Scientific paper ID 651 : 2012/1

The exploitation of the trams in Sofia show that at starting conditions often arise slippage regimes. The break of this regime is dependent only of the ability and qualification often tram driver who must return the controller at a lower position or feed sand under the wheels. The practice however shows that these two ways for re-adhesion are low effective and the slip rate of the axle increases greatly. Therefore the wheels and the rails are worn out strongly and the faults of the motors are growing.

In the paper are summarized, the results obtained in investigation of the tendency for slipping and the choice of the suitable protection against that. It?s comparing two types protections against slipping ? shunting of the armature and feeding of the field winding from external source.