Various options for dc grid protection strategies are currently investigated which differ in terms of speed and selectivity. In order to compare these options fairly, the impact on the connected ac grid needs to be studied. This paper analyzes the ac grid impact in terms of frequency stability and calculates the reserve capacity necessary to retain the stability. Assuming fast frequency reserves as a possible mitigation, a probabilistic method is provided to determine a trade-off between under frequency load shedding and additional reserve requirement. In general, non-selective strategies require higher and faster reserves compared to their fully selective counterparts for both cases analyzed in this paper. Both the selectivity and the speed of protection have an influence on the reserve requirement. The dc grid topology also plays an important role in the reserve sizing by determining the impact of dc contingencies on the ac grid. The concept of reserve sizing based on temporary loss of supply shows value in terms of lower capacity requirement. A grid specific CBA study shows that it is possible to compensate the higher investment cost associated with dc breakers by the benefit of lower reserve procurement cost.

中文翻译：

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直流电网保护策略对连接交流系统频率稳定性的影响：定量分析

目前正在研究直流电网保护策略的各种选项，它们在速度和选择性方面有所不同。为了公平地比较这些选项，需要研究对连接的交流电网的影响。本文分析了交流电网对频率稳定性的影响，并计算了保持稳定性所需的备用容量。假设快速频率储备作为可能的缓解措施，提供了一种概率方法来确定低频减载和额外储备要求之间的权衡。一般来说，与本文分析的两种情况下的完全选择性策略相比，非选择性策略需要更高和更快的储备。选择性和保护速度都对储备要求有影响。通过确定直流突发事件对交流电网的影响，直流电网拓扑结构在备用容量规划中也发挥着重要作用。基于临时供应损失的储备规模概念在降低容量需求方面显示出价值。一项针对电网的 CBA 研究表明，可以通过降低备用采购成本的优势来补偿与直流断路器相关的较高投资成本。