Ultra-fast disconnector (UFD) is a key component of hybrid DC circuit breakers and it is also studied as the main switch in some DC grid topologies. A UFD model suitable for DC grid studies and ...considering both normal operation and failure mode is presented. The dynamic motion of contacts is analysed in detail and it is concluded that Thomson coil inductances including parasitic parameters play an important role and it is recommended to use finite element modelling. The arcing mode of UFD is repressed using a variable resistance in series with an ideal switch. The variable resistance is calculated analytically based on the instantaneous position of contacts and the circuit conditions. Two different arc models are recommended: for the air-insulated UFD and SF6 UFD, and in each case, two operating regimes should be considered: high and low currents. The UFD model is verified for both normal operation and failure mode using measurements on a 5 kV laboratory UFD and the results show very good matching. The 320 kV SF6 UFD model is evaluated using limited reported results from manufacturers.
•Proposes novel dc grid device based on capacitive energy storage.•Reduces fault current and voltage drop of voltage source converters under dc faults.•Reduces overvoltages under pole-to-ground ...faults in symmetrical monopole grids.•Improves power flow security by preventing converter blocking.•Improves transient dc grid stability.
A major and very important challenge in dc grid development is maintaining continuous converter operation under dc faults. This paper proposes a novel capacitive energy storage device which improves security of dc grids by avoiding terminal blocking. The device provides current from the capacitor bank during dc faults, reducing fault current contribution and voltage drop of dc grid converters. Moreover, the device also helps in balancing pole voltages which is of particular significance during pole-to-ground faults in symmetrical monopole systems. Other benefits like improved transient grid stability are also demonstrated. Device’s design and performance is assessed using theoretical analysis and verified on a three-terminal offshore dc grid model in PSCAD. The cost of the device’s electronics is minimized and the total cost and weight estimation are also shown.
This paper examines two new bidirectional hybrid dc circuit breaker (CB) topologies for application in meshed dc grids. The goal is to retain performance of hybrid dc CB with bidirectional current ...interruption while reducing semiconductor count, dc CB size, and weight. The fault current is routed to the unidirectional internal valve using multiple additional ultrafast disconnectors. Operation of both topologies is studied using a 320-kV, 16-kA simulation model, as well as demonstrated on a 900-V, 500-A lab prototype. The control systems are presented and discussed in detail. The low-voltage hardware prototypes verify performance of several new technical and operating solutions in laboratory conditions. A comparison is made with the existing dc CB topologies and performance and reliability compromises of each topology are assessed. The conclusion is that it might be possible to halve the dc CB semiconductor count while retaining same 2 ms opening speed and bidirectional operation.
HVDC grid protection with adequate speed and reliability is required to minimise the impact of DC faults. In particular, fast breaker failure backup protection algorithms are needed to meet the ...expected reliability requirements of HVDC grids. In this paper, existing breaker failure backup protection algorithms are shown inadequate to detect partial failures like a single module failure of breakers with a modular structure. This paper proposes a backup protection algorithm which rapidly detects a DC breaker failure based on estimating the counter-voltage created by the energy absorption branch during an interruption. The performance of the proposed algorithm is evaluated using a four-terminal test network with both hybrid and mechanical DC breaker technologies. The simulation results show that the proposed algorithm is able to quickly detect both complete and partial failures of the two breaker technologies even considering measurement errors, noise and ageing of the energy absorption components.
Vulnerability of voltage source converters to DC faults is recognized as the main obstacle towards widespread implementation of meshed DC networks. Because of low surge current capability of IGBTs, ...the converters are blocked under high currents in order to prevent permanent damage to the modules. Converter blocking abruptly interrupts the power flow and causes a major power imbalance in both the AC and DC grid. This thesis aims to improve reliability and security of DC grids by preventing loss of terminals under DC faults. Fault response of a modular-multilevel converter is studied analytically and through simulations. It is identified that the MMC goes through several stages under a DC fault and each stage has different dynamics. The impact of converter modelling is also taken into account. DC grid topology has a major impact on protection system design and performance. If multiple converters are connected to the same bus, fault current is shared between the converters and fault current slope of each individual converter is reduced. Converter blocking can consequently be avoided and protection system requirements can be relaxed. A novel DC grid protection device based on capacitive energy storage is proposed. It is demonstrated that the device reduces the magnitude and frequency of MMC fault current, as well as DC voltage drop. In symmetrical monopole grids, pole voltage deviations under pole-to-ground faults are greatly reduced and converter blocking is avoided. Temporary MMC blocking is studied as another method for avoiding loss of terminals under DC faults. The benefit of this approach is low protection system cost and reduced impact on normal grid operation. A thermal valve model is developed to assess peak thermal stress on antiparallel diodes. Coordination between MMC self-protection and fault detection relays is proposed, as well as the use of converter DCCBs for backup protection.
The anti-CD20 antibody rituximab (RTX; Rituxan®, MabThera®) was the first anti-cancer antibody approved by the US Food and Drug Administration in 1997 and it is now the most-studied unconjugated ...therapeutic antibody. The knowledge gained over the past 15 y on the pharmacodynamics (PD) of this antibody has led to the development of a new generation of anti-CD20 antibodies with enhanced efficacy in vitro. Studies on the pharmacokinetics (PK) properties and the effect of factors such as tumor load and localization, antibody concentration in the circulation and gender on both PK and clinical response has allowed the design of optimized schedules and novel routes of RTX administration. Although clinical results using newer anti-CD20 antibodies, such as ofatumumab and obinutuzumab, and novel administration schedules for RTX are still being evaluated, the knowledge gained so far on RTX PK and PD should also be relevant for other unconjugated monoclonal antibody therapeutics, and will be critically reviewed here.
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