Showing papers in "High Voltage Engineering in 2015"

Research Status and Prospect of Gas-insulated Metal Enclosed Transmission Line

Abstract: Gas insulated metal enclosed transmission line(GIL) is widely applied in high-power, long-distance transmission system thanks to its larger capacitance, lower transmission losses, and greater safety and environmental friendliness in comparison with traditional overhead transmission lines and cables. We reviewed GIL development's history, introduced its features, typical application situations and development status in and outside China, summarized key GIL technologies, and analyzed its development prospect from both manufacture and application perspectives. It is revealed that, with four decades of development, AC GILs have achieved comparatively mature manufacturing techniques, better structure design, more diversified installment, and greater reliability in real operation, whereas DC GILs have lagged relatively behind due to inadequate knowledge on the effect of surface charge accumulation on insulation performance as well as higher manufacturing costs. With the overall development of power industry and advancement of science and technology, future GIL studies are expected to make influencing breakthroughs in key technologies covering insulation surface charge, insulation optimization, alternative gas, as well as low-cost manufacturing. Wider application of GIL apparatus should provide necessary technical backstopping in safeguarding the operation of a clean, safe, self-recovery, economic and interactive smart grid in China.

Review on Discharge Mechanism and Breakdown Characteristics of Transmission Line Gap Under Forest Fire Condition

Abstract: The high temperature, high electrical conductivity and ashes of forest fire flames can greatly reduce the insulation strength of high voltage overhead transmission line gaps, and can cause transmission line trip out, and the probability of successful re-closing is very low, this may lead to the serious accidents of transmission line out of operation. In recent years, frequent occurrences of forest fire bring great challenge to the safe and steady operation of the power grid. The discharge mechanism and breakdown characteristics of transmission line gap under forest fire condition are reviewed in this paper. The study status of the transmission line forest fire simulation test platforms, experimental methods, discharge mechanism and breakdown characteristics of AC and DC transmission line gap under forest fire conditions in China and abroad are analyzed. The analysis indicates that some test platforms only consider single influencing factor; the differences and disparity are large for the differences of the simulation tests' dimension, vegetation forms, and experimental methods; the influencing mechanism studies of flame combustion characteristics and products to the gaps' discharge also consider single influencing factor. There is a limitation for the guidance of transmission line trip-out prevention under fire conditions. The systematically study of breakdown characteristics of AC and DC transmission line gaps under forest fire conditions with different dimensions and electrodes, and the single and multi-factor influencing mechanism to the gap discharge study with electric field, flame temperature, conductivity, ashes and particles is suggested.

Review of Research Advances and Fronts on International Lightning and Protection

Abstract: After analyzing the achievements in 32 nd International Conference on Lightning Protection(ICLP 2014) and recent international publications, we summarized and reviewed the advances and fronts of researches of lightning and its protection. These researches cover various areas such as lightning physics and phenomena, lightning location and observation, lightning activities and characteristics, lightning electromagnetic impulses(LEMP) and induced effects, and lightning protection of various systems(power systems, transportation, renewable energy systems, electronic devices, etc.). Main conclusions are drawn as follows:(1) With rapid development and wide application of observation techniques, a rich supply of data of lightning activities and characteristics is obtained, which further reveals the high energy processes involved in lightning. Upward flashes have drawn increasing attention. Upward leaders significantly affect the lightning stroke failures of high voltage transmission lines.(2) The mechanisms of several basic lightning processes are still poorly understood. Researches on lightning protection in new areas such as wind turbine systems are still in an early stage.(3) Improvement in detection techniques of sensitivity, accuracy, spatial and temporal resolution is required to obtain detailed lightning parameters. Theories and models of lightning initiation, stepped propagation and attachment(especially the upward leaders) need to be further developed. Lightning protection of renewable energy systems and smart grid will draw more and more attentions.

Safety Inspection and Intelligent Diagnosis of Transmission Line Based on Unmanned Helicopter of Multi Sensor Data Acquisition

Abstract: To meet the demand of effective, automated power-line emergence management and maintenance inspection, we developed a multi-sensor power-line inspection system of unmanned helicopter. Firstly, through precise time synchronization and calibration, the system unifies the time and space criteria of its sensor, including ultraviolet sensors, infrared sensors, visible-light sensors, and laser sensors. Then, the multiple on-board sensors collect images of transmission lines simultaneously including precision 3-D laser point clouds, high-resolution aerial images, infrared video images, and ultraviolet video images. These fused multi-source data are put through intelligent diagnosis reciprocally and independently to accomplish the detection of defect and hazard on power lines, as well as the detections of safe distance and abnormal heat. Finally, diagnosis reports are given for on-the-spot investigation. We conducted inspection tests of actual lines to verify the proposed unmanned helicopter inspection system's functions. It is obtained that the system achieves the same diagnosis results as that made by skilled power-line inspection technicians. The system is able to find multiple kinds of defects and safety risks of transmission lines and accordingly provide decision basis for operation companies. It also offers visualization models and scene information of defects or hazard positions, which is useful for artificial auxiliary diagnosis and improving the efficiency and reliability of fault detections.

Comprehensive Fault Line Selection Method for Resonant Grounded System Combining Wavelet Packet Transform with Fifth Harmonic Method

Abstract: In order to improve the reliability and accuracy of fault line selection for single-phase earth fault in resonant grounded system, we put forward a comprehensive fault line selection method, which takes the transient information of ground fault into consideration. Taking into account the polar and modulus values of wavelet packet decomposition coefficients of zero-sequence current of fault line and health lines, we defined and calculated the fault characteristic value of each line firstly, and got the selection results directly by comparing these values if each line has the same characteristic frequency band. When such bands were different, it could select the fault line adaptively by combining fifth harmonic method with wavelet analysis. Moreover, we set 20 kinds of single-phase earth fault randomly and then selected the fault line with proposed method. Surprisingly, the selection accuracy rate has reached 100%. The results show that the proposed method has a high accuracy and reliability and is not affected by fault location, transitional resistor, and initial fault angle. Furthermore, it has a higher efficiency in selecting fault line when the network has many hybrid feeders.

Improved Thermal Circuit Model of Hot Spot Temperature in Oil-immersed Transformers Based on Heat Distribution of Winding

Abstract: To calculate the hot spot temperature(HST) of transformer windings more precisely and to provide reference for the over-load capacity and insulation life of power transformer, we proposed an improved dynamic equivalent calculation model based on the traditional bottom oil temperature(BOT) thermal circuit model, by which the heat distribution of winding and heat conduction are analyzed. In the proposed model, the equivalent heat source of hot spot is clearly defined according to the axial temperature distribution of winding and the dynamic temperature properties of oil viscosity and loss are considered. We set up the temperature rise experiment platform of power transformer and applied the optical fiber temperature measurement system to obtain the HTS of transformer winding. Then, we compared the calculated results of the improved HST model with results of other calculation methods and measured temperature curve of power transformer. It is concluded that the winding temperature rise curve from the improved HST model is more effective, and error coefficient of this model is smaller than that of other methods, and is of higher prediction precision. The error coefficient is reduce least 40%.

Cable Section and Laying of Xiamen ±320 kV Flexible DC Cable Transmission Project

Abstract: Xiamen ±320 k V Flexible DC Transmission Project is designed to work at the highest voltage among similar power transmission lines presently and it faces a lot of challenges. We discussed the selection of crosslink cable and cable accessory, cable operating temperature, length of cable segments, and cables' current-carrying capacity, as well as laying AC and DC cables in common tunnels. As a result, reasonable solutions for technology difficulties in the project are presented: setting the operating temperature of 70 ℃ for DC cables ensures good performance of the cables' insulation; cable conductors with sectional area of 1 800 mm2 have current carrying capacity of 1 617 A, satisfying the requirements of engineering; 962 m is a reasonable length of segment cables that reduces the number of joints as well as the project cost; the cable accessories should be injection in-site type; for the project under either transient state or steady state, common-cable-tunnel laying of AC and DC power cables satisfies the requirements of both security and stability.

Research on Contamination Deposition Characteristics of Post Insulator Based on Computational Fluid Dynamics

Abstract: In order to study the factors influencing insulators' contamination deposition, we gathered the dimensions of some post insulators and set up numerical models for wind tunnel simulation On the basis of the theory of computational fluid dynamics, we discussed four factors that affect the trapped mass of insulators It is concluded that the concentration of particles has a linear function on the taped mass of the insulator surface Higher wind velocity will lead to more trapped mass on both the top surfaces and the bottom surfaces of insulators, though different profiles of the top and bottom surfaces can result in distinct tends Meanwhile, growth in the mean diameter of particles will increase the trapped mass of the top surfaces but barely affects the bottom surface Moreover, for any certain shape of insulator, increasing the diameter of insulator rod significantly will reduce the density of contamination deposition Further comparison indicates a considerable difference between the simulation results and some reported experimental data from wind tunnel tests, which is probably due to the insufficient consideration of the adhesion effect in the simulations

Design of DC Cable Accessories for Suppressing Interface Space Charge

Abstract: Space charge accumulation at the interface of cable accessory insulation causes distortion of partial electric field, and it has become one of the main factors restraining the development of DC cable accessory. To this end, we presented a novel concept for DC cable accessory design, i.e. molding crosslink polyethylene material, which has similar properties to cable insulation, on cable insulation layer to form stress-relief cone and enhanced accessory insulation. Cable insulation and the enhanced insulation of accessory fuse well at the interface between them; this eliminates the interface to an extent and hence suppresses the accumulation of space charge fundamentally. Following this concept, interface-free accessories for ±200 k V DC power cables were developed and passed the type test recommended by CIGRE TB 496, which verified the proposed design concept.

Pattern Recognition for Partial Discharge Based on Multi-feature Fusion Technology

Abstract: The independent identification by analysis pattern of single feature cannot effectively and reliably determine the partial discharge(PD) type,leading to the problem of recognition "diagnosis" In order to maximize use of rich information of insulation condition which is acquired by the UHF method, combining the differences of the time resolved partial discharge(TRPD), the phase resolved partial discharge(PRPD) and the relationship between UHF signal energy and charge quantity, we proposed a pattern recognition method which is based on multi-features fusion technology The PD testing information accessed from the PD experiment which was carried out on a real three-phase 110 k V GIS(ZF-10-126) was adopted to analyze the experimental results The results show that the difference and uncertainty for four defects which are designed in this paper exist in the recognition of single feature While after using the similarity and complement of three features, the recognition has a higher recognition rate and certainty by the D-S evidence theory Moreover, the advantages and effectiveness of the proposed method are verified by the experimental results

Relationship Between Transient Enclosure Voltage and Very Fast Transient Overvoltage Generated During Disconnector Operations in Gas Insulated Switchgear

Abstract: Disconnector operations in gas insulated switchgear(GIS) may induce very fast transient overvoltage(VFTO) and transient enclosure voltage(TEV). To obtain the relationship between TEV and VFTO from the viewpoint of experiment, we analyzed the theory of TEV generation and propagation. TEV and VFTO waveforms during disconnector operations were obtained by self-developed measurement systems at Wuhan ultra-high voltage AC test base. The transient waveform-time analyses show that the subtle differences [-90 μs, 20 μs] between the breakdown time and its corresponding pulse time indicate a good relationship between TEV and VFTO. Meanwhile, analyses of breakdown time and amplitude ratio by Spearman correlation coefficient show that TEV pulse voltage is directly proportional to the corresponding VFTO breakdown voltage between contacts. Then, TEV magnitudes at different measurement points in the test circuit are analyzed through the introducing ratio coefficient, so as to validate the transmission line theory from the experimental view. Furthermore, we provided a method to obtain the largest TEV magnitude through a small amount of on-site measurements, by which the maximum TEV value of 51.37 k V in the test circuit was estimated. Moreover, this method would be helpful to TEV theoretical analysis and simulation.

Analysis on the Problems of Three-phase Short-circuit Current Over-limited of 500 kV Bus When UHV Connected to Hunan Power Grid

Abstract: After Chang-sha UHV project being put into operation, the three-phase short-circuit current of 500 k V bus at Chang-sha UHV substation may exceed the maximum rated breaking current of the 500 k V circuit breaker in the later 13 th Five Year, which brings security and stability risks to Hunan grid. Aiming at three-phase short-circuit current over-limit of 500 k V bus at Chang-sha UHV substation, based on self-impedance analysis model of two-port network theory, the over-limited mechanism is disclosed with the analysis software of electric power system PSD.Thereby, some schemes of current-limiting measures are proposed. Considering the factors such as economic cost, the techno-economy of limiting short-circuit schemes are respectively analyzed and compared. The analysis shows that while taking the economic cost into account, the scheme with the most remarkable short-circuit current limitation effect or the least influence on power network operation is not always the best. The obtained results are available for references in the study of short-circuit current control in other power grids.

Mitigation of Transformer DC Bias in Complicated Operation Conditions

Abstract: To suppress the transformer DC bias in complicated operation conditions, we proposed a DC current distribution calculation model of transformer winding and a magnetomotive force risk assessment model with suppression method considered. A practical example was taken to compare the effect of each suppression method. The results show that the equivalent DC magnetomotive force of windings is a main factor of transformer DC bias risk. In complicated operation conditions, inappropriate use of suppression method will intensify transformer DC magnetic bias. The current injection method can make reverse direct current to flow through series and public winding of autotransformer so as to counteract equivalent magnetomotive force, which can effectively restrain the DC bias of 500 k V transformer in complicated operation conditions.

Distance Correction of Corona Discharge Photon Count in Ultraviolet Imaging Detection

Abstract: To reasonably compare the discharge photon count measured at different observation distances using solar-blind ultraviolet(UV) imagers, it is necessary to normalize the results with a common distance. Hence, we selected three discharge models as the objects, and used Coro CAM504 UV imager to measure discharges with different intensities at different distances in laboratory. Moreover, we analyzed the variation of photon count regarding to different observation distances, fitted the results with power functions and exponential functions, and proposed an empirical formula for the distance correction of photon count. The results show that because of the external interference and the UV imager's count error, when the discharge is too weak or the observation distance is far, the photon count no longer reduces but tends to increase with increasing distance. When the photon count is more than 10 and more than d/2, where d is the observation distance, it can be taken as an effective value. Within the range of observation distances 4~50 m, the relation between effective photon count and observation distance approximately meets power functions, the power exponent of which is about 1.222 for all the three tested discharge models. Further tests show that the proposed empirical formula is accurate enough to satisfy the needs of field engineering detection.

Transformer Failure Prediction Based on Cloud Reasoning and Weighted Implicit Semi-Markov Model

Abstract: In order to analyze the state variation of power transformer and predict transformer's operation failure, on the basis of the existing studies, we proposed a transformer fault prediction method based on cloud-based reasoning and a weighted semi-Markov degradation model. Firstly, through the cloud model, sample data of dissolved gas in transformer were transformed into multiple qualitative cloud concepts, which could be used to build the state space of dissolved gas. Then, according to the operation principle of transformer, we introduced an aging factor and historical operating status information into the Markov chain through multi-step weighting, and constructed a weighted hidden semi-Markov aging model to predict transformer states. If a transformer has dissolved gas on an abnormal level, it will be diagnosed by the rules-based generator based on cloud reasoning. Multiple case studies indicate that the proposed model is able to predict the operation state of transformer accurately, while keeping better robustness and higher accuracy under non-interval or fluctuant observation data interval fluctuations comparing with other commonly used prediction methods. Hence, the fault diagnosis method combining with cloud-based fault reasoning mechanism machine realizes the accurate status prediction and fault diagnose of transformer.

Substation Infrared Image Fuzzy Enhancement Algorithms Based on Improved Adaptive Genetic Theory

Abstract: In order to enhance the visual effect of infrared image of electric power equipment in substation, to highlight the thermal anomaly area, and to help engineers analyze the faults, a fuzzy enhancement technology infrared image based on the adaptive genetic algorithm was proposed. After the wavelet transform of the infrared image, homomorphic filtering enhancement and fuzzy enhancement were processed, and the dynamic adaptive genetic algorithm was used to optimize the parameters of fuzzy method, finally, the images were reconstructed. Experimental results show that the effect of proposed method is better than enhancement homomorphic filtering, fuzzy enhancement, and fuzzy genetic algorithm, and the image contrast, resolution, and clarity can be improved by at least 12.6%, 27.7%, and 33.7% respectively. It is favorable for the maintenance of electric power equipment, especially in thermal anomaly location and fault diagnosis.

Influences of Various Coupled Patterns and Coupling Strength on Power-communication Coupled Networks

Abstract: To look for methods for improving the robustness of power-communication coupled networks and guiding the construction of the smart grid, we proposed a cascading model for the power-communication networks with failure probability based on DC power flow optimization model and the scheduling function of communication network. We conducted edge attacks to study the effects of coupled patterns and coupling strength on the robustness of power-communication coupled networks, and analyzed the effects of failure probability p0 of nodes between the two networks. Simulation results show that the inner inter-similarity coupled links can significantly improve the robustness of power-communication coupled networks, and reduce the failure scales, especially the betweenness-degree(B-D) coupled pattern. Meanwhile, there is no effect of p0 on the cascading propagation of small-scale power-communication networks with scale-free property. Furthermore, results also show that a similar phenomenon can be found that the average load loss of different coupling strength has a downward trend after rising first with the increasing failure ratio of communication edge. High coupling strength can effectively reduce the scales of failures when the failure ratio of communication edges is small.

Online Detecting Winding Deformation of Power Transformer Based on Transient Overvoltage

Abstract: In order to realize online detection of transformer winding deformation and to excavate latent faults inside transformer, combining with the theory of frequency response analysis, we proposed a new online method to detect winding deformation based on the characteristics of transient overvoltage. We developed a voltage sensor, which is used to measure overvoltage when the transformer is in service, based on the principle of coupling capacitor and finite element method(FEM) simulation technique, and then conducted corresponding performance tests. Meanwhile, the simulated fault winding tests with different fault types, fault degrees, and fault positions are conducted. The test results show that both the developed 110 k V and 10 k V voltage sensors are capable of detecting overvoltage when the transformer is in service, with the voltage divider ratios of 109 723 and 10 231, respectively, and the response time less than 50 ns. Moreover, the frequency response curves show diversities in different faults type tests, and show regularities in different faults degree and faults location winding tests. The peaks and troughs of frequency response curves could reflect the information of winding faults, which indicates that the proposed online detection method has potential to be practically implemented.

Research on the Calibration Method of Radio Interference Measurement Result at the Low-voltage Side of Corona Cage

Abstract: Corona cage is an important measurement tool which is well used in the research of the electromagnetic environment of transmission lines. Since there is a need for calibration when the measurement results are used to calculate the excitation function, we proposed two calibration methods, and studied the calibration method of the measurement result. The first one is an experiment method which uses the high frequency source as a current source. The second method is a calculating method which is based on the theoretical analysis. A distributed parameter equivalent circuit is established to calculate the calibration factor. Bundled conductors of 6×LGJ-720/50 are used in the comparison of the experiment method and calculation method. The experimental result of calibration factor is 0.03 and the calculation result is 0.033, showing that the error of these two methods is only 10%. The comparison result indicates that the methods proposed in this paper are feasible. Finally, the impact of the conductor parameters on the calibration factor is analyzed. The result indicates that the calibration factor errors of different conductors used in HVDC transmission lines are no more than 7%.

Impact on HVDC Systems by the Sending AC System with Large-scale Wind Farms

Abstract: With the development of large-scale energy bases and 800 k V UHVDC system putting into operation in northwest of China, the Northwest Power Grid has formed as such kind of a main grid structure in which both HVDC transmission and HVAC transmission run at the same time. The interaction between AC system and DC system has become one of the most concerned issues in Xinjiang grid. Three kinds of network topology with AC and DC systems were built and used to study the delivery properties of the power generated by large-scale DFIG wind farms and send from Xinjiang grid to the east parts of China. The simulation models were built using PSCAD/EMTDC software. Three conditions: the wind speed variation of the wind farm, the short circui fault of the wind farm and the AC bus of the converter station were simulated and analyzed. The simulation data and curves were obtained. From the simulation results, the concolutions are: when the types of the wind speed are different, the required amounts of thermal power capacity aredifferent; the degrees impact on the different topology of DC-systems caused by the wind farm fault are different; but the degrees are similar caused by the fault on AC bus of converter station.

Technical Research of Accurate Digital Integrators for Rogowski Coil Current Transformer

Abstract: Analog integrators can be easily influenced by temperature and some other environmental factors, meanwhile, accuracy of commonly used digital integration algorithms is not high enough, and is affected by the DC component of input signals. Hence, we have proposed an improved Al-Alaoui digital integration algorithm based on DC negative feedback, which is hardly affected by temperature changes, so it resolves the problems of zero drift and temperature drift for analog integrators. Moreover, since the algorithm adopts PID feedback controller and attenuation coefficient to improve the DC response of digital integrators, it can prevent the influence from DC component in input signals. Compared with conventional integrators, a digital integrator with the improved algorithm can obtain frequency responses closer to those of ideal integrator. Further simulation and tests show that improved digital integrator has high accuracy up to 0.05 class in the range of 5%~120% of rated current.

Influence Analysis of Inductance Effect and Spark Effect on Lightning Impulse Characteristics of Grounding Conductors and Its Ambient Soil

Abstract: In order to study the influences of inductance effect and spark effect on the impulse characteristics of grounding bodies, and to distinguish the ranges dominated by these two effects, we established an electrical network model and its corresponding iterated algorithm of grounding bodies by taking spark discharge into consideration The model and algorithm were verified in the aspects of validity and accuracy by calculations using the full-scale test data in the case of high impulse current Moreover, we used the model and algorithm to calculate the impulse characteristics of horizontal grounding bodies with different lengths influenced by impulse currents with different waveforms The results indicate that, with increasing soil resistivity, the dominant factor determining grounding impulse characteristics turns from inductance effect into spark effect gradually The obtained critical value of the normalized parameter of 450 k A·?, can be taken as the threshold to discriminate the conditions with dominate inductance effect from the conditions with dominant spark effect The results above can be used for selecting the lengths of extended grounding bodies and horizontal ray conductors

Effect of Space Charge on Electric Field Distribution at the Insulating Interface Between DC Cable and Accessory

Abstract: The interface between cable and accessory(a terminal or a joint) is always the weakest point of cable due to the space charge accumulation driven by direct current(DC) voltage combined with influences of temperature Therefore, we measured the space charge characteristics of silicone rubber(SR)/cross-linked polyethylene(XLPE) double-layer dielectrics under working DC electrical stress based on temperature effect in the running DC cable system Moreover, we established a model of accessory fitted on cable according to the measured results and the relation between resistivity and temperature, and discussed the effect of space charge on field distribution at the insulating interface between DC and accessory under temperature gradient The test results show that space charges at the interface between cable and accessory increases with temperature gradient(temperature difference), which enhances the electric fields near the stress cone at the SR/XLPE interface On the other hand, under temperature gradient, the space charges contribute to slightly weakening the field near the stress cone, but slightly enhancing the field near the high voltage shielding tube

Field Test Research on Temperature Detection of Overhead Transmission Line Based on BOTDR Distributed Fiber Sensing Technology

Abstract: To monitor the temperature state of the long distance overhead line in real time,we developed an integrated distributed optical fiber sensing system based on the Brillouin optical time domain reflectometer(BOTDR) distributed fiber sensing technology In the laboratory environment, the system has a maximum sensing distance of 30 km, a temperature resolution of ±2 ℃, and a temperature measurement range from-60 ℃ to 90 ℃, while the spatial resolution is 10 m We used the system to conduct the temperature field test for the optical power ground wire(OPGW) of 110 k V lines in 19 hours and compared the test results of 154 km location with the results of fiber Bragg grating(FBG) sensor The results show that, this system can detect the distributed temperature of OPGW cable in the site environment, and the results are basically in agreement with the local temperature variation trend In the place of 154 km, the monitoring result is consistent with the temperature profile of the FBG sensors, and the biggest difference is 18 ℃ Affected by the fiber production process and splices loss, the segmentation phenomenon appears on the Brillouin scattering spectra and the maximum sensing distance of field test is only 16 km These test results can provide references for further application the distributed Brillouin scattering fiber optic sensing system in electric power engineering

Creeping Discharge Monitoring of Epoxy Spacers in GIS Using a New Target Gas CS_2

Abstract: Creeping discharge on the epoxy spacer is a major kind of fault in gas insulated switchgear(GIS). It is important to monitor the insulation condition of epoxy spacers and to study the variations of target gases when partial discharges occur on the epoxy spacer in GIS. A new decomposed gas CS2 is found in the simulation experiments by current researchers. It is detected when creeping discharges occur on the surface of epoxy spacer, and is validated by experiment on a small apparatus and 110 k V GIS. B3P86, a method of calculation based on quantum chemistry, is adopted to explore the formation of the CS2 and energy conditions. Experiments and theoretical calculations show that complex chemical reactions happen when creeping discharges occur on the epoxy spacer in GIS, and CS2 is generated through various ways. Carbon is the component of CS2 derived from the charring epoxy spacer. As an effective target gas, CS2 can be applied to diagnose faults related to creeping discharge on the epoxy spacer in GIS. Many latent faults leading to creeping discharge on the epoxy spacer have been diagnosed using target gas CS2 in actual production.

Accurate Calculation Method of Electric Field on the Surface of Converter Valve Fittings in UHVDC System

Abstract: Complex internal structures of valve halls in ultra-high voltage direct current systems make them difficult to mesh in calculations using the finite element method(FEM). To solve this problem, we built a 3-D model of ±800 k V ultra-high voltage converter station valve hall, and proposed a regionalization mesh generation method following the principle of modularity and independence. The method overcomes the difficulty in mesh generation for complex models, lowers the demands of computer hardware, and can obtain meshes with high quality. Since the complex model has huge number of elements, we choose the incomplete Cholesky conjugate gradient(ICCG) algorithm to solve the model's FEM equations. Eventually, combining the regionalization mesh generation method with the sub-model technology, we have realized the accurate electric field calculation of certain local parts in valve hall. The calculation results show that setting the size of solution region as large as 1.3 times the devices in sub-models, the obtained cut boundaries can meet the demands of sub-model calculation. The maximum error on the boundary is less than 2%, and the calculated sub-model electric field is accurate.

Quantum Detection of Trace Acetylene Gas Based on the Peak Area of Photoacoustic Spectroscopy

Abstract: Acetylene is a symbolic gas to distinguish transformer overheating and discharging faults, and its content has important significance in detecting the power transformer internal insulation fault type and severity. We set up a trace acetylene detection platform based on photoacoustic spectroscopy peak area using a distributed feedback diode laser. Absorption line of acetylene at 1 529.18 nm was selected for experimental study. The temperature drift characteristics of the distributed feedback laser diode and the photoacoustic spectroscopy response characteristics of trace acetylene were analyzed by experiments. The photoacoustic response characteristic curves of trace acetylene with different volume fraction based on Lorentz nonlinear fitting were obtained. The least squares linear regression was used to analyze the quantitative relationship between the photoacoustic spectroscopy peak area and the volume fraction of the acetylene. The experimental results show that when the gas absorption saturation effect does not occur, a good linear relationship exists between the acetylene gas photoacoustic spectroscopy peak area and volume fraction, and the trace acetylene detection limit of the test platform is 0.46×10-6. This result laid the foundation for the online monitoring of dissolved gas in transformer oil and insulation fault diagnosis of power transformer.