Comparison of DC and AC container crane drive systems

The reliability of container handling equipment is of prime importance to container terminal operators. This leads to specifications for container crane drive systems to be very detailed. As a side effect of this, new technology only very reluctantly is accepted. The following paper summarizes the key aspects of crane drive system reliability in the light of most recent developments of drive technology. Most relevant is the maturing of field-oriented controlled AC drives. The main focus of the paper is on a comparison between DC and AC drive technology. For DC drives brushes and commutators are identified as the main reliability bottleneck. The sensitivity of the commutator-brush arrangement to various ambient conditions is explained. For AC drives their general characteristics are presented together with known restrictions in terms of motor winding insulation stress and the reliability impact of different AC infeeder configurations.