The following aspects should be paid attention to when eliminating the sparks caused by commutation of DC permanent magnet motor

There are many reasons for the production of commutation sparks in DC permanent magnet motors. The main reason must be found among many factors in order to eliminate the fault and improve the commutation. The method of checking the cause of commutation deterioration is called commutation condition normalization inspection and adjustment. It is a common method in the handling of commutation accidents of DC permanent magnet motors. The principle is as follows: When a DC permanent magnet motor is just put into operation or in the past operation, the commutation has always been normal. In the subsequent operation process, it gradually changes or suddenly deteriorates, indicating that before the commutation deteriorates, the sliding contact, motor structure and the running conditions of the motor components are normal. During the operation of the motor, the working state of some components has changed, or the surrounding environment has changed, thereby destroying the sliding contact and changing the normal commutation state, and the commutation deteriorates after the knife. If these factors affecting the commutation of the motor are fully inspected and adjusted so that the device can return to its original normal state, the commutation can return to normal.

Commutation normalization inspection is a common method for finding the cause of commutation accidents and troubleshooting of DC permanent magnet motors. It includes the following main items:

1. Commutator inter-segment resistance measurement

Measuring the resistance between commutator segments can reveal whether the armature winding is broken, welded, or short-circuited between turns, whether the riser is broken, and whether there is a short circuit between commutator segments. The inter-segment resistance is usually checked using the voltage reduction method, and a special inter-segment resistance measuring instrument can also be used.

2. Commutator ferry measurement

When the commutator is deformed or eccentric, the brushes will jump during operation, and the sliding contact is not ideal. When it exceeds a certain value, it will cause the commutator to deteriorate. High-speed motors and motors with multiple armature windings are more sensitive.

3. Inspection of the brush profile

The neutral line position of the brush of a DC permanent magnet motor should generally be strictly on the center line of the main magnetic pole. This is especially true for large motors, reversible motors and high-speed motors, because when the brush deviates from the neutral line, the commutation will be advanced and delayed. The longitudinal armature reaction changes the external characteristics of the motor. For a DC permanent magnet motor, the speeds are different in the two directions, and the external characteristics are also different. The commutation strengths of the two directions are also different. When the brush deviates from the neutral position by a large margin, the motor will generate no-load sparks because the commutation element enters the main pole flux area.

Check the sparks caused by the deterioration of commutation in DC permanent magnet motors and the corresponding solutions, focusing on the inspection and adjustment of pole pitch, brush pitch and air gap

The distance between each row of brushes in a DC permanent magnet motor and the distance between the main poles and the commutation poles should be equal. Because the brush spacing and pole spacing are not equal, the short-circuited components under each row of brushes will be in different positions in the magnetic field, the commutation pole magnetic field and the commutation element reactance potential waveforms will not overlap, and the unequal sparks under each brush holder will cause abnormal commutation of the motor.

1. The allowable error of brush spacing is usually 0.5mm, and it is generally checked and adjusted by the paper-laying equal division method. The method is as follows: first adjust the position of the brushes on the brush holder of the motor so that the edge of this brush is just combined with a commutation edge, then lay a piece of paper on the surface of the commutator, make a matching mark at a joint and remove it, divide the paper into equal parts according to the number of poles, mark the equal division line, and then lay it on the commutator so that the edge of the adjusted brush is just pressed on an equal division line, and then drop all the brushes. The distance between the brush edge and the equal division line is the error of brush spacing equal division. If all brushes are adjusted according to the equal division line, the brush spacing error can be corrected.

2. Pole pitch inspection and adjustment. The allowable error of pole pitch is 0.75mm. The more accurate measurement of pole pitch is generally done by measuring the center line of the magnetic pole shoe with a vernier caliper and calipers. A more accurate result can be obtained. When the DC permanent magnet motor is assembled and the armature cannot be withdrawn, the distance between the pole shoe edges can be measured with a caliper, and the pole pitch equal division error can also be checked.

3. Check and adjust the air gap. The air gaps of the main poles and commutation poles of the DC permanent magnet motor must be equal. If the air gap is uneven, the magnetic resistance under each pole will be unequal. Under the same excitation magnetic potential, the magnetic current will be unequal, and the spark will be larger under some brush holders. At the same time, due to the unequal magnetic flux under the main pole, there will be internal circulation current and unilateral magnetic pull in the armature winding. The allowable deviation of the main poles and commutation poles of the DC permanent magnet motor is 5%. The air gap is usually measured with ordinary feeler gauges and special fixed-angle feeler gauges. When the air gap exceeds the specified tolerance, the fixing screws of the main pole or commutation pole can be loosened, and the air gap can be adjusted by adjusting the magnetic gasket on the top of the pole to meet the specified tolerance.