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The increasing demand for the development and utilization of renewable energy resources has lead to a growing interest in the development of LVDC systems. The dc grid provides more flexibility in integrating different forms of renewable energy sources effectively. However, the lack of a reliable protection mechanism remains the main drawback in the growth of dc distribution systems. Unlike ac systems, the absence of a natural zero crossing in dc systems for arc extinction makes the use of a conventional mechanical circuit breaker (MCB) a less reliable solution. The use of a solid-state circuit breaker (SSCB) results in fast fault interruption but reduces the overall efficiency of the system due to the on-state voltage drop of the semiconductor devices. A hybrid circuit breaker (HCB) combining MCB and SSCB yields better static and dynamic performances but the main challenges remains in the demagnetization of the transmission line inductance after a fault interruption and an arc formation between the MCB contacts. This paper proposes a hybrid circuit breaker (HCB) which is suitable for fast fault interruption in low voltage dc (LVDC) systems while alleviating the above issues. Proposed topology employs a semiconductor switch as well as an actively switched capacitor branch in parallel with the main mechanical breaker to facilitate fast current commutation during a fault. The mechanical breaker forming the main branch is turned off at zero voltage. This eliminates the arc formation across the moving contacts of the breaker. Moreover, the fault interruption process does not require a varistor for network demagnetization following the fault current commutation. This paper also presents a discharging mechanism for the capacitor in a practical implementation. Operation of the proposed dc circuit breaker is evaluated through a prototype tested in the laboratory.

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Subsea electrification is envisaged as one of the key building blocks of deep-water oil and gas (O&G) production. Present power transmission and distribution (T&D) schemes almost exclusively employ high voltage AC (HVAC) technology to drive the electrical processing units in the seabed, such as pump and compressor motors. Although HVAC transmission is reliable and simple to control, it exhibits a serious drawback with increasing step-out distance in terms of high reactive power requirements and reduction in peak power transfer capability for the subsea transmission cable. Moreover, most of the existing subsea T&D architectures employ a hub-and-spoke architecture with a single power receiving node. As a result, these systems are vulnerable to single-point failure. In order to address the above issues, two novel subsea architectures, based on high voltage DC (HVDC) transmission, are proposed in this paper. HVDC offers a significant advantage over HVAC systems for longer transmission distances with additional power processing units embedded in the system. Both these architectures employ a subsea DC distribution bus concept to supply multiple subsea loads which represent current scenario of increasing subsea consumers. The performance of the proposed architectures is illustrated through simulation for distinct events such as rated power flow, load step-up/down and load side breaker closing. Relevant results are discussed to summarize the advantages and challenges for the proposed power transmission architectures.

No abstract