Assessment of electric power quality in ship systems fitted with converter subsystems

Assessment of electric power quality in ship systems fitted with converter subsystems - Janusz Mindykowski

Introduction

The issue of electric power quality onboard ships has seemed of utmost importance, in particular nowadays when a great progress in implementation of electric drives for ship’s thrusters, propellers and other smaller drives is evident. Ship’s electric power systems are isolated power systems. Similar systems are installed on aircraft, oil platforms and small islands, in industrial plants with seasonal character of operation and also as emergency electric supply systems in banks, hospitals, hotels, large supermarkets and skyscrapers [1], [2]. Characteristics of those systems are: scarce in other cases proportion of single consumer power to electric source power (some consumer powers are often comparable to generator power supplying them) [3] and relatively high short-circuit impedance of generators installed in the systems under consideration [1]. Finally, electromagnetic disturbances observed in isolated power systems are more serious than those observed in large connected systems in their normal operation. What is unique in ships power systems ? Answer is simple. System is installed on mobile object – the ship - and simultaneously is deciding for its operational control. Effects of incorrect system operation can be very serious and consequences of ship’s casualties are known very well from the news. Indeed, question of the electromagnetic disturbances determining electric energy quality in ship’s power systems has not only technical aspect and / or vessel operational safety. Paltry quality of electrical energy on ships has also its economic dimension. In spite of relatively not big power (normally no more than few MVA) of a single electric plant, large number of ships (30 395 of 1000 gt and above as of 1.01.2003 [4]) shows the measure of presented problem excellently.