Contributions for improving the stability of marine power generation plants

Abstract

The Electrical Engineering department of the University FNB/UPC -Barcelona Tech. conducted a large set of real tests on a hybrid propulsion platform with compressed natural gas (CNG) fuel at the facilities of Marina Barcelona 92 in 2018, to simulate the electrical transients that may cause dangerous situations such as “Blackouts“ in marine power generation plants. The commercial generator set used in this hybrid platform is composed of a reciprocating alternative internal combustion engine of 91 kW and a synchronous alternator of 175 kVA and a set three squirrel-cage induction motors of different ratings (i.e., 20 kW, 22 kW and 55 kW). It should be underscored that, as can be seen, the rated apparent power of the synchronous generator has been slightly oversized when compared with the rated active power supplied by the prime mover. In fact, the latter is defined as one of the main criteria of this article. As mentioned above, the synchronous alternator has been oversized, mainly to overcome the effects caused by the induction motors during its on-line starting, to fulfil smooth recovery while avoiding a general “blackout”. With this purpose in mind, one of the main goals of the article is to demonstrate that the proposed criteria are useful during severe transients, which are likely to cause undesired events in the ship. The transient originated by the induction motors during the on-line direct starting causes large overcurrent. Therefore, by oversizing the alternator and adding more inertia to the electrical system (i.e., the electrical system of the ship), we achieve a better response during this contingency. Indeed, this design criterion has not been taken into consideration by the maritime sector, which most of them are only designed for the steady state at a particular point of operation. Therefore, this point stresses the fact that without considering this design criterion, the electrical system may become more vulnerable. The aforementioned “Power Blackouts”, have historically produced numerous accidents (officially reported by the “Maritime Accident Investigation Commissions” of the most developed countries), sometimes associated with undesirable consequences. A set of 5 technical recommendations and good practices has been studied and tested to improve the stability of the on-board electrical system.