Fig 5
![Variation of insulation resistance versus time of insulation drying [66].](profile/Hossein-Torkaman/publication/266620155/figure/fig5/AS:562784091861000@1511189591489/Variation-of-insulation-resistance-versus-time-of-insulation-drying-66.png)
Source publication
![Fig. 1. Types of currents for Asphaltic-mica insulation [48].](profile/Hossein-Torkaman/publication/266620155/figure/fig1/AS:562784091021313@1511189591305/Types-of-currents-for-Asphaltic-mica-insulation-48_Q320.jpg)
The concept of insulation system is chiefly concerned with the stator winding lifetime of the high voltage (HV) electrical machines. Along with the insulation testing, insulation resistance (IR) and polarization index (PI) techniques are suitable for different types of HV electrical machines and transformers. Since the power plant industries have t...
Context in source publication
Context 1
... IR values are functions of insulation dryness in spite of being the function of time. Fig. 5 shows the IR variations in one minute and 10 min as a function of time in which the insulation is under the drying process. In the first period of insulation drying, the insulation temperature does not reach the vaporization temperature of the mois- ture inside, and therefore drying process is not started yet. So IR values in this ...
Citations
... Todėl PI ir DAR IVM metodai tinka profilaktinei besisukančių EM priežiūrai ir jų izoliacijos stebėjimui. Įprastai šiais metodais gauti Riz matavimo rezultatai nėra užrašomi, tačiau rekomenduojama registruoti periodinius Riz matavimus siekiant numatyti ir vykdyti prevencinės EM priežiūros programą(Torkaman and Karimi, 2015). ...
... Iškrovus apvijų izoliaciją, atliekamas kitas bandymas esant aukštesnei bandomajai įtampai UTest2 (UTest2 > UTest1), pavyzdžiui, 2500 V ir Riz reikšmė vėl užrašoma. Bet koks skirtumas tarp šių dviejų izoliacijos varžos matavimo reikšmių nurodo galimus suprastėjimus, kuriuos reikia toliau tirti(Torkaman and Karimi, 2015). pav. ...
Straipsnyje analizuojamos elektros įrenginių izoliacijos varžos nusidėvėjimo priežastys ir pasekmės. Apžvelgiami integruoti įprastuose matuokliuose besisukančių elektros mašinų izoliacijos varžos matavimo metodai. Pateiktas izoliacijos varžos matavimo metodų taikymo algoritmas.
... A power transformer's likelihood of failure depends on the behavior of its subsystems, which include the insulation system (IEEE Standards Association, 2017). The insulation of a transformer can be diagnosed through a set of electric tests, among them the Megger DC resistance test (Torkaman and Karimi, 2015), the dissipation factor tan-δ test (Malpure and Baburao, 2008), the power factor tip-up test (IEEE Standards Association, 2000), the dielectric frequency response test (IEC, 2006), and frequency response analysis (Sardar et al., 2017). These tests require the transformer to be off-line, which leads to economic impacts for the owner. ...
Dissolved gas chromatography (DGA) analysis and Megger DC insulation tests are performed to diagnose the condition of a power transformer. In this context, the objective of this study is to assess whether there is a relationship between both types of tests. To this effect, a database with DGA and Megger DC test protocols is analyzed, using the theory of variable correlation as well as current DGA techniques. The results allow stating that there is indeed a relationship between both tests under specific conditions. Therefore, the DC isolation status of a transformer can be estimated via DGA tests.
... Generally, motor winding insulations are based on classes. The National Electrical Manufacturers Association (NEMA) dictates operating temperatures for every insulation class, as shown in Table 3 [8,9]. These allowable temperatures are based on a full-load operation. ...
Switched Reluctance Motors (SRMs), Permanent Magnet Synchronous Motors (PMSMs), and induction motors may experience failures due to insulation-related breakdowns. The SRM rotor is of a non-salient nature and made of solid steel material. There are no windings on the rotor. However, the stator is composed of windings that are intricately insulated from each other using materials such as enamel wire, polymer films, mica tapes, epoxy resin, varnishes, or insulating tapes. The dielectric strength of the insulation may fail over time due to several environmental factors and processes. Dielectric breakdown of the winding insulation can be caused by rapid switching of the winding current, the presence of contaminants, and thermal aging. For reliable and efficient operation of the SRMs and other electrical machines, it is necessary to take into account the physics of the winding insulation and perform appropriate diagnostics and estimations that can monitor the integrity of the insulation. This article presents the estimation problem using a Genetic Algorithm (GA)-optimized Random Forest Regressor. Empirical properties and measurable quantities in the historical data are utilized to derive temperature and leakage current estimation. The developed model is then combined with a moving average function to increase the accuracy of prediction of the stator winding temperature and leakage current. The performance of the model is compared with that of the Feedforward Neural Network and Long Short-Term Memory over the same winding temperature and leakage current historical data. The performance metrics are based on computation of the Mean Square Error and Mean Absolute Error.
... Therefore, during the test phase, the previous measurement's initial conditions should be provided by the standards. During the measurement, the instantaneous measurement values of the resistance values that change during the test process are taken at the time intervals determined according to the standards, and the absorption rate and polarization index values are also found [84,85]. The turn ratio test is used to determine whether the number of turns of the windings is suitable for the transformer rating and whether there are faults such as short circuits or open circuits between the windings [86,87]. ...
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... The current is obtained when a DC voltage is applied to the insulation. The current can be divided into three parts: charging currents, absorption currents, and conduction currents, as shown in Figure 2 [30]. The charging current can be expressed as shown in (1). ...
The demand and necessity of direct current (DC) has been increasing owing to large capacity and long distance power transmission. DC application of TP (thermal plastic) materials, which can increase the power transmission capacity compared to existing insulation materials, has been the primary focus of existing studies. This study presents the development of a highly reliable accelerated aging system that can implement the aging conditions of DC power cables. Moreover, we verify its reliability by testing TP model cables and analyzing the aging characteristics. Accordingly, we developed an accelerated aging system that can simulate thermal, electrical, and mechanical stresses collectively. We used the accelerated aging system to perform an accelerated aging test of the TP model cable for 40 cycles. The control precision of the accelerated aging system during the test was numerically calculated. The system was evaluated by using the conduction current and chemical characteristics of the aged TP model cables. The experimental results show that the precision of accelerated aging system is 1 % for 1 cycle. The conduction current of the aged TP model cables was increased by more than 100% before aging, thereby it is verified the performance of the system accelerates the aging of power cables. It is expected that the highly reliable accelerated aging system of power cables can be used to perform long-term reliability tests and as diagnostic technology during the development of DC power cables.
... This type of test can be used on most motors. It is ideal for detecting insulation damage or assembly errors [25]. The method uses DC voltage for measurement. ...
... Measuring the insulation resistance after 15 s and 60 s, respectively, from the moment the test voltage is applied, the absorption coefficient DAR is determined. The DAR absorption coefficient is defined as the ratio of the insulation resistance measured after 60 s from the moment of starting the R60 measurements to the resistance measured after 15 s, R15 [25]. The dependence of the absorption coefficient on the condition of the insulation system is presented in Table 3. Table 3. Dependence of the absorption coefficient DAR on the condition of the insulation system. ...
... The polarization index (PI) is defined as the ratio of the insulation resistance measured after 10 min. R600 to resistance is measured after 1 min, R60 [25,26]. This is one of the several tests included in the Megger test. ...
The presented article concerns issues related to the diagnostics of the technical condition of the insulation of electrical machines. It discusses the importance of the operational supervision, maintenance and diagnostics of electrical machine insulation systems. The structure of the insulation system is presented and known solutions for making winding insulation are described. The negative impact of conditions and various exposures on the technical condition of the insulation system is described. Special attention is focused on the review of available diagnostic methods for insulating systems of electrical machines. These methods have been arranged in a systematic order according to the type of tests to be carried out.
... The dissipation factor [180] is the quotient of resistive and capacitive current. The capacitive current's magnitude is nearly identical to the leakage current's at low [182]. Frequency response analysis (FRA): The FRA method is also known as the transfer function method. ...
A challenging problem in the protection of power transformers is the fault detection and diagnosis (FDD). FDD has an essential role in the reliability and safety of modern power systems; thus, it has been recently the center of attention in both industrial and academic studies. Due to unpredictable nature of fault, it should be located and isolated fast so that its impact on transformers is minimized. The main advantage of FDD is that it prevents costly repairs, costly downtimes, putting human into danger, and destruction of the equipment nearby. Thus, understanding failure modes, their cause and effects, and developing real-time automated devices for fault diagnosis with the ability to capture the early fault signs. Recently, various studies have been conducted on FDD in transformers using different views, methods, constraints, and objectives. There are good reviews in this context, but they are mainly focused on a specific area of this vast context. The purpose of this study is to classify the publications and make a systematic review of the FDD techniques and algorithms from different aspects and views from 1990 to 2020. This paper also summarizes the pros and cons of the existing methods. This paper provides a comprehensive background for future studies by evaluating the studies of this area and categorizing them.
... IR value reveals the insulation degradation due to contamination, moisture, and severe cracking. The test is performed by applying a constant DC voltage for 10 min between windings or windings and ground [24,25]. IR values are measured every minute or less in MΩ using a metering instrument called Megger or Megohmmeter. ...
... IR values are measured every minute or less in MΩ using a metering instrument called Megger or Megohmmeter. Typical trend of IR measurements is shown in Figure 5 [25]. A single IR result is not enough to determine the insulation status [26]. ...
... An insulator is considered to be a capacitor where, with the application of voltage, a charging current will flow. If the insulation is contaminated, the charging time is typically 1 min [25]. After 10 min of testing, the IR value can reach a stable level. ...
A power transformer is one of the most critical and expensive assets in electric power systems. Failure of a power transformer would not only result in a downtime to the entire transmission and distribution networks but may also cause personnel and environmental hazards due to oil leak and fire. Hence, to enhance a transformer’s reliability and extend its lifespan, a cost-effective and reliable condition monitoring technique should be adopted from day one of its installation. This will help detect incipient faults, extend a transformer’s operational life, and avoid potential consequences. With the global trend to establish digital substation automation systems, transformer online condition monitoring has been given much attention by utilities and researchers alike. Several online and offline condition monitoring techniques have been recently proposed for oil-immersed power transformers. This paper is aimed at providing a state-of-the-art review for the various condition monitoring technologies used for oil-immersed power transformers. Concept of measurements and analysis of the results along with the future trend of condition monitoring techniques are presented.
... Polarisation index (PI) is frequently used to identify how clean and dry solid insulation of windings are, depending on insulation categories A B and C, as well as windings parts [41] [42]. ...
... Insulation is a limiting element in the reliability of any electrical equipment, as evidenced by numerous studies presented in the works of various scientists [1][2][3][4][5]. ...
The article is devoted to the assessment of the comparative experimental studies’ results of various technologies for drying impregnated insulation of power electrical equipment in the process of manufacturing and repair: standard technology, which provides for convective drying using high-power electric ovens, and the proposed technology and methods for accelerated drying in hardware complexes using infrared (IR) radiation. In particular, the article presents the results of the polymer insulation surface microstructure analysis after drying by the indicated methods. The research was carried out in an industrial environment, using specialized certified equipment. In theoretical terms, the article presents the calculations on the rationale for the use of IR radiation during drying of a multilayer insulating structure of various compositions. The studies carried out confirm the hypothesis about the formation of microcavities on the surface and in the thickness of the polymer insulation when using convection during drying, which reduce the quality and reliability of the electrical equipment insulation as a whole. At the same time, the proposed technology and technique for accelerated drying of electrical equipment insulation using IR-radiation gives an opportunity to improve the quality of the resulting polymer insulation, increasing its reliability. In addition, this technology can significantly increase the productivity of insulation repair and reduce energy costs.
