Disassembly Inspection Research Articles

Application Study of Acoustic Reflectivity Based on Phased Array Ultrasonics in Evaluating Lubricating Oil Film Thickness

Bearings play a key role in rolling mills, and the uniformity of their lubricant film directly affects the degree of wear of bearings and the safety of equipment. Due to long-term stress, the lubricant film inside the bearing is not uniformly distributed, resulting in uneven wear between the journal and the shaft tile, which increases the potential safety hazards in production. Traditional disassembly inspection methods are complex and time-consuming. Ultrasonic nondestructive testing technology, which has the advantages of nondestructive and adaptable, has become an effective means of assessing the thickness of the oil film in bearings. In this study, an experimental platform for calibrating the lubricant film thickness in bearings was constructed for the first time, and the acoustic characteristics of different thicknesses of the oil film were measured using ultrasonic detection equipment to verify the accuracy of the simulation process. The experimental results show that after discrete Fourier transform processing, the main features of the frequency channels of the reflected acoustic signals of different thicknesses of the oil film are consistent with the finite element simulation results, and the errors of the oil film thicknesses calculated from the reflection coefficients are within 10% of the set thicknesses, and the measurement ranges cover from 5 μm to 250 μm. Therefore, the above method can realize the accurate measurement of the thicknesses of the oil film in bearings.

Research and Analysis on the Optimization of the Preventive Disassembly Inspection Intervals of Important Wedge Gate Valves in the Primary Cooling System of CPR1000 Nuclear Power Plant

At present, the important wedge gate valve of the primary coolant system of the CPR1000 nuclear power plant performs preventive disassembly inspection according to the intervals of 5 years, the average dose of a single disassembly is about 10mSv, the average time of each overhaul occupies the critical path is 1 hour, and the valve has been disassembly inspection in good condition. Based on the historical maintenance data, operating environment, failure mode, failure mechanism, operation and maintenance experience feedback of the same type of valve, and failure risk control of the important wedge gate valve of the primary coolant system, this paper demonstrates and analyzes the feasibility of extending the disassembly inspection intervals of the important wedge gate valve of the primary coolant system from 5 years to 10 years. This work plays an important role in improving the economic efficiency of nuclear power plant maintenance and reducing the radiation dose of maintenance.

Research on the electrical performance variation characteristics of internal damp roof arrester of EMU

In order to study the reason of performance deterioration of roof arrester, this paper conduct the disassembly inspection of the burst arrester, and conducts the SEM test and EDS test to the valve plates, and the microscopic variation characteristics of the valve plates were analyzed and the electrical parameters variation characteristic under different internal damp was studied. Microscopic test results show that the white matter on the valve plate surface is caused by moisture oxidation of the aluminum spray layer. The results of simulation damp test show that the DC reference voltage decreased obviously, it is only 55.2 kV even under mild damp, which is lower than the standard value of 58.0 kV. At the same time, the leakage current rises to 46 μA under 0.75 times of DC reference voltage, and the full current reaches 1.21 mA under 42 kV with AC voltage. The peak value of the fundamental wave of the resistive current reached 1.35 mA.

Application of comprehensive diagnosis technology in fault analysis of 35kV box transformer in wind farm

Using on-line monitoring means to monitor the state quantity of power equipment is the trend of equipment diagnosis and evaluation, but it is usually difficult to accurately judge the hidden dangers of equipment by using a single means. This paper puts forward the transformer comprehensive on-line monitoring technology, which can effectively identify the equipment faults through multi state quantity and long-time comprehensive analysis. The relevant achievements are applied to the fault analysis of 35kV box-type transformer in a wind farm. The qualitative classification of fault category is realized by integrating three state quantities: temperature, oil color spectrum and iron core grounding current; Through disassembly inspection, the effectiveness of the integrated on-line monitoring system is proved; The analysis of fault mechanism is realized by using finite element electromagnetic field calculation. The technology of transformer comprehensive diagnosis in this paper has a very important reference for the defect analysis of transformer equipment.

Analysis and detection of fault for substation GIS insulating part based on integrated automation system data

Insulators are important components in gas-insulated metal-enclosed switchgear (GIS), and their safe operation is of great engineering significance. In an air leakage fault accident caused by the cracking of the insulating part of the grounding knife switch of 500kV HGIS equipment, the following measures were taken to find out the cause of the failure: disassembly inspection, equipment assembly review, insulation performance test and residual stress analysis during casting and curing. It turned out that the failure was caused by a lack of cache firmware in the production process. The thermal conductivity and thermal expansion coefficient of the central copper conductor and epoxy resin are different. When the two are solidly adhered, the incompletely reacted insulating parts shrink too quickly when the temperature difference is too large. The copper conductor locally produces excessive residual stress to the epoxy resin, which causes the insulation to crack. According to the causes of the fault, suggestions are put forward, such as replacing the central copper conductor with aluminum material, adding secondary pre-curing procedure in the production process, and adding Remote longitudinal Wave probe on the Insulated Basin side to monitor residual stress in real time.

A potential fault of circuit breaker found using SF6 decomposition products detection

A 126kV circuit breaker was found to have latent fault by SF6 decomposition product detection method. It was found that the sulfur hexafluoride gas decomposition products of the circuit breaker contained a large amount of CO gas, a certain amount of SO2 and H2S, and a small amount of HF gas. The characteristic components and their contents of the decomposition products were analyzed, it is preliminarily concluded that there is insulation material fault in the circuit breaker, and the potential fault is further confirmed by the disassembly inspection that the MoS2 lithium base grease is overcoated at the metal tie rod joint.

Cause analysis and simulation verification of a 220kV GIS basin insulator along surface discharge

A surface discharge fault of 220kV GIS basin insulator during power transmission has been analyzed. Combined with on-site disassembly inspection, data from previous tests and structural design, the fault point is determined and the fault cause is preliminarily analyzed. In order to verify the correctness of the analysis results, this paper uses the finite element method to mathematically model the accident basin insulator, and formulates the boundary conditions for the calculation of the electric field inside the basin insulator. The simulation results show that there is a distorted electric field on the surface of the basin insulator, which is the main reason for creeping discharge. The preventive measures are summarized for the creeping discharge fault of the basin-type insulator to avoid the occurrence of similar accidents.

Analysis of Total Hydrocarbon Exceeding Standard in Oil Chromatogram of a 500kV Main Transformer

Oil chromatographic analysis is widely used in transformer fault diagnosis However, the problem of excessive total hydrocarbons in the oil chromatogram caused by the failure of the transformer submersible pump is different from the failure of the transformer body. Technicians need to be able to accurately identify these two types of failure. For this problem, this article proposes a method of judging by manually starting and stopping the submersible pump and monitoring the change law of the transformer chromatographic data. This article first finds out suspicious submersible pumps through current data. Subsequently, the operator starts and stops the submersible pump and monitors the change law of the transformer chromatographic data. From this, the correlation between the start or stop of the submersible pump and the chromatographic data was found. Finally, the effectiveness of this method is verified by the submersible pump disassembly inspection and simulated live test.

Research on operation and fault diagnosis technology for EHV/UHV SF6 circuit breakers pre-insertion resistors

Pre-insertion resistors (PIR) are critical components for suppressing the closing inrush current and operating overvoltage during the closing process of the circuit breaker. And it is widely adopted in 800kV and above transmission lines and alternating current filters of converter substations. These special application environments lead to higher failure rates than other electrical components. However, in the daily operation and fault diagnosis of PIR, there is no systematic method to analyze whether there are defects in PIR and the cause of failure after the PIR fails. Based on two PIR failure in series and parallel structures, this paper proposes methods such as dynamic resistance fitting, acoustic and vibration signal detection, insulation performance test, and heat capacity test during operation. In the aspect of fault diagnosis, methods such as PIR splicing based on Iterative Closest Point , stress analysis, and electric field simulation are proposed. Finally, proposed methods can be adjusted to estimate the operating state of PIR through the disassembly inspection to avoid the GIS breakdown accident during the operation of the circuit breaker.

Investigation of tail pipe breakdown incident for 110 kV cable termination and proposal of fault prevention

For cable termination, which is regarded as a key segment of power grid connecting cable lines with other electrical equipments, its insulation parts withstand much higher electric field strength than the average electric field strength of overall cable line. The excessive local electric field strength may result in the appearance of cable termination breakdown fault which can cause serious harm to the power supply reliability of whole transmission line. Historical statistics show that the breakdown location of cable termination is not confined to the vicinity of stress cone. However, the existing researches have not attached enough importance to the breakdown faults at the tail pipe of cable termination. Thus, it is of considerable significance to study the mechanism of breakdown fault at the tail pipe of cable termination. In this paper, a breakdown fault case of cable termination tail pipe on a 110 kV transmission line is investigated. Firstly, the disassembly inspection is applied to cable terminations of this fault line, and the possible breakdown reasons are preliminarily inferred. Then, a three-dimensional electric field simulation model of intact cable termination is established, and the mechanism of creeping discharge and air discharge inside the tail pipe occurred at the initial stage of breakdown fault is explained by this model. Subsequently, by setting defects on cable insulation surface in the simulation model of intact cable termination and varying the size of defects, the process of cable insulation damage inside the tail pipe formed in the initial stage developing into a penetrating cable insulation damage is simulated. Finally, the mechanism of breakdown fault case of cable termination tail pipe is concluded, and some improvement measures for the installation of cable terminations are proposed to reduce the incidence probability of such breakdown fault at the tail pipe of cable termination. The method for analyzing the breakdown fault case of cable termination tail pipe presented in this paper, which combines the disassembly inspection and simulation analysis, can provide reference and suggestions for the investigation and solution in similar cases.

Analysis and Disposal of Typical Breakdown Failure for Resin Impregnated Paper Bushing in the Valve Side of HVDC Converter Transformer

This paper presents analysis, diagnosis and disposal with a typical internal breakdown failure of the resin impregnated paper (RIP) valve side bushing in high voltage direct current (HVDC) converter transformer. Based on the analysis of fault current characteristics at the time of the RIP valve side bushing failure, and field test results of insulation parameters, a method of diagnosing typical breakdown failures of valve side bushings is proposed. Through disassembly inspection of the internal overheating and arcing traces on the failure bushing, the root cause of this typical breakdown failure is found, which is upper axial flashover along the RIP condenser/SF6 interface caused by the abnormal contact of two current-carrying conductive tubes. Temperature distribution inside the bushing with an abnormal contact resistance between the copper conductive tube and aluminum conductive tube under different load current is simulated by using the finite element method. An special device is also developed for repairing defective bushing on-site, and 75 bushings with conductive contact defects have been repaired on the premise of not pushing converter transformers away from the valve hall and even without pulling out defective bushings.

An oil monitoring method of wear evaluation for engine hot tests

Abnormal wear of a piston ring-cylinder liner pair may happen after 9 min hot tests of internal combustion engines, while the engine performance parameters were within predetermined threshold ranges. Few differences were observed among oil samples from the engines with or without abnormal wear in the spectrometric and Kittiwake Analex PQ analysis. Therefore, a manual confirmation by disassembling the oil pan was often required. In this work, an oil monitoring method for wear evaluation of the engines was proposed. The oil samples were rapidly analyzed on site by on-line visual ferrograph (OLVF). For the abnormal engines, it was found that the index of particle coverage area (IPCA), characterizing the wear debris concentration, was low. Moreover, large debris was rarely observed on OLVF ferrograms, which was consistent with the results obtained from analytical ferrography, and the reason was analyzed and discussed. In addition, an on-site abnormal wear evaluation procedure for the 9 min hot tests was proposed based on a trained Naive Bayes Classifier. As observed from the results of 27 engines, 4 abnormal engines were found. Among one of them, longitudinal scratches were found on the cylinder wall, which were evaluated as abnormal wear by the classifier. This method can cut down the quantity of disassembly inspection and is more efficient.