Comparison of conventional and frequency converter-driven overhead bridge crane control systems

Overhead bridge cranes (OHBC) as basic material handling devices are in use in many industries. Larger steel mills for instance typically operate several hundred OHSC on one single site. Today a variety of different drive technologies for bridge crane applications are available. But, modern drive concepts do not find widespread practical use predominantly due to cost reasons. The paper provides an analysis of the electrical and operational behavior of a conventional contactor controlled OHBC rated for a load of 10 metric tons. The behavior of this simple conventional control is compared with performance of the crane after a frequency converter drive system was retrofitted. This paper details aspects like mechanical stress on the gearbox and motor shaft, peak current surges in the supply grid, power consumption, operational performance and reliability. The paper thus provides a basis for an evaluation of modern AC drive systems away from a point of view that considers only the initial investment.