When the motor is running lightly, it will cause:
(1) the motor power factor is low;
(2) low motor efficiency.
Will cause equipment waste, run uneconomical.
4, the reasons for the motor overheating?
(1) the load is too large;
(2) lack of phase;
(3) air duct blockage;
(4) low speed running time is too long;
(5) power supply harmonic is too large.
5, long time to put the motor before the need to do what work?
(1) to measure the stator, winding and the insulation of the winding to ground insulation.
Insulation resistance R should meet the following formula:
R> Un / (1000 + P / 1000) (MΩ)
Un: Motor winding rated voltage (V)
P: Motor power (KW)
For motors with Un = 380V, R> 0.38MΩ.
Such as low insulation resistance can be:
A: motor no load running 2 ~ 3h drying;
B: 10% of the rated voltage of the low-voltage AC access winding or three-phase winding in series with DC baking, to maintain the current at 50% of the rated current;
C: with a fan into the hot air or heating element heating.
(2) clean the motor.
(3) Replace the bearing grease.
6, why can not arbitrarily start the cold environment of the motor?
The motor is too long in a low temperature environment and will:
(1) motor insulation cracking;
(2) bearing grease freeze;
(3) wire connection solder powder.
Therefore, the motor in the cold environment should be heated to save, should be run before the winding and bearing inspection.
7, the motor three-phase current imbalance What are the reasons?
(1) three-phase voltage imbalance;
(2) the motor within a certain branch of poor welding or poor contact;
(3) motor winding inter-turn short circuit or ground, phase short circuit;
(4) Wrong wiring.
8, why 60Hz motor can not be connected with 50Hz power supply?
When the power supply voltage is constant, the frequency reduction will increase the magnetic flux and the excitation current will increase, which will lead to the increase of the motor current and the increase of the copper consumption, which will lead to the increase of the temperature rise of the motor. In the case of the motor, Serious may also be due to coil overheating and burn the motor.
9, what is the reason for lack of motor?
Power supply:
(1) switch bad contact;
(2) transformer or line disconnection;
(3) insurance fuse.
Motor:
(1) the motor terminal box screws loose contact bad;
(2) poor internal wiring;
(3) The motor winding is broken.
10, what caused the abnormal vibration and sound of the motor?
Mechanical aspects:
(1) bearing lubrication is bad, bearing wear;
(2) fastening screws loose;
(3) There are debris in the motor.
Electromagnetic aspects:
(1) motor overload operation;
(2) three-phase current imbalance;
(3) lack of phase;
(4) stator, rotor winding short circuit failure;
(5) cage rotor welding part of the welding caused by broken bar.
11, before starting the motor to do what work?
(1) measuring insulation resistance (for low voltage motor should not be less than 0.5MΩ);
(2) Measure the supply voltage. Check whether the motor wiring is correct, whether the power supply voltage meets the requirements;
(3) check whether the starting device is good;
(4) check the fuse is appropriate;
(5) check the motor ground, then zero is good;
(6) check the transmission is defective;
(7) Check the motor environment is appropriate to remove flammable and other debris.
12, motor bearing overheating causes of what?
Motor itself:
(1) bearing inner and outer ring with too tight;
(2) parts and geometric tolerances are problems, such as the base, cover, shaft and other parts of the coaxial degree is not good;
(3) improper selection of bearings;
(4) poor bearing lubrication or bearing cleaning is not clean, grease inside the debris;
(5) axis current.
Use:
(1) improper installation of the unit, such as the motor shaft and the drag of the device axis coaxial degree requirements;
(2) pulley pull too tight;
(3) bearing maintenance is not good, lack of grease or more than the use of time, dry deterioration.
13, the motor insulation resistance is low because of what?
(1) winding moisture or water intrusion;
(2) the accumulation of dust or oil on the winding;
(3) insulation aging;
(4) motor lead or wiring board insulation damage.