Why do brushed motors spark?
There are many reasons for the occurrence of brush sparking, relevant information, regulations have made a detailed description of it, but in actual production really caused by brush sparking reasons are probably the following.
1, Brush current density is too large.
I egentlig drift, if one or two brushes are stuck due to mechanical reasons, spring pressure is not enough, in order to maintain normal load, the current through the other brushes will increase, in the increased flow of brushes, if there is a brush by the Mo bias, because the contact area with the slip ring is reduced, the contact surface flow density increases.
According to Q=I*IRT, heat generation is proportional to the square of the current, the accumulated heat can not be dissipated, the temperature rises sharply, the brush and slip ring contact surface will produce sparks. Ud over, after the generation of sparks, so that the brush working environment is even worse, thus the vicious circle, so that the brush sparking more serious, several have this situation will occur in serious ring fire.
2, Brush pressure is not uniform or does not meet the requirements.
Brush factory manufacturers have related: brush pressure adjustment to the minimum pressure of the non-sparking, after scientific proof and practice summary, the pressure between the requirements of each brush should also be uniform, the difference is not more than 10. motor in long-term operation if a brush friction is too short, or brush in the brush frame stalled card, the pressure will appear uneven.
In addition by mechanical, spring itself heat softening and other factors caused by the pressure does not reach the brush does not spark the minimum theoretical requirements. There are also we in the pressure, lifting carbon brush, sometimes rely on the feeling, no experience, operating error is very large.
3, The brush surface is not clean.
This is the most ignored, the normal operation of the motor brush sealed in a closed cabinet, two poles brush in the middle of the set on the shaft gear-like axial fan, relying on the rotor rotation to grind down the graphite carbon powder, brush heat in time to pump away, to clean and cool the role. If the cabinet door is not closed, or forget to close the door when inspection, the dust outside along with the hot air sucked into the brush, attached to the brush column, on the one hand, affect the brush heat dissipation.
På den anden side, the brush spark occurs because the brush column surface is not clean, the brush column between the insulation strength is not enough easily ring fire.
Ud over, the slip ring on the car has a spiral groove, which is to increase the brush heat dissipation area, improve contact with the brush, so that the brush more fully cooled, while easier to let the toner pumped away. If the cabinet door is not closed tightly, the fan pumping force is not enough outside dust is also easily attached to the spiral groove, the consequences are conceivable. The exciter brush considering its voltage level is relatively low exposed outside, here also suggest a little overhaul regular cleaning.
4, Bearing vibration is large.
One or two large shaft with exciter, due to the long bearing, with more additional equipment, vibration is naturally difficult to control to a minimum,. Long operation of the unit, fatigue, aging and other complex factors cause bearing vibration increases, brush with vibration, will make the brush column friction uneven, lead and spring loosening, local sparking slowly further affect the overall situation.
Other reasons such as poor brush manufacturing process, poor grinding, brush position is not right, its gap is not uniform, contact resistance is too large, high load, short circuit, etc., in practice there may be, but to production practice to see the above 4 points of the reasons mostly.
DC motor manufacturers to speak to the theory of electromagnetic nuisance, if the DC motor commutation element within the synthetic potential is not equal to zero, the additional commutation current generated in the commutation element will make the brush before and after the brush side current density distribution is not uniform, brush and commutator contact or disengagement, it will produce a higher contact potential difference;.
Ud over, when the brush and commutator disengage, the additional commutation current in the element is not zero, the electricity in the element will be released in the form of human sparks, the delayed commutation sparks will be generated in the back brush side, and the over commutation sparks side will be generated in the front brush side.
In order to make the DC motor play an efficient role in industrial production, staff need to do the necessary fire prevention measures when storing or using the motor, the main fire prevention measures are as follows.
1. no miscellaneous objects should be stacked around the DC motor, and a proper distance should be maintained between the motor and its starting device and combustible materials so as not to cause a fire.
2. motor start should follow the prescribed number of starts and interval time, and start as little as possible to avoid fire due to the accumulation of overheating of the stator winding.
3. during operation, the current and voltage of the motor shall not exceed the allowable range, and the motor cooling system shall be normal.
4. found that the motor is out of phase operation, should immediately cut off the power supply, so as to avoid the motor out of phase operation overload heating fire.
5. According to the working environment of the motor for moisture-proof, anti-korrosion, dust-proof, explosion-proof treatment, the installation process should meet the requirements of fire prevention.
DC motor in the process of operation once the fire, should immediately cut off the power supply, and use the special fire extinguisher for electrical equipment to extinguish the fire, if the dry powder extinguishing agent to extinguish the fire, should be careful not to make the dust fall into the bearing, if necessary, fire water spray into moldy fire.
