Cause and grade of DC motor commutator spark

The principle of commutation spark division is to keep the brush and commutator in good working condition, and to keep the excellent commutation performance is an important condition to ensure the safety of DC motor. In general, the motor runs without spark (or runs under weak harmless spark), the oxide film on the commutator surface is uniform and shiny, and the brush and commutator are slightly worn, which can be considered as the characterization of good commutation performance.

On the contrary, strong reversing sparks, damaged or abnormal oxide film on the commutator surface, unstable sliding contact between the brush and the commutator, and abnormal wear of the brush and the commutator are all symptoms of poor commutation, which will directly threaten the operation of the motor. Spark is the arc discharge phenomenon between the brush and the commutator, and is the most obvious sign of poor commutation of DC motor. As the slight brush spark releases weak energy, it will not pose a hazard to the motor operation, so it is called harmless spark.

The energy of a strong brush spark will destroy the sliding contact between the brush and the commutator, burn the oxide film on the mirror surface of the brush and the commutator surface, increase their wear, and cause a vicious cycle. This spark is harmful. What's more, because the strong brush spark makes the air on the brush mill free, the ring fire accident caused by the arc flying over will cause huge damage to the motor, posing a threat to the operation of DC motor.

Different commutation sparks have different effects and hazards on the operation of DC motor. In order to determine the impact and hazards of commutation sparks on the operation of DC motor, it is necessary to classify the sparks. Reversing spark is the electromagnetic quantity released from the reversing element when the brush and the reversing blade are out of contact, which is shown in the form of arc discharge. According to the research on reversing spark, it is a kind of electromagnetic wave with broad spectrum, whose spectrum mainly ranges from 30KHZ to 1MHZ. The hazard of reversing spark shall be based on the sign of spark energy, which can be used as the standard for evaluating reversing spark.

However, due to the complexity and difficulty of spark measurement, spark brightness, density and size are usually used as the basis for spark classification. Spark classification standards vary from country to country, but all these standards are based on the brightness, density, size of the reversing spark and the damage to the brush and commutator. Since there is no instrument that can accurately measure the reversing spark level, which is determined by the observer visually, there are inevitably some subjective factors of the spark observer.