Nebojša Mitrović

Electrical Drives for Crane Application

A crane is the type of machine mainly used for handling heavy loads in different industry branches: metallurgy, paper and cement industry. By the construction, cranes are divided into the overhead and gantry cranes. An overhead crane, also known as a bridge crane, is a type of crane where the hook and line mechanism runs along a horizontal beam that itself travels on the two widely separated rails. Often it is in a factory building and runs along rails mounted on the two long walls. A gantry crane is similar to an overhead crane designed so that the bridge carrying the trolley is rigidly supported on two or more legs moving on fixed rails embedded in the floor. Stationary or mobile units can be installed outdoors or indoors. Some industries, for example port containers application or open storage bins, require wide span gantry cranes. In outdoor applications, the influence of the wind on the behavior of the drive may be considerable (Busschots, 1991). Wind and skew can significantly influence a safe operation of the crane. This will certainly dispose the type design of the crane (lattice or box type design) from a mechanical aspect as well as the selection, size and control of crane electrical drives.

Effects of unsymmetrical voltage sags on adjustable speed drives torque ripple

This paper researches unsymmetrical voltage sag influence on torque ripple in scalar controlled (VHz), rotor field oriented (RFO) and direct torque controlled (DTC) drives. Electric drives performance degradation during voltage sag mainly depends by used control algorithm. The simulation results of the study suggest that C type sag is the most critical and can cause drive fault. The performance of adjustable speed drives with all three types control methods experimentally tested under sag condition. Furthermore, sag induced vibration measured and achieved results are compared.

THE MONOSPIRAL MOTORISED CABLE REEL IN CRANE APPLICATIONS

The main consideration of any reeling system is the effect it has on cable tensions and hence cable life. This paper explains the relationship of reel torque to cable tensions and the reasons why this relationship is so important. Such system is characterized by variable parameters, primarily a variable moment of inertia and a variable diameter of the coiled cable. For these reasons, in order to ensure proper dimensioning of the drive, it is necessary to know the motor torques that need to be developed as a function of the coiled cable. The motor should be able to develop the required torques in a very wide speed range. It is shown that for properly sizing the motor it is necessary take into account the dynamics of the cable reel drive. In this paper monospiral motorized cable reel for winding power cable in crane applications with frequency converter fed induction motor is analyzed. Also, the equipment selection procedure for the real crane with concrete data is shown. Experimental results are recorded during the crane commissioning in real condition.

VOLTAGE SAG SENSITIVITY OF INDUSTRIAL VECTOR CONTROLLED INDUCTION MOTOR DRIVES – A COMPARATIVE STUDY

Sensitivity of adjustable speed drives (ASDs) on voltage sag events represents one of the most challenging problems in modern industrial facilities. In this paper, a comprehensive experimental verification of vector-controlled ASDs is conducted under the most-frequent sag types. The obtained results are faced with static and dynamic requirements in speed and torque controlled applications. Besides influence of DC-link parameters, selection of the applied control method and the controller settings can have crucial impact on performance deterioration. Examined industrial ASDs exhibited voltage sag susceptibility with fault error codes under the deeper voltage sags, while under the voltage sags with residual voltage above under-voltage limit they showed speed degradation.