Condition monitoring of an operating apparatus is essential for lifespan assessment and maintenance planning in a power system. Electrical insulation is a critical aspect to be monitored, since it is susceptible to failure under high electrical stress. To avoid unexpected breakdowns, the level of partial discharge (PD) activity should be continuously monitored because PD occurrence can accelerate the aging process of insulation in high voltage equipment and result in catastrophic failure if the associated defects are not treated at an early stage. For on-site PD detection, the ultra-high frequency (UHF) method was employed in the field and showed its effectiveness as a detection technique. The main advantage of the UHF method is its immunity to external electromagnetic interference with a high signal-to-noise ratio, which is necessary for on-site monitoring. Considering the detection process, sensors play a critical role in capturing signals from PD sources and transmitting them onto the measurement system. In this paper, UHF sensors applied in PD detection were comprehensively reviewed. In particular, for power transformers, the effects of the physical structure on UHF signals and practical applications of UHF sensors including PD localization techniques were discussed. The aim of this review was to present state-of-the-art UHF sensors in PD detection and facilitate future improvements in the UHF method.

Application of UHF Sensors in Power System Equipment for Partial Discharge Detection: A Review

Among the different solutions which allow onsite partial discharge measurement in energized power transformers, the UHF technique is gaining general interest. In order to apply this method in existing transformers, it is considered advantageous to design a UHF sensor to be fitted inside the transformer tank. This paper describes the constraints affecting the development of such sensor and the process followed to optimize its design. During this process, different solutions for broadband UHF antennas were analysed. The selection was based on computer simulation and experimental results. Computer simulation was used to evaluate differences in radiation pattern, antenna impedance, gain and effective area. Measurements of the antenna response to different partial discharge sources in oil were performed using an oil dielectric breakdown test set in an electromagnetic shielded laboratory. A group of selected antennas were then tested in a power transformer simulating the broadband signals generated by partial discharges by injecting controlled voltage pulses in the transformer. Finally, a sensor based on a conical monopole antenna structure was built and attached to a specially designed housing to be fitted inside the transformer tank through the drain valve. This final prototype was benchmarked during a high voltage factory test of a power transformer which showed a significant partial discharge activity.

Optimisation of a sensor for onsite detection of partial discharges in power transformers by the UHF method

A new, bio-inspired printed monopole antenna (PMA) model is applied to monitor partial discharge (PD) activity in high voltage insulating systems. An optimized sensor was obtained by designing a PMA in accordance with the characteristics of the electromagnetic signal produced by PD. An ultra-wideband (UWB) antenna was obtained by applying the truncated ground plane technique. The patch geometry was bio-inspired by that of the Inga Marginata leaf, resulting in a significant reduction in size. To verify the operating frequency and gain of the PMA, measurements were carried out in an anechoic chamber. The results show that the antenna operating bandwidth covers most of the frequency range of PD occurrence. Moreover, the antenna presented a good sensitivity (mean gain of 3.63 dBi). The antenna performance was evaluated through comparative results with the standard IEC 60270 method. For this purpose, simultaneous tests were carried out in a PD generator arrangement, composed by an oil cell with point-to-plane electrode configurations. The developed PMA can be classified as an optimized sensor for PD detection and suitable for substation application, since it is able to measure PD radiated signals with half the voltage levels obtained from the IEC method and is immune to corona discharges.

/pdf/bio-inspired-printed-monopole-antenna-applied-to-partial-57rdfdxmuv.pdf

Bio-inspired Printed Monopole Antenna Applied to Partial Discharge Detection

In this paper, the design and development of a bio-inspired UHF sensor for partial discharge detection in power transformers is presented. The UHF sensor was developed for external use in dielectric windows of power transformers. For this purpose, a microstrip antenna was designed with a radiating element shape based on the leaf of the Jatropha mollissima (Pohl) Baill plant. Then, an epoxy coating and an aluminium enclosure were developed to protect the antenna against corrosion and to provide mechanical support, external noise immunity, and a lifetime compatibility with power transformers. In order to verify the electrical parameters of the developed sensor, measurements of the gain and the reflection coefficient were performed in an anechoic chamber. Lastly, the antenna sensitivity for denominated partial discharge (PD) detection was compared with the IEC 60270 standard method. For this purpose, simultaneous tests were carried out in a partial discharge generator setup, composed of an oil cell with needle-plane electrodes. The experimental tests demonstrated the effectiveness of the sensor for detecting PD signals with apparent charge values higher than 35 pC.

Design and Development of a Bio-Inspired UHF Sensor for Partial Discharge Detection in Power Transformers.

Partial discharge (PD) is a symptom of insulation defect or degradation in high-voltage power equipment. To detect the occurrence of PDs inside oil-filled power transformers, the ultra-high frequency (UHF) detection method is one that can be applied. To date, the sensors, as the most important part in the UHF method, have not been adequately addressed in terms of sensitivity and accuracy. This paper presents a novel UHF sensor called microstrip-fed planar elliptical monopole antenna. This antenna has a simple structure and ultra-wide frequency band. It is designed and simulated using CST software for parametric optimization. Following fabrication, its performance verification is carried out using an experimental test setup for PD source. In addition, comparison is made between various UHF antennas regarding their advantage and limitation. The results show that the new UHF antenna is suitable for PD detection in oil-insulated transformer and its ultra-wide bandwidth frequency response can be a useful means for PD recognition.

Development of UHF Sensors for Partial Discharge Detection in Power Transformer

As important fundamental equipment, high voltage switchgears are widely used in electric power systems and directly relative to the power reliability and quality. Partial discharge (PD) online monitoring is one of the most effective methods used for insulation testing and diagnosis in high voltage switchgears and power systems. This paper proposes a unique ultra-wide-band (UWB) antenna with high performance for PD ultra-high-frequency (UHF) detection in high voltage switchgears. Actual PD experiments were carried out, and the designed antenna was used for PD measurements. The measured results demonstrate that the proposed antenna has wide work frequency band, good omnidirectional radiation patterns and appreciable gain, which indicate that the proposed antenna is suitable for UHF online monitoring of PDs in high voltage switchgears.

https://www.jpier.org/pierc/pierc69/11.16052102.pdf

An UWB Printed Antenna for Partial Discharge UHF Detection in High Voltage Switchgears

Double-sided power modules provide another heat dissipation channel to meet the demands of rapidly increased power density for power module. However, double-sided structure incurs reliability issues resulting from chip tilt with large area solder during reflowing process, especially in the region of gate pad. Copper pillar interconnection has been proposed to solve this problem by providing anchoring support during reflowing, though it brings higher thermal stress simultaneously. In this work, the height, diameter and pitch of copper pillar interconnection structures in double-sided power module are analyzed via finite element method. Besides, equivalent thermal model, block model and strip model based on FEM are employed to investigate the influence of different copper pillar interconnection structures on thermal and thermomechanical performance. The results indicate that a finer pitch, larger diameter and smaller height of copper pillar interconnections generate smaller thermal resistance and can obviously reduce the thermal stress. Specifically, the maximum junction temperature variation caused by different structures reaches to 7.49°C. The stresses of chip, copper and solder are decreased up to 33.08%, 33.37% and 9.16% respectively with pitch of 200μm, diameter of 130μm and height of 40μm compared to the structure with maximum stress. The stress distribution of chip and copper pillar at different locations are analyzed, and the stress concentration appears at the interface of chip and copper pillar.

Structure Optimization and Reliability Investigation on Copper Pillar Interconnections for Double-sided Cooling Power Module

With the increasing power density and integration of power electronics for motor drive applications, lower parasitic parameters, higher heat dissipation, thermomechanical reliability, and manufacturability have become the focused requirements of automotive power modules. New structures and materials have been investigated for the packaging of power modules, and wire-bondless packaging technology has become a research focus. In this article, a wire-bondless power module packaging technology based on ball-grid array (BGA) was developed, and a double-sided cooling (DSC) power module was then fabricated and thoroughly investigated. Thermal, electrical, and mechanical properties of the BGA packaged module were analyzed from the aspects of electrothermal coupling, shear performance, and electrical test. Specifically, by using the BGA interconnection, the thermal resistance was decreased by 27.4% compared to the wire-bond module. Parasitic inductance of BGA-based module was measured to be 10.13 nH by the dynamic test under the conditions of 310 V/120 A, which decreased by 33.3% compared to the wire-bond module counterpart. The findings of this work can help advance the design and fabrication of power modules, specifically DSC power modules.

Investigation of Vehicle-Oriented Double-Sided Cooling Power Module With BGA Technology

In comparison to the traditional single-sided cooling (SSC) power module, the double-sided cooling (DSC) power module has gradually become a research hotspot in the electric vehicle (EV) industry. A new Flip chip double-sided cooling (FCDSC) design scheme is proposed in this article, which is adopted Gate-free wire and Pb-free solder, and the Fabrication only needs one reflow. Compared with traditional double-sided cooling (DSC) package forms, the former has better heat dissipation capacity and lower thermo-mechanical stress caused by the mismatched coefficients of thermal expansion (CTE). In this paper, the differences in thermal management and thermomechanical reliability were compared based on finite element analysis (FEA) tool under different power loss and temperature. A parametric study shows that, Compared the FCDSC with the DSC power module, the junction temperature decreased 5.67%, and the thermomechanical stress of IGBT chip decreased 26.34 MPa 31.11%, and the warping of chip is reduced by 1.76μm (15.8%). This study will provide some reference for the development of electric vehicle (EV) implementation.

Cheng Peng

Papers

An UWB Printed Antenna for Partial Discharge UHF Detection in High Voltage Switchgears

Structure Optimization and Reliability Investigation on Copper Pillar Interconnections for Double-sided Cooling Power Module

Investigation of Vehicle-Oriented Double-Sided Cooling Power Module With BGA Technology

Comparative Thermal and Thermomechanical Analyses of Traditional and Flip Chip Double-Sided Cooling Power Module

A New Detection Method for Three-Phase Unbalanced Voltage Sag