Mold Transformer Research Articles

Hysteresis response of rotary friction dampers developed for seismic operational performance of non-structural components vulnerable to overturning

The electrical facilities in buildings play important roles in maintaining operational performance during and after earthquakes. In this study, rotary friction dampers were developed for electrical facilities vulnerable to overturning, and cyclic loading tests were performed for the corresponding sub-assemblies (comprising friction plates), aiming to investigate the hysteresis response(s) of the friction dampers. The primary test parameters included the number of bolts used for fabricating the friction plates, torque applied to the bolts for their fixation to the friction plates, and cyclic loading frequency. In total, three series of 24 full-scale friction damper specimens were fabricated and tested according to the guidelines specified in the Korean seismic design standard (KDS 41 17, 2019). Based on the test results, the mechanical characteristics and seismic performance of the friction dampers were assessed and investigated in details. A macro-analytical model was developed to simulate the load–displacement response of the friction dampers, and its prediction showed a good correlation with the experimental results. Finally, dynamic analysis was performed by applying the developed friction damper to the entire system (mold transformer). As a result of the analysis, the response displacement of the detail with friction damper was reduced by about 95% in the X-direction and about 70% in the Y-direction compared to the displacement of the conventional detail.

Study on Seismic Performance of a Mold Transformer through Shaking Table Tests

This study presents an experimental seismic investigation of a 1000 kVA cast resin-type hybrid mold transformer through tri-axial shaking table tests. The input acceleration time histories were generated in accordance with the specifications recommended by the International Code Council Evaluation Services Acceptance Criteria ICC-ES AC156 code, with scaling factors in the range of 25–300%. The damage and the dynamic characteristics of the mold transformer were evaluated in terms of the fundamental frequency, damping ratio, acceleration time history responses, dynamic amplification factors, and relative displacement. The shaking table test results showed that the damage of the mold transformer was mainly governed by the severe slippage of the spacers and the loosening of the linked bolts between the bottom beam and the bed beam. In addition, the maximum relative displacement at the top beam in Y and Z-directions exceeded the boundary limit recommended by the Korean National Radio Research Agency. Moreover, the operational test of the specimen was performed based on the IEC 60076-11 Standard before and after the shaking table test series to ensure the operational capacity of the transformer.

Seismic Vulnerability Assessment of Hybrid Mold Transformer Based on Dynamic Analyses

In the present study, the seismic vulnerability of a hybrid mold transformer was investigated using a dynamic analytical approach incorporating the experimental results of shaking table tests. The analytical model consisted of linear springs and plastic beam elements, and it has six degrees of freedom simulating the hybrid mold transformer. The dynamic characteristics of the analytical model were determined based on the shaking table tests. The reliability of the analytical model was verified by comparing the test results and analytical results. In order to assess the seismic vulnerability, three critical damage states observed during the shaking table tests were investigated by incorporating the three performance levels specified in ASCE 41-17. Comprehensive dynamic analyses were performed with a set of twenty earthquakes in consideration of the variation of the uncertain parameters (such as the effective stiffness and coil mass) of the mold transformer. Based on the analytical results, fragility curves were established to predict the specified exceedance probability of the mold transformer according to the performance levels.

배전용 몰드변압기의 온도특성 파악을 위한 열유동해석

In this paper, the temperature characteristics of mold transformer for the distribution power system have been analyzed by using computational fluid dynamics(CFD). The model has been modeled by coil, cores, insulating materials and frames about 3MVA grade mold transformer and analyzed the temperature distribution of the structure with a heat fluid. The fluid, which is incompressible ideal gas, is analyzed as a turbulent flow phenomenon on the assumption that it is natural cooling of transformer cooling system. Through this study, by examining the temperature distribution and hot-spot of the structure field of the mold transformer, cooling design and temperature distribution information, which are demanded for designing are estimated.

Optical Diagnostic Technique for the Epoxy Resin Degradation of Mold Transformer

The mold transformers which use epoxy resins for coil insulation have superior characteristics in fire retardancy and environment resistance. Because of their high reliability, they have been excluded from electric equipment diagnosis in most cases. However, the mold transformers need to diagnose aged deterioration of their resin material because they have been used for more than 40 years. Therefore, we developed the simple and on-site degradation diagnostic device for the epoxy resin.

DC 변전소 몰드변압기 온라인 상태 감시 시스템 구현

The mold transformer is a complex and critical component of DC substations in Metro system. In this paper, a cost effective and intelligent condition monitoring system for mold transformers in DC substations was developed. This paper also provides an overview of the management program using PD (partial discharge) data on mold transformers. Prior to application of the proposed system to Metro DC substations, experiments were performed at the metro line substation located in Seoul and presented case studies for the use of the intelligent condition monitoring system for mold transformer in DC substations. The experiment results indicated that the developing system can be need in helping mange the risk of unexpected failure of mold type transformers.

2[MVA] 배전용 몰드변압기의 글라스넷 형상 최적설계

In this paper, the optimum design of the glass net shape was studied to minimize the electric field of mold transformer. The glass net is used for reinforcement in structure between coils and epoxy, but it can cause to increase the electric field and the partial discharge. Therefore, the optimum design of glass net is required to minimize the electric field. In this paper, the objective function was approximated by using response surface method and then Zoom-in method was used for optimal design to minimize the electric field. The electric field was analysed using finite element method for each shape of glass nets.

2[MVA] 배전용 몰드변압기의 과도전계해석에 관한 연구

This paper presents the electric field for 22.9[㎸]/380[V], 2[MVA] mold transformer are analysed using FEM(finite element method). The electric field was calculated for the voltage applied to the transformer. Then, it is analysed that the maximum electric field occurred between high voltage turns. Capacitance is calculated with energy method. Surge impulse test simulation is studied by modeling circuit with capacitance and inductance. This paper obtain the result that is about influence of electric field in distribution mold transformer adopted.

2[MVA] 몰드변압기 절연물내 기포 영향을 고려한 전계해석

This paper presents the electric field analysis for 2[MVA] mold transformer using finite element method. The electric field was calculated for the voltage applied to the mold transformer without voids in the insulating material. Then, it was analysed the maximum electric field when the voids was in the insulating materials. And the starting voltage of partial discharge was predicted due to the voids. The effects of voids in epoxy resin on the electric field were investigated for different sizes, shapes, positions and arrangements of voids.

여러종류의 Organoclay에 대한 에폭시-나노콤포지트의 열적, 유전특성에 관한 연구

Nanostructured materials are attracting increased interest and application. Exciting perspectives may be offered by electrical insulation. Epoxy/Organoclay nanocomposites may find new and upgraded applications in the electrical industry, replacing conventional insulation to provide improved performances in electric power apparatus, e.g, high voltage motor/generator stator winding insulation, dry mold transformer, etc. In the paper work, the electrical and thermal properties of epoxy/organoclay nanocomposites materials were studied. The electrical insulation characteristics were analyzed through the permittivity characteristics. by analyzing the permittivity spectra, it was found that dielectric constant becomes smaller with increase frequency and becomes larger with increase temperature. This indicates restriction of molecular motion and strong bonds at the epoxy/organoclay nanocomposites. The morphology of nanocomposites obtained was examined using TEM and X-ray diffraction. It has been shown that the presence of polar groups leads to an increased gallery distance and partial exfoliation. Nevertheless, full exfoliation of clay platelets has not been achieved.

일체형 주상용 몰드 변압기의 온도분포 및 특성 비교

The mold transformers have been widely used in underground substations of large building and have some advantages when compared with oil-transformer. Those advantages are low fire risk, environmental compatibility, compact size and high reliability. The mold transformer is generally known to have cooling duct between low voltage and high voltage coil. To achieve better compact structure and low loss, mold transformers made by one body molding method has been developed. Nevertheless, such kinds of transformer need better cooling method because heat radiation between each winding is still of problem. The life of transformer is significantly dependent on the thermal behavior in windings. Many designers have calculated temperature distribution in transformers and hot spot point by finite element method(FEM) to analyze winding temperature rise. In this paper, the temperature distribution analysis of 100 kVA pole mold transformer for power distribution were investigated by FEM program and the thermal analysis results were compared with temperature rise test.

일체형 주상용 몰드 변압기의 덕트에 따른 열해석 특성 연구

일체형 주상용 몰드 변압기의 덕트에 따른 열해석 특성 연구