On some imperative IEEE Standards for usage of natural ester liquids in transformers

From the recent past, biodegradable dielectric fluids are becoming popular across the global utilities for use in oil-filled transformers. To date, several utilities have started using biodegradable insulating fluids for new and retro-filled power and distribution transformers. The intent of this article is to compare and analyze various aspects that are involved in the successful operation and maintenance of mineral oil and ester filled transformers. The comparative analysis in this article is aimed at properties, condition monitoring, diagnostic, and reclamation aspects of ester filled transformers. The imperative and pertinent standards, including IEEE Std C57.106, IEEE Std C57.104, IEEE Std 637, IEEE Std C57.147, and IEEE Std C57.155 remain the target objectives for potential analysis. It is hoped that this critical analysis will be useful for utility and condition monitoring engineers in understanding several key aspects of ester fluids vis-à-vis traditional insulating fluids. The present analysis might also be useful for researchers and industry interested in alternative dielectric fluids for transformer insulation technology

Verification of insulation oil reclamation by turbidity and spetrophotometry measurements

Oil reclamation with Fuller’s earth is known to have an improved effect on conditioning aged oil. In this paper it is shown that aged oil reclamation effectiveness can be monitored with turbidity and spectrophotometry measurements. These low cost testing techniques offer a useful tool to quantify the effect of Fuller’s earth. Experimental investigations performed in laboratory conditions have shown that the quality of properly reclaimed aged oil can compete with that of new oils. Thus, in addition to extending the life cycle of this non-renewable resource, on-line reclamation of liquid might also prevent the premature ageing of paper insulation. Studying the stability of reclaimed service aged oil samples emphasized the important role played by Fuller’s Earth absorption capability

Lessons to learn from post-installation pollution levels assessment of some distribution insulators

Among the main causes of outdoor insulation failures is their poor specifications in terms of leakage distances. This happens when the selected criteria are unable to cope with all the stresses imposed by the changes in environmental pollutions. Therefore, it is important for utilities to fully understand the actual pollution characteristics of the service environment in which the insulators are operating. In this paper, the pollution severity and performance of some 13.2 kV ceramic insulators, sampled in different areas of a Canadian aluminum factory, are assessed. The investigations were performed taking into account the influence of air humidity. Various characteristics were investigated to assess the pollution levels of the insulators, such as equivalent salt deposit density (ESDD) and non-soluble deposit density (NSDD), surface resistance, and leakage current characteristics (density, 3rd harmonic amplitude, and phase). It was witnessed that the insulators, collected around the factory, were much more polluted in comparison to the initial expectation. The pollution level should not be considered static due to the environmental parameters’ dynamics. Lessons to learn: the reliability of an electrical grid is dependent on components whose own reliability is strongly affected by external factors, of which there is often a poor awareness. If care is not taken to re-evaluate the post-installation pollution levels of the insulators, the light may simply turn out

Development of modern diagnosticand oils reclamation techniques for power transformers

L’indisponibilité d’un transformateur de puissance a de fortes répercussions financières aussi bien pour les exploitants de réseaux d’énergie électriques que pour les clients qui y sont connectés. Afin de prévenir les pannes et d’optimiser la performance de ces équipements d’importance stratégique, de nombreuses techniques et outils de diagnostic ont été développés. L’huile contient environ 70 % des informations de diagnostic sur l’état des transformateurs. Le défi consiste à y accéder et à les utiliser efficacement. L’atteinte d’un tel objectif passe nécessairement par des techniques de diagnostic fiables. En plus des techniques traditionnellement utilisées, trois nouvelles techniques de diagnostic issues des normes ASTM sont utilisées : (1) le test de stabilité qui permet de simuler le comportement sous champ électrique d’une huile en fournissant des informations sur la qualité de celle-ci ; (2) la spectrophotométrie UV/Visible qui permet de mesurer la quantité relative de produits de décomposition dissous dans l’huile ; et (3) la turbidité qui mesure la pureté d’une huile neuve ou usagée. Une méthode quantitative permettant de déterminer les paramètres affectant la formation du soufre corrosif sur les conducteurs en cuivre dans les transformateurs de puissance est proposée. Il est montré entre autres que la tendance au gazage des esters naturels est plus faible que celle de tous les autres types d’huile (minérales, esters synthétiques, silicone). La turbidité et la spectrophotométrie UV/Visible permettent de quantifier efficacement les contaminants qui résultent de l’action d’une décharge électrique sur l’huile isolante. Un nombre important de cycles de régénération (au moins 15) est nécessaire pour qu’une huile vieillie en service retrouve les aptitudes d’une huile neuve. Une nouvelle technique de régénération est présentée pour réduire le nombre de cycles de régénération ; celle-ci consiste à utiliser la terre à foulon traitée avec de l’azote. Il est montré également que le temps constitue le paramètre le plus nuisible dans la formation de soufre corrosif. L’action combinée du temps et de l’agressivité de l’oxygène dissous l’accélère fortement.A power transformer outage has a dramatic financial consequence not only for electric power systems utilities but also for interconnected customers. In order to prevent any failure and to optimize their maintenance, various diagnostic techniques and tools have been developed. Insulating oil contains about 70% of diagnostic information on the transformer condition. The challenge is to access and use them efficiently. To meet this objective reliable diagnostic techniques are required. In addition to traditional testing methods, three recently developed ASTM testing techniques were used: (1) oil stability testing that simulates the behaviour of oil under electrical stress by providing information on its quality; (2) the UV/Visspectrophotometry that measures the amount of the relative dissolved decay products in insulating oil; and (3) the turbidity that measures the purity of virgin and aged oil. A quantitative laboratory technique capable of determining the parameters affecting the formation of corrosive sulphur deposition on copper conductors in power transformer is proposed. It is shown among other that the gassing tendency of natural esters is lower than that of the other types of insulating fluids (mineral oil, synthetics esters and silicone oil). The turbidity and UV/Vis spectrophotometry allow quantifying effectively, the relative amount of contaminants resulting from electrical discharge in oils. A large number of reclamation cycles (around 15 passes) are required for in-service aged oil to regenerate to the level of new oil. Anew technique enabling reducing the number of reclamation cycles is proposed; this latter consists in the use of Fuller’s Earth previously treated with dry nitrogen. It is also shown that time is the most influential parameter in the formation of corrosive sulfur. The process is accelerated when time and aggressiveness of oxygen are partnered

Review of fiber optic diagnostic techniques for power transformers

Diagnostic and condition monitoring of power transformers are key actions to guarantee their safe operation. The subsequent benefits include reduced service interruptions and economic losses associated with their unavailability. Conventional test methods developed for the condition assessment of power transformers have certain limitations. To overcome such problems, fiber optic-based sensors for monitoring the condition of transformers have been developed. Flawlessly built-up fiber optic-based sensors provide online and offline assessment of various parameters like temperature, moisture, partial discharges, gas analyses, vibration, winding deformation, and oil levels, which are based on different sensing principles. In this paper a variety and assessment of different fiber optic-based diagnostic techniques for monitoring power transformers are discussed. It includes significant tutorial elements as well as some analyses

Pretreatment of Fuller's earth with nitrogen

International audienceThis paper summarizes experimental findings of the regenerative capability of nitrogen on Fuller's earth. Regenerating new oil from aged oil involves several cycles requiring a large volume of Fuller's earth. The use of large amounts of Fuller's earth is not economically profitable for companies that carry out regenerative operations to service transformer oils and can have environmental implications, since Fuller's earth is usually used to reclaim transformer oil in a one-time batch basis then disposed of. To improve the situation, a new technique to reduce the number of regeneration cycles is proposed. It is shown that Fuller's earth can be improved by purging it with continuous flowing of a fluid, preferably dry nitrogen

Studying the Electrostatic Charging Tendency of some environmentally friendly fluids in a spinning disk system

International audienceThe aim of this contribution is to report investigations on Electrostatic Charging Tendency (ECT) of two commercially available ester fluids. Comparisons are made with mineral oil, as this is a fluid we are familiar with. The investigations were carried out using a spinning disk system designed in our laboratory, where the disk is coated on both sides with different types of cellulose paper. It should be noticed that this system was adopted by CIGRE for international comparative measurements of both insulating liquids and solid transformer materials. The obtained results indicate that electrification current vary with fluid motion. This variation is very important at higher speeds (above 600 rpm). In the majority of the tests carried out, esters tend to generate more charges than mineral oil

Développement de nouvelles méthodes de diagnostic et de régénération des huiles pour transformateurs de puissance

L indisponibilité d un transformateur de puissance a de fortes répercussions financières aussi bien pour les exploitants de réseaux d énergie électriques que pour les clients qui y sont connectés. Afin de prévenir les pannes et d optimiser la performance de ces équipements d importance stratégique, de nombreuses techniques et outils de diagnostic ont été développés. L huile contient environ 70 % des informations de diagnostic sur l état des transformateurs. Le défi consiste à y accéder et à les utiliser efficacement. L atteinte d un tel objectif passe nécessairement par des techniques de diagnostic fiables. En plus des techniques traditionnellement utilisées, trois nouvelles techniques de diagnostic issues des normes ASTM sont utilisées : (1) le test de stabilité qui permet de simuler le comportement sous champ électrique d une huile en fournissant des informations sur la qualité de celle-ci ; (2) la spectrophotométrie UV/Visible qui permet de mesurer la quantité relative de produits de décomposition dissous dans l huile ; et (3) la turbidité qui mesure la pureté d une huile neuve ou usagée. Une méthode quantitative permettant de déterminer les paramètres affectant la formation du soufre corrosif sur les conducteurs en cuivre dans les transformateurs de puissance est proposée. Il est montré entre autres que la tendance au gazage des esters naturels est plus faible que celle de tous les autres types d huile (minérales, esters synthétiques, silicone). La turbidité et la spectrophotométrie UV/Visible permettent de quantifier efficacement les contaminants qui résultent de l action d une décharge électrique sur l huile isolante. Un nombre important de cycles de régénération (au moins 15) est nécessaire pour qu une huile vieillie en service retrouve les aptitudes d une huile neuve. Une nouvelle technique de régénération est présentée pour réduire le nombre de cycles de régénération ; celle-ci consiste à utiliser la terre à foulon traitée avec de l azote. Il est montré également que le temps constitue le paramètre le plus nuisible dans la formation de soufre corrosif. L action combinée du temps et de l agressivité de l oxygène dissous l accélère fortement.A power transformer outage has a dramatic financial consequence not only for electric power systems utilities but also for interconnected customers. In order to prevent any failure and to optimize their maintenance, various diagnostic techniques and tools have been developed. Insulating oil contains about 70% of diagnostic information on the transformer condition. The challenge is to access and use them efficiently. To meet this objective reliable diagnostic techniques are required. In addition to traditional testing methods, three recently developed ASTM testing techniques were used: (1) oil stability testing that simulates the behaviour of oil under electrical stress by providing information on its quality; (2) the UV/Visspectrophotometry that measures the amount of the relative dissolved decay products in insulating oil; and (3) the turbidity that measures the purity of virgin and aged oil. A quantitative laboratory technique capable of determining the parameters affecting the formation of corrosive sulphur deposition on copper conductors in power transformer is proposed. It is shown among other that the gassing tendency of natural esters is lower than that of the other types of insulating fluids (mineral oil, synthetics esters and silicone oil). The turbidity and UV/Vis spectrophotometry allow quantifying effectively, the relative amount of contaminants resulting from electrical discharge in oils. A large number of reclamation cycles (around 15 passes) are required for in-service aged oil to regenerate to the level of new oil. Anew technique enabling reducing the number of reclamation cycles is proposed; this latter consists in the use of Fuller s Earth previously treated with dry nitrogen. It is also shown that time is the most influential parameter in the formation of corrosive sulfur. The process is accelerated when time and aggressiveness of oxygen are partnered.LYON-Ecole Centrale (690812301) / SudocSudocFranceF

Review of physicochemical-based diagnostic techniques for assessing insulation condition in aged transformers

A power transformer outage has a dramatic financial consequence not only for electric power systems utilities but also for interconnected customers. The service reliability of this important asset largely depends upon the condition of the oil-paper insulation. Therefore, by keeping the qualities of oil-paper insulation system in pristine condition, the maintenance planners can reduce the decline rate of internal faults. Accurate diagnostic methods for analyzing the condition of transformers are therefore essential. Currently, there are various electrical and physicochemical diagnostic techniques available for insulation condition monitoring of power transformers. This paper is aimed at the description, analysis and interpretation of modern physicochemical diagnostics techniques for assessing insulation condition in aged transformers. Since fields and laboratory experiences have shown that transformer oil contains about 70% of diagnostic information, the physicochemical analyses of oil samples can therefore be extremely useful in monitoring the condition of power transformers

Comparison of parameters in the formation of corrosive sulphide deposition on copper conductors

Copper is a catalyst that promotes the formation of corrosive sulphur but it is also corroded by the latter. Corrosive sulfur in oil has been identified as the cause of recent failures in power transformers and shunt reactors. The most common reason of such failures is arcing between adjacent disks or conductors of windings due to the formation of copper sulphide deposition on cellulosic insulating paper. Synergetic effects with temperature, time and oxygen are recognized to play a role in the formation of corrosive sulphur. Which of these factors has the most impact on copper sulphide deposition? To address this concern, a quantitative laboratory technique has been developed. It is shown that by using a series of laboratory experiments in accordance with ASTM D 1275 B, it is possible to investigate this problem and to map the influence of these parameters by manipulating some variables such as oxygen, temperature and time on the copper samples. The obtained results show that temperature is the most influential parameter in the formation of corrosive sulphur. The process is accelerated when both temperature and time act conjointly