The Use of Permanent-Magnet Machines in Ship Electrical Systems

Abstract

Ships are autonomous objects in which the capacity of the power plant and volume of available space are limited. Permanent-magnet machines with the maximum coefficient of efficiency and minimum mass and dimensions can be widely used on the ships, first of all, in high-power ship systems—generator sets, propulsion systems, and thrusters. However, there is a danger of fire during interturn faults in the stator winding in permanent-magnet machines. If such a fault occurs in the standard operating mode, then, when the rotor turns by inertia or, under the action of slowing water flow, moves to the propeller in the closed circuit of the stator winding, an electromotive force will be induced since the magnetic field of the rotor remains. This electromotive force will produce a current in the closed circuit, and a large amount of heat will be released in the winding-fault area, which can lead to a fire on the ship. This article considers a method of “damping” of the magnetic field in the rotor in an emergency situation. In this method, the magnetic system of the rotor is made of two parts, one of which is fixed on the rotor, while the second is installed on the rotary sleeve. In the normal condition of the machines, the angular positions of the analogous poles fixed on the rotor and installed on the rotary sleeve coincide. In the emergency condition of the machine, the sleeve turns so that the angular positions of the opposite poles of the rotor and sleeve coincide. As a result, the induction of the magnetic field in the gap and the electromotive force in the stator windings in the emergency condition of the machine will be close to zero.