Insulation Failure Mechanisms Research Articles

High-Temperature Failure Mechanism and Lifetime Assessment of Silicone Gel Package Insulation for High-Power Electronic Devices Based on Pyrolysis Kinetics

High-Temperature Failure Mechanism and Lifetime Assessment of Silicone Gel Package Insulation for High-Power Electronic Devices Based on Pyrolysis Kinetics

Insulation Failure Mechanism of Polyimide under High-Frequency Electrical Stress: A Synergistic Analysis of Aging Experiments and Molecular Dynamics Simulations

Insulation Failure Mechanism of Polyimide under High-Frequency Electrical Stress: A Synergistic Analysis of Aging Experiments and Molecular Dynamics Simulations

Impact of step voltage parameters on accuracy of evaluating XLPE insulation DC voltage endurance coefficient

AbstractThe voltage endurance coefficient n of cross‐linked polyethylene (XLPE) insulation is an important indicator for the analysis of insulation failure mechanism. Accurately obtaining the value of n can provide technical support for the reliability evaluation of cable operation. The constant stress method and the step stress method are used to obtain the values of n, but the test parameters can influence the accuracy of the obtained n values. Two methods for selecting test parameters are proposed. The equivalence between the two methods is established, providing theoretical support for the accurate evaluation of the n value of solid insulation materials by using the step stress method. The accuracy of the evaluation results is verified by analyzing the test data. The test results show that the nstep = 13.04 evaluated by the step stress test with the proposed parameter selection method is consistent with the test result of constant stress nconstant = 12.83.

The Time, Electric Field, and Temperature Dependence of Charging and Discharging Currents in Polypropylene Films.

The insulating properties of polypropylene (PP) film play a very important role in the operating status of direct current (DC) support capacitors. Charging and discharging currents in PP film under high DC electric fields and temperatures correspond to charge transportation and accumulation, which significantly influence the electrical insulating properties of PP. In this paper, we have comprehensively studied the dependence of charging/discharging currents in PP film on time, electric field (150-670 kV/mm), and temperature (40-120 °C). The results showed that the charging current increased by almost an order of magnitude from 150 kV/mm to 670 kV/mm and exhibits a steep increase with temperature above 80 °C. The discharging currents are about 10 times less than the corresponding charging currents. Carrier mobility varies little with the electric field and becomes slightly larger with an increase in temperature. The quantity of the accumulated charges was calculated by the integral of the charging and discharging current differentials and showed a significant increase with the electric field and temperature. The corresponding electric field distortion becomes larger above 80 °C compared to 20-60 °C. Both electric field and temperature have an important effect on PP film and capacitors based on charge transport and accumulation and their electric field distortion. This study is innovative in that it combines the operating status of DC support capacitors with traditional methods to research synthetically charged transport mechanisms of PP film. The findings are meaningful for understanding the insulation failure mechanisms of PP film and capacitors under complex stresses.

The Lifetime Prediction and Insulation Failure Mechanism of XLPE for High-Voltage Cable

The performance parameters and service life of the insulation layer of high-voltage cables are the key to ensure safe cable operation. Through extracting the mechanical parameters of high voltage cable insulation layer under different thermal aging temperatures, a normal linear regression model is established to predict the service life of high voltage cables. Meanwhile, the physicochemical characteristics such as microscopic morphology and molecular structure changes of the cable insulation layer are analyzed, the dielectric properties and breakdown field strength under ac condition are tested and the macroscopic electrical properties of the insulation layer are studied, and the insulation failure mechanism is further analyzed. The experimental results show that the elongation at break retention rate of cross-linked polyethylene (XLPE) increases slowly with the aging time, and then decreases rapidly when it reaches 50% of the initial elongation at break retention rate. The normal linear regression prediction model is established based on the Arrhenius formula, and it can be obtained the life endpoint of XLPE high voltage cable about 65 years at an operating temperature of 70 °C. Further analysis, under the action of heat and oxygen, the crystal zone structure of cable insulation is seriously damaged, and the carbonyl index is significantly increased. Accordingly, when the aging failure point is reached, the dielectric permittivity and dielectric loss of insulation are significantly increased, and the breakdown performance is significantly decreased. The work has an important guiding significance for insulation condition assessment and life prediction of high voltage cable.

An Advanced Ceramic Material for Internal Insulation Used in Gas-Insulated HVDC Apparatus

The traditional polymer insulating material has encountered a bottleneck in improving the surface insulation performance in gas-insulated high voltage direct current (HVDC) apparatus. In this article, an advanced ceramic insulating material is proposed, which has great potential to be utilized in HVDC apparatus. The short-time and long-time surface insulation properties of the ceramic material are researched and compared with those of epoxy composite widely used at present. The conductivity and temperature dependence of the ceramic material is significantly lower than the epoxy composite. The surface charge accumulation and trap evolution characteristics of the ceramic can improve the surface electric field distribution. The long-time test further verifies its reliability, where the failure probability of the ceramic is 74% lower than that of the traditional material. This work may provide a basis for the application of the ceramic material in gas-insulated HVDC apparatus and may be helpful in understanding the surface insulation failure mechanisms in electro-thermal conditions.

Study on Failure Mechanism of Oil Paper Insulation Under Partial Discharge of Interlayer Bubble

Partial discharge (PD) induced by bubble will reduce the insulation performance, lead to insulation failure and seriously affect the safe operation of power transformer. Studying the influence of PD in internal bubble on oil paper insulation and understanding the insulation failure mechanism can provide guidance for engineering practice. In this paper, a bubble PD defect model is designed to obtain the mechanism of PD degrading insulation. The inception and breakdown voltage of PD decrease seriously with the increase of bubble area and height. Combined with the surface state of breakdown paper observed by electron microscope, it is concluded that PD can induce the breakdown of oil paper insulation. Then, through the comparative analysis of bubble area and PD parameters, a positive feedback model for insulation degradation is obtained, representing that bubble defects will deteriorate rapidly in exponential form under the effect of PD. Finally, combined with the electron microscope and energy spectrum analysis, the deterioration process of insulating paper is divided into four stages, obtaining the micro deterioration and failure mechanism of insulating paper. This study contributes to understanding the mechanism of insulation failure by bubble, as well as provides a reference for risk assessment of transformers.

Electro-thermal comprehensive analysis method for defective bushings in HVDC converter transformer valve-side under multiple-frequency voltage and current harmonics

The insulation failure mechanism of the resin impregnated paper (RIP) valve-side bushings of HVDC converter transformer under high ambient temperature and strong electromagnetic field conditions is explored in this study via a novel electro-thermal comprehensive analysis method. Considering that the bushings are operating under Multiple-Frequency Voltage and Current Harmonics, a superposition analysis method is established for voltage and current with five frequencies based on a Fourier spectrum analysis of the rated voltage waveform and full-load current waveform. Calculation methods for the heat loss, temperature field, and electric field of RIP bushings at the converter transformer valve-side are then established under two defect conditions: (1) overheating defect caused by an abnormal spring contact at the copper-aluminium conductive tube transition joint and (2) electric potential suspension caused by disconnection between the outmost condenser’s foil layer and grounded flange. An overheating defect in a valve-side bushing with spring contact at the conductive tube is successfully identified by the proposed method to prove its effectiveness. This method can be used to optimize bushing insulation and current-carrying structures as well as to diagnose insulation failures in RIP valve-side bushings.

Electrochemical Migration of Immersion Silver Plated Printed Circuit Boards Contaminated by Dust Solution

Due to the severe air pollution, printed circuit boards (PCB) in electronic products are apt to be covered by airborne dust deposition. The trace amounts of soluble salts in the dust particles increase ion concentration in the moisture condensed on the PCB surface so that the electrode reaction of electrochemical migration (ECM) is aggravated and the time to insulation failure also changes. In this article, based on the ion compositions analysis of soluble salts in natural dust collected indoor in northwest Beijing and eastern Shanghai, China, the effect of the anions in typical soluble salts (NaCl, Na2SO4) in natural dust on insulation failure mechanism and TTF of ECM of PCB is investigated by water drop tests on parallel wires on immersion silver plated PCB. Compared with PCB contaminated by single salt solution with different concentrations, the ECM characteristics of PCB covered by natural dust solution of various mass concentrations are analyzed. A failure physics-based life model of ECM of PCB under contamination of salt solution is fitted by the simulation tests of both the single salt solution and natural dust solution respectively. The mechanism and degree of action of soluble salts in natural dust on the ECM failure on PCB is discussed finally.

Effect of Air Gap on Electrical Tree in Epoxy Resin Under High Frequency Bipolar Square-Wave Voltage.

Insulation fails quickly under high-frequency AC high voltage, especially bipolar square-wave voltage with a high dV/dt. It is of great significance to study the failure mechanism of epoxy casting insulation under such kind of voltage. In this paper, pin-plane epoxy casting insulation samples with air gaps were prepared, and the relation between the electrical trees under the high frequency bipolar square-wave voltage and the air gap conditions and voltage frequencies (1~20 kHz) were studied. Results indicated that, with the presence of air gaps, the electrical trees were bush-type and had a relatively slow growth rate, which was different from the fast-growing branch-type trees in the samples without air gap. The electrical tree characteristics related with the size of air gap and voltage frequency were also studied. The electrical tree grew faster under higher voltage frequency or with a smaller air gap. Results proved that discharge introduced a lot of defects for the surface layer of the epoxy resin samples and hence induced the possibility of multi-directional expansion of electrical trees. In addition, the resulting heat accumulation and unique charge transport synergistically affected the electrical tree characteristics under the high frequency bipolar square-wave voltage.

Degradation Monitoring of Insulation Systems Used in Low-Voltage Electromagnetic Coils under Thermal Loading Conditions from a Creep Point of View.

Electromagnetic coils are a key component in a variety of systems and are widely used in many industries. Because their insulation usually fails suddenly and can have catastrophic effects, degradation monitoring of coil insulation systems plays a vital role in avoiding unexpected machine shutdown. The existing insulation degradation monitoring methods are based on assessing the change of coil high-frequency electrical parameter response, whereas the effects of the insulation failure mechanisms are not considered, which leads to inconsistency between experimental results. Therefore, this paper investigates degradation monitoring of coil insulation systems under thermal loading conditions from a creep point of view. Inter-turn insulation creep deformation is identified as a quantitative index to manifest insulation degradation changes at the micro level. A method is developed to map coil high-frequency electrical monitoring parameters to inter-turn insulation creep deformation in order to bridge the gap between the micro-level and macro-level changes during the incipient insulation degradation process. Thermally accelerated tests are performed to validate the developed method. The mapping method helps to determine the physical meaning of coil electrical monitoring parameters and presents opportunities for predictive maintenance of machines that incorporate electromagnetic coils.

Failure mechanism of transformer oil-immersed cellulosic insulation induced by sulfur corrosion

The life of transformer oil-paper insulation is determined by the insulation property of transformer cellulosic insulation. Existing studies have shown that sulfur corrosion poses a serious threat to the properties of transformer oil-immersed cellulosic insulation due to the reaction of corrosive sulfur dissolved in oil with copper winding. This paper investigated the effect of sulfur corrosion on the characteristics of transformer cellulosic insulation, cellulosic insulation winding samples with different degrees of sulfur corrosion were obtained through an accelerated thermal aging experiment. Then, short-/long-term withstand voltage tests for the cellulosic insulation winding were conducted. Experimental results showed that the contamination of sulfur corrosion had a minimal effect on the power–frequency breakdown voltage of the cellulosic insulation winding but considerably decreased its long-term electrical life. Combined with the analysis of the electrical/physical and chemical parameters of oil-immersed cellulosic insulation, the failure mechanism of transformer oil-immersed cellulosic insulation induced by sulfur corrosion was synthetically discussed and analyzed.

Insulation Failure Mechanism of Immersion Silver Finished Printed Circuit Board Under NaCl Solution

Various kinds of contaminants depositing on printed circuit board (PCB) assembly in electronic products, such as the airborne dust and the process residues, can aggravate the condensation on the PCB surface and increase the ion concentration of the water film on the PCB, which further degrades the insulation of the PCB based on electrochemical migration (ECM). This paper investigates the insulation failure mechanism of immersion silver (ImAg) finished PCB under sodium chloride (NaCl) solution. A Y-pattern PCB was adopted to simulate the ECM failure of the PCB under different concentrations of NaCl solution by water drop tests. Through the on-line monitoring of the surface insulation resistance of PCB, as well as the dendrite morphology and the compositions detection at different reaction stages and different locations between two parallel electrodes, the similarities and differences of the insulation failure characteristics and mechanism of ImAg finished PCB under various concentrations of NaCl solution were analyzed. The effect of chloridion on ECM was discussed by combining the electrochemical theory.

Development and performance of a ductile shear tie for precast concrete insulated wall panels

This paper presents the development and experimental evaluation of a new ductile shear tie system for precast concrete insulated wall panels subjected to large flexural demands from blast or impact loading. The ties develop a stable plastic hinge mechanism with a multi-legged design, enabling larger inter-wythe shear deformations without sacrificing structural integrity. The performance of these ties is assessed in conjunction with two types of rigid insulation, extruded (XPS) and expanded polystyrene (EPS), that are commonly used for insulated precast concrete façade panels. Shear test specimens with either bonded or unbonded insulation layers were both fabricated to determine the individual contributions of the shear ties and insulation to the total shear strength. A double shear experimental test procedure is proposed to mechanically emulate the flexure-induced behavior of shear ties in insulated wall panels. A series of shear tests was conducted, first under semi-static loading and then at higher strain rates to quantify shear resistance of panels subjected to blast loading. A qualitative comparison is made between failure mechanisms of XPS and EPS insulation, and the new tie is able to achieve a reliably high level of shear deformation ductility relative to other commercially available ties. The shear resistance backbone curves obtained from this study can be used as input for enhanced design and analysis of precast concrete insulated wall panels to resist blast loading.

Thermal response properties and surface insulation failure mechanism of epoxy resin under arc ablation

Arc ablation during the operation of HVDC circuit breakers can cause irreversible damage to the epoxy resin (EP) insulation pull rod. This is one of the critical factors that affect the reliability and lifetime of a HVDC circuit breaker. In this work, we built an arc ablation experimental platform and studied the thermal response properties of EP insulation under arc ablation. The surface charge evolution characteristics and the dielectric properties were analyzed to reveal the underlying surface insulation failure mechanism of EP after arc ablation. The results indicate that arc ablation can cause severe carbonization to EP insulation. With increasing arc duration, the EP gradually transforms into carbide and pore products. Arc ablation can decrease the molecular moment orientation polarizability and the relative dielectric constant of EP insulation, and thereby increasing the current density formed by Schottky injection. Therefore, when the external electric field is applied, the charge on EP insulation surface migrates from high voltage electrode to the ablating area, causing the regional accumulation of surface charge and the formation of local failure area. This can decrease the surface electrical performance of EP insulation and lead to insulation failure finally.

Review of accumulative failure of winding insulation subjected to repetitive impulse voltages

The premature failure phenomenon that occurs in solid insulation under the application of repetitive impulse voltages is known as the accumulative effect of impulse voltages on a solid dielectric. The accumulative failure of winding insulation is considered to be a core problem resulting from this phenomenon. The main problems include the accumulative failure of motor winding insulation under pulse-width modulation impulses and the accumulative failure of transformer winding insulation under the application of overvoltages, and these problems represent new challenges in the safe and stable operation of power grids. With regards to the above problems, this study reviews the results of recent research on the accumulative failure characteristics and mechanisms of winding insulation when subjected to repetitive impulse voltages. The challenges faced are discussed at the end of this study.

Bulletin board [2019 IEEE Electrical Insulation Conference

The 37th IEEE Electrical Insulation Conference (EIC) will be held in Calgary, Canada, June 16 to 19, 2019. The EIC is the primary conference of the IEEE Dielectrics and Electrical Insulation Society that is devoted to the practical application of electrical insulation to electrical and electronic apparatus. Almost 200 abstracts have been accepted for presentation in three parallel oral sessions and two poster sessions at the Hyatt Regency in Calgary. A review of the abstracts shows that the 2019 conference will continue with its strong focus on the practical aspects of new insulation materials, failure mechanisms, and testing. As usual, the papers are from both industry and academia.

Partial discharge measurement and analysis in PPIs

Electrical insulation capability is one of the most critical challenges for press-pack insulated gate bipolar transistors (IGBTs), but the knowledge of its insulation failure mechanism is much less mature. To understand the insulation failure mechanism, partial discharge (PD) measurement and analysis in press-pack IGBT (PPI) submodule were performed in this study. A dedicated PD measurement system for PPIs was designed and fabricated, and fast oscilloscope, PD detector and ultraviolet (UV) image camera were employed to observe the PD. PD-induced insulation failure phenomenon in the submodule was observed under direct current voltage, and UV images indicated that the discharge occurred at the periphery of the die. Phase-resolved PD (PRPD) analysis method for PPIs was developed and three elementary structures were used to simulate the PD in the electric field reinforcement areas identified by electric field analysis. According to PRPD patterns, the observed PD in the submodule was considered to be mainly caused by a mismatch between the electric field and critical electric field on the surface of passivation layers of the die. The inference was verified at different gas pressures because a decrease of PD inception voltage in the submodule and the bare die was observed at lower gas pressure.

Abstract 14872: Sensitivity of Cinefluoroscopy Compared With Visual Inspection of the Extracted Lead for Detection of Conductor Externalization of Riata/Riata St ICD Leads

Background: The Riata/Riata ST implantable cardioverter defibrillator (ICD) lead series (St Jude Medical, Sylmar, CA) is vulnerable to a characteristic insulation failure mechanism which results in conductor externalization (CE). This may be visible on cinefluoroscopy, however the sensitivity of this test is unknown when compared with direct visible inspection of extracted leads. Methods: We retrospectively reviewed the records of patients with Riata leads extracted at our center since 01/01/2011, and compared CE on fluoroscopic imaging before extraction with the visual appearance of the extracted lead ex vivo. Cinefluoroscopy of the Riata lead was performed in three planes: posteroanterior, left and right anterior oblique. CE was defined as a conductor that had breached the outer insulation material and was clearly visible outside the lead body on fluoroscopy. Ex vivo, CE was defined as externalization of the conductor cable(s) visible on inspection of the extracted lead with a corresponding linear insulation defect. Results: Of 424 patients with Riata leads 37(8.7%) patients underwent extraction with a mean implant duration of 6.24 years ±1.9 years. The indication for extraction was infection in 12 (32.4%); 7 (18.9%) for electrical or structural lead failure and other indications in 18 (48.6%). CE was evident on cinefluoroscopy in 8 (21.6%) patients before extraction including 2 (25%) leads extracted for electrical failure. Post extraction, CE was visible in an additional 3 (8.1%) leads including 1 (33%) extracted for electrical failure. Overall sensitivity was 72.7%. Conclusions: Cinefluoroscopy has suboptimal sensitivity for detection of CE in Riata ICD leads. The absence of CE on cinefluoroscopy does not imply that the outer insulation is structurally intact. Our results suggest that routine cinefluoroscopy of Riata/Riata ST leads is of limited utility.

Partial discharge characteristics of interturn insulation used for inverter-fed traction motor under bipolar impulses

Inverter-fed traction motors, which are employed for electric-multiple-units (EMUs), are subjected to Pulse Width Modulated (PWM) impulse voltage. Impulse voltage has fast rise/fall time and high repetition frequency. The failure mechanism of insulation under impulses is different from that of standard 50 Hz sinusoidal condition. Partial discharge (PD) characteristics (discharge number, mean discharge quantity and phase resolved partial discharge (PRPD) pattern) with different frequencies and different rise times of impulse voltage were investigated. The results reveal that discharge number and mean discharge quantity increase, while PRPD pattern moves to the zero of impulse voltage with decrease of rise time. Discharge number and PRPD pattern follow that trend with increase of frequency, the value of mean discharge quantity is similar. Memory effect of the deposited space charges on PD was studied. PRPD pattern moves to the zero of bipolar impulse voltage due to the role of space charges, with increase of frequency and decrease of rise time. It is revealed that available discharge time is prolonged and overvoltage across the cavity increases with augment of frequency, which results in discharge number increasing. Under the condition of shortening the rise time, with the same statistical time lag tL, ∆V would increase if dV/dt is higher, which results in enhancement of discharge quantity. Discharge number increases with reduction of rise time, because the decreased multiple of td is lower than the increased multiple of dV/dt. Study of PD characteristics and role of space charges is helpful to the exploration of the destructive mechanism of insulating materials under bipolar impulse. partial discharges, bipolar impulse, interturn insulation, electric-multiple-units, memory effect, space charges