Traction Motor Brushes

There are numerous manufacturers of DC traction motors which are employed globally including products from companies such as ABB, Bombardier,AEG, Siemens, Brush, GEC, Hitachi, Mitsubishi, Dong Feng to name a few, with each application with respect to brush and brush holder configuration and number of motors employed differing

People moving Metro or Tram systems generally employ carbon materials which are treated grades to cater for “lighter” loadings, however in some parts of the

world such as Australia, Grade DE7000 has become the standard widely long life high performance material on GEC and ABB machines. Film or Patina formation and maintenance is key to providing excellent brush performance and many of our materials are also treated to cater for both low humidity environments, whilst the combination of treatments controls the patina thickness levels under all operating conditions.

As Metro and Tram systems slowly move toward AC traction systems, most of the applications encountered will be well established with long standing material approvals, with customers hesitant to change grades. As opportunities arise a focus on reliability and asset utilisation should be employed in the sales process to promote a “Total Cost of Ownership” uniques selling point. For Metro systems in the table to the right we have listed grade DE7000 as a premium material for EMU Metro Systems, Whilst grade N2000 has been nominated for

lighter loaded tram systems. These recommendations are based on experience, and although we have many other carbon grades which could be employed, the nominated grades provide an excellent start point for technical differentiation. Seeking guidance from In-house technical resource should be used as part of both the grade selection combined with brush design, as both will have a marked effect on performance.

Auxiliary & Earthing Brushes

Metro (EMU) and tram systems generally employ small auxiliary drives for applications such as Air provision via compressors for door opening and closing, MA – Motor Alternator sets, pumps, air conditioners and blower fans. For simplicity in this document we have nominated our Resin based graphite material R783 for these applications. This grade works well at low current densities providing low friction performance combined with excellent film forming capabilities. Consultation with internal

technical resource is recommended for difficult applications, and it will be important for these applications that information such as the currently fitted material, brush force and machine rated and running currents are understood for grade selection.

Earthing Brushes

Earthing brush patterns are used on both Metro (EMU) and tram systems in order to provide a path of low resistance for both leakage and fault currents for both equipment and personal protection.

Two types of systems are generally employed either “Frame” mounted as per the lower picture or “axle” hung as per the top picture. Frame hung earthing brushes are generally found on EMU systems, whereas Axle hung can be found on both EMU and Tram based machines.

Copper Graphite materials are employed for earthing applications and from experience our grade of choice for earthing applications especially “Frame hung” is grade CM1S or alternatively grade M2688, which have a copper content in the region of 88%.

Axle hung units depending on the manufacture can employ one to three brushes and in most cases use copper graphite materials with an approximate copper content of 75%-88%. Common axle earthing units experienced in the field will be Ferraz, Frost and Stemmen.