Increased voltage blocking capability and the development of packaging technology for IGBTs can enhance the local electric field that may become large enough to increase partial discharges (PDs) within the module. The study presents a survey on (i) simulation the electric field within an IGBT module; (ii) current standards for evaluation of the insulation systems of IGBTs; (iii) PD detection and localisation methods as well as other diagnostic and quality control test methods about IGBTs; and (iv) various methods for PD control in an IGBT module. The survey shows remarkable technical gaps in all four areas. More sophisticated numerical and theoretical techniques are needed to model complicated geometries, e.g. extremely sharp edges of the copper metallisation and protrusions in the substrate, and composite non-linear field grading materials. There is no model to take into account defects in the gel and on the ceramic substrate. IEC 61287-1 cannot sufficiently assess the behaviour of PDs on IGBT module under the actual operating conditions exposing fast rise pulse-width modulation-like voltages. There is no agreement on the exact origin and location of PDs in the module with relying on measured phase-resolved PD patterns. PD control methods using non-linear grading materials are not mature enough.

PD measurements, failure analysis, and control in high-power IGBT modules

The power electronics research community is balancing on the edge of a game-changing technological innovation: as traditionally silicon (Si) based power semiconductors approach their material limitations, next-generation wide bandgap (WBG) power semiconductors are poised to overtake them. Promising WBG materials are silicon carbide (SiC), gallium nitride (GaN), diamond (C), gallium oxide (Ga 2 O 3 ) and aluminum nitride (AlN). They can operate at higher voltages, temperatures, and switching frequencies with greater efficiencies compared to existing Si, in power electronics. These characteristics can reduce energy consumption, which is critical for national economic, health, and security interests. However, increased voltage blocking capability and trend toward more compact packaging technology for high-power density WBG devices can enhance the local electric field that may become large enough to raise partial discharges (PDs) within the module. High activity of PDs damages the insulating silicone gel, lead to electrical insulation failure and reduce the reliability of the module. Among WBG devices, electrical insulation weaknesses in WBG-based Insulated Gate Bipolar Transistor (IGBT) have been more investigated. The chapter deals with (a) current standards for evaluation of the insulation systems of power electronics modules, (b) simulation and modeling of the electric field stress inside modules, (c) diagnostic tests on modules, and (d) PD control methods in modules.

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Electrical Insulation Weaknesses in Wide Bandgap Devices

Insulated power cables are becoming increasingly popular in today’s developing distribution and transportion networks. However, due to aging, deterioration, and various operational and environmental stresses, insulation defects may appear and so the cable needs to be monitored in a timely manner to avoid unexpected failures. Many of these defects are responsible for partial discharge (PD) activity. The localization of the sources of these discharges is a highly decisive facet in the condition-based monitoring of power cables. The techniques for the localization of single-PD defects in insulated power cables are well presented in the current bibliography. However, when several simultaneous PD sources are active, the localization of the sources becomes quite complex. This paper develops an efficient technique for the separation and localization of multiple PD sources in a medium voltage cable. The experimental results are obtained with single-end-based measurements using a high-frequency current transformer in a laboratory environment. The data processing based on the spectral characteristics of the signals is carried out by using the power ratios technique in order to determine the presence of different types of PD. Once the signals are separated, the PD sources can be localized with an individualized analysis of each source through time-domain reflectometry. The proposed methodology can be very valuable to improve the location diagnostic capability of the condition-based monitoring solutions, especially for underground cables.

Multiple Partial Discharge Source Localization in Power Cables Through Power Spectral Separation and Time-Domain Reflectometry

Field-winding fault detection in synchronous machines with static excitation through frequency response analysis

Experimental evaluation of detecting power transformer internal faults using FRA polar plot and texture analysis

This paper investigates on dielectric condition assessment of high power Insulated Gate Bipolar Transistor (IGBT) modules through modern dielectric and diagnostic test methods. Two groups of IGBT samples (new and aged) are selected for this purpose. The new IGBT samples are grouped as 'set-1/virgin' and marked as 'A', 'B', 'C', 'D' and 'E' respectively. Amongst all, a fault (electric puncture) is introduced into the sample 'E'. The samples 'A' and 'B' are maintained virgin while samples 'C', 'D' and 'E' are subjected to partial discharge measurements as recommended by IEC60270. The samples are qualitatively ranked based on their PD level. Subsequently, the dielectric condition of each sample is measured and analyzed over a wide span and frequency. Following this, similar experiments are carried out on IGBT samples that were aged under service and their behaviour over a wide frequency is analyzed. In conclusion, the present study might provide an opportunity in improvement of diagnostic and quality control test methods that are currently exercised on IGBT modules and power conversion devices. Also, these findings enable discrimination of electrical discharges caused by IGBT modules in power conversion equipments which might help in accurate determination of their dielectric condition and reliability.

Dielectric and partial discharge investigations on high power insulated gate bipolar transistor modules

Experimental investigation on terminal connection and system function pair during SFRA testing on three phase transformers

This paper investigates on understanding the influence of condensable hydrocarbons (collectively known as tar) over the dielectric condition of ceramic insulators. Multiple dielectric and diagnostic test methods over a wide frequency range are employed for this purpose. Initially, experiments are conducted on chosen clean and contaminated insulator samples. The influence of tar contaminations on the surface of the chosen samples are quantified through surface dielectric properties such as insulation resistance, loss factor or dissipation factor, impedance and so on. In addition, the partial discharge (PD) that arises over the contaminated surface of the insulator sample is measured and the respective phase resolved PD pattern is analyzed. The recorded PD signals are de-convoluted in frequency domain. Following this, similar experiments are conducted on test insulators contaminated under laboratory condition. The findings of the clean and contaminated samples are experimentally cross-verified on test insulators and later validated on an actual electrostatic precipitator unit. In summary, it is believed that such an investigation might provide an opportunity to gain more knowledge about the electrical characteristics of condensable hydrocarbons.

Dielectric and partial discharge investigations on ceramic insulator contaminated with condensable hydrocarbons

Moisture in a high power Insulated Gate Bipolar Transistor (IGBT) module raises serious concern on component and system level reliability. Employing diagnostic test methods on high power IGBT modules might provide an opportunity in detection and estimation of moisture, however has not received wide attention. This paper investigates on understanding the influence of moisture in high power IGBT modules through time and frequency dependent dielectric response measurements and partial discharge analysis. The moisture in the main insulation of an IGBT module under DC excitation produces a sharp rise in its response current introducing deviation in their respective time dependent dielectric properties. Alternatively, the frequency dependent dielectric response measurements under wide frequencies provide more information than their DC counterpart. This method enables discrimination of various defects such as moisture, physical defects, etc., thereby revealing a clear picture about the actual status. In particular, the lower frequencies reveal longer range ion movements, hence could be used for more accurate estimation of moisture. The higher frequencies though not accurate in moisture estimation reveal deviation in the material properties. These deviations alter the apparent dielectric characteristics such as loss factor, permittivity, etc., of the IGBT samples which becomes clear through simple comparative analysis. In conclusion, the findings in this paper might help in understanding the influence of moisture over the dielectric integrity of a high power IGBT module. Additionally, the permissible or acceptable level of moisture which might act as a threshold to initiate necessary precautionary measures could be subsequently developed.

Influence of moisture on dielectric condition of high power Insulated Gate Bipolar Transistor modules

https://onlinelibrary.wiley.com/doi/pdf/10.1002/eng2.12036

Theoretical considerations while applying sweep frequency response analysis method in determining the interwinding capacitance of power transformers at higher frequencies

Saravanakumar Arumugam

Papers

Dielectric and partial discharge investigations on high power insulated gate bipolar transistor modules

Experimental investigation on terminal connection and system function pair during SFRA testing on three phase transformers

Dielectric and partial discharge investigations on ceramic insulator contaminated with condensable hydrocarbons

Influence of moisture on dielectric condition of high power Insulated Gate Bipolar Transistor modules

Theoretical considerations while applying sweep frequency response analysis method in determining the interwinding capacitance of power transformers at higher frequencies