MSB for Autonomous Power Plant with SEFR circuit breakers

The increasing complexity of electrical systems in modern ships, especially those incorporating unattended or autonomous engine rooms, makes the Main Switch Board (MSB) an extremely critical system. MSB activates and deactivates various consumers, but also performs the power management, generation, synchronization, and distribution, ensuring that vital systems remain operational even in the event of partial power plant failures. An MSB for an autonomous ship without personnel on board aims to ensure that consumers always have a power supply, which requires guaranteeing both generation and distribution. Generation can be guaranteed, among other things, if the equipment supplying services to the auxiliaries remain powered. Distribution can be guaranteed if the contacts follow a logical scheme based on the functional importance of each piece of equipment to maintain the power plant and the vessel active. This paper analyses the features that electrical contacts must satisfy to guarantee both generation and distribution in MSBs for unattended engine rooms, and introduces the concept of a SEFR contact, defined as a contact that provides Safety, EFfectiveness and Reliability. SEFR contacts are essential to keep the power plant active and provide the final consumer with an uninterrupted supply and therefore must comply with specific electrical and mechanical parameters. Safety implies that the power supply must be protected against any failure that could cause a supply cut-off, whether due to fire, technical failure, redundancy failure, etc. Efficiency implies that the contact has to achieve its purpose, whether the contact or the power line is fine or if they have an internal problem. Whatever the situation, the supply must be met. Reliability refers to the technical part of the contact and power line where it can be trusted that the line does not fail and the purpose is fulfilled. The SEFR concept is also applicable to the procedures and actions taken to guarantee the safety, efficiency and reliability of pieces of equipment and processes. This paper explores the relationship between the SEFR requirements and the levels of criticality of the contacts involved in the generation and distribution stages. At the generation stage, for an MSB and the power supply lines, each electrical contact is rated according to the criticality of the equipment for the survival of the power plant. According to (1), three levels of criticality are defined: Level 1 primarily for non-essential equipment, Level 2 primarily for essential equipment, and Level 3 for equipment dependent on the survival of the power plant and the vessel. The robustness of the system depends on the capacity of the MSB and the contacts with levels 1, 2, and 3 to keep the power plant and other onboard systems active. At the distribution stage, Level 1 contacts feed equipment whose temporary interruption does not compromise the operation or safety of the power plant or the vessel. In the MSB design, Level 1 lines are mostly connected to equipment that is non-essential. For this equipment, the design is planned with simple redundancy. Level 2 contacts feed equipment essential for the SEFR operation of the power plant. These systems must guarantee availability during normal navigation and manoeuvres (3). A failure in Level 2 equipment may not cause a serious problem immediately, but it can incapacitate part of the power plant. Within the electricity generation system, Level 2 includes all equipment that keeps the auxiliary generators operational. Level 2 contacts have total redundancy to avoid a supply failure. Level 3 contacts feed equipment upon which the survival of the power plant and the vessel strictly depends. These types of contacts have total redundancy as well as consumption control for each redundant line capable of detecting an internal failure in the contact even while it continues to provide service. With this measure, the capacity of the contact to continue functioning can be analysed if the MSB needs to be informed to perform additional management. The table below shows the classification of the different supply lines for the MSB of a reference vessel with two independent generators, but the study can be extended to larger vessels, with more than two independent generators (2). Designing MSB supply lines with SEFR levels guarantees the continuous power supply of equipment during the route. With this assured power service, an autonomous ship without personnel on board can maintain its power plant operational without the risk of losing any equipment.