As a power device widely used in modern industry and daily life, the stability of the motor directly affects the operating efficiency and safety of mechanical equipment. However, when the motor is running, sparks are easily generated between the brush and the commutator, which will harm the operation of the motor. When the level of the spark is too large, it may even burn the motor and the operating equipment.
The generation of sparks may be caused by a variety of factors, such as voltage fluctuations, brush wear, poor contact and overload operation, etc. These factors may cause drastic changes inside the motor, forming arcs and then sparks. Therefore, this article will start from these perspectives, deeply explore the reasons for the generation of sparks in the motor, and propose effective suppression measures.
The principle of motor spark generation
Spark generation is based on the principle of spark corrosion, that is, when the tool electrode and the part are close to each other, the inter-electrode voltage will ionize the dielectric between the positive and negative electrodes to form spark discharge.
It can be understood this way: when two conductors are close to but not in complete contact, the electric field intensity will increase significantly due to the change in the curvature of the contact surface. Under the action of a strong electric field, the air is ionized, producing a large number of charged ions. These ions move under the influence of an electric field, creating an electric current. When neutral particles in the air meet charged ions, they release energy, which manifests as light and heat. Many electric sparks gather to form an arc. The temperature can be as high as 8000°C, which is enough to cause combustion or metal melting.
Hazards of motor sparks
- Impact on power system stability：Electric sparks may prolong the time it takes for switchgear to disconnect faulty circuits, increasing the risk of short circuits in power systems.
- Equipment damage：The high temperature generated by sparks can melt or evaporate the contact surface, damage insulating materials, and pose a threat to the long-term stability and safety of motor equipment.
- Safety risks：In oil-filled or other flammable environments, electric sparks may cause fires or explosions, resulting in serious safety accidents.
Causes of motor sparks
1. The voltage between the commutator segments is too high
When the motor is under drastic load or speed changes, the contact between the commutator segments and the brushes may be unstable or intermittently disconnected and connected. This instability causes the current to generate arcs during the switching process, thus forming sparks.
2. Brush wear
The brush is one of the important parts in the motor, responsible for transmitting current to the rotor. When the brush is severely worn, the contact area between it and the rotor is reduced, resulting in increased current density and sparks.
3. Poor brush contact
Poor contact between the commutator and the brush. Due to brush wear, uneven commutator surface or dirt accumulation, the current is unevenly distributed and sparks are generated.
4. Overload operation
When the motor load exceeds the rated capacity, the motor rotor speed will decrease and the current will increase, which is prone to sparks.
The following is a further explanation of the motor spark level.
| Spark Level | Spark Characteristics | Commutator and brush status | Allowed to run | |
| 1 | No Sparks | No black marks on the commutator | ||
| 1¼ | There are only a few intermittent sparks on a small part of the brush edge | No burns on the brushes | Can run continuously | |
| 1½ | Most of the brush edges have continuous and sparse granular sparks | There are black marks on the commutator (can be wiped off with gasoline); there are slight burn marks on the brushes | Can run continuously | |
| 2 | There are dense granular sparks on all or most of the brush edges | There are serious black marks on the commutator (which cannot be removed by scrubbing with gasoline); there are burn marks on the brushes | Short-term impact load and overload are allowed | |
| 3 | There is a strong tongue-shaped spark along the entire edge of the brush, accompanied by a popping sound | There are serious black marks and burn marks on the commutator (which cannot be washed away by scrubbing with gasoline); the brushes are burnt and damaged | It only exists during the instantaneous operation of direct starting or reversing, but it must not damage the commutator and brushes. | |
From the above table, we can see the degree of damage caused by sparks to the operation of the motor. Motors affected by higher-level sparks need to replace the deflector and brushes immediately.
