Abstract
This paper introduces groundbreaking research on how to assess the Cable Length Limit (CLL) to ensure effective protection by Z-source Circuit Breakers (ZCBs) in DC power networks. It has been revealed that the line parameters of power cables have a significant impact on the cutoff performance of ZCBs. The question of assessing the CLL has been raised as an unsolved problem. In this paper, a method of CLL assessment is proposed based on physical models and simulation tests. To verify the proposed method, two studies were performed to assess the Cable Length Limits depending on fault levels and power delivery levels, respectively. The ZCB parameters were specified for a simulation testing system for a 5 MW distribution line feeder. The effectiveness of ZCB protection was tested in groups of simulation tests with various impacting quantities, i.e., cable lengths, fault current levels, and power delivery levels. The effective cable lengths for the ZCB to detect and successfully interrupt a faulty branch in the DC network were assessed and analyzed. The testing results prove that the CLL decreases along with a decreasing fault current level, as well as an increasing power delivery level. Based on data analysis, an equation was derived to calculate the effective length of the ZCB for DC lines, and the equation can be used to generate new CLL curves for various load-power requirements. This study could increase the reliability of a ZCB’s response to a fault in DC transmission and distribution lines. It could also help power system designers/operators to maintain reliable protection with ZCBs in DC power system networks.
Highlights
The study formulized the efficiency of power delivery in Z-source Circuit Breakers (ZCBs) at rated load conditions as a cost function and revealed that the Inter-Cross-Connected Bi-directional Z-source Circuit Breaker (ICC-BZCB) topology, as shown in Figure 1, had low overall power loss compared to the other two topologies
This paper reveals and analyzes the unsolved problem of Cable Length Limit (CLL) assessment
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Summary
More and more renewable energy resources in DC format and High-Voltage DC (HVDC) transmission and Medium-Voltage DC (MVDC) distribution networks are forming and being integrated into modern electric power systems. They can provide a long-term sustainable solution for future energy demands. In fault current protection, the opening of an arc-based circuit breaker cannot itself extinguish the arc generated in a DC system due to the lack of a natural zero crossing point [3] The quenching of such an arc is the most significant concern since it increases the cost of maintenance and reduces the lifespan of the breaker [4,5,6].
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