Insulation Resistance Research Articles

A Simple Magnetic-Flux-Based Method for Localizing High-Resistance Stator Ground Faults in Synchronous Machines

This paper presents a new offline method based on the analysis of the magnetic flux to determine the location of stator ground faults in synchronous machines. First, the defective phase is identified via the insulation resistance (Megger) test, and then the longitudinal axis of the rotor is aligned with the faulty phase winding. During two measuring modes, a voltage is applied separately to each end of the faulty phase while the other end is floating and the core is grounded. The application of the voltage between each terminal of the faulty phase and ground will lead to the circulation of a current through the stator winding to the fault point, being its path closed by the grounded core. A magnetic flux will then be created, which can be sensed indirectly by measuring the induced voltage in the rotor field winding. The fault point can be identified by measuring the applied current or voltage and the magnetic flux created in both measuring modes. Since stator ground faults usually occur via high resistances, the method is extended for the detection of such faults by processing the data using the stationary wavelet transform. The experimental results show that the proposed method is very sensitive and is able to identify the ground fault location for fault resistances up to a few hundred of k-Ohms.

Performance Evaluation of Micro Automatic Pressure Measurement Sensor for Enhanced Accuracy

The major objective of this research is to design sensitive components, conversion components, and various sensor circuits to achieve the miniaturization design for more accurate measurements. This article conducts performance testing on the designed miniaturized pressure sensor to determine whether it meets the qualified standards. The response time of designed sensor results increases with the increase of pressure under experimental conditions of different pressure application values (5MPa to 50MPa). The detection accuracy of the micro automatic pressure measurement sensor designed in this paper can reach 0.0452\%; the average pressure is 0.00364%, and the insulation resistance is 68.44 megohms, which meets reliability requirements. The sensitivity is 0.0582%; the nonlinearity is 0.0741%; the hysteresis is 0.0266%; the repeatability of 0.0625% meets the qualification standard for this instrument. Still, compared with traditional sensors, the sensor reduces the response time of results by about 60%. However, the author conducted the detection in an ideal environment. The actual working environment of sensors is relatively good. Therefore, the detection results obtained in this article may have some errors compared to the actual situation, and further analysis and testing are needed to optimize the performance of the designed sensor.

PERFORMANCE INVESTIGATION OF SINGLE-PHASE TRANSFORMERLESS PV INVERTER CONNECTED TO LOW VOLTAGE NETWORK

Due to their high efficiency and reduced size and weight compared to transformer-based inverters, transformerless single-phase inverters are the most widely used in photovoltaic systems connected to the low-voltage grid. Unfortunately, the absence of galvanic isolation leads to ground faults caused by capacitive leakage current flow and deterioration of the inverter's insulation resistance on the dc side. This paper examines the performance of the three transformerless single-phase inverters of the first grid-connected photovoltaic system in Algeria under adverse weather conditions, such as rain, as there is no galvanic isolation between the dc and ac side of the inverter, making operation of the photovoltaic system more difficult. The flow of capacitive leakage current from the earth to the inverter output is one of the two phenomena, resulting in protection devices being triggered involuntarily. The second phenomenon is system shutdown due to a decrease in the inverter's insulation resistance at the input. The VDE 126-1-1 standard integrated into the inverter, which defines the safety requirements for grid-connected photovoltaic systems, is used in this article to manage and analyze both phenomena.

A Detection Method for Slight Inter-Turn Short-Circuit Fault in Dry-Type Air-Core Shunt Reactors

Dry-type air-core shunt reactors are integral components in power transmission and distribution networks, designed to control reactive power and enhance system stability. However, inter-turn short-circuit faults (ISCFs) are common occurrences in shunt reactors, which are caused by various factors, including manufacturing defects, insulation degradation, or operational stresses. At the early stage of the ISCFs, the current does not reach a sufficient level to activate the protective equipment. These faults may lead to serious consequences, such as overheating, insulation breakdown, and even catastrophic failures, posing risks to the entire power system. Therefore, developing an effective and reliable detection method for ISCFs at the early stage is paramount. In this paper, a new method named the fault detection factor (FDF) based on equivalent resistance is presented to detect the slight ISCFs in dry-type air-core shunt reactors considering insulation resistance. In addition, the effect of noise signal existence in the monitoring process is taken into account. A moving average filter is adopted to guarantee both the sensitivity and the reliability of the proposed method. Ultimately, the simulation results of the FDF under different conditions are presented, which show the effectiveness and potential of the proposed method in observing and monitoring slight ISCFs.

Lightweight carbon nanotube/aramid nanofiber aerogel with superior electromagnetic wave absorption, thermal insulation, and flame resistance

Carbon nanotubes, presenting distinguished electromagnetic wave (EMW) loss capacity and light-weight advantage, are promising candidates for EMW absorption materials. However, poor dispersibility, inadequate processibility, and excessive permittivity leading to impedance mismatch limit the application of carbon nanotubes. Herein, branched aramid nanofiber (ANF) acting as a surfactant, gelling agent, and electromagnetic parameter regulator is utilized to ameliorate the performances of carboxylic multi-walled carbon nanotube (c-MWCNT). The c-MWCNT/ANF aerogels with anisotropic structures are assembled through electrostatic-repulsion-assisted dispersion, hydrogen-bond-induced gelation, unidirectional freezing, and freeze-drying. By adjusting the proportion of c-MWCNT and ANF to optimize the impedance matching and electromagnetic parameters, the composite aerogel with ultralow density (∼26.2 mg cm−3) shows an extraordinary minimum reflection loss of −60.43 dB and a maximum effective absorption bandwidth of 5.34 GHz along the vertical direction of oriented channels. Moreover, benefiting from high porosity and remarkable thermal stability, the aerogels possess prominent thermal insulation and flame resistance. This work provides a strategy for the advanced EMW absorption materials, which have great potential value for aerospace applications under harsh environments.

Ultralow-loss soft magnetic composites with temperature-resistant and insulated Al2O3/SiO2 layers through pyrolysis

Soft magnetic composites (SMCs) with low power loss are urgently needed to meet the increasing demand for high frequency and miniaturized inductors and transformers. Ultrathin cladding with good insulation and high temperature resistance is the key to achieve low-loss SMCs. In this study, we used MQ silicon resin as precursor to produce in-situ grown Al2O3/SiO2 composite insulating layer in FeSiAl SMCs through pyrolysis process and high-temperature reaction. The morphologies, microstructures and compositions of the coatings on the surface were characterized by SEM, TEM, EDS, TG, XRD, FTIR and XPS, and the results show FeSiAl powders are evenly and entirely covered with an inner Al2O3 and outer SiO2 composite insulating layer. The results of powder resistivity show that the insulating layer still maintains very high resistance after annealing at 750 °C. The composite insulating layer had high resistivity and reduced eddy current loss, while the high temperature annealing process reduced stress and defects and resulted in low hysteresis loss. The best magnetic properties were obtained from samples coated with 2.0wt% MQ and annealed at 750 °C, with an effective permeability of 76 and the lowest power loss of 72.2mW/cm3 at 50 mT/100kHz, 88.5mW/cm3 at 100 mT/50kHz and 304.1mW/cm3 at 100 mT/100kHz.

FPGA-Based VFF-RLS Algorithm for Battery Insulation Detection in Electric Vehicles

As the adoption of electric vehicles (EVs) continues to rise, attention has switched to ensuring the safety of EV operations. The exponential growth in battery technology over the past several years has changed the face of energy storage and sparked a revolution in several industries. The degradation of battery insulation during regular use is a significant concern. The high voltage (HV) and current levels in HV electric vehicles pose a significant electrical threat.The advancement of electric vehicle technology has led to an increasing presence of HV electric equipment throughout the vehicle. The insulation strength and early health status detection of the batteries are essential in ensuring safety in EVs. This paper studies the different insulation detection techniques and the development of adaptive filter (AF) algorithms based on field-programmable gate arrays (FPGAs) for insulation detection. FPGAs are amongst the most accurate and fast detection techniques among all the insulation detection techniques used so far in electric vehicles. This study proposes an FPGA-based VFF-RLS algorithm for effectively implementing insulation detection in EVs. The experimental test results using FPGAs demonstrate that the proposed method can rapidly monitor changes in insulation resistance (IR). The VFFRLS-based FPGA technique works sufficiently well to reduce errors when dealing with variations in voltage and resistance conditions at the battery terminals.

High-purity rayon-based carbon fiber felt prepared by halogen gas purification for superior thermal insulation and oxidation resistance

High-purity rayon-based carbon fiber (CFRay) felt holds significant promise for applications in thermal protection systems and semiconductor crystal growth furnaces. This study employs halogen gas purification and high-temperature purification techniques in the fabrication of high-purity CFRay felt. Additionally, the influence of the purification process on the thermal insulation and oxidation resistance of CFRay felt is investigated. The glow discharge mass spectrometer analysis reveals that purification at a lower temperature of 2300 °C achieves a purity level of 6.9 ppm, surpassing both purified CFRay felt without halogen at 2300 °C (56.1 ppm) and high-temperature treated CFRay felt at 3000 °C (10.4 ppm). Thermal insulation and dynamic-static oxidation resistance tests show that the properties of CFRay felt are concurrently affected by the heat treatment temperature. Compared to high-temperature purification, halogen gas purification operates at lower temperatures, preventing the graphitization of CFRay, thereby ensuring high purity while enhancing thermal insulation and demonstrating relatively superior oxidation resistance. This study offers novel insights into the preparation and performance adjustment of high-purity CFRay felt.

Failure analysis on the abnormal cracking of Si3N4 ceramic substrates for SiC power modules in new energy vehicles

Si3N4 ceramic with good thermal conductivity, high mechanical strength and low thermal expansion coefficient is an advanced thermal management material which has been applied to new energy vehicles. At present, with the rapid development of the electric driving technology for new energy vehicles, Si3N4 ceramic has been gradually used in SiC power modules so as to efficiently achieve the functions of heat dissipation, insulation and voltage resistance. Due to its important role in the power conversion process, the reliability of Si3N4 ceramic was vital, and any factor that might lead to its premature failure must be attached importance to. In this paper, a case about abnormal cracking of Si3N4 ceramic substrates during the high and low temperature cycling tests was reported. To solve this problem, various characterization methods were conducted to analyze the density, thermal conductivity, flexural strength, phase structure, morphology characteristics. Finally, through comprehensive analysis, the root cause that resulted in abnormal cracking of Si3N4 ceramic substrates was determined and meanwhile corresponding countermeasures were also proposed. Hopefully, the achievements of this paper will have positive significance for upgrading the quality of Si3N4 ceramic substrates and improving the service reliability of power modules.

High stability and reliability additively manufactured metal-insulator-metal capacitors for high-temperature applications

Throughout the last few years, there has been a significant increase in demand for high-temperature capacitors due to the rising need for electronics in harsh environments, including aerospace, automotive, and oil and gas industries. With the continued growth of electronics in these environments, there is a need for the development of new materials and manufacturing techniques to drive advances in high temperature capacitor technology. Additive manufacturing is one promising approach for producing electronics that can withstand high temperatures, leading to improved performance and reliability in a wide range of applications. The present work describes the fabrication and testing of MIM (metal-insulator-metal) capacitors at high temperatures using gold as the conductor material. The substrates used in this work is 3D printed Lithoz 350D 99.8% alumina. The work details the fabrication process and evaluates the relative permittivity and the dielectric loss of high-temperature dielectric material at temperatures up to 800°C. The adhesion strength at the interfaces is examined before and after aging for up to 250 hours at temperatures as high as 750°C. The leakage current is measured for 100 hours at varying temperatures and the insulation resistance is calculated. Furthermore, the capacitance is monitored during aging at temperatures up to 700°C and frequencies as high as 1 MHz. Finally, the capacitance is measured at room temperature before and after subjecting the capacitors to 100 cycles of thermal cycling at three different temperature ranges. The adhesion between all interfaces of the MIM capacitors is found to remain high even after aging at 700°C, leakage currents are minimal and stable, and the capacitance remained very stable during and after aging and after thermal cycling.

Silica aerogel-PVA dough: A high internal phase composite with superior thermal insulation and gas barrier

Silica aerogel (SA) has shown great promise in constructing thermal insulation composites in various forms. However, it is still challenging to disperse a huge amount of SA particles into other matrices for fabricating superior thermal insulation materials or highly filled masterbatch, owing to its high specific surface area and ultra-low density. Herein, inspired by high internal phase emulsion (HIPE), we successfully prepare processable SA/polyvinyl alcohol (PVA) composites (SA-PVA dough) with over 74 vol% dispersed SA, using a PVA aqueous solution as a binder. This is achieved by gradually mixing a large amount of hydrophobic SA filler into a small amount of PVA aqueous solution. The resulting SA-PVA dough exhibits an internal structure resembling that of HIPEs, with hydrophobic SA particles stabilized in the water phase by amphiphilic PVA chains, tightly packed within the thin continuous PVA aqueous phase. Benefiting from such a HIPE structure, the SA-PVA dough can be easily shaped into various forms and exhibits good applicability in further processing. The dried dough inherits the excellent properties of SA, including ultra-low density, superhydrophobicity (water contact angle: 153°), thermal insulation (thermal conductivity: 0.03 W m−1 K−1), and flame resistance. Moreover, the continuous PVA network structure, combined with the nanoscale pore structure of SA, provides the dough with excellent gas barrier properties, greatly expanding the application scope of SA-based composites.

Maintenance of Pole Mounted Circuit Breaker as Medium Voltage Network Protection at PT PLN (Persero) UP3 Sidoarjo

The increasing demand for electricity requires PT PLN (Persero) to provide a sufficient, reliable, safe, high-quality, and efficient source of electrical energy. In serving customers, especially those in the Medium Voltage (MV) category, good protective equipment is needed. However, conventional protective equipment often tends to be large, requires ample land space, and installation is time-consuming. This research covers variables such as contact resistance measurement, PMT (Power Circuit Breaker) synchronism testing, and insulation resistance measurement. Using the Research and Development (R&D) method, the results of maintenance on the 20 kV PMT at PMCB KPI P. Sidomulyo, Buduran Subdistrict, revealed that the contact resistance measurement values for phases R, S, and T were below 100 µΩ, indicating good contact resistance. PMT synchronism testing produced time difference values that were within the permissible standard limits. The time difference when opening (open) was 0.7 ms, while when closing (close), it was 1.05 ms. Insulation resistance measurements showed values that met the standards, which were above 20 MΩ. Based on the research results, PMCB KPI P. Sidomulyo, Buduran Subdistrict, can still be considered suitable for use. With good protective equipment and measurements that meet the standards, the use of 20 kV PMT can remain efficient and safe for consumers.
 Highlights:
 
 Rising Electricity Demand: PT PLN (Persero) faces increasing electricity needs.
 Advanced Protection Solutions: Innovative equipment addresses conventional limitations.
 Research Insights: Findings ensure safety and reliability in medium voltage systems.
 
 Keywords: Contact Resistance, Insulation Resistance, PMCB, Synchronism Testing

Testing of The Insulation Resistance and Turns Test Ratio (TTR) of The Distribution Transformers at PT PLN (Pesero) UP3 Sidoarjo

Electricity plays a vital role in human life and the economic growth of Indonesia. Therefore, a reliable electrical transmission and distribution system is essential. Transformers, especially in an industrial context, play a key role in power supply. Transformer maintenance is a critical step in maintaining a stable flow of electricity. This study adopts the Research and Development (R&D) method and focuses on measuring insulation resistance and voltage ratios in the context of transformer maintenance. The research was conducted at the Pole Transformer Substation (GTT) in P. Melati, Sidoarjo Regency, East Java, starting in August 2023. The research variables involve measuring the insulation resistance referring to IEC standards and measuring the voltage ratio to ensure proper transformer performance. The test results indicate that the insulation resistance in the transformer, both on the primary and secondary sides, meets the standards, demonstrating that the transformer functions well and safely. Voltage ratio measurements closely approximate theoretical calculations and fall within a tolerance of ± 0.5%. This study underscores the importance of transformer maintenance in maintaining a stable flow of electricity. Proper maintenance will prevent disruptions that can be detrimental, such as current leakage or short circuits. With good maintenance, the continuity of a reliable and safe electricity distribution service for consumers can be ensured.  

A coupled electromagnetic and heat transfer model for casket designing for efficient microwave heating: An insight from theoretical analysis, Multiphysics simulation, and experimental investigations

Microwave heating is extensively used in several industries due to its advantageous capabilities such as volumetric heating, reduced processing time and less energy consumption as compared to conventional heating. Refractory casket insulation is primarily used in microwave heating systems for the purposes of insulation and effective microwave transmission. This investigation aims to provide knowledge and insights for selecting suitable high-temperature refractory insulating casket materials, particularly focusing on three different types: dense alumina, dense alumina-silica, and porous alumina-silica casket. The investigation involves evaluating the microwave transmission efficiency (PTC) and insulation resistance capability of the three casket materials concerning their dielectric and thermophysical properties at varying temperatures. Among three casket materials, porous alumina-silica casket showed a significantly lower values of dielectric constant (1.50 to 1.68), loss tangent (0.000086–0.00318) and thermal conductivity (0.26 W/m·K to 0.50 W/m·K) over the entire temperature range. Consequently, the porous alumina-silica casket exhibited superior insulation and PTC (0.9997 to 0.9876) during microwave heating. The heating phenomenon of each casket material has been established. The COMSOL Multiphysics model was used to analyze the microwave heating behavior of SiC susceptor with varying casket composition and geometry under similar parameters for the first time. A higher heating rate was observed by COMSOL simulation for the porous alumina-silica (58.8 °C/ min) casket than dense alumina-silica (22.31 °C/ min) and dense alumina (9.63 °C/min) casket during microwave heating of SiC susceptor at 1200 W, 1500 s. The COMSOL simulation data were corroborated with experimental results. The study serves a general guideline to select an appropriate casket material for any microwave processing.

A novel method for electric vehicle insulation detection based on the extended Kalman filter algorithm

Addressing the critical need for enhanced safety in the burgeoning electric vehicle market, this study presents a novel insulation detection method based on the Extended Kalman Filter (EKF) algorithm. To resolve the conflict between the response speed and detection accuracy of the insulation detection system caused by Y-capacitors, the Levenberg–Marquardt (L-M) algorithm is employed to effectively estimate the parameters of the feedback voltage model developed for an unbalanced electrical bridge. The state equation of the insulation testing system has been constructed, and the EKF algorithm is applied innovatively to monitor insulation resistance and Y-capacitance, demonstrating superior anti-interference capabilities. Simulation experiments have underscored the significant contributions of the L-M algorithm in expanding the detection scope of the system. Bench tests confirmed the ability of the approach to monitor changes in insulation resistance and Y-capacitance rapidly and accurately. Under normal conditions, the maximum relative error for insulation resistance measurement is 1.56%, with a response time of 1.5 s.

A mixture of Si3N4 powder and SiO2 sand as a novel DC arc quenching medium for improvement of the current-limiting performance of a model electric fuse

A current-limiting and consequent direct current (DC) arc interruption requires an increase in arc resistance rarc for a DC fuse. Flattery silica (SiO2) sand has been used as an arc quenching medium in fuses for decades. However, there are few reports about a novel arc quenching medium which enables more rarc increases compared to flattery SiO2 sand. This paper uniquely selected a novel arc quenching medium based on the following material properties: (1) electrical resistivity and thermal conductivity in the solid phase, (2) the possibility of rarc increasing in the gas phase, (3) the possibility of electrical insulation after re-solidification, and (4) the cost of materials. As a result, we originally selected a powder mixture of silicon-nitride (Si3N4) and flattery SiO2 sand as a promising novel arc quenching medium. Therefore, DC interruption experiments were performed using a Si3N4/flattery SiO2 sand powder mixture under different Si3N4 concentration conditions. As a result of 1000 A DC arc quenching experiments, the utilization of Si3N4 powder with the flattery SiO2 sand successfully increased the arc resistance rarc during the arc quenching process. The increasing Si3N4 concentration exhibited a further increase in rarc during the arc quenching process. As a result of the rarc increase, the arc quenching time was significantly shortened to 30 ms for 30 wt.% Si3N4 conditions from 54 ms for the SiO2 sand conditions. In addition, utilization of Si3N4 powder achieved high insulation resistance over few MΩ after DC arc interruption. The above results clearly indicate that utilization of Si3N4 powder with flattery SiO2 sand can increase the DC interruption performance of the fuse.

Development of Electrolyte with Enhanced Corrosion Resistance for Sn Electroplating on Multi-Layer Ceramic Capacitors

Capacitors not only store and release electricity but selectively conduct alternating current. Among the various types of capacitors, multi-layer ceramic capacitors (MLCCs) have been widely used in automotive, smartphone, and wearable devices because of their compact size and high capacitance capabilities. In this study, we have developed an electrolyte for tin electroplating on multi-layer ceramic capacitors (MLCCs) to address the barium leaching issue at the termination points of the MLCCs. This issue has been effectively mitigated by introducing NaHSO<sub>4</sub> into the conventional tin plating electrolyte as a corrosion inhibitor. This addition facilitates a rapid reaction between the dissolved barium ions and NaHSO<sub>4</sub>, resulting in the formation of a thin passivation layer on the surface of the MLCC. The BaSO<sub>4</sub> passivation layer effectively prohibits excessive leaching of barium ions from the glass in MLCCs, thereby maintaining chip insulation resistance and preventing crack formation. However, the chemical reaction of NaHSO<sub>4</sub> and the formation of the passivation layer can lead to the generation of tin hydroxide precipitates due to pH fluctuations. To address this issue, we increase the amount of complexing agent from 100 g/L to 130 g/L. This adjustment enhanced the ability of tin ions to form stronger complexes, thereby enabling stable electrodeposition on the termination of MLCC. Consequently, the final electrolyte for Sn electroplating (denoted as LW-3) simultaneously achieves corrosion resistance and practical working efficiency, resulting in a uniform 5.4 μmthick tin plating layer with outstanding solderability, and high temperature/humidity stability.

EXTINGUISHING TIME OF OIL PRODUCT TANK FIRES WITH SELF-EXPANDING GAS-AEROSOL-FILLED FOAM

EXTINGUISHING TIME OF OIL PRODUCT TANK FIRES WITH SELF-EXPANDING GAS-AEROSOL-FILLED FOAM

Influence of different test methods on the accuracy of high current busbar insulation resistance

Compared with the traditional cable, the high current busbar fully embodies its superiority in the process of current transmission, and thus its insulation performance test is of great significance to the safe operation of the line. In this paper, the insulation resistance of the high current busbar is measured by the basic test principle and the voltage injection test method respectively, and then the accuracy and precision of the two test methods are compared. The test results show that the relative error of insulation resistance of positive and negative busbar fluctuates in the range of 0.35%-4.20% and 0.10%-3.33%, respectively, while that of voltage injection test fluctuates in the range of 0.60%-2.80% and 1.10%-1.80%, respectively. Regardless of the basic test principle or voltage injection test, the relative error of insulation resistance in the high current busbar is less than 5%, and the voltage injection test method is more accurate. Compared with the basic test principle, the maximum relative error of Rn and Rp is reduced by 0.87% and 1.00% respectively.

High-efficiency electromagnetic wave absorption of lightweight Nb2O5/CNTs/polyimide with excellent thermal insulation and compression resistance integration

With the widespread application of electronic devices, multifunctional electromagnetic wave (EMW) absorbing materials suitable for complex high-temperature and high-pressure environments, have attracted tremendous research attention. Herein, multifunctional polyimide (PI) composites doped with fluffy Nb2O5/CNTs microspheres (NBCP) were prepared by combining the ultrasonic spraying process and freeze-drying technique. Introduction of fillers results in the formation of diverse conduction paths and heterogeneous interfaces, which enhance the dielectric loss. Furthermore, the multi-porous structure of the PI matrix induces multiple reflection scattering events and improves the impedance matching. Such a multi-loss mechanism endows NBCP with an excellent EMW absorption performance. At 15 vol% filling, the minimum reflection loss is −41.66 dB, the effective absorption bandwidth is 2.63 GHz, and the radar cross-section is reduced by 85%. Furthermore, NBCP exhibits outstanding mechanical properties and a thermal insulation of over 100 °C in thermal environment at 150 °C. The proposed multifunctional NBCP is thus an efficient EMW absorber that offers significant potential for applications in harsh environments.