Crane motor speed control

Abstract

Many cases arise in industry (especially in ship-building or ship repairs industries like the Malta Drydocks and where heavy machinery such as cranes are used) where the speed of a rotating shaft must be varied or controlled. In some of these cases, manual control is adequate, in others automatic control is essential. Hydraulic (oil) motors are sometimes used, but in cranes the vast majority of drives are electric. The aim of this project is to state and analyze some of the electrical motor speed control systems which are in use on cranes existing at the Malta Drydocks. Every crane has got four motions. The speed control system used for every motion may differ from one motion to another and even from one crane to another because of the type and make of such cranes. This Project is stipulated as follows: 1. Introduction 2. Motions on a crane: i) hoist ii) slewing iii) luffing (derricking) iv) travelling 3. DC speed control: a description on different types of d.c. speed control systems when used on cranes. i) Series resistance control ii) Ward Leonard 4. AC speed control systems: a description on the wide range of speed control with respect to torque used on the cranes of the Malta Drydocks. i) Wound rotor with external resistances ii) Frequency converters iii) Cascade iv) Change from one motor to another with a difference in stator poles v) Drives with mechanically coupled electric motors (for low speeds). 5. Maintenance