中性点不接地系统中,电磁式电压互感器(PT)极易与线路对地电容发生铁磁谐振,产生持续时间较长的暂时过电压或过电流,甚至造成PT高压熔断器异常熔断和PT损毁事故。铁磁谐振二次消谐措施的重点在于提高铁磁谐振检测的精确性和消谐开关动...中性点不接地系统中,电磁式电压互感器(PT)极易与线路对地电容发生铁磁谐振,产生持续时间较长的暂时过电压或过电流,甚至造成PT高压熔断器异常熔断和PT损毁事故。铁磁谐振二次消谐措施的重点在于提高铁磁谐振检测的精确性和消谐开关动作的快速性,尤其是对工频谐振的识别。笔者基于PSCAD/EMTDC仿真软件建立了铁磁谐振仿真电路,通过仿真分析发现PT电流波形在工频谐振条件下有明显区别于正常工作状态的特征,并以此为工频谐振主要判据,进而建立了基于零序电压和PT电流复合检测的二次消谐控制模型,以零序电压和PT电流为判据控制开关闭合,以PT开口三角电流和阻尼电阻发热为判据控制开关断开。通过模拟试验系统和变电站铁磁谐振仿真,验证了该二次消谐模型可以有效识别并消除多种频率的铁磁谐振,且仿真结果表明10 kV和35 kV系统的PT二次侧开口三角绕组的电流断开阈值宜分别取30~80 m A和50~100 m A,二次消谐器中阻尼电阻宜分别取2~10Ω和5~20Ω。展开更多
Reduction of energy consumption in comminution is of significant importance in mining industry. To reduce such energy consumption the energy efficiency in an individual operation such as blasting must be increased. By...Reduction of energy consumption in comminution is of significant importance in mining industry. To reduce such energy consumption the energy efficiency in an individual operation such as blasting must be increased. By using both new investigations and previous experimental results, this paper demonstrates that (1) kinetic energy carried by moving fragments in rock fracture is notable and it increases with an increasing loading rate;(2) this kinetic energy can be well used in secondary fragmentation in crushing and blasting. Accordingly, part of the muck pile from previous blast should be left in front of new(bench) face in either open pit or underground blasting. If so, when new blast occurs, the fragments from the new blast will collide with the muck pile left from the previous blast, and the kinetic energy carried by the moving fragments will be partly used in their secondary fragmentation.展开更多
This paper presents the results obtained for the effluent dewatering properties of anaerobic digestion of secondary sludge （SS） and anaerobic co-digestion of mixture of this sludge with the distillery wastewater （D...This paper presents the results obtained for the effluent dewatering properties of anaerobic digestion of secondary sludge （SS） and anaerobic co-digestion of mixture of this sludge with the distillery wastewater （DW） under thermophilic （55±1 ℃）, 5 L of working volume, three parallel lab-scale conditions. Its mixtures were prepared with a DW content of 25%and 50% and the C/N ratios of mixtures are 13.1 and 17.6, respectively. The effluent dewatering properties were evaluated under stable conditions which the biogas yield and the effluent pH were steady. The natural settleability, biogas yield, centrifugal dewatering, centrifugal supernatant turbidity and specific resistance filtration （SRF） were investigated. The results showed that the effluent dewatering properties of anaerobic co-digestion of mixtures between SS and DW were better than that of anaerobic digestion of SS alone. In the anaerobic digestion system with the feed were SS, mixture of SS and a DW content of 25%and 50% in order, the net biogas yield of secondary sludge in ADSA,ADSB and ADSC were 0.42 0.507 and 0.511 m3 biogass/kg.VS.d ; compared with the biogas yield in anaerobic digestion system A （ADSA）, the biogas yield in anaerobic digestion system B （ADSB） and anaerobic digestion system C （ADSC） had been increased by more than 20% respectively; the SRF of three digested sludge are（were） from 6.8×10^13, 1. 1×10^13 to 5.1×10^12 m/Kg, natural settling rates of 12 h are 26, 37 and 56% and that of 24 h are 32%, 45% and 59% respectively; the centrifugal dewatering rate of 3 min at speed of 1000 rpm were 16%, 31% and 51% respectively; the turbidity of centrifugal supernatant were 804, 754 and 678FTU simultaneously.展开更多
文摘中性点不接地系统中,电磁式电压互感器(PT)极易与线路对地电容发生铁磁谐振,产生持续时间较长的暂时过电压或过电流,甚至造成PT高压熔断器异常熔断和PT损毁事故。铁磁谐振二次消谐措施的重点在于提高铁磁谐振检测的精确性和消谐开关动作的快速性,尤其是对工频谐振的识别。笔者基于PSCAD/EMTDC仿真软件建立了铁磁谐振仿真电路,通过仿真分析发现PT电流波形在工频谐振条件下有明显区别于正常工作状态的特征,并以此为工频谐振主要判据,进而建立了基于零序电压和PT电流复合检测的二次消谐控制模型,以零序电压和PT电流为判据控制开关闭合,以PT开口三角电流和阻尼电阻发热为判据控制开关断开。通过模拟试验系统和变电站铁磁谐振仿真,验证了该二次消谐模型可以有效识别并消除多种频率的铁磁谐振,且仿真结果表明10 kV和35 kV系统的PT二次侧开口三角绕组的电流断开阈值宜分别取30~80 m A和50~100 m A,二次消谐器中阻尼电阻宜分别取2~10Ω和5~20Ω。
文摘Reduction of energy consumption in comminution is of significant importance in mining industry. To reduce such energy consumption the energy efficiency in an individual operation such as blasting must be increased. By using both new investigations and previous experimental results, this paper demonstrates that (1) kinetic energy carried by moving fragments in rock fracture is notable and it increases with an increasing loading rate;(2) this kinetic energy can be well used in secondary fragmentation in crushing and blasting. Accordingly, part of the muck pile from previous blast should be left in front of new(bench) face in either open pit or underground blasting. If so, when new blast occurs, the fragments from the new blast will collide with the muck pile left from the previous blast, and the kinetic energy carried by the moving fragments will be partly used in their secondary fragmentation.
文摘This paper presents the results obtained for the effluent dewatering properties of anaerobic digestion of secondary sludge （SS） and anaerobic co-digestion of mixture of this sludge with the distillery wastewater （DW） under thermophilic （55±1 ℃）, 5 L of working volume, three parallel lab-scale conditions. Its mixtures were prepared with a DW content of 25%and 50% and the C/N ratios of mixtures are 13.1 and 17.6, respectively. The effluent dewatering properties were evaluated under stable conditions which the biogas yield and the effluent pH were steady. The natural settleability, biogas yield, centrifugal dewatering, centrifugal supernatant turbidity and specific resistance filtration （SRF） were investigated. The results showed that the effluent dewatering properties of anaerobic co-digestion of mixtures between SS and DW were better than that of anaerobic digestion of SS alone. In the anaerobic digestion system with the feed were SS, mixture of SS and a DW content of 25%and 50% in order, the net biogas yield of secondary sludge in ADSA,ADSB and ADSC were 0.42 0.507 and 0.511 m3 biogass/kg.VS.d ; compared with the biogas yield in anaerobic digestion system A （ADSA）, the biogas yield in anaerobic digestion system B （ADSB） and anaerobic digestion system C （ADSC） had been increased by more than 20% respectively; the SRF of three digested sludge are（were） from 6.8×10^13, 1. 1×10^13 to 5.1×10^12 m/Kg, natural settling rates of 12 h are 26, 37 and 56% and that of 24 h are 32%, 45% and 59% respectively; the centrifugal dewatering rate of 3 min at speed of 1000 rpm were 16%, 31% and 51% respectively; the turbidity of centrifugal supernatant were 804, 754 and 678FTU simultaneously.
