三绕组主变变损率分析及其电能计量回路的改进

通过对三绕组主变的变损率分析 ,指出了主变的变损率偏高是由于其电能计量回路产生的误差所致 ,对进一步提高主变电能计量准确性提出了改进意见并给予实施 ,达到了预期的效果。

主变压器变损率对电气设备潜在性故障的预判特性

300 MW、600 MW等大中型单元式接线的发电机–变压器组电气设备和二次回路的潜在性故障,在告警和跳闸之前难以被发现,而主变压器变损率计算数据的稳定性对该类故障表现敏感。研究表明,主变压器正常运行时,变损率与其平均负载系数的正相关性较弱,当主变压器日平均负载系数为0.6~1.0时,其变损率趋近于某个固有常数。当发电机–变压器组电气设备和二次回路故障,如电能表、电压互感器、电流互感器、熔断器和二次回路等发生非突发性异常,主变压器变损率的计算值将大幅度变化,与正常运行时的固有常数形成明显偏差。发电企业可据此特性,统计和分析各主变压器的变损率计算值,监测电气设备和二次回路的状态,预判其异常和故障。

“变损率”对发变组计量监视作用

随着电气设备的老化和其它方面的原因，总会在运行中出现一些故障，尤其是电气二次设备。本文针对野马寨发电厂电量统计情况，通过构建“变损率”这一理念，以实例阐述了其对发变组计量故障监视作用，可有效地将故障消除在未遂或初始阶段。

某电厂主变压器变损率综合计算与分析

针对某电厂2×110MW发电机组主变压器变损率上报数据异常偏大的问题,通过公式计算对此问题进行了分析,找到了导致此问题发生的原因,并提出解决方法。

主变变损分析

准确的电量计量对发电厂的经济分析和经济效益有很大的意义，而计量准确与否，可以从变损率上反映出来，定期分析变损率，就可以找到降低主变变损的办法。

电压互感器更换后主变变损增大问题分析

针对某电厂更换上、下母电压互感器后,主变变损率突然增大这一问题,从变损率计算公式入手,对变损率增大的原因进行了分析。有针对性地提出了调整电压互感器误差,降低电压互感器二次负载回路电压降的解决方案,以使主变变损率降低,保障电力企业的合理经济效益。

发电厂关口电能计量装置故障时差错电量的计算

由高电压等级发电厂关口计量装置的设置情况,以及发电厂主要统计的电能经济指标,提出当某电能计量装置故障,造成其所计量的电量出现差异时,可以通过某一经济指标的正常统计值推算出异常电量的正常电量值,并结合实例分别介绍利用发电机升压变压器变损率计算关口差错电量、利用综合厂用电率和发电量计算关口差错电量的方法。

Strain rate-dependent high temperature compressive deformation characteristics of ultrafine-grained pure aluminum produced by ECAP

To explore the effect of strain rate ε on the high temperature deformation characteristics of ultrafine-grained materials, the deformation and damage features as well as microstructures of ECAP-treated pure Al at different temperatures T and strain ratesε were systematically studied through compression tests and microscopic observations. The increase in ε eliminates strain softening at T≤473 K, and largely enhances the yield strength and flow stress at 473?573 K. The shear deformation dominates the plastic deformation of ECAP-treated Al. Many cracks along shear bands (SBs) are formed at T≥473 K and secondary SBs basically disappear at 1×10?3 s?1; however, at 1×10?2 s?1, cracks are only observed at temperature below 473 K, and secondary SBs become clearer at T≥473 K. The microstructures of ECAP-treated Al mainly consist of sub-grains (SGs). The increase in ε inhibits the SG growth, thus leading to the increases both in yield strength and flow stress at high temperatures.

利用拟合曲线法识别异常变损数据研究

变压器损耗在网损中占的比重很大,根据2021年负荷代表日理论计算结果显示,国网郴州供电公司35k V及以上变压器日损耗电量约占总体网损的48.8%,可见研究变压器损耗对指导电网经济运行具有指导意义。当变压器空载运行时,变损率(即变压器损耗率)为100%;随着负载率的增加,变损率逐渐降低,当负载率为65%左右时,变压器达到经济运行点,其变损率最小。

DAMAGE DETECTION FOR COMPOSITE STRUCTURE UNDER TEMPERATURE CHANGES USING LAMB WAVES

A two-step method is proposed for detection and identification of invisible impact damage in composite structure under temperature changes using Lamb waves.First,a statistical outlier analysis is employed to distinguish whether the changes of Lamb wave signals are induced by damage within a monitoring area or are only affected by temperature changes.Damage indices are defined after the Lamb wave signals are processed by Fourier transform,and a Monte Carlo procedure is used to obtain the damage threshold value for the damage indices at the undamaged state.If the damage indices in the operation state exceed the threshold value,the presence of damage is determined.Then,a probabilistic damage imaging algorithm displaying probabilities of the presence of damage within the monitoring area is adopted to fuse information collected from multiple actuator-sensor paths to identify the location of damage.Damage indices under damaged state are used to generate the diagnostic image.Experimental study on a stiffened composite panel with random temperature changes is performed to demonstrate the effectiveness of the proposed method.

Mechanical and energy dissipation characteristics of granite under cyclic impact loading

This study investigated the effect of repeated blasting on the stability of surrounding rock during the construction of a tunnel or city underground engineering.The split Hopkinson pressure bar(SHPB)was used to carry out cyclic impact tests on granite samples,each having a circular hole,under different axial pressures,and the cumulative specific energy was proposed to characterize the damage characteristics of the rock during the cyclic impact.The mechanical properties and the energy absorbed by the granite samples under cyclic impact loads were analyzed.The results showed that under different axial pressures,the reflected waveform from the samples was characterized by“double-peak”phenomenon,which gradually changed to“single-peak”wi th the increase in damage value.The dynamic peak stress of the sample first increased and then decreased with an increase in impact times.The damage value criterion established based on the energy dissipation could well characterize the relationship between the damage and the number of impacts,which showed a slow increase,steady increase,and high-speed increase,and the damage value depended mainly on the last impact.Under the action of different axial pressures,all the failure modes of the samples were axial splitting failures.As the strain rate increased,with an increase in the dimension of the block,the sizes of the rock fragments decreased,and the fragmentation became more severe.

Acoustic emission characteristics and stress release rate of coal samples in different dynamic destruction time

Considering the importance of the prediction of rock burst disasters, and in order to grasp the law of acoustic emission(AE) of coal samples in different dynamic destruction time, the SH-II AE monitoring system was adopted to monitor the failure process of coal samples. The study of the change rule of the AE numbers, energy, ‘b' value and spectrum in the micro crack propagation process of the coal samples shows that as dynamic damage time went by, AE presented high-energy counts and the accumulated counts increased during the compression phase. The AE energy and cumulative counts increased during the elastic stage. The AE blank area increased gradually and the blank lines were more and more obvious in the molding stage. The AE counts and energy showed a trend of decrease in the residual damage phase.AE ‘b' values gradually became sparse, and the large scale cracks percentage compared with micro cracks decreased and the degree of damage decreased. The AE frequency spectrum peak went from the residual damage phase to the molding phase, and finally it was nearly stable, besides the bandwidth of the main frequency is gradually narrowed. Also, the frequency peak changed from single peak frequency to bi-peak frequency and to the single peak frequency. Uniaxial compressive strength is more sensitive than the elastic modulus to dynamic damage time.

THE USE OF A SHUTTLE PLASMID TO STUDY NONTARGETED MUTAGENESIS AND ITS SEQUENCE SPECIFICITY

Intact pZ189 DNA was replicated in monkey kidney vero cells which had been pretreated with Nmethyl-N’-nitro-N-nitrosoguanidine (MNNG) . The mutants were selected in E. coli MBM7070 and the mutation frequencies involving mutants with unchanged electrophoretic mobilrty of their plasmid DNA were scored. When compared to the spontaneous mutation frequency. the mutation frequencies were increased by 5.8 and 2.9-fold in cells pretreated with 0. 2 and 2μmol/L MNNG, respectively. The supF genes of these mutants were sequenced. and it was found that the types of base substitution and the sites of frameshifts differed from findings in studies of spontaneous and targeted mutagenesis. The results suggest that nontargeted mutagenesis occurs in mammalian cells and may have a sequence specificity.

OPTIMIZATION OF WDM OPTICAL PACKET SWITCHES WITH SPARSE WAVELENGTH CONVERTERS AND NON-DEGENERATE FIBER DELAY-LINES

This paper investigates the untraditional approach of contention resolution in Wavelength Division Multiplexing (WDM) Optical Packet Switching (OPS). The most striking characteristics of the developed switch architecture are: (1) Contention resolution is achieved by a combined sharing of Fiber Delay-Lines (FDLs) and Tunable Optical Wavelength Converters (TOWCs); (2) FDLs are arranged in non-degenerate form, i.e., non-uniform distribution of the delay lines; (3) TOWCs just can perform wavelength conversion in partial continuous wavelength channels, i.e., sparse wavelength conversion. The concrete configurations of FDLs and TOWCs are described and analyzed under non-bursty and bursty traffic scenarios. Simulation results demonstrate that for a prefixed packet loss probability constraint, e.g., 10-6, the developed architecture provides a different point of view in OPS design. That is, combined sharing of FDLs and TOWCs can, effectively, obtain a good tradeoff between the switch size and the cost, and TOWCs which are achieved in sparse form can also decrease the implementing complexity.

Three-Step Damage Identification Method Based on Dynamic Characteristics

A three-step damage identification method based on dynamic characteristics is proposed to improve the structure reliability and security and avoid serious accident. In the proposed method, the frequency and difference of modal curvature(DMC) are used as damage indexes. Firstly, the detection of the occurrence of damage is addressed by the frequency or the square of frequency change. Then the damage location inside the structure is measured by the DMC. Finally, with the stiffness reduction rate as a damage factor, the amount of damage is estimated by the optimization algorithm. The three-step damage identification method has been validated by conducting the simulation on a cantilever beam and the shaking table test on a submerged bridge. The results show that the method proposed in this paper can effectively solve the damage identification problem in theory and engineering practice.

电压互感器容量对主变电能计量影响

文章主要叙述了变电所系统增容后，电压互感器容量未增，导致主变的变损率增大，影响电能计量，为解决这一问题，最初用简单的排除法查找原因，先后排除了变压器自身损耗、电能表的精确度、计量回路的正确性、电流互感器的精度误差，后进行有目的测试，核查电压互感器容量对主变计量的影响，分析原因，寻求降低主变变损率的解决方法。

Trend of mass change in the Antarctic ice sheet recovered from the GRACE temporal gravity field

It is important to quantify mass variations in the Antarctic ice sheet hybrid filtering scheme employing a combination of the decorrelated to study the global sea-level rise and climate change. A filter P3M6 and 300 km Fan filter was used, and the sur- face mass variations over the Antarctic are recovered from GRACE CSR RL04 monthly gravity field models from August 2002 to June 2010. After deduction of leakage errors using the GLDAS hydrological model and postglacial rebound effects using the glacial isostatic adjustment model IJ05, the variations in the ice sheet mass are obtained. The results reveal that the rate of melting of the Antarctic ice sheet is 80.0 Gt/a and increasing and contributes 0.22 mm/a to the global sea-level rise; the mass loss rate is 78.3 Gt/a in the West Antarctic and 1.6 Gt/a in the East Antarctic. The average mass loss rate increases from 39.3 Gt/a for the period 2002-2005 to 104.2 Gt/a for the period 2006-2010, and its corresponding contribution to the global sea-level rise increases from 0.11 to 0.29 mm/a, which indicates accelerated ice mass loss over the Antarctic since 2006. Moreover, the mass accumulation rates for Enderby Land and Wilkes Land along the coast of East Antarctica decrease for the period 2006-2008 but increase evidently after 2009.