基于故障挖掘的电能表失效分析研究

该文研究分析了智能电能表故障原因及其规律,快速准确地判断电表故障位置,对提高智能电能表工作的可靠性具有重要意义。在分析电表现场故障类型的基础上,建立智能电表故障树,梳理电表故障特征规律,通过数据挖掘的关联规则算法,在大量的故障数据中寻找具有特定关系的信息,分析故障原因。应用结果表明,故障树分析法结合数据挖掘算法能有效帮助技术人员快速进行故障定位,减少故障处理时间,具有很好的实用价值。     

基于FTA-FMMEA综合分析法的发动机曲柄连杆机构可靠性研究

为了提高发动机曲柄连杆机构的可靠度,采用FTA-FMMEA综合分析法对其进行分析。通过分析曲柄连杆机构各零件的故障,建立故障树模型,对其进行定性分析找出对系统影响较大的故障模式;对其中的活塞环磨损这一故障模式进行FMMEA分析,得到了其故障原因及故障机理,确定了其故障影响,并根据分析结果提出改进方案。改进前后的RPN值对比结果表明,FTA-FMMEA综合分析方法可以很好的分析系统故障并提高系统可靠性水平。     

浅谈变压器的继电保护

本文所说的变压器的继电保护是指当电力系统的变压器外部发生故障时或者是内部发生故障时,变压器的外部环境不断变化,导致了变压器的各种故障会发生一些故障改变。我们要及时的发现变压器的突发故障,分析变压器的故障原因和变压器的故障性质,及时的作出相应的改变。本文针对变压器设备的继电保护来分析变压器的故障问题。     

高压电力电缆故障探测技术研究

电力电缆故障是电力系统中的常见故障,电缆测距是排除电缆故障的前提条件,准确的电缆故障测距可以缩短发现故障点的时间,有利于快速排除故障,减少由电缆故障带来的损失。本论文通过对电力电缆故障产生的原因及故障点探测方法进行分析,并对电力电缆故障测距的常用方法及新的故障测距技术进行系统分析。     

基于主元分析的多联式空调系统传感器故障检测和诊断

作为多元数据分析方法之一,主元分析(PCA)被广泛运用于诊断制冷空调系统的传感器故障。本文首先结合热平衡原理以及多联机运行的控制逻辑,筛选系统中常用的18个传感器变量建立多联机(VRF)传感器的故障分析(FDD)模型。然后结合主元分析的算法原理,给出以Q统计量和Q贡献率为检验标准的传感器故障检测与诊断流程。接着用实测数据进行验证工作,引入不同类型和程度的传感器故障,分析得到不同故障条件下的故障检测和诊断特性。结果表明,总体上,主元分析应用于多联机传感器故障检测与诊断过程是可靠的。其具体特征表现为：不同类型的传感器在不同故障类型及程度条件下,故障检测效果差异明显;在小偏差故障条件下,基于主元分析的传感器故障检测方法的故障检测效率较低,并且针对个别传感器而言,其整体故障检测效率偏低。鉴于故障诊断是基于故障检测的结果,因此上述故障检测方法在FDD过程中将起到重要的作用。     

空分设备稳定运行的研究与应用

为提高空分设备的运行安全性和稳定性,对空分设备的故障进行了分析、归类。介绍空分设备运行故障的种类,分别阐述仪/电控故障、机械故障、工艺故障的具体情况,分析了故障产生的原因和排除故障的措施。     

一起10kV电容器组事故分析与预防措施

本文针对一起10kV户外电容器组故障进行调查分析,通过现场设备检查、保护动作情况、结合电压波形图与相关试验情况进行故障定性分析故障发展过程,对故障产生的直接和间接原因分析总结,对防止发生类似故障提出了一些建议,以供读者参考。     

一起110kv线路不对称故障相继动作分析

不对称相继速动保护利用故障被对侧保护切除后引起的负荷电流的变化来判定不对称故障区段,从而加速II段保护,快速切除故障线路,可谓独具匠心。众所周知,输电线的故障有单相短路接地故障、两相短路接地和不接地故障及三相短路故障10种。单相短路故障的几率最大,其次是两相接地短路。两者合计即不对称故障约占输电线路故障总数的90％。因此,不对称故障相继速动保护原理在？10kV线路中广泛运用的意义是很显著的,本文通过对一起典型110kv线路不对称故障相继保护动作的分析,处理了事故隐患,指出运行人员在发生事故后要注意的事项,提出保护动作分析应特别关注的一些要点,避免错误分析故障,同时对变电站的故障录波的电源,保护装置的GPS校时的配置提出建议。     

通用模拟示波器故障的分析与诊断

本文将通用模拟示波器电路分成五部分,总结和分析了每一部分电路故障可能引起的几种异常显示,给出了每一部分电路故障诊断方法及在相应电路中出现故障的常见器件,对有些故障与故障现象之间的因果关系做了进一步分析。     

某型号航空发动机轴承故障问题研究

某航空发动机在生产过程中重复出现了轴承故障。为降低轴承的故障率,我们开展了对轴承故障问题的研究。将生产过程中常见轴承故障分为3类:轴承表面划伤、磕伤故障;轴承锈蚀故障;轴承试车后压坑、麻点故障。本文介绍这3类故障的形貌特点,为轴承故障的分析提供一定的思路;分析3类轴承故障产生的原因,针对性制定防护措施,达到降低轴承故障率的目标,减少经济损失,提高外场发动机使用可靠性。     

JT9D—7R4G2型发动机八级压气机盘及叶片失效原因分析

通过对失效的第八级压气机盘和叶片观察和金相分析，探讨了该失效件断裂的原因。结果表明，微动磨损引起疲劳断裂。     

Investigations on fretting fatigue in aircraft engine compressor blade

An investigation of several cracked blade tangs in the military aircraft engine compressor was conducted to identify the root cause of the failure. These cracks were found during the scheduled maintenance with fluorescent penetration inspection. The engine compressor blade made of Ti–6Al–4V is attached to compressor rotor by means of inserting retaining pin through rotor and blade tang. By analyzing the fracture surface of the failed blade tang, it is found that the crack in the blade tang was initiated by fretting fatigue and propagated under low cycle fatigue. Stress analysis of the blade using a non-linear finite element method is coincident with the results of fractography. The clearance between retaining pin and tang hole caused small amplitude of sliding motion leading to fretting wear during engine operation. Consequently, the damaged area due to fretting wear acts as a stress raiser inside tang hole and contributes to accelerate fretting fatigue.     

Improving the fretting performance of aero-engine tenon joint materials using surface strengthening

This paper summarises the regulation mechanism of the traditional and emerging surface strengthening treatments – mechanical shot peening (SP) and laser shock processing (LSP) treatment, respectively – on the fretting fatigue behaviour of the tenon joint materials of aero-engine cold-end parts, as surface strengthening treatment contributes to the improvement of service performance. From the point of view of the actual service environment of turbine components, this paper also expounds on the key problems faced by surface strengthening treatments in improving the mechanical properties of joint materials for aero-engine hot-end components. The application of LSP in the fretting fatigue life extension of turbine joint materials has strong feasibility and development prospects.     

Gas turbine disk-blade attachment crack

Evaluation of a gas turbine disk revealed a crack in the blade attachment area. The subsequent effort to understand the origin of this crack led to a series of analyses that included computing the stresses on the attachment, characterization of fatigue crack growth, and a model for fretting fatigue crack growth. These elements were brought together to simulate the conditions that led to the cracking. It is concluded that the crack was probably caused by fretting fatigue induced by the stresses related to normal takeoff and landing cycles and exacerbated by aircraft maneuvers, and that short periods of blade resonance may have contributed to the cracking. If material had not been removed from the attachment surface of the disk by service-induced wear, it is likely more cracks would have been found.     

Vibration analysis for failure detection in low pressure steam turbine blades in nuclear power plant

This paper presents an investigation of the failure of a low-pressure steam turbine blade in a pressurized water reactor (PWR) nuclear power plant. The dynamical behaviour of the blade is analyzed theoretically and experimentally. A three-dimensional finite element model is used to predict the blade resonances in the operational speed range. Natural frequencies and mode shapes of the blade at static condition are obtained, then natural frequencies of the blade at different rotational speeds are calculated with consideration of centrifugal force and steam flow forces. A Campbell diagram is plotted to predict the likely operational conditions that may cause resonant vibration of the blade. Vibration tests are conducted to determine the vibration characteristic of the blade. It is found that the 2nd natural frequency of the blade is very close to the 9th rotor speed harmonic. The experimental natural frequencies are in good agreement with the finite element predicted values. Fretting wear is observed at the concave root surfaces of the blade trailing edge caused by resonant vibration. The fracture surface of the cracked blade shows typical fatigue patterns. The fretting wear characteristics in the crack initiation regions are observed.Stress distribution of the blade at the 9th harmonic frequency is analyzed using an elastic-plastic finite element model. Fretting fatigue experiments indicate that the fatigue life of the blade is greatly reduced due to fretting wear. The results of the investigation show that the failure of the blade is attributed to a combination of high cycle fatigue (HCF) and fretting wear.     

Failure investigation of blade and disk in first stage compressor

A matched blade tenon and disk mortise of the first stage compressor in an aeroengine fractured simultaneously. Apparently, both had fatigue features on the fracture surfaces. Macro observations showed the cracking sites were roughly at the central region of the matched tenon and mortise. Contact surfaces examination revealed there were important marks, showing abnormal contact of the tenon and mortise in service. Material qualities were inspected and the stresses in the tenon and in the mortise were calculated under normal conditions. These demonstrate that the failures were not due to the insufficiency of failure resistance but the deviation from expected conditions. Conclusively, the bad contact of the tenon and the mortise is responsible for the failures. Field non-destructive inspection was performed on other aeroengines of the same type, and some cracks, which were very similar to those in the fractured tenon and mortise, were found. Further investigation revealed that the design shortcoming resulted in over-compensation of centrifugal bend moment and bad contact condition.     

Threshold fatigue measurements and fractographic examination of fretting induced cracks in Ti-17

Fretting damage is a common problem for titanium alloys used in turbomachinery equipment, particularly in the blade and disc contact regions. Under careful laboratory controlled conditions at Purdue University, the fretting process was recreated in specimens known as contact pads. Fretting in the contact pads is recognized for its highly localized damage, which results in the formation of cracks, minor propagation, and then crack arrest. This project studied the threshold behavior of fretting induced cracks in the titanium alloy Ti-17 with and without shot-peening surface enhancements. The approach utilized a unique C-specimen (created from the contact pads) for fatigue threshold experiments in addition to fractography to compare bare (untreated Ti-17) to shot peened Ti-17 contact pads with fretting induced damage. The results show that shot-peening does not mitigate fretting crack nucleation but does cause them to nucleate at steeper angles and arrest at depths less than the untreated specimens. Fracture surfaces are also presented to show the nature and physical characteristics of fretting damage in Ti-17.     

THE APPLICATION OF FRACTURE MECHANICS TO FRETTING FATIGUE

Abstract— A fracture mechanics model of fretting fatigue has been developed. This enables the calculation of the critical size of defect which can grow under fretting conditions. The model has been applied to the fretting of aluminium alloy 2014A fatigue specimens in contact with 3.5NiCrMoV steel fretting contact pads. The input parameters to the model include externally applied stresses, contact pressure between pad and specimen and frictional forces between the two contacting surfaces. The latter have been measured using a strain gauge technique. Small fretting defects in the fatigue specimens have been investigated metallographically and fractographically. There is good agreement between their size and critical defect sizes calculated using the fretting model.     

TC8合金转子叶片锻造工艺研究

为研制一项TC8合金转子叶片,并达到提高锻造生产效率、降低生产成本的目的,进行了锻造工艺性试验、工艺参数试验,研究了TC8合金锻造工艺适应性以及加热温度、变形程度对低倍组织、显微组织及力学性能的影响.结果表明,TC8合金十分适合锻造工艺,采用较低的锻造加热温度能够获得初生α相含量更高的等轴组织,变形程度在40%以内所获得的组织均匀性较好.在此基础上,依据TC8合金转子叶片单榫头、小尺寸的结构特点,采用了高效的挤压制坯+终锻成形工艺,通过叶片锻造成形试验,试制出了具有均匀且状态理想的金相组织、良好表面质量的TC8合金转子叶片锻件,表明了所制定的叶片成形工艺及工艺参数合理可行.     

Failure analysis of Ti6Al4V gas turbine compressor blades

The failure mechanism of Ti6Al4V compressor blades of an industrial gas turbine was analysed by means of both experimental characterisations and numerical simulation techniques. Several premature failures were occurred in the high pressure section of the compressor due to the fracture of the blade roots. Metallurgical and mechanical properties of the blade alloy were evaluated. A 2D finite element model of the blade root was constructed and used to provide accurate estimates of stress field in the dovetail blade root and to determine the crack initiation in the dovetail.

The results showed no metallurgical and mechanical deviations for the blade materials from standards. SEM fractography showed different aspects of fretting fatigue including multiple crack initiation sites, fatigue beach marks, debris particles, and a high surface roughness in the edge of contact (EOC). The numerical model clearly showed the region of highest stress concentration at the front EOC of the blade root in the dovetail region, correlated closely with the experimentally characterised fatigue crack region. It was concluded that this failure has occurred due to the tight contact between the blade root and the disk in the dovetail region as well as low wear resistance of the blade root.