Short-circuit Impact Research Articles

Analysis of Transformer GSB Bushing Fault Causes Based on Finite Element Simulation

Abstract In response to a sudden explosion and fire fault during the operation of a GSB dry-type transformer bushing in a certain power grid company, based on the structural parameters of the bushing measured by the supplier and on-site, a reverse design of the capacitor core was carried out on the faulty bushing. Based on the measured parameters and reverse design results, a finite element simulation model of the bushing electric field and structural force field was established. Calculate the electric field distribution of the casing under normal operation, 60s power frequency withstand voltage, lightning impulse, operation impulse, and other operating conditions; Conduct finite element simulation of structural mechanics to calculate the stress distribution of the casing under conditions such as cantilever load and short circuit impact; Based on the discharge traces discovered during disassembly, simulation calculations were conducted by assuming the defect situation of the casing, and the electric field distribution of the casing under different defect types was quantitatively analyzed. The simulation calculation results of the electric field under various working conditions have verified that the occurrence of this fault is the result of multiple defects working together, providing quantitative support for fault analysis and providing a certain reference for the operation and maintenance of similar casings.

Analysis of Transformer Gas Relay Action under Short Circuit Impact

A gas relay is an important non-electric protection device for transformers. Under the action of vibration caused by sudden short circuit impact, misoperation of gas relay leads to transformer tripping accidents frequently. In order to explore the relationship between the vibration intensity of the gas relay and the anti-vibration performance of the gas relay during a sudden short circuit, the sudden short circuit capacity test of the transformer and the vibration test of the gas relay were carried out. The analysis of test data shows that the sudden short circuit process of the transformer will cause the misoperation of some gas relays, which provides data support for the inspection test of gas relays. Finally, the optimization scheme of the detection method of the gas relay is proposed, which further effectively reduces the possibility of misoperation and improves the operation reliability of the transformer equipment.

An Improved Radial Buckling Analysis Method and Test Investigation for Power Transformer Under Short Circuit Impact

The inner winding of the power transformer is subjected to uniform compressive stress in the radial direction during the short circuit, which makes circular radial stability a crucial component of reliability. The radial stability evaluation system currently needs more state characteristic judgment quantity considering the manufacturing deviations(MD) and assembly gaps. Thus, there is a significant deviation in the transformer design, which seriously endangers the operation safety of the power system. This paper proposes an improved radial buckling analysis method (IRBAM) to investigate the circular radial stability of inner winding. The IRBAM is implemented by defining two characteristic parameters: equivalent flexibility and MD. Besides, the relative change ratio of impedance (RCRI) is proposed as the buckling judgment for ending each short-circuit test. The destructive short-circuit tested transformer is designed with the rated power of 50 MVA and the high-voltage (HV) rated voltage of 110 kV. Then, 73 cumulative short-circuit tests are performed until impedance exceeds the permissible value based on the judgment. Finally, it is verified that IRBAM can effectively match the winding failure modes by comparing the buckling phenomena and calculation results. Further, the IRBAM can provide a reference for similar designs and verification with more minor deviations.

Research on cumulative effect and diagnosis method of transformer short-circuit impulse

After transformers suffer from short-circuit impact, their mechanical performance decreases significantly. This article establishes a two-wire vibration model to represent the coupling between forces and mechanics and analyzes the transient vibration signals of a 400 V transformer during 22 short-circuits impact. To illustrate the cumulative effect of short-circuits, the vibration entropy, and energy ratio of the main vibration frequency and half frequency are adopted. The results show that transient vibration signals of transformer in short-circuits contain half frequency components, such as 25 Hz and 75, etc., and with the increase of the number of short-circuits, plastic deformation exists in insulation material, which leads to the loss of winding clamping pressure, the reduction of natural frequency, and the upsurge of parametric resonance. With the increase of short circuits, the vibration entropy and half-frequency energy ratio increase, and the main frequency energy ratio decreases. After winding completely lose the axial stability, the vibration entropy and half frequency ratio decrease, and the main frequency ratio increases. The conclusion is of great significance to the analysis of the cumulative effect of short circuits on power transformers.

Buckling Strength Investigation for Power Transformer Winding Under Short Circuit Impact Considering Manufacture and Operation

Power transformers are inevitably subjected to external short circuit impact during their service period. The electromagnetic force generated by the fault current may cause winding destabilization and collapse. The radial buckling of the inner winding accounts for a considerable proportion. Based on the effective contact of the sticks, the traditional analytical methods ignore the manufacturing deviation and operation impact (MDOI) characterized by assembly gaps and insulation shrinkage. To address the limitation of the contact-constrained approach, this paper proposes the equivalent support stiffness (ESS) analytical method. The ESS method can investigate the issues of support weakening and failure, which are affected mainly by assembly gaps and insulation shrinkage. Further, two transformers are implemented in the short-circuit tests to demonstrate the feasibility of the ESS method. Among them, the assembly gaps are investigated by the first and second windings of the newly manufactured transformer, and the influence of insulation shrinkage is researched through a 30-year-old transformer. Furthermore, the application of the ESS method is expressed based on the tests and the simulations. The research presents quantitative references for transformer design and operational reliability assessment. The ESS method can be an improvement and supplement to traditional methods.

Analysis of Transformer Winding Deformation and Its Locations With High Probability of Occurrence

Power transformer, as a crucial equipment for power transmission, frequently suffers winding deformation defects, owing to the impact of huge external short-circuit current in actual operation. To resist the rapid deterioration of the defects, online monitoring for winding states is imperative, depending on a thorough understanding of the deformation defects. Unfortunately, there are not much related research on the deformation form and location, as two key objects online diagnosed. In this paper, we concentrate on the analysis of winding deformation and investigation of its high-probability location to deeply understand the winding deformation. For the form of the deformation, a three-dimensional finite element model of the transformer is established to obtain the form and extent of the short-circuit impact force, and a buckling model of the low-voltage winding is designed to analyze the mechanism and form of winding deformation under the impact of huge force induced by short-circuit current. For the location of the deformation, the three-dimensional simulation models are established to analyze the force characteristics of different winding structures in three locations (the conductor transposition area, the area with imbalanced amp-turns and the area with uneven circumferential distribution of force). Then we clarify the possibility of winding deformation in these areas, defined as high-probability locations. Finally, the analyzed results are found to be highly consistent with the actual winding deformation, demonstrating the correctness of the research methods and conclusions. Next stage, the results will provide effective theoretical support for online diagnosis of winding deformation and optimal design of winding structure.

Simulation research on large capacity power supply technology suitable for distribution transformer short-circuit withstand capability test

The existing transformer short-circuit test equipment and technology have several limitations. The purpose of short-circuit test is to simulate the test of high-voltage equipment under the short-circuit fault condition of the power system, usually, a large capacity test such as transformer burst short-circuit test, circuit breaker dynamic heat stability test, to verify the reliability and stability of related equipment under extreme working conditions. At present, the large capacity test generally uses methods of power grid dedicated line power supply and short-circuit testing alternator group. However, these two methods have difficulties in construction approval, high investment costs, complex site requirements, a large impact on the power grid, and low control accuracy. Theoretical studies on equivalent simulation verification method of short-circuit withstand capability test of distribution transformer demonstrated the feasibility of using modern power electronics and advanced energy storage technology to replace conventional power grid dedicated line power supply, short-circuit testing alternator and other short-circuit impact test equipment. It could complete the transformer short-circuit impact test specified by (IEC60076-5) with lower cost and higher efficiency, verify the short-circuit impact resistance of the transformer, and improve the test capacity.

Simulation test of transformer short-circuit impedance based on equivalent model at different frequencies

A distribution transformer is one of the most important equipments in the power grid, and its operational status is directly related to the security and stability of the entire power system. The performance of transformer windings determines the service life of the transformer. It is of great significance to evaluate the performance of transformer windings accurately, reliably, and effectively after the short-circuit test of the transformer. Aiming at the problem that the natural vibration frequency of the transformer measured before and after the short circuit may not be the same under the impact of the short circuit of the transformer, this paper puts forward the evaluation method for the performance evaluation of the winding of the transformer after the short circuit test and adopts the method of combining the analytic hierarchy process with the fuzzy evaluation method to quantitatively obtain the score for the performance evaluation of the winding. And that evaluation language is given according to the score. Finally, the evaluation of the transformer winding performance after the short-circuit test is realized. The evaluation results show that this method can effectively get the performance index of the transformer winding, without the need for hanging cover inspection, and solve the subjectivity of human eye observation to objectively, accurately, and quantitatively describe the performance state of the transformer winding. The method is favorable for power grid monitoring and maintenance personnel to accurately evaluate the operation stability of the transformer and has very positive significance for improving the short-circuit impact resistance of the transformer and ensuring the safety and stability of the operation of a power system.

Experimental study on the dynamic behavior of prismatic lithium-ion battery upon repeated impact

The daily use of electric vehicles may cause mechanical loading on their batteries, either from one-time impact or repeated/accumulated impact from vibrations, curbstone impact, or minor contacts/scratches. Such repeated impact may ultimately lead to short-circuit failure of the batteries. Open literature comprehensively discusses the one-time impact, but a gap remains regarding battery safety behaviors in repeated impact cases. Therefore, in this study, the dynamic behavior of prismatic lithium-ion battery (PLIB) under repeated impact is experimentally investigated for the first time. The relationships between battery failure of short circuit with impact velocity, impact energy and impact times are revealed. The quantitative relationship between battery failure and indentation depth is constructed. Results show that the increase of impact velocity and energy significantly decreases the number of short-circuit impact. For the prismatic lithium-ion battery studied in this work, under the drop-weight impact test with 34.6 kg weight and 25 mm diameter of the hemispherical impact indenter, once the impact velocity reaches more than 1.75 and 4.0 m/s, the soft and hard short circuits are triggered, respectively. When the impact speed is less than the corresponding velocity, the battery failure of soft and hard short circuits can occur only after multiple impacts. Results provide new insights for understanding battery failure behaviors upon repeated impact and important guidance for battery design.

Investigation of welding bridge occurrence and short circuit impact on wire breakages during WEDM

The paper provides the results of a short circuit impact on wire breakages during wire electrical discharge machining (WEDM) of AISI 9840 steel by the SODICK VZ300L machine. A method of scanning electron microscopy (SEM) is used for debris size, morphology and shape analysis. The carried out investigation led to the conclusion that the most probable reason of the welding bridge formation is due to the non–spherical (conglomerates) particles’ presence with a large number of surface irregularities in a dielectric liquid. A classification of debris particles is proposed from the point of view of their dimensions and ability to overlap the spark gap – «effective» and «ineffective» particles.

Evaluation of Loss Generated by Edge Burrs in Electrical Steels

In large motor cores, faults caused by edge burrs between the core laminations can result in short circuit currents which may be large enough to cause burning or complete machine failure. This study simulates the impact of edge burrs on large motor lamination (300mm*300mm) by applying artificial shorts to lamination edges. This twofold study has investigated the impact of short circuit and the impact of short circuit positions on total power loss. Multiple shorts have been applied at different positions. It has been found that the induced eddy-currents are largely dependent on the fault position (edge burrs) and the number of shorted laminations even when only two laminations are involved. This study was further extended to include power loss separation into three components, the power loss separation has been applied to the case of higher power losses obtained under specific short circuit conditions at different magnetizing frequencies. Power loss separation has shown a significant increase in eddy current loss components with increasing number of shorted laminations.

Relationship between hydraulic efficiency and phosphorus removal in a submerged aquatic vegetation-dominated treatment wetland

A tracer study (Rhodamine-WT dye) was performed on a 147-ha submerged aquatic vegetation (SAV)-dominated free-water surface treatment wetland in south Florida that received agricultural drainage waters (ADW). Two dimensional, time series plots of the dye concentrations revealed that a disproportionate amount of tracer flowed along the eastern and western levees of the cell. The tracer response curve developed from the outflow data indicated a prominent short circuit, which conveyed 44% of the volumetric flow based on model analysis. This large fraction of flow bypassed the SAV community and exited the wetland with only partial treatment for total phosphorus (TP) removal. The volumetric efficiency of the wetland was high (∼100%), but the hydraulic efficiency was low due to the low tanks-in-series number ( N = 1.3). Even though the short-circuit channels promoted near-plug flow, the dispersion number for the wetland was nevertheless still high ( D = 1.25), due to the wide distribution of detention times among the multiple flow paths. A dynamic hydraulic model based on a tanks-in-series network with mixing between the short-circuited and shallower, vegetated zones simulated the tracer response curve to an accuracy of 0.99 (as the coefficient of determination). The amount of time that a parcel of water resided within the wetland affected TP removal. Hydraulic retention times (HRTs) > 2.5 days consistently produced TP concentrations less than 35 μg/L, or 64% TP removal based on the inflow concentration of 96 μg/L. “Steady-state” TP concentrations among the internal and outfall stations during the tracer study enabled direct analysis of the impact of short-circuits on P concentrations and removal effectiveness. Based on longitudinal P concentration gradients, faster flowing short-circuit channels that contain little SAV were less effective in reducing TP concentrations ( k = 0.24 day −1) than the more densely SAV-occupied areas ( k = 0.50 day −1) that characterize 56% of the wetland. This was likely due to both the shorter detention time and the sparse SAV community within the channels. The lack of SAV contributed to an environment that reduced the sedimentation rate, direct plant uptake, and the pH, all of which contribute to removal and retention of P in the more quiescent, shallower SAV zones. Our results suggest that tracer studies, coupled with internal P concentration gradient analyses, are useful for determining hydraulic efficiency of a wetland and its effect on P removal. These types of investigations can also serve as the basis for modeling, optimization, and design studies.