Quenched Flux-Coupling Superconducting Fault Current Limiter Scheme and Its Electromagnetic Design Method.

In order to solve the problem of excessive short-circuit current in the present power system, a fault current limiter has become a new type of power device with high demand and is one of the current research hotspots. The flux-coupling type superconducting fault current limiter (FC-SFCL) generates a current-limiting impedance through decoupling superconducting parallel inductance based on the circuit breakers' fractional interruption. The principle is simple, and the impedance is low during normal operation. It can directly use the existing circuit breaker to open a short circuit that is much higher than its own breaking capacity. Thus, it can be used for large-capacity fault current limiting and effective failure breaking. This paper focused on exploring and studying the implementation scheme of practical products of FC-SFCL. Considering that the quenched-type parallel inductance can limit the first peak value of the fault current, a quenched-type improvement scheme was proposed. Then, an electromagnetic design method based on the simplified calculation of the number of parallel tapes was proposed, which simplified the design process and reduced the design difficulty of the quenched FC-SFCL. Taking a 10 kV/500 A/5 kA quenched prototype as an example, its electromagnetic design was completed, and the performances of the non-quenched and quenched schemes were compared. The results showed that, compared to the non-quenched structure, the technical economics of the quenched one were more prominent, and it can be used preferentially for engineering prototypes. This study about the scheme of the quenched FC-SFCL and its electromagnetic design method is useful for promoting the implementation of the current limiter engineering prototype.

Pilot-scale enrichment of anammox biofilm using secondary effluent as source water.

Enough biomass of anaerobic ammonium oxidation (anammox) bacteria is essential for maintaining a stable partial nitrification/anammox (PN/A) wastewater treatment system. Present enrichment procedures are mainly labor-intensive and inconvenient for up-scaling. A simplified procedure was developed for enrichment of anammox biofilm by using secondary effluent as source water with no supplement of mineral medium and unstrict control of influent dissolved oxygen (DO). Anammox biofilm was successfully enriched in two pilot-scale reactors (XQ-cul and BT-cul) within 250 and 120 days, respectively. The specific anammox activity increased rapidly during the last 2 months in both reactors and achieved 2.54 g N2-N/(m2·d) in XQ-cul and 1.61 g N2-N/(m2·d) in BT-cul. Similar microbial diversity and community structure were obtained in the two reactors despite different secondary effluent being applied from two wastewater treatment plants. Anaerobic ammonium oxidizing bacteria genera abundance reached up to 37.4% and 43.1% in XQ-cul and BT-cul biofilm, respectively. Candidatus Brocadia and Ca. Kuenenia dominated the enriched biofilm. A negligible adverse effect of residual organics and influent DO was observed by using secondary effluent as source water. This anammox biofilm enrichment procedure could facilitate the inoculation and/or bio-augmentation of large-scale mainstream PN/A reactors.