IEEE C57 Research Articles

A comprehensive evaluation and advancements in dissolved gas analysis for biodegradable oil in photovoltaic solar plants

Over the past three decades, the energy industry has embraced the adoption of a new type of biodegradable oil. Presently, the prevailing international standard for its evaluation is IEEE C57.155–2014. Various working groups, including those within CIGRE A2.68, IEC, and industry manufacturers, have embarked on endeavors to explore new evidence and methodologies for assessing the accuracy and alternatives in detecting failures. These failures are often indicated by elevated levels of seven gases: Hydrogen, Ethane, Acetylene, Methane, Ethylene, Carbon Monoxide, and Carbon Dioxide. Consequently, instances of high oil temperatures have been observed during the optimization of dimensions near hot-spot limits, particularly in renewable energy applications. This research article presents an in-depth analysis of a substantial database comprising 2834 units, aimed at establishing new thresholds for dissolved gas analysis applied to biodegradable oil in photovoltaic solar plants. The developed methodology successfully identified 844 oil samples in poor condition, 332 samples exhibiting one or more failure modes without fault or disconnection, and 1658 units in good condition. Validation of the instrumentation was conducted on 87 transformers through internal inspection, verifying the classification according to the new methodology for evaluating relevant variables and limits of gases through Gaussian distribution and seven algorithms. This validation aimed to enable early detection of failures and establish a health index, achieving an accuracy rate of 90.8 % with support vector machine, 97.6 % with random forest, and 98.3 % with XGBoost. Future research directions should consider evaluating viscosity as a factor in assessing the quality and degradation of transformers utilizing biodegradable oil.

Neural networks and damage pattern recognition in power transformer diagnostics

The results of detecting deformations and damage of power transformer windings using the transformer Frequency Response Analysis (SFRA) are presented taking into account RG CIGRE A2.26, Standard IEC 60076-18, Standard IEEE C57.149. The technology of pattern recognition by signal images for diagnostics of winding damage, type of defect, its localization is implemented. Neural networks are used - where in a multilayer perceptron with backpropagation of error - the work of neurons in a hierarchical network is imitated. Parametric methods - such as the Naive Bayes classifier - a probabilistic classifier based on the Bayes formula with the assumption of independence of features among themselves for a given class, which greatly simplifies the classification task due to the assessment of one-dimensional probability densities instead of one multidimensional. An algorithm for recognizing patterns of defects and damage to power transformers using the results of diagnostics by the FRA method has been developed.

Fuzzy logic applied to the diagnosis of technical conditions of distribution transformers

The distribution transformers are one of the most important elements for the operation of the distribution networks, considering their quantity and dispersion in the network, and that the failures cause great economic losses, both from the point of view of the transformer itself and of the cost of the energy left to serve. The technical condition of the distribution transformers depends on multiple external factors that influence the loss of useful life of the same, and therefore, it is necessary to relate them for a correct diagnosis. In the present work, a method based on fuzzy logic is developed for the diagnosis of distribution transformers, considering the international regulations that govern its operation. The resulting procedure was implemented using the fuzzy toolbox of MATLAB programming tools version 9.8 (R2020a). A random sample of transformers in three distribution circuits was evaluated, and the results correspond to that established in the IEEE C57.91 standard of 2011.

Analysis and mitigation of the impact of electric vehicle charging on service disruption of distribution transformers

The transition to electric mobility could overload distribution transformers to unprecedented levels. Sustained overloads produce excessive heat within the transformer and hasten insulation deterioration. As EV deployment rises and the severity of overloads increases, the focus shifts from long-term effects that reduce transformer life to more immediate impacts that can disrupt normal functioning. The latter typically manifest as the blowing of protection fuse, the triggering of pressure relief device, or the breakdown of winding insulation, each of which could result in transformer outage. The transformer’s vulnerability can be monitored in terms of its apparent power flow, top-oil temperature and hottest-spot temperature. The IEEE C57.91 standard specifies the permissible range for these parameters, beyond which the transformer operation could get interrupted. A study to determine the range of EV penetration that can be accommodated by a distribution transformer without any discontinuity in its operation is presented in this paper. The non-linear nature of EV charging is incorporated in the analysis to account for the effect of higher-order harmonics on the transformer’s internal temperature. The effectiveness of a controlled charging strategy, which seeks to regulate transformer loading by minimizing its variance, in preventing service disruption is also validated in this simulation study.

The Investigation Of The Synthesis Cooking Oil As A New Power Transformer Oil

Abstract Background: The mineral oil has been widely used in a power transformer for the purpose of insulation and suppression of corona and arcing. But due to its extremely low flashpoint, this can also cause an explosion in the case of a fire and the mineral oil has been found to be non-biodegradable. In this research, an alternative of mineral oil is proposed, which is the usage of used cooking oil which will undergo chemical modification via transesterification in order to achieve its expected properties which fits into the requirements of the power transformer according to the IEEE standard of IEEE C57.147 Methods: the synthesis of oil process will begin by the selection of the most suitable vegetable oil, in this case the palm oil in which, the water content and acidity were taken into consideration. The oil will then undergo transesterification process for the removal of free fatty acids and water content, before being tested for its acidity, water content and the breakdown down voltage in the high voltage lab to evaluate the electrical properties of the oil. Results: The results obtained during testing is that the breakdown voltage and water content is 6 kV and 125 ppm and the acidity 0.13 mg KOH/g. Conclusion: It is expected that the potential synthesized oil which has undergone transesterification process and the removal of all water content and free fatty acids in the oil, can be able to replicate the values replace the mineral oil in a power transformer despite having a higher acidity than the mineral oil.

Case Study and Comparison of High Voltage Power Transformer Dissolved Gas Analysis Assessed by Different Standards

A power transformer is a vital equipment in a power system. To prevent transformer failure, it is necessary to assess the transformer condition, one of which is through the DGA test. IEC 60599 and IEEE C57.104 become guidance for transformer assessment through the DGA test. DGA is a method of determining transformer conditions and fault diagnosis by assessing transformer oil data samples. H2, CO2, C2H4, C2H2, C2H6, CH4, CO, O2, and N2 are among the dissolved gases measured to monitor transformer conditions. To determine the faults, the IRM, RRM, and DTM are used. The fault detected on 8 transformer case studies showed T1, T2, T3, PD, D1, and D2. Maintenance recommendations for 8 power transformers evaluated were presented.

Effects of Thermal Aging on Blended Oil Characteristics in Comparison to Mineral Oil and Synthetic Esters

The paper aims to investigate the long-term behavior of insulating oil in high-voltage applications by analyzing and correlating the changes in its physicochemical properties over the high-temperature range. To comprehend the rate of oil degradation, uninhibited mineral oil (MO), blended oil (MSO), and synthetic ester (SE) have been exposed to enhanced thermal stresses in combination with solid insulation. In compliance with IEEE C57.100, a five-point aging mechanism for thermal aging was taken into account. Thermal stresses ranging from 100 to 195 °C were applied continuously for 168 hours with a temperature variation of 25 °C. The effects of thermal stress have been deliberated by analyzing changes in physicochemical properties, such as density, kinematic viscosity, acidity, flash point, and visual observation of the mineral oil, synthetic ester, and mixed oil. The results demonstrated that the inclusion of esters into mineral oil enhances its characteristics and functionality and accentuates its suitability for assessing the state of high-voltage transformers.

Experimental Study of Sealed Tube Accelerated Aging Test Parameters and Determination of the Thermal Class of Transformerboard

The latest 2011 edition of the IEEE C57.100 standard introduced a new sealed tube accelerated aging test (STAAT) procedure and methodology for evaluating the thermal index (TI) of liquid-immersed transformer insulation systems. The application of this standard becomes increasingly important, as new insulating materials (both solid and liquid) have been developed, and their thermal performance shall be qualified. The experimental work presented in this article investigated the effects of different test parameters on the aging test results and data interpretation. The new findings on the dependence of the aging process on the ratio and type of materials in the system, as well as on the selected aging criteria provide a better understanding of the accelerated aging and interpretation of the data along with practical recommendations for the improvement of the test procedure. In parallel, for the first time, the TI of the Transformerboard, as a component of the so-called industry-proven insulation system, was investigated and defined based on the standard industry test. The results confirmed that the Transformerboard’s thermal class is, at least, 120 °C; this validates an empirically based application of this material as a part of the 120 °C class insulation system in both power and distribution transformers.

A new approach for top‐oil thermal modelling of power transformers using Unscented Kalman filter considering IEEE C57.91 standard

Determining the transformer top-oil temperature (TOT) is one of the key issues in determining the transformer insulation life and reliability of the power system. Due to the non-linear nature of the model presented in the IEEE C57.91 standard to determine this temperature, a more precise method is needed to estimate the equation coefficients to estimate the TOT in the future. This paper presents a method for online thermal modelling of the transformer according to the IEEE C57.91 based on the Unscented Kalman filter (UKF). This method can be applied to transformers with a variety of cooling modes and estimates the TOT with an acceptable error. In order to evaluate the proposed method, the practical data of the 800 kVA distribution transformer with unknown equation coefficients and simulated data with known coefficients are used, and finally, by calculating the estimation error, the proper performance of the presented method is proved. It is proved that the proposed method predicts TOT even in the presence of noise with an error of less than 0.5°C and a delay of less than 1.5 h. It makes the proposed method can be implemented for purposes such as load management, and insulation life estimation of the transformer.

Assessing the Degradation of Transformer Oil From Partial Discharge Measurement Data Using Histogram Similarity Measures

In this paper, a method is proposed to classify the in-service transformer oil by assessing the level of degradation in oil. Initially, 135 oil samples are classified into Class 1, Class 2 and Class 3 as per IEEE C57.106 (2015) standard by the conventional techniques which require five tests. The proposed method attempts to classify the oil samples by a single non-destructive Partial Discharge (PD) test measurement. The PD data of the 135 transformer oil samples are represented as one-dimensional histograms and classified by statistical analysis using Histogram Similarity Measures including Cross-correlation test, Kolmogorov-Smirnov distances, and Chi-square test. This classification technique achieves an accuracy of 94.9 %. The results are further subjected to class likelihood measures in the post-processing stage and this improves the accuracy of classification to 97.5 % establishing the efficiency of the proposed method.

Top‐oil temperature modelling by calibrating oil time constant for an oil natural air natural distribution transformer

© The Institution of Engineering and Technology 2020. Integration of low carbon technologies poses a technical challenge on distribution transformers due to the dynamic loading and potentially frequent overloading scenarios. Transformer dynamic thermal rating is hence required, which is the most economical approach to tackle this challenge and ensure a safe operation. To reach the aim, it is important to enhance the accuracy of the dynamic thermal model, where the top-oil temperature is a key thermal parameter. In this study, a wide range of constant load temperature-rise tests were carried out on an 11/0.433 kV distribution transformer to study the dynamic thermal behaviour of the top-oil temperature. A model based on the IEC 60076-7 thermal model but with an improved oil time constant calibration was deduced for top-oil temperature modelling. The oil time constant calibration was inspired by IEEE C57.91 and verified by eight temperature-rise tests with load factors ranging from 0.7 to 1.4 pu. In addition, the improved top-oil temperature modelling was further verified in experiments under multiple load profiles.

Overload Distribution Transformer With Natural Ester and Aramid-Enhanced Cellulose

The load of a distribution transformer can be daily or seasonal fluctuant, which submits the transformer to the risk of overload through thermal stress. In this research, it is demonstrated that the aramid-enhanced cellulose in natural ester, as a high-temperature insulation system, is a solution by which the overload capability of a transformer can be improved. First, the thermal and ageing model stipulated in IEEE C57.91 Annex G, which was proposed to evaluate the Kraft and thermally upgraded Kraft, has been modified to incorporate the ageing rate benchmark derived from Arrhenius law, so the improved model can now cover various combinations of insulation systems. The top liquid temperatures, hot spot temperatures and equivalent ageing factors of transformers with aramid-enhanced cellulose in natural ester and Kraft in mineral oil under different load scenarios generated from field loading data were analyzed. The results showed that the overloading capability of the transformer with aramid-enhanced cellulose was improved, as its equivalent ageing factor was 13 percent of the equivalent ageing factor of the transformer with Kraft under the heavy overload scenario. Furthermore, an overloading test and field test were also conducted for a prototype transformer with aramid-enhanced cellulose and natural ester. The measured top liquid temperature and hot spot temperature and the calculated equivalent ageing factor after the overloading test verified that the transformer with aramid-enhanced cellulose operated well below the safety thresholds. Additionally, the results from the transformer upon installation in the field proved that the transformer also operated well under an overloading status.

Transformer Bushing Thermal Model for Calculation of Hot-Spot Temperature Considering Oil Flow Dynamics

Thermal stress plays a prominent role in the reliability of bushings and contributes to the reliability of power transformers, especially during overload conditions. Thus, exploring the temperature distribution in the bushings is essential. This paper proposes a new thermal model to estimate the hotspot temperature (HST) of oil-impregnated paper (OIP) bushings, based on a modified thermal-electrical analogy model. The proposed model is developed based on the finite element method (FEM) to accurately model all fluid flow and internal convection as well as the thermal conduction mechanism. To this end, convection thermal resistances are defined, and their nonlinear characteristics are calculated for different overloading conditions. The proposed approach is applied on a 245 kV, 800 A OIP bushing to analyze not only the normal loading condition but also short-term overloading beyond the rated current. In addition, the oil flow condition with different load currents and transformer top oil temperatures (TTOT) are investigated. The results show a consistent temperature rise with the typical test conditions with no identified problematic situation. However, during overloading, the temperature rise exceeds beyond the permissible limits recommended by IEEE C57.19. Hence, the overloading of transformers may deteriorate the bushing insulation and reduce its lifetime.

Increased loadability of transformers using natural ester and cellulosic materials as high temperature insulation systems

The use of natural ester–filled transformers started in 1996, with two industrial transformers installed at the Cooper Power System factory to provide power for two core annealing ovens. Investigations conducted according to the IEEE C57.100 accelerated transformer life test method (Lockie Test) [1] and the sealed tube accelerated insulating system material life test method [2]–[4] indicated a possible extension of transformer life, associated with reduction of the paper degradation rate when impregnated with natural ester liquids.

Environmentally Friendly Fire Safe Superior Synthetic Ester Dielectric Fluids for Green Transformers

Electricity is the engine powering the economic development and growth of any country. Transformer is the most vital equipment in the application of the electrical energy for diverse needs like domestic, indoor and outdoor distribution, high voltage, extra high voltage and ultra-high voltage applications. The transformers and reactors are critical links in the transmission and distribution systems. Over the period rapidly expanding power transmission systems involving HV, EHV & UHV equipments, have seen vast changes in the material concept and designs also. Today we have an installed capacity of electricity is 330.86 GW as of 22 December 2017, and we find thousands of transformers are ubiquitous in human environment. Added to it in today’s overriding concerns about environment and fire safety compact transformers capable of taking higher loads, electrical & thermal stress and meeting environmental requirements are increasingly in use. Distribution transformers are very crucial parts of transmission & distribution domain these units require dielectric fluids which ensure excellent performance and absolute safety. The synthetic ester based dielectric fluids having extraordinary properties are ideal for these power equipments. In this paper we present the results of the study undertaken by us on a vastly superior synthetic ester dielectric fluid in accordance with IEC 61099, 61125 Method C, OECD 301B & IEEE C57.104

Heat analysis of the power transformer bushings in the transient and steady states considering the load variations

Bushings are considered as one of the main components of the power transformers. This is due to the fact that the reliable and efficient performance of the bushings significantly influences the reliability of the transformers which, in turn, are counted as the fundamental part of the power systems. The thermal behaviour of the bushings, as a consequence of the power dissipation, significantly affects the bushing’s performance and design. In this paper, a novel algorithm is proposed for the heat analysis of the bushings. This algorithm aims at specifying the hot spot temperature and the temperature distribution of the bushing. Therefore, the problem is formulated using the Joule Heating equations as the partial differential equations for both transient and steady states. Then, the finite element method is employed to solve the problem. The algorithm is implemented on an oil-impregnated paper bushing. In the steady state, the temperature distribution of the whole bushing is determined. In addition, the effects of different currents on the location and magnitude of the hot spot temperature have been investigated. In the transient state, three overload scenarios are simulated two of which are from the IEEE C57.19.100 and IEC 60076-7 standards. In addition, the effects of the wind speed and electric load on the bushing’s temperature distribution for 48h have been investigated.

Forensic Examination and Failure Analysis of a 220-MVA Step-Up Transformer Fire

The paper presents the results of investigation and engineering analysis by Exponent of the failure of a 220-MVA generator step-up transformer in Southern California. The incident was caused by a dielectric breakdown from the high-side C-phase bushing to the side wall of the transformer. The ensuing fire continued for 27 hrs, fueled by approximately 11,000 gal of dielectric HYTRANS 61 oil. The paper will discuss the investigation conducted as per the IEEE C57.125 “Guide for Failure Investigation, Documentation, and Analysis for Power Transformers and Shunt Reactors,” [1] and the engineering review and analysis to identify the likely failure scenario(s).

Development of a novel dual temperature model for insulation aging in oil immersed transformers

Power transformer is one of the most expensive equipments in a high voltage AC power system. Adequate monitoring system for power transformers can help in reducing the failure rate and thereby enhancing system reliability and economic efficiency. The failure of power transformer has serious consequences on system reliability. Long term and comprehensive testing cannot be done in working transformer, so prorated model of transformer is preferred. In the proposed work, a new dual temperature test cell is developed based on IEC 62332 and IEEE C57.100. The cell provides for a current carrying conductor wrapped with insulating paper and further insulation is provided with high-density pressboard as per arrangements in power transformer. In this paper a new mathematical model is developed using activation energy and preexponential constant calculated from experimental results at different temperatures. The expected life based on degree of polymerization (DP) value, shows nonlinear aging of insulation based on investigation carried out on prorated model.

Estimation of the inductive current transformer derating for operation with distorted currents

Abstract The aim of the paper is to present a new method for estimation of the CT (Current Transformer) rated primary current and / or load of the secondary winding derating levels for transformation of distorted current in relation to the rated values fixed for transformation of sinusoidal current. This ensures the values of the CT composite errors/transformer correction factors as resulting from its IEC 60044-1/IEEE C57.13 accuracy class in condition of distorted currents transformation.

Comparing Transformer Derating Under Harmonic Load and Unbalanced Supply Voltage Based on IEEEC57.110 Standard and TESFEM By FHL And K_Factor

Transformers are generally designed in order to deliver the required power to the connected loads with minimum losses at nominal fequency. Nowadays , power quality affected by non-linear loads and unbalanced condition and causes deflection from a perfect sinusoidal waveform. This condition leads to additional losses, increase temperature and reduction of the useful life of the transformers. In order to avoid of these difficulties, the nominal capacity of transformer should be reduced. This paper studies the increase of losses and Derating of Distribution transformer, working under Different harmonic load and unbalanced supply voltage conditions. In this paper, the three dimensional finite element method (3-D) is utilized as a Instruments for viewing magnetic flux density on core and windings of distribution transformers. The computer simulation according to the use of the FEM has been improved in Ansoft - Maxwell. In section 2, a 3-D time stepping finite element method (TSFEM) is used in order to modeling the transformer under different harmonic load with (THD I =12% and 23%). The maximum flux density in the transformer windings under sinusoidal and different harmonic load condition has been investigated in this section. In section 3, the effect of harmonic load on transformer load losses Has been examined. The result shows that under harmonic load current , copper loss an eddy current losses significantly increases. In section 4, derating of transformer under harmonic load based on IEEE c57.110 standard and TSFEM by using k-factor and harmonic loss factor (H FL ) Has been done. The result shows that IEEE standard is a Conservative method for transformer derating under high harmonic current (THD I ) and TSFEM is a Convenient method for transformer derating in this condition. In section 5, The Performance of the transformer when the supply voltage are balanced compared to the case in which supply voltage is unbalance , the result shows that , the unbalanced voltage Causes increase in the both copper loss and core loss. Afterwards, Based on the data obtained from the TSFEM, a distribution transformer under different unbalanced condition has been derated