How is the polarity of commutation pole and main pole of DC motor different in the state of motor and generator?

The principle is as follows: a DC motor has always been normal when it was first put into operation or in the past, but it gradually deteriorated or suddenly deteriorated in the later operation process, indicating that the sliding contact, motor structure and working conditions of all parts of the motor were normal before the commutation deteriorated. During the operation of the motor, the working state of some components has changed, or the surrounding environment has changed, thus destroying the sliding contact and changing the normal commutation state, leading to the deterioration of commutation. If these prisoners who affect motor commutation are comprehensively inspected and adjusted to restore their original normal state, commutation can be restored to normal.

Commutation normalization inspection is a common method for DC motor to find out the cause of commutation accident and troubleshoot, including the following main items.

I. measure the resistance between commutator segments.

By measuring the resistance between the commutator segments, we can find out whether the armature winding is broken, welded or short-circuited between turns, whether the lifting segment is broken or not, and whether the commutator segments are short-circuited. Inter-chip resistance inspection usually adopts voltage drop method, or special inter-chip resistance measuring instrument can be used.

Second, the commutator swing measurement.

When the commutator is deformed or eccentric, the brush will jump during operation, and the sliding contact is not ideal. After exceeding a certain value, commutation will deteriorate. High-speed motors and multi-channel armature winding motors are more sensitive.

Third, brush neutral surface for inspection.

The neutral line position of DC motor brush should generally be strictly on the geometric center line of the main magnetic pole, especially for large motors, reversible motors and high-speed motors. Because when the brush deviates from the neutral line of the main engine, the commutation will lead and delay. The armature reaction of the longitudinal axis changes the external characteristics of the motor. For reversible motors, the speed and external characteristics are different under the two steering directions, and the commutation intensity under the two steering directions is also different. When the brush deviates greatly from the neutral position, the motor will produce no-load spark because the commutation element enters the main pole flux area.

Four, electrode distance, brush distance and air gap inspection and adjustment.

The distance between each row of brushes, the distance between main poles and the distance between commutation poles of DC motor should be equal. Because the brush distance and the pole distance are unequal, the short-circuit elements in each row of brushes have different positions in the magnetic field, and the reactance potential waveforms of the commutating pole magnetic field and the commutating elements are not coincident, and the unequal sparks held by each brush will make the motor commutate abnormally.

1, the allowable error of brush distance is usually 0.5mm, and it is generally checked and adjusted with flat paper. The method is as follows: first, adjust the position of a row of brush holders on the motor so that the edges of the brushes are just combined with the edges of the commutator; Then, spread a piece of paper on the commutator surface, mark a joint and take it off; Divide the paper into poles, draw a bisector, and then spread it on the commutator, so that the adjusted brush edge just presses on a bisector, and then put all the brushes down. The distance between the edge of the brush and the bisector is the error of the brush from the bisector.

2. Inspection and adjustment of polar distance. The allowable error of the polar distance is 0.75 mm Generally, the more accurate polar distance measurement is to draw the center line on the magnetic pole shoe, and then measure it with vernier caliper and caliper, which can get more accurate results. When the armature cannot be pulled out after the motor is assembled, the distance between the edge of the pole shoe can be measured with calipers, and the error of equally dividing the pole distance can also be checked.

3. Air gap inspection and adjustment. The air gap between the main pole and commutation pole of DC motor must be equal. If the air gap is not uniform, the reluctance under each pole is not equal. Under the same excitation magnetic potential, the magnetic current is the most unequal, and the spark will be greater under some brushes. At the same time, due to the unequal magnetic flux under the main pole, internal circulation and unilateral magnetic pull will also appear in the armature winding. The allowable deviation of main pole and commutation pole of DC motor is 5%. Air gap inspection is usually carried out with common feeler and special fixed inclination feeler. When the air gap exceeds the specified tolerance, the fixed screw of the main pole or the commutation pole can be loosened, and the air gap can be adjusted by adjusting the magnetic gasket at the top of the pole to make it conform to the specified tolerance.

Five, brush and brush grip performance inspection.

1, adjustment of spring pressure. The brush unit pressure of DC motor is generally defined as 1. 6-2.4 N/cm2, and the pressure difference of all brushes should be less than 10%. Brush pressure is also an important condition to ensure normal commutation. If the brush pressure is too small, it will cause brush jumping and unstable contact pressure drop; When the pressure is high, the contact pressure drop decreases; However, if the pressure is too high, it may lead to the increase of mechanical wear of brushes and the increase of temperature rise of commutator.

2. Check the brush grip clearance. The clearance between the brush and the brush holder should meet a certain tolerance. If the gap is too large, the brush will shake in the brush holder, which will affect the stability of contact and sometimes cause the phenomenon of "undercut". However, if the gap is too small, it will affect the free sliding of the brush in the brush grip, and even be "stuck".

3. Check the distance between the brush holder and the commutator surface. The distance between the brush holder and the commutator surface should be kept at (2. 5) mm range. The distance between the brush holder and the commutator surface is closely related to the stability of the brush and the prevention of brush vibration. The distance between the double inclined brush holder and the commutator surface also affects the brush width. When the distance is too large, the brush will also produce "vertex angle", which will affect the work. The brushing distance can be checked by insulating strips with thicknesses of 2mm and 3mm. When the distance exceeds the allowable value, 2.5mm thick insulation board can be used as the adjustment benchmark under the brush grip.

4. Brush materials and mirror inspection. Brush is an important part of sliding contact. Abnormal brush material and working state will affect sliding contact or cause commutation deterioration. Generally speaking, it is best not to mix different types of brushes. The brush mirror is smooth and bright when the commutation is normal. When the commutation spark is large, fog and burn marks will appear. When the brush contains impurities such as silicon carbide and emery, white spots will appear on the mirror surface or small grooves will be left in the rotation direction.

Six, commutator table and working state inspection.

So as to keep good sliding contact, reduce brush wear and prevent the possibility of flashover between sheets.

Seven, the main pole, commutation pole winding polarity and turn-to-turn short circuit inspection.

Individual polarity error and turn-to-turn short circuit of DC motor stator winding will affect commutation. Especially when the polarities of the commutating poles are opposite, because the commutating potential and the reactance potential can't be offset, but added, serious sparks will appear even under small load. Polarity inspection can be carried out according to the drawings, or with a resistance magnetic needle. AC voltage drop method is usually used to check the short circuit between main poles. Compensation and commutation pole winding turn-to-turn short circuit can generally be found by visual inspection. For example, when the terminal connecting wire is deformed and short-circuited, it can be found through careful observation. Short-circuit faults that are not easy to find can be detected by DC voltage drop method by introducing appropriate current into the winding.