Generator Slip Ring Wear
Face between brushes and slip ring wear, there are two: First, purely mechanical wear; another is electrical wear and mechanical wear in the current action.
1) Purely mechanical wear
Brush and a conductive ring contact, due to the action of the spring pressure and elastic deformation of the reason, make direct contact portion embedded mutual. When the relative sliding action, of course there is friction and wear form. If the carbon brushes soft particles, the toner easily dip in the slip ring surface, the slip ring slip into a bright stone mirror, brushes grinding surface is also very smooth, both of which are small mechanical wear. But if the mass excess carbon brushes, coarse particles, or even contain few, such as silicon carbide hard particles like, then bound to scratch cut the surface of the slip ring, so that the latter again in metallic luster or texture, brushes itself will worn.
2) Under the current role of the electrical wear and mechanical wear
Under current role, not only mechanical wear, but also electrical wear. The so-called electrical wear, referring to the high temperature since the arc discharge of the role of the surface material has been damaged. And because the wear of electrical pole, it will also affect the occurrence of mechanical wear.
Since the current through the contact surfaces of the carbon brush and the slip ring, and the direct conduction site constantly changing, and the current density is large, so that at some point the temperature is very high; and arcing due to high temperature, causes local melting of the pole faces on both sides, metal will lead to metal vapor, carbon brushes the structure is loose, by oxidative attack and fall off. In the electric arc, the anode (positive electrode) local hot and evaporated 'metal vapor "so that the anode surface wear and tear, called" anode evaporation "; cathode (negative) impact due to positive ions and electrons are emitted high temperature, the cathode Profiles also suffered damage, called "cathode powder." Since the anode and the cathode powder evaporation effect, brushes and a conductive ring because the purpose of the current disagreements will float to the surface polarity difference.
When the current flows from the carbon brush to the slip ring, brushes is positive at this time, the conductive ring is negative, the effect is: brush surface of the anode evaporation occurs small level, carbon, graphite ions migrate to the conductive ring, brushes electrical wear. A cathode conductive ring slightly pulverized and adhered carbon particles, graphite, into the lubrication, specular gloss. Since the conductive ring smooth surface, mechanical wear is small.
When current is made of a conductive ring to the brush, this time for the negative brushes, slip ring is positive, the effect is: the surface of the brush cathode powder occurs, electrical wear small. Conductive ring anode evaporation occurs, a large number of metal evaporation, severe erosion damage to the surface, while the metal particles are easily attached to the surface of the carbon brush wear, which in turn causes serious wear commutator surface, appearing streak. Under such circumstances, the slip ring surface rough, a metallic light, mechanical wear serious.
In general, when the carbon brushes is anode: electrical brushes wear big, small mechanical wear, electrical conductive ring wear is very small; when the brushes is negative, brushless electric wear is small, mechanical wear large , electrically conductive ring are great.
In order to make the average wear, the polar of rings should always be replaced. The power plant overhaul often exchange positive and negative ring adjoining cable, it is the reason.
As spring pressure, wear is also affected. Pressure is too small, brushes and a conductive ring surface contact is unstable, prone to lead to an arc, so that the electrical wear increases. Pressure is too large, the conductive ring surface badly worn, and will increase the mechanical wear, so spring pressure to moderate.
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