Extending Protection Selectivity in DC Shipboard Power Systems by Means of Additional Bus Capacitance

Abstract

DC shipboard power systems have been considered as a promising solution for stricter environmental regulations on ships due to their main benefits in fuel savings with variable speed engines and easy integration of energy storage systems. In order to employ the DC solution in the shipboard power systems, the DC power systems have to be protected from a system fault with protection selectivity to minimise impacts of the fault or to avoid other undesirable situations in the system. For lowvoltage DC shipboard power systems, a three-level protection has been proposed: fast action (1 st)-bus separation by solid-state DC bus-tie switch, medium action (2 nd)feeder protection by high-speed fuse and slow action (3 rd)-generator-rectifier fault controls. This paper proposes a new method by means of additional bus capacitance added in main DC buses to help the reliable operation of the threelevel protection. The principle of the proposed method is introduced and the sizing of the additional bus capacitance is addressed in this paper. With the modelling of the DC shipboard power systems, the analyses of voltage drops for the bus separation failure and fault clearing time for the feeder protection are carried out to verify the proposed method. The results show that the proposed method not only mitigates the voltage drop for the bus separation failure, but also achieves the selectivity and the sensitivity for the feeder protection.

Impact of Synchronous Generator Deexcitation Dynamics on the Protection in Marine DC Power Distribution Networks

“…The three-level protection consists of three different fault controls which have different operating time frames ( Fig. 2): fast action (1 st level) -bus separation with DC bus-tie switch based on solid-state technology (10 −40 µs), medium action (2 nd level) -feeder protection with high-speed fuse (0.2 −1 ms) and slow action (3 rd level) -power supply protection (0.003 −10 s) [14].…”

Four Quadrant Bus-Tie Switch for Protection of Shipboard Power Systems

“…Nevertheless, as the SSBTS is first and foremost a protection device, an increase in losses is outweighed by an increased protection capability that allows an extended range of employment for the device. Additionally, the conducted current in the SSBTS is rarely equal to it's nominal current, as a balanced operation of the PDN with generated power similar to the load power in each switchboard is generally preferred [9]. Overall, the advantages offered by the simplicity of connection, single active semiconductor device and most importantly scalability result in the topology being a very suitable for the application.…”

“…To achieve this, the PDN is separated into multiple switchboards each clustering various loads and power supplies, that are then interconnected through the use of solid state bus tie switches (SSBTSs). In addition to the reconfigurability offered by the solutions, these devices prevent the propagation of a fault by quickly isolating the malfunctioning sector in the event of a fault, effectively acting as a first line of defence and providing selectivity as a part of the protection coordination scheme in which they operate [8,9,10]. There are several characteristics that an SSBTS must have in order to fulfil this role, differentiating it from a circuit breaker in the traditional sense:…”

Solid-State Bus-Tie Switch for Shipboard Power Distribution Networks

“…The first is a final protection device able to interrupt a fault current several times higher than its nominal current, protecting downstream equipment from damage in the event of a fault. Conversely, an SSBTS provides much faster interruption (in the range of tens of µs), but has lower current interruption ability and operates as part of a protection coordination scheme together with other means of system protection, such as high-speed fuses and generator/rectifier fault control [4], [10], [11]. Fig.…”

“…DC shipboard PDN protection coordination schemes employ multiple means of protection operating in different time scales[4].…”