Search

The heating of the fittings of the substation is a major hidden danger affecting the safe and stable operation of the substation. As a load of substations has increased, several heating defects of fittings joints have been found during daily inspections and live inspections. Facing the defects of fittings and joints, operation and maintenance personnel often use methods such as dismantling the equipment to polish the oxide layer, applying conductive paste on the contact surface, and tightening connecting bolts [1]. However, the current methods all require power outage maintenance, which not only increases the daily workload of operation and maintenance personnel, but also inevitably causes a certain load loss. Therefore, it is urgent to study a new method to effectively suppress the heating defect of the fittings without power failure, which also provides a certain theoretical and experimental basis for improving the detection and operation and maintenance of fittings [2]. In order to verify the performance of memory alloy smart gaskets, this paper selects memory alloy smart gaskets and ordinary steel spring gaskets, and develops the effects of current and torque on the temperature rise and loop resistance of the fittings of different types of gaskets under AC current [3]. Experimental results show that under the same torque, the temperature of the memory pad end is lower than that of the ordinary end, and the greater the current, the more obvious the effect; under the same current, the temperature of the memory pad end is lower than that of the ordinary end, and the smaller the torque, the more obvious the effect. It proves that memory pads have certain advantages over ordinary pads.

The shape memory alloy (SMA) is a new kind of metal intelligent material, which has the characteristics of shape memory effect (SME), pseudo-elasticity (PE) and high damping (HD). Therefore, it is widely used in many industries, such as construction engineering, mechanical engineering, space shuttle, energy engineering, medical engineering and so on. In order to solve the heating defects of fittings, the typical six split fittings joints in the main flow circuit of converter station was selected in this paper. And the memory alloy intelligent gaskets and ordinary steel spring gaskets on both sides of the fitting joints were installed. The experimental research on the influence of current on the temperature rise of fittings with different types of gaskets were carried out. The test results showed that the shape memory alloy gasket could automatically generate the deformation force which increased with the increase of temperature, so as to reduce the contact resistance of the joint and the temperature of the contact during operation.

The shape memory alloy (SMA) is a new type of metal intelligent material, which has been widely used in power system such as hardware connector, circuit breaker, disconnector and relay protection. In order to solve the heating defect of fittings, the typical six split fittings in the main flow of converter station was selected in this paper. The memory alloy smart gasket and ordinary steel spring gasket are installed on both sides of the joint. The effects of vibration and aging on the temperature rise of different types of gaskets and pipe fittings were experimentally studied. The test results showed that after long-term power frequency vibration, the temperature rise of memory alloy smart gasket changed little before and after vibration. At the same time, after several temperature rise tests, the temperature rise before and after the smart gasket fittings joint of memory alloy change little.

B phase of the no 2 main transformer of 500 kV XX substation was suddenly stopped on August 20, 2021 due to acetylene and an abnormal sudden increase. Acetylene reached 10.5uL / L, far exceeding the acetylene attention value of 1.0uL / L, and there is a trend of continuous growth. An internal inspection was carried out after the power outage, and no obvious abnormality was found. Then it was sent to factory for de-oiling and drying. Inspection found the following problems: 1. The upper and lower iron yoke clamps of main transformer and their pull straps, the fourth pull strap shielding cover from the left of lower clamp on the high pressure side was found to be abnormal; 2. Check the iron core silicon steel sheet, found that there are about 15mm burrs between the iron yoke (high-voltage side) core stages under the side post position; 3. There is a black mark at the connection part of low-voltage lead and the casing oil, but no signs of discharge or overheating are seen; 4. Check that there is no obvious abnormality in other parts of the body, such as insulation, lead wires, and electrical shielding. Combined with the inspection situation, analyze specific causes of the failure and propose follow-up improvement suggestions.

In order to accumulate preliminary data of mechanical characteristics of the fast switch, and to verify whether the design parameter requirements are met. This paper selects three prototypes and three engineering prototypes respectively, collects and analyzes mechanical characteristics of three engineering machines before and after the prototype test, the life prototype before and after the life test, the capacity prototype before and after the capacity test. It is proved that the opening and closing time of quick-switch prototype and engineering prototype meet design requirements. Data results measured by all parties are in good agreement. Among three prototypes, the maximum phase difference between fast switch opening time, opening speed, closing time, and closing speed is only 10.7%, 6.7%, 8.8%, and 9.5%. In three-phase engineering prototype, the maximum inter-phase difference of fast switch opening time, opening speed, closing time, and closing speed is only 8.3%, 4.9%, 3.5%, and 7.8%.

The surface charge accumulation on polymers can reduce the insulation performance of the materials and even cause surface flashover. The characteristics of surface charge accumulation and dissipation for epoxy resin (EP) exposed to various nanosecond pulse voltage parameters (i.e. pulse rise time, pulse width and voltage amplitude) are investigated. The results show that the fractional decay of surface charge increases with pulse rise time and decreases with pulse width and voltage amplitude. However, abnormal dissipation phenomenon appears when the pulse voltage reaches 9 kV. Analysis suggests that the abnormal dissipation phenomenon can be attributed to surface charge transport primarily along the surface. Furthermore, the surface charge fractional decay is less than 30% for a dissipation time of 30 min under different nanosecond pulse voltage parameters. In addition, the method of atmospheric pressure plasma jet (APPJ) is utilized to deposit SiCxHyOz thin film on the surface of epoxy resin (EP) samples. It is found that the fractional decay of surface charge for treated EP samples is promoted approximately by an average of 90%. The trap density distribution indicates that the shallow traps that are formed by APPJ treatment result in a decrease in the trap energy level.

According to a live detection of 252kV GIS, this paper describes the principles and technical advantages of UHF-based and ultrasonic-based GIS partial discharge detection methods; in addition, it analyzes the spectrogram information of portable PD analyzer to preliminarily judge the defect type. At last, the discharge source is precisely located by means of time difference positioning method and ultrasonic associated with electromagnetic wave method. Through the on-site basin-type insulator fastening screw inspection, the judgment is consistent with the test conclusion, which verifies the accuracy of the onsite live detection. Practice shows that UHF and ultrasonic partial discharge detection technique can recognize partial discharge due to GIS defects, and timely discover and prevent GIS insulation faults to ensure the operation security and stability of GIS.

As an important part of distribution network, maintaining the reliability and stability of public transformer operation is of great significance for the safe and stable operation of distribution network. In this paper, a method based on neural networks for pre-warning of heavy overload in distribution networks transformer was proposed. First, based on the online monitoring of big data resources in the distribution network, the public variable load rate, heavy overload duration, and temperature information of the station area during the historical peak summer was extracted. The method of cluster analysis was used to divide the trend of common variable load during the summer period of historical peak. Then, based on the method of neural network, the load trend prediction model of public distribution transformer is established during the summer peak time. Combined with the temperature information of the station area, the trend of heavy overload is judged by the prediction results. Finally, the data mining method of principal component analysis was used to calculate the weight of evaluation index, and calculated the comprehensive score of heavy overload situation of each station area and classified the warning level. The early warning method proposed in this paper is helpful for the early warning and risk assessment of the public variable heavy overload in the distribution station area during the summer. It provides the basis for formulating the Countermeasures of heavy overload of distribution transformer, eliminating the hidden trouble in time and ensuring the reliability of residential power consumption.

Surface charge accumulation of polymer insulating materials is harmful to the safe operation of electrical equipment, especially under DC electric field excitation. In order to ensure the safety and stable operation of HVDC power system such as Gas-insulated transmission line, it is necessary to understand the influence of the surface charge on the flashover and improve the surface charge dynamic characteristics. In this paper, Epoxy resin (EP) is deposited by SiO x thin films with different plasma treatment conditions. The flashover voltages are measured with and without surface charges. The results show that the flashover occurs at lower voltage due to the accumulated charges on the EP surface. In particular, the surface charge with the same polarity of flashover discharge can reduce the surface flashover voltage significantly. Moreover, the charge decay rate is increased up to 90% by plasma treatment of 3 min, corresponding flashover voltage is increased. In addition, the flashover voltages of samples during the surface charge dissipation are obtained. Both static impact index I and dynamic impact index S are introduced to estimate effect of surface charge on dielectric surface flashover.

Based on the actual failure of the bushing, this paper conducts analysis and research. Firstly, it analyzes the protection action, on-site harmonic components, bushing structure and disassembly step by step. Then it conducts the research on the discharge and breakdown characteristics of epoxy insulation. Finally, we results show that there are bubbles or impurities in the outer capacitor layer of the capacitor core inside the casing, and the harmonic content is higher under the operating conditions of the converter station. Meanwhile, we gives some relevant suggestions for the through-wall bushing in the design and manufacturing stage to consider relevant harmonic factors are of certain significance to extend the life of the bushing.

The surface insulation properties of insulating material under DC voltage are closely related to the characteristics of surface charge accumulation, and the surface roughness of these materials has a direct impact on the surface charge distribution in vacuum. Therefore, it is significant to study their connection. In this paper, based on the secondary electron emission avalanche model, the surface charge accumulation on polymethyl methacrylate (PMMA) with different surface roughness was simulated by using particle in cell and Monte Carlo Collision method. The simulated environment was under the finger shaped electrode and in vacuum. The results showed that under the action of the electric field the electrons emitted from the cathode triple junction moved forward and collided with the insulating material, which may lead to the generation of secondary electrons or the accumulation of surface charge. The surface charge near the cathode was mostly negative since the effect of surface electron injection was greater than that of the collision ionization. Due to the change of electron energy and the influence of electric field distribution, the number of positive charge on the insulator gradually increased, reached the maximum, and then gradually reduced with the approaching of the anode. Moreover, when the surface roughness of the material increases or the secondary electron emission coefficient decreases, the amount of surface charge accumulated on the PMMA will reduce. This paper can provide some guidance for the practical application of insulating materials.

The grounding technique is one of the important measures to protect the personal safety and reliable operation of electricity equipment in electric power system. Nowadays, the protection grounding, working grounding and lightning protection grounding are widely used in high voltage equipment. This paper is based on 500kV XLPE insulated submarine cable in Zhoushan transmission project. In order to get the influence of working and protective grounding on submarine cable in AC voltage withstand voltage test, theoretical analysis and experimental application are combined to analyze. The advantages and disadvantages of independent grounding and also common grounding are discussed in this paper. The results show common grounding fully meets the long submarine cable line AC withstands voltage test requirements.

In HVDC transmission system, surface charges accumulate easily on the surface of insulating materials, which cause surface discharge and surface flashover. This phenomenon reduces the insulation performance of insulating materials and restricts the engineering application of HVDC transmission. The researches of surface charges on insulating materials and its suppression measures in DC system have become a hot research direction. According to the current research of surface charges characteristics, this paper systematically describes the source, accumulation characteristics and dissipation characteristics of surface charges. In order to further reduce the influence of surface charges on HVDC transmission system, this paper also discusses the surface modification methods of controlling surface charges.

This study proposes a novel dynamic reliability network-equivalent approach (RNEA) for distribution generations (DGs) enhanced distribution system. This method includes a bottom-up process and a top-down process, which are developed based on equivalent principle, and the synthesis of both processes yields the reliability performance of any node in the system. In addition, a novel switch zone concept is defined and introduced into the bottom-up equivalent process as to save the computation cost. Besides, a hybrid restoration model is proposed to account for the practical restoration process in power grids, and solved using particle swarm optimisation. The most significant of the proposed approach over other equivalent methods such as section technique, RNEA, and zone-branch method is that it provides a more generalised element-by-element equivalent approach that can greatly simplify the network for reliability assessment irrespective of the network topology. The proposed methodology has been successfully tested on a real 362-node urban distribution system in China, with and without DGs considered.

The loss of submarine cable is an important problem in the process of design and manufacture. In this paper, the technology of the energy-saving and loss reducing conductor joint was introduced. The current carrying capacity test of energy-saving and loss-reducing conductor was carried out. At the same time, the same current was applied to the common stranded conductor and the energy-saving loss-reducing conductor, and the heat loss of the conductor under the same test environment was compared. The experimental results showed that at the connection of outgoing terminal and connecting pipe, the contact resistance of the layer insulated conductor was greatly reduced after depainting treatment. Meanwhile, the temperature of thermocouple after paint removal was obviously reduced in the current carrying capacity test. Compared with bare copper single wire stranded conductor, laminated enamelled insulated stranded conductor could reduce the power loss.

In order to realize the dynamic evaluation of transformer status and gradually improve the level of equipment fault diagnosis, a transformer condition assessment method based on fault feature extraction was proposed in this paper. Based on the data of the key state quantity of dissolved gas in transformer oil, this method extracted the transformer fault characteristics through various mathematical methods such as hypothesis testing and logistic language regression, and selected new indexes that could better reflect the operating state of transformer, so as to judge the operating state of transformer. In this paper, a large number of indicators were screened, and the regression method was used to find the indicators to judge the fault, without other external conditions. The analysis results showed that the average prediction accuracy of the proposed method was more than 95% under multiple cross validation, which had high engineering application value.

The dynamic characteristic of the surface charge on insulating material is an important electrical characteristic, which can effectively reflect the insulation performance of materials. The phenomenon of surface charge accumulation leads to surface discharge and surface flashover. In this paper, the surface charge accumulation and dissipation of epoxy resin under different pulse parameters were studied. The experimental results showed that the increase of pulse frequency intensified the phenomenon of surface charge accumulation and inhibited the process of charge dissipation. Meanwhile, the increase of the number of pulses led to the increase of surface charge accumulation first and then saturation. At the same time, it inhibited the process of surface charge dissipation.

On-load tap-changer is widely used in current power systems. Its main function is to change the position of the transformer winding tap-connect when operating under transformer excitation or load. The on-load tap-changer is in the process of changing taps. In the middle, the resistor must be used to achieve the transition to limit the circulation during its transition. The structure of the on-load tap-changer can be divided into three parts, namely the switch, the tap selector and the operating mechanism. The complexity of the mechanism causes frequent failures of the on-load tap-changer. Through the analysis of the causes of multiple faults occurring on the on-load tap-changer of the transformer, the abnormal physical information of the on-load tap-changer before the fault occurs is discussed. A joint detection technique based on vibro-acoustic fingerprint and driving motor current (acoustic and electric) is proposed.

An effective surface charge removal is critical to diverse applications of polymer and other soft organic materials in electrical devices and systems. Here, we report on the application of atmospheric pressure dielectric barrier discharge (AP-DBD) to deposit SiOx thin films to improve the surface charge dissipation on an epoxy resin surface. The SiOx nanofilms are formed at atmospheric pressure, with the replacement of organic groups (C-H, C=O and C=C) with inorganic groups (Si-O-Si and Si-OH) within the thin surface layer. After the plasma deposition, the initial surface charge decreased by 12% and the surface charge dissipation was accelerated. The flashover voltage which characterizes the insulation property of the epoxy resin is increased by 42%. These improvements are attributed to the lower density of shallow charge traps introduced by SiOx film deposition, which also corresponds to the surface conductivity increase. These results suggest that the SiOx deposition by AP-DBD is promising to accelerate surface charge dissipation. This method is generic, applicable for other types of precursors and may open new avenues for the development of next-generation organic-inorganic insulation materials with customized charge dissipation properties.