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Motor 13 asks

From: 本站 Author: admin Posted: 2022-04-15 14:30:28 View: 163

why does the motor produce shaft current?The current in the axle-bearing-base loop of the motor is called the axial current.

1, why does the motor produce shaft current?

The current in the axle-bearing-base loop of the motor is called the axial current.

Reasons for axial current generation:

(1) Asymmetric magnetic field;

(2) Harmonics in the power supply current;

(3) The manufacturing and installation are not good, and the air gap is uneven due to the eccentricity of the rotor;

(4) There is a gap between the two semicircles of the detachable stator core;

(5) The number of pieces of the stator core with a fan-shaped stack is not suitable.

Hazard:

The surface or ball of the motor bearing is eroded, and the micro-holes in the form of points are formed. The performance of the bearing is deteriorated, and the friction loss and heat increase, eventually causing the bearing to burn.

Prevention:

(1) Elimination of pulsating flux and power harmonic(such as the installation of an AC reactor on the output side of the inverter);

(2) When the motor is designed, the bearing seat and base of the sliding bearing are insulated, and the outer ring and end cover of the rolling bearing are insulated.

Why can't the general motor be used in the plateau area?

Altitude has adverse effects on motor temperature rise, electrical corona(high voltage motor) and DC motor direction change. Attention should be paid to the following three aspects:

(1) At high altitude, the greater the temperature rise of the motor, the smaller the output power. However, when the temperature decreases with the elevation, it is enough to compensate for the influence of the elevation on the temperature rise, the rated output power of the motor can remain unchanged;

(2) High-voltage Motors should be used in the plateau to take measures to prevent corona;

(3) The altitude of the DC motor is unfavorable, and it is necessary to pay attention to the selection of carbon brush materials.

3, why should not the motor light load operation?

When the motor is light loaded, it will cause:

(1) Low motor power factor;

(2) Low motor efficiency.

It can cause equipment to waste and run uneconomical.

What are the reasons for the overheating of the motor?

(1) Overloading;

(2) Lack of phase;

(3) blockage of the wind passage;

(4) The low speed running time is too long;

(5) The harmonic of the power supply is too large.

5, what work do you need to do before the long-used motor is put into operation?

(1) Measurement of the stator and winding interphase and winding insulation resistance to the ground.

Insulation resistance R shall satisfy the following formula:

R > Un /(1000 + P/1000)(MΩ)

Un: Motor winding rated voltage(V)

P: Motor power(KW)

For Un = 380V Motors, R > 0.38 MΩ.

If the insulation resistance is low, it can:

A: The motor is operated with an empty load of 2 to 3 H to dry;

B: low voltage alternating current access winding with a 10 % rated voltage or direct current baking with a three-phase winding in series, keeping current at a rated current of 50 %;

C: Heat hot air or heating elements with a fan.

(2) Clean up the motor.

(3) Replacement of bearing grease.

6, why can not start the motor in the cold environment arbitrarily?

If the motor is too long in a low temperature environment, it will:

(1) electrical insulation cracking;

(2) The bearing grease is frozen;

(3) tin soldering of wire joints.

Therefore, the motor should be heated and preserved in a cold environment, and windings and bearings should be checked before operation.

What are the reasons for the unbalanced three-phase current of the motor?

(1) three-phase voltage imbalance;

(2) Poor welding or poor contact of an internal branch of the motor;

(3) short circuit between turns of motor winding or between ground and interphase short circuit;

(4) Wrong wiring.

Why can't a 60Hz motor use a power supply connected to 50Hz?

When the motor is designed, the Silicon steel sheet is generally operated in the saturated zone of the magnetization curve. When the voltage of the power supply is fixed, the lower frequency will increase the flux, increase the excitation current, lead to an increase in the current of the motor, increase in copper consumption, and eventually lead to an increase in the temperature of the motor. In severe cases, the motor may also be burned due to overheating of the coil.

9, what are the reasons for the lack of motor phase?

Power supply:

(1) Poor switch contact;

(2) A transformer or line is broken;

(3) Insurance meltdown.

Electrical aspects:

(1) Loose contact of motor junction box screw is not good;

(2) Poor internal wiring welding;

(3) Disconnection of motor winding.

What are the reasons for the abnormal vibration and sound of the motor?

Mechanical aspects:

(1) Poor lubrication of bearings and wear of bearings;

(2) loosening of fastening screws;

(3) There are sundries in the motor.

Electromagnetic aspects:

(1) overload operation of the motor;

(2) three-phase current imbalance;

(3) Lack of phase;

(4) Short circuit failure occurs in the stator and rotor windings;

(5) The welded part of the cage rotor is welded to cause a break.

What should I do before starting the motor?

(1) Measurement of insulation resistance(not less than 0.5 MΩ for low-voltage Motors);

(2) Measurement of power supply voltage. Check whether the motor wiring is correct and whether the power supply voltage meets the requirements;

(3) Check the starting equipment is good(public number: pump housekeeper);

(4) check whether the fuse is suitable;

(5) check whether the motor is grounded and the connection is good;

(6) check whether the transmission is defective;

(7) Check whether the motor environment is suitable and remove inflammable and other debris.

What are the reasons for the overheating of motor bearings?

The motor itself:

(1) The internal and external rings of the bearings are too tight;

(2) There are problems with the form tolerance of the parts, such as poor coaxial degree of the parts such as the seat, end cover, and shaft;

(3) improper selection of bearings;

(4) Bad lubrication of bearings or non-clean cleaning of bearings, and debris in the grease;

(5) Axis current.

Use aspects:

(1) Improper installation of the unit, such as the shaft coaxial alignment of the motor shaft and the dragged device;

(2) The pulley is too tight;

(3) The bearings are not well maintained, the grease is not enough or exceeds the service life, and the dry deterioration occurs.

What are the reasons for the low electrical insulation resistance?

(1) The winding is subjected to moisture or water intrusion;

(2) accumulation of dust or oil on the winding;

(3) insulation aging;

(4) Insulation damage of motor leads or wiring boards.