Insulation Resistance Measurements Research Articles

A review of condition monitoring techniques and diagnostic tests for lifetime estimation of power transformers

Power transformers are a key component of electrical networks, and they are both expensive and difficult to upgrade in a live network. Many utilities monitor the condition of the components that make up a power transformer and use this information to minimize the outage and extend the service life. Routine and diagnostic tests are currently used for condition monitoring and appraising the ageing and defects of the core, windings, bushings and tap changers of power transformers. To accurately assess the remaining life and failure probability, methods have been developed to correlate results from different routine and diagnostic tests. This paper reviews established tests such as dissolved gas analysis, oil characteristic tests, dielectric response, frequency response analysis, partial discharge, infrared thermograph test, turns ratio, power factor, transformer contact resistance, and insulation resistance measurements. It also considers the methods widely used for health index, lifetime estimation, and probability of failure. The authors also highlight the strengths and limitations of currently available methods. This paper summarizes a wide range of techniques drawn from industry and academic sources and contrasts them in a unified frame work.

Погрешность способа измерения сопротивления изоляции в цепях постоянного тока и ее устранение

Погрешность способа измерения сопротивления изоляции в цепях постоянного тока и ее устранение

The Uncertainty Evaluation and Analysis of Influencing Factors for the Insulation Resistance Measurement of Wire and Cable

阐述了绝缘电阻的定义及重要性；分析了测量方法对绝缘电阻测量结果的影响；建立了绝缘电阻测量不确定数学模型，并确定了不确定分量的灵敏度系数。测量了BV线的绝缘电阻，并确定了不确定分量的评定方法，计算得到测量扩展不确定度。最后提出了测量绝缘电阻的建议。 The importance and definition of insulation resistance were discussed. The influence produced by measurement method was analyzed. The mathematical model was built, and sensitivity coefficient of uncertainty components was determined. Insulation resistance of wires with the model BV was measured, and evaluation method of uncertainty components was determined, and expanded uncertainty was obtained. Proposal for measurement of insulation resistance was presented.

Inter-laboratory proficiency tests in measuring thermal insulation and evaporative resistance of clothing using the Newton-type thermal manikin

Clothing acts as an important barrier for heat and vapor transfer between the human body and the environment. Parameters that could describe that transfer include, inter alia, thermal insulation (the so-called dry heat exchange) and evaporative resistance (the so-called wet heat exchange). Once the above-mentioned parameters are determined, it is possible to consciously adapt clothing ensembles to the existing thermal environment in the workplace. In order to validate the mentioned method of thermal insulation and evaporative resistance measurements, proficiency tests (PTs) were organized. The main goal of the PT was to compare thermal insulation and evaporative resistance for one set of clothing using the Newton-type thermal manikin. In total, four laboratories participated in the PT study. The reference value of the thermal insulation ( It) and evaporative resistance ( Ret) were calculated as the mean of all the results. The assessment criteria included permissible errors for thermal insulation and evaporative resistance measurements, which were 4% and 10%, respectively. Calculations included, inter alia, z-scores and indicators, such as the inter-laboratory coefficient of variation or the reproducibility limit. The results contribute to the worldwide discussion on standardized studies of evaporative resistance of clothing.

발전소에서 운전 중인 고전력 케이블의 절연저항의 변화를 감시하는 장치의 개발

발전소에서 운전 중인 고전력 케이블의 절연저항의 변화를 감시하는 장치의 개발

활선 고전력 케이블의 절연저항을 측정하기 위한 시스템 설계 및 측정결과

활선 고전력 케이블의 절연저항을 측정하기 위한 시스템 설계 및 측정결과

Degradation of mono-crystalline photovoltaic modules after 22 years of outdoor exposure in the composite climate of India

The understanding of degradation modes and mechanism is very important in order to ensure the lifetime of 25–30years of PV modules. In the present study, degradation analysis of 90 mono-crystalline silicon PV modules installed on the rooftop of the guest house of National Institute of Solar Energy (NISE), Gurgaon has been carried out after 22years of outdoor operation in a composite climate of India. A comprehensive analysis has been carried out through visual inspection, thermal imaging, I-V characteristic and insulation resistance measurement as well as rate of degradation has been calculated. The defects in bus bar, cell inter-connection ribbon, string inter-connection ribbon and chalking in back-sheet are found to be most frequently observed defects. Hot spot in solar cell, burn mark and delamination in back-sheet are also observed in some PV modules. The average power degradation rate of 90 PV modules over period of 22years has been found to be about 1.9%/year with maximum rate of power degradation 4.1%/year and minimum is 0.3%/year. Insulation resistance measurement of all the modules both in dry and wet condition showed that only 9 modules have shown insulation resistance <400MΩ. The study addresses the degradation mechanism in order to assess the safety issues related to the large scale PV plants in Indian climatic condition.

Testing of the fire-proof functionality of cable insulation under fire conditions via insulation resistance measurements

Two different designs for low-fire-hazard cables were tested under conditions similar to those of the fire test specified in IEC 60331-21. In addition to the other standard requirements, an insulation resistance meter was connected directly to the measurement circuit to monitor the actual state of the cable insulation during the fire tests. The suitability of this measurement of the insulation resistance was demonstrated by testing cables with fire barriers made from mica glass tape and from ceramifiable silicone rubber. The results showed that insulation resistance is sensitively affected by the melting of the organic components of insulation, by the decomposition of the fire retardant, by the ignition of the core insulation and by the formation of a silica layer during a fire test. The results also helped to reveal the importance of flame conductivity in performing such tests. The initial observations are supported by thermogravimetry and differential scanning calorimetry, which are beneficial as a first step towards understanding the mechanisms of fire-proof functionality in cables. The suggested procedure can assist in the comparison of the fire-proof functionalities of different cable designs, in the analysis of their failure mechanisms and in cable design optimisation.

Ultrahigh impedance method to assess electrostatic accelerator performance

This paper describes an investigation of problem-solving procedures to troubleshoot electrostatic accelerators. A novel technique to diagnose issues with high-voltage components is described. The main application of this technique is noninvasive testing of electrostatic accelerator high-voltage grading systems, measuring insulation resistance, or determining the volume and surface resistivity of insulation materials used in column posts and acceleration tubes. In addition, this technique allows verification of the continuity of the resistive divider assembly as a complete circuit, revealing if an electrical path exists between equipotential rings, resistors, tube electrodes, and column post-to-tube conductors. It is capable of identifying and locating a ``microbreak'' in a resistor and the experimental validation of the transfer function of the high impedance energy control element. A simple and practical fault-finding procedure has been developed based on fundamental principles. The experimental distributions of relative resistance deviations ($\mathrm{\ensuremath{\Delta}}R/R$) for both accelerating tubes and posts were collected during five scheduled accelerator maintenance tank openings during 2013 and 2014. Components with measured $\mathrm{\ensuremath{\Delta}}R/R&gt;\ifmmode\pm\else\textpm\fi{}2.5%$ were considered faulty and put through a detailed examination, with faults categorized. In total, thirty four unique fault categories were identified and most would not be identifiable without the new technique described. The most common failure mode was permanent and irreversible insulator current leakage that developed after being exposed to the ambient environment. As a result of efficient in situ troubleshooting and fault-elimination techniques, the maximum values of $|\mathrm{\ensuremath{\Delta}}R/R|$ are kept below 2.5% at the conclusion of maintenance procedures. The acceptance margin could be narrowed even further by a factor of 2.5 by increasing the test voltage from 40 V up to 100 V. Based on experience over the last two years, resistor and insulator failures are less common now due to the routine use of the noninvasive ultrahigh impedance technique.

Analysis of Partial Discharge Patterns for Generator Stator Windings

Forced outage of generators due to stator winding insulation failure can result in significant financial loss because of the high cost repair and loss of production. In recent years, the demand for insulation diagnosis is increasing to prevent unexpected failures, as the capacity of generators has increased. Insulation diagnosis is composed of the insulation resistance measurement, polarization index measurement, dissipation factor (DF) tip-up test, AC current increasing ratio measurement, and the partial discharge (PD) measurement. In this paper, the results of the PD measurement and PD pulse pattern analysis performed on a healthy generator and two generators that experienced dielectric breakdown failure during operation is presented.

Insulation Resistance and Leakage Currents in Low-Voltage Ceramic Capacitors With Cracks

Measurement of insulation resistance (IR) in multilayer ceramic capacitors (MLCCs) is considered a screening technique that ensures the dielectric is defect-free. This paper analyzes the effectiveness of this technique for revealing cracks in ceramic capacitors. It is shown that absorption currents prevail over the intrinsic leakage currents during standard IR measurements at room temperature. Absorption currents, and consequently IR, have a weak temperature dependence, increase linearly with voltage (before saturation), and are not sensitive to the presence of mechanical defects. On the contrary, intrinsic leakage currents increase super-linearly with voltage and exponentially with temperature (activation energy is in the range from 0.6 to 1.1 eV). Leakage currents associated with the presence of cracks have a weaker dependence on temperature and voltage compared with the intrinsic leakage currents. For this reason, intrinsic leakage currents prevail at high temperatures and voltages, thus masking the presence of defects.

Methods for predicting corrosion on electronic products

Surface insulation resistance (SIR) measurements have become necessary to perform, especially due to the introduction of lead free solders. It has been reported that SIR and other test methods have to be used for evaluating the reliability of printed wiring boards. This paper presents an investigation on how the SIR test environment influences the test results. The factors varied were temperature and humidity. The temperature was varied between 40 and 85°C, and the relative humidity was varied between 60 and 85%. Furthermore, the influence of different types of process chemicals on SIR was evaluated. Seven lead free solder pastes, of which five were no-clean and two were water soluble, were compared. The influence of using conformal coating was also studied. These solder pastes were used to verify the developed method. A proper test method for SIR measurements is suggested in the paper, as well as a recommendation for use of conformal coating.

Design of Insulation Resistance Measurement System for Electrical Steel Sheet Surface Coating

The surface coating of insulation resistance is one of the key technical indexes of electrical steel sheet, and one of the important parameters of the products of electrical steel sheet. Nowadays the surface coating of insulation resistance device is relatively heavy, measurement error is relatively large, and measurement repeatability is not good. To solve these problems, we design an insulation resistance measurement system based on Infineon XE166 microcontroller. This article analyzes the measuring principle of silicon steel coating surface insulation resistance and includes the three aspects of mechanical, circuit and software. The experimental results validate the feasibility of this system. The measurement system is stable and reliable, high repetition rate, and has a good application prospect.

The Protective Effect of the Intumescent Coating on the Fire Resistance Performance of Cable

The failure time of polyvinylchloride (PVC) insulated power cables was studied using an infrared radiation heating furnace and insulation resistance measurements. The temperature-time curve inside the furnace was similar to that of the ISO 834 standard. Two popular fire protection methods were employed for the cables; one method applied fire-retardant coatings directly on the cable surface, and the other inserted the cables into metal conduits coated with structural steel fire-retardant coating. The results showed that for both protection methods, the failure time of the cable increased with the thickness of the coating. However, if the cable coatings were thicker than 1.5 mm, the coating will crack in the case of cable movement. When the steel structural coating was thinner than 1 mm or thicker than 3 mm, the protective effect was not remarkable for the relatively small expansion multiple. For the longest failure time of the cables, less than 10 minutes in these tests, neither of the two methods was effective in protecting the electrical cables that supply power (on transmit a signal) to equipment required to operate over a relatively long duration in fire conditions.

Insulation resistance of metallized polypropylene film capacitors under different electric fields

In pulsed power systems, metallized polypropylene film capacitors (MPPFCs) facilitate the operation of the polypropylene film with a relatively small margin to its dc breakdown strength. The insulation resistance (IR) is one of the important factors that result in the reduction of the energy efficiency, as it represents a current leakage path through the dielectric. This paper concentrates on the leakage phenomenon in MPPFCs by the measurement and analysis of IR. Measurement of the IR under high electric fields is feasible due to the self-healing capability and a measuring system is established to measure IR under various electric fields. To sufficiently investigate IR changing with the electric fields, IR under low electric fields are also investigated. The results indicate that the time constant (called Equivalent IR) is extremely sensitive to the electric field and IR changes little under electric field lower than 10 V/μm. The assumption that influence of surface leakage in the margin on IR could be neglected is also validated by experiments. Finally, theoretical calculation of Equivalent IR based on the Poole-Frenkel (PF) effect is carried out.

The protective effect of a fire-retardant coating on the insulation failure of PVC cable

The failure time of polyvinyl chloride (PVC) insulated power cables was studied using an infrared radiation heating furnace and insulation resistance measurements. The temperature–time curve inside the furnace was similar to that of the ISO 834 standard. Two popular fire protection methods were employed for the cables; one method applied fire-retardant coatings directly on the cable surface, and the other inserted the cables into metal conduits coated with structural steel fire-retardant coating. The results showed that for both protection methods, the failure time of the cable increased with the thickness of the coating. However, if the cable coatings were thicker than 1.5mm, the coating will crack in the case of cable movement. When the steel structural coating was thinner than 1mm or thicker than 3mm, the protective effect was not remarkable for the relatively small expansion multiple. For the longest failure time of the cables, less than 10min in these tests, neither of the two methods was effective in protecting the electrical cables that supply power (on transmit a signal) to equipment required to operate over a relatively long duration in fire conditions.

Proposal of a New Detection Method for Damaged Transmission Line Arresters using Frequency Characteristics of its Equivalent Series Resistance

About 70% of overhead transmission line faults have been caused by natural forces. Above all, more than 60% of those faults are due to lightning. As transmission line arresters (TLAs) are effective to prevent the faults caused by lightning, we have installed them in many of our transmission lines. Nevertheless, TLAs have been damaged by a very large electric charge of lightning, particularly in winter. Through investigation of the damaged TLAs collected from our transmission lines, we found some of the internal zinc oxide (ZnO) elements of TLAs were damaged. But it is difficult to detect those damaged TLAs by the conventional measurement of insulation resistance between terminals of TLAs. Therefore, this paper proposes a new detection method for the damaged TLAs using the frequency characteristics of its equivalent series resistance. The detection rate of the damaged TLAs by the new method is remarkably higher than that by the conventional method.

The Effectiveness of Screening Techniques for Revealing Cracks in High Volumetric Efficiency MLCCs

Multilayer ceramic capacitors (MLCCs) constitute the majority of components used in electronic assemblies and most of their failures are related to cracks. It is often assumed that dissipation factor (DF), insulation resistance (IR), and breakdown voltage (VBR) are characteristics that are sensitive to the presence of mechanical defects, and screening of capacitors by measurements of these characteristics, and by dielectric withstanding voltage (DWV) testing assures high quality products. This work analyzes the effectiveness of these screening techniques for revealing cracks in high-volumetric efficiency, low-voltage ceramic capacitors. Various types of class II dielectric capacitors with rated voltages from 6.3 V to 100 V, and capacitances from 0.1 μF to 100 μF from different manufactures were used in this study. Fractures in the parts were introduced mechanically and by thermal shock stress. It has been shown that cracking results in relatively minor variations of capacitance and DF. Absorption currents prevail over leakage currents during standard IR measurements at room temperatures, and at high temperatures the intrinsic leakage currents exceed substantially leakage currents caused by cracking thus masking the presence of defects. Analysis of distributions of breakdown voltages in normal capacitors and capacitors with cracks showed that the majority of defective capacitors can pass the DWV testing. New, more effective methods of electrical testing and possible improvement of the existing techniques are discussed.

An analysis of heat flux induced arc formation in a residential electrical cable

The interaction between an energized size 14 American Wire Gauge (1.6mm conductor diameter) nonmetallic-sheathed cable and a fire simulated using radiative heating was investigated. The time from the beginning of radiative exposure to an electrical arcing event was measured as a function of the heat flux and nominal alternating current voltage in air and nitrogen environments. The trends observed in these experiments were captured with simple mathematical expressions. Highly time-resolved voltage and current readings were collected around the time of the arcing events to better understand the dynamics of arc formation. These observations, together with cable insulation resistance measurements, were used to gain insight into the mechanism of heat flux induced cable failure. It was also demonstrated that a numerical pyrolysis model describing transient thermal degradation of cable insulation can be used to extrapolate the time of arc formation measurements conducted in this work to fire scenarios not realized in the cable testing experiments.

고압전동기 고정자 권선의 온도변화에 따른 절연특성 분석

A variety of diagnostic tests are widely applied in the field in industry to evaluate the condition of high voltage (HV) motor stator insulation. In this paper, the influence of temperature on the stator insulation diagnostic tests such as the insulation resistance, AC current, dissipation factor, and partial discharge measurements are studied and reported. The tests are performed with the HV motor stator winding temperature set between to in intervals. It is shown that the AC current, dissipation factor, and partial discharge magnitude steadily increase with temperature, which suggests that temperature must be taken into account in the interpretation of the test results.