对地方电网小水电自励磁判断方法的探讨

结合理论研究和仿真分析,探讨地方电网内小水电自励磁判断方法的合理性。研究发电机甩负荷机电过程对自励磁的影响,发现发电机减速释放功率可能导致系统产生极大的暂态自励磁过电压;研究地方电网内有功负荷对发电机自励磁判据的影响,发现地方电网有功负荷的存在将降低等值串联容抗 ,使系统更容易满足自励磁条件。最后通过一个仿真实例对提出的观点进行佐证。本研究对含有小电厂的地方电网自励磁的准确判断具有参考借鉴意义。     

工业生产过程中变频器的故障排除方法

通过对变频器控制回路的剖析,提出了变频器控制回路抗干扰的具体措施。针对变频器在运行过程中出现的充电起动电路故障、变频器不能高速运行、变频器显示过流、变频器显示过压、电机发热,变频器显示过载故障进行了分析,提出了排除方法。     

Initial stages of nucleation of molybdenum and tungsten carbide phases in tungstate–molybdate–carbonate melts

The electrochemical nucleation of Mo₂C and W₂C crystals for tungstate–molybdate–carbonate melts of specific compositions on Ag, Au, Cu, Pt, and Ni substrates was studied by the electrodeposition method. The influence of electrocrystallization conditions (temperature, deposition time, initial current pulse, and current density) was investigated. Experimental measurements indicate that crystallization overvoltage is associated with three-dimensional nucleation. Carbide deposition onto the substrates prepared from the same solid materials was not associated with crystallization overvoltage. The maximum value of the initial overvoltage, η_max, which includes crystallization and electrolysis overvoltages, is proportional to the electrode surface area. Under these conditions, surface diffusion limits the electrode process rate. An increase in carbide deposition rate leads to an increase in the number of crystallization centers. This reduces the duration of surface diffusion. A rise in the melt temperature complicates the crystallization process by alloy-formation phenomena. Overvoltage maximum height for metals, which do not form alloys, is proportional to the reciprocal of their formation time. Melt temperature increase promotes interdiffusion of refractory metal, carbon, and substrate, and also intensifies their chemical interaction. Structural mismatch is observed during molybdenum and tungsten carbide electrodeposition onto different single-crystal substrates.     

Cathodic protection monitoring of buried carbon steel pipeline: measurement and interpretation of instant-off potential

The criterion used to verify the cathodic protection condition of a structure is based on structure-to-electrolyte potential measurement, which can include an ohmic drop contribution. Among the available techniques, the use of potential probes with internal reference electrode and of corrosion coupons with a so-called soil-access tube represents the most appropriate way to measure the IR-free potential, eliminating the ohmic drop contribution. An alternative is represented by on-off technique if equalising, galvanic or stray currents are not present. Laboratory tests have been carried out in soil-simulating solution on cathodically protected carbon steel in order to evaluate the effectiveness of off-potential for the assessment of cathodic protection. Instant-off potential is not reliable in overprotection condition; moreover, the accuracy of the measurement is strongly influenced by the presence of external current as galvanic or equalising currents. The effect of low-pass filter in the data acquisition system on the potential reading is discussed.     

发电机退电制动时转子过电压的分析

分析了隔河岩电厂发电机在退电制动时转子过电压的原因,提出了在制动变压器之前增加一个接触器以解决转子过电压的方法,结果表明,所用方法是可行的。建议将电厂目前的制动方式(恒流方式)改造成柔性制动方式,以便进一步提高机组运行效率。     

二次电缆感应过电压的ATP- EMTP计算及分析

变电站的电磁环境主要包括正常运行时的电磁场和暂态空问电磁场以及短路、雷电流和开关操作时产生的电磁暂态对二次系统的干扰,而二次系统的运行可靠性对变电站的运行起决定性作用.因此文章主要研究的是雷击变电站通过引下线进入地网后,通过接地体在二次电缆上产生耦合和干扰,用ATP- EMTP计算出地网对电缆的感应过电压.     

35 kV电缆雷电过电压仿真与分析

介绍了由于雷害造成电缆击穿事故的实例。根据故障记录波形和电磁暂态仿真软件EMTP-ATP对事故成因和过程进行仿真分析。结果表明,对于进线具有电缆段的变电站,当电缆末端空载时,雷电过电压波会沿着架空线路传到电缆末端产生全反射,造成电缆电压过高,超过绝缘水平继而击穿接地发生事故。此类变电站应注意避免电缆末端开路的运行方式,并且考虑在进线端处加装避雷器等保护装置。该结论为变电站防雷设计提供了参考。     

Control of dynamic overvoltages due to load rejection by static shunt compensation

A digital computer method used to evaluate the performance of a static shunt compensator as a device for controlling dynamic overvoltages caused by load rejection is presented. A typical system of a generating station connected to a load centre through an EHV transmission line with a static compensator at the load end is considered, and the envelopes of dynamic overvoltages following load rejection are evaluated. Detailed mathematical models incorporating the dynamics of a synchronous machine, transmission network and static shunt compensator are employed in the analysis. The static shunt compensator is shown to be an effective tool for controlling dynamic overvoltages. The application of this analysis for choosing an economic voltage rating of the surge arrestor is highlighted.     

发电机停机电气制动控制的优化设计

阐述了隔河岩水电厂发电机停机电制动的工作原理,分析了励磁系统改造后灭磁开关运行方式变化,引起电制动投运后退出运行时转子绕组过压的原因,提出了电制动控制优化改进方案,经过试验检验,证明此方案可行。