The performance of high voltage; outdoor insulation in polluted environments

"An iron wire, 12000 feet in length, was suspended about five feet from the ground by silk cords; one end of it was connected to the globe of an electrical machine, and at the other a lead ball was hung in order to perceive when the matter reached it. After five or six turns of the wheel, the matter had passed along the whole wire and communicated its virtue to the ball, which instantly attracted and repelled light bodies. 2. As this ball was equally electrified with every part of the wire, it is probable that the electric matter would instantly pervade a wire of a still greater length, provided we had a proper apparatus for the purpose. 3. Several metals and other conductors were substituted in place of the ball, and all received the electricity in the same manner. The ball and touched with other non-conductors, :when' the finger, gave a luminous spark and as smart a shock as when the end of the wire next to 'the 'gTobe·vas touched. All these effects instantly ceased whenever .. any person not electrified touched any part of the wire and commenced again a few seconds after his hand was withdrawn. The same effects are produced, though with more difficultly, when hair or woollen ropes were substituted in place of the silk ones: But they were entirely stopped by hemp ropes or when the silk ones were wetted.

Non-contact measurement and analysis of trapped charge decay rates for cable line switching transients

During reclosure of 275 kV cable circuits used for voltage control, excessive overvoltages were observed on the network. Such events cause onerous and costly failures. Transient simulations have shown that the normal voltage on its own cannot generate such excessive switching overvoltages. Initial investigations by the network operator pointed towards trapped charge on the unearthed as the cause of the failures. Measurement of these trapped charge voltages and their slow decay without interfering with the charge has, to the author’s knowledge, not been done before in an operational substation. This work introduces a technique to measure trapped charge at a 275 kV substation using the Electrostatic Field Mill. Since the electric field is a proxy measurement of surface voltage, field mills can also be used to measure voltage. In this paper, an on-site substation measurement setup using an electrostatic field mill has been developed for the non-contact measurement of trapped charge voltage on a 275 kV underground cable circuit following switching operations at a National Grid substation. Results of field measurements within the substation and laboratory experimentation are discussed. It is demonstrated that with adequate calibration, achieved by using the known pre-switching power frequency steady state voltage, the slowly decaying DC voltage caused by the cable trapped charge can be measured using this non-contact technique. The correlation between the instantaneous time constant and the relative humidity is also analysed

Effect of water on electrical properties of Refined, Bleached, and Deodorized Palm Oil (RBDPO) as electrical insulating material

This paper describes the properties of refined, bleached, deodorized palm oil (RBDPO) as having the potential to be used as insulating liquid. There are several important properties such as electrical breakdown, dielectric dissipation factor, specific gravity, flash point, viscosity and pour point of RBDPO that was measured and compared to commercial mineral oil which is largely in current use as insulating liquid in power transformers. Experimental results of the electrical properties revealed that the average breakdown voltage of the RBDPO sample, without the addition of water at room temperature, is 13.368 kV. The result also revealed that due to effect of water, the breakdown voltage is lower than that of commercial mineral oil (Hyrax). However, the flash point and the pour point of RBDPO is very high compared to mineral oil thus giving it advantageous possibility to be used safely as insulating liquid. The results showed that RBDPO is greatly influenced by water, causing the breakdown voltage to decrease and the dissipation factor to increase; this is attributable to the high amounts of dissolved water

A study of the variation of electric distance and electric strength with the type of voltage stress and portion of the gap covered by flames.

Masters Degree. University of KwaZulu-Natal, Durban.South Africa has a large network of high voltage substations and transmission lines (over 28 000 kilometers) across the country designed to supply power to households, industry and businesses, railways and mines. This transmission system must be strong and capable of withstanding the loss of any single circuit without loss of supply to key customers. Veld fires burning under or near high voltage transmission lines are a potential hazard capable of disrupting transmission and distribution of power. Forest fires under high voltage transmission lines reduce the breakdown strength of the air insulation due to the influence the heat and particles have on the electric field surrounding electrical conductors and insulators. The performance of the high voltage transmission lines is most likely to be affected by the occurrence of veld fires under these power lines. The fire under high voltage transmission lines generates heat and increases the temperature of the air surrounding the conductors and insulators. The increase in temperature due to the presence of the fire decreases the breakdown strength of the air insulation, this results in flashovers and undesirable power supply interruptions in the electrical transmission network. Due to the past experience of AC transmission lines tripping as a result of sugar cane fires that occurs under these lines during cultivation seasons, this study was initiated to provide an understanding of how burning can cause outages of transmission lines and give recommendations on how to prevent outages due to burning. This dissertation is a research based modeling aimed at giving an understanding of how the electric distance and electric strength vary with the type of voltage stress and the portion of the gap covered by flames. The study reviewed how different authors have conducted studies related to this dissertation and compared the results. The different failures due to burning occurring next to the transmission lines and contamination was grouped and analysed in terms of the time of occurrence, time of the day, season of the year and time of the day. The results shows that most of the faults on contamination occur on the DC lines and that the voltage level that’s affected the most is 220 kV. The time of the day analysis shows that most of the faults occur between 13:00 to 15:00, this is because the temperature around those times are very hot and temperature has a direct influence on the fire behavior.List of symbols is on page xii-xiii

Study of the influence of altitude on the characteristics of the electrical arc on polluted ice surface = L'étude de l'influence de l'altitude sur les caractéristiques de l'arc électrique à la surface de glace polluée

Dans les régions froides et montagneuses, la présence d'une pression atmosphérique plus faible ainsi que la présence de glace atmosphérique peuvent diminuer la performance électrique des isolateurs extérieurs utilisés dans les réseaux de transport d'énergie. Cette diminution de la performance électrique peut mener à des contournements d'isolateurs pouvant entraîner des interruptions partielles, voire totales, de la distribution électrique. Cette thèse a donc pour but d'étudier les processus et les mécanismes fondamentaux des contournements électriques d'isolateurs recouverts de glace polluée dans des conditions de pression atmosphérique faible. Cette étude contribuera à la compréhension du phénomène de contournement en haute altitude observé sur surface de glace polluée, au développement d'un modèle numérique de prédiction de la tension de contournement des isolateurs recouverts de glace et à la détermination des niveaux d'isolation externe des réseaux de distribution dans les régions froides en haute altitude. Pour mener à bien cette recherche, deux modèles physiques de glace ont été utilisés: un échantillon de glace de forme triangulaire et un isolateur réel court recouvert de glace en régime humide. Une série d'études expérimentales systématiques a été effectuée à l'aide d'une chambre de basse pression utilisée à l'intérieur d'une chambre climatique aux laboratoires de la chaire industrielle CIGELE à l'UQAC. Le processus de contournement sous basse pression atmosphérique sur surface de glace a été étudié en détail, et les paramètres associés ont été enregistrés en utilisant une caméra à haute vitesse et un système d'acquisition. Ces paramètres incluent la tension appliquée, le courant de fuite, le temps de contournement, la longueur d'arc et le rayon de racine d'arc. Par la suite, l'influence des facteurs spécifiques tels que la pression atmosphérique, le type et la polarité de la tension appliquée, la conductivité de l'eau formant la glace ainsi que le profil de l'isolateur sur les performances de contournement des deux modèles physiques utilisés ont été déterminés, ainsi que leur influence sur les exposants m (la valeur de m indique le degré de l'influence de la pression atmosphérique sur la tension de contournement) correspondants à chaque modèle. En utilisant une électrode de mesure, les caractéristiques de tension-courant de l'arc électrique se propageant à la surface de la glace en condition de basse pression atmosphérique ont été étudiées sous des tensions CC et CA. Les constantes A, n d'arc ainsi que la chute de tension aux électrodes ont été déterminées pour des conditions diverses. L'étude des résultats expérimentaux et les analyses théoriques ultérieures ont permis de proposer les mécanismes physiques spécifiques à la propagation de l'arc à la surface de la glace. Ces mécanismes physiques se traduisent par : l'ionisation thermique de l'air devant le pied de l'arc entraînant un mouvement de l'arc; la force électrostatique avec un effet auxiliaire d'entraînement de la propagation de l'arc et enfin, le claquage électrique ne se produisant que pendant le saut final du contournement. De plus, une diminution de la tension de contournement a aussi été observée dans le cas des isolateurs recouverts de glace en condition de haute altitude. Ainsi, les quatre propositions d'explication de ce phénomène sont les suivantes: une diminution des caractéristiques de gradient de tension-courant d'arc, une augmentation de la densité du courant dans le pied d'arc, une diminution de la chute de tension des électrodes et finalement, les phénomènes d'arc flottant. Basées sur les résultats et les déductions de cette étude, plusieurs recommandations ont été proposées pour de futures études

An evaluation of different material line insulators under high voltage AC and bipolar DC excitation in a marine polluted environment

Thesis (MScEng)--Stellenbosch University, 2012.ENGLISH ABSTRACT: The worldwide increase in the popularity of high voltage direct current (HVDC) power transmission application has led to questions regarding the performance of high voltage alternating current (HVAC) insulators when energized under HVDC excitation. These questions have led researchers conduct numerous research projects worldwide. A particular question NamPower (the power utility in Namibia) has faced is: how do these insulators perform and age when energized under HVDC excitation in heavily polluted environments? This question was only partly answered by some insulator ageing tests conducted under laboratory conditions for HVDC excitation. However, the natural ageing tests on insulators, which are preferred, have to date been confined predominantly to HVAC excitation voltages. Thus, this research was initiated to investigate the natural ageing performance of insulators under both HVAC and HVDC excitations, when subjected to harsh marine pollution environments. This research project involved performance and ageing tests on three identical sets of line insulators made from different insulator materials, energised under HVAC and both polarities HVDC excitations respectively. The tests were conducted at Koeberg insulator pollution test station (KIPTS), which is a natural marine pollution insulator test station located near Cape Town, along the west coast of South Africa, approximately 50 m from the sea. The set of insulators consisted of EPDM silicone alloy rubber, HTV silicone rubber, RTV silicone rubber coated porcelain, Porcelain and Glass insulators. The HVAC excitation voltage was chosen as 12.7 kV r.m.s. phase-to-ground and it was decided to use a HVDC excitation voltage equal to this value. The research results showed that the insulators made from HTV silicone rubber performed better than the insulators made from EPDM silicone alloy rubber under all excitation voltages. It is also showed that RTV silicone rubber coated porcelain insulators performed better than Glass and Porcelain insulators under all excitation voltages.AFRIKAANSE OPSOMMING: Die wêreld wye toename in gewildheid van hoë spanning gelyk stroom (HSGS) krag transmisie aplikasie het gelei na vrae oor die effektieweteit van hoë spanning wissel stroom (HSWS) insolators in HSGS aplikasies. Hierdie vrae het gelei na baie navorsings projekte. Een vraag waarmee NamPower (die krag voorsienings maatskapy in Namibia) gekonfronteer was, was hoe gaan die insolators wat onderworpe is aan ’n HSGS toevoer reageer in ’n baie besoedelde omgewing. Hierdie vraag was slegs gedeeltelik beantwoord deur verouderings toetse op insolators wat gedoen is in ’n labaratorium met ’n HSGS toevoer. Inteendeel, die meeste natuurlike verouderings toetse op insolators, soos verkies, is meestal gedoen met ’n HSWS toevoer. Om hierdie rede was hierdie navorsing begin om natuurlike verouderings toetse te doen op insolators onderworpe beide aan HSWS en HSGS toevoere binne ’n marien besoedelde omgewing. Hierdie navorsings projek gaan oor prestering en verouderings toetse op drie, identiese, transmissie lyn insolator stelle, wat onderskeidelik onderworpe was aan HSWS en beide polariteite HSGS toevoere. Die toetse was gedoen by Koeberg insolator besoedeling toets stasie (KIBTS) wat naby Kaapstad geleë is langs die weskus van Suid Africa omtrent 50 m van die see. ’n Stel toets insolators bestaan uit EPDM silikon allooi rubber, HTV silikon rubber, RTV silikon rubber bedekte porselein, Porselein en Glas insolators. Die HSWS waarde waarmee die insolators getoets was, was 12.7 kV w.g.k., fase-na-grond, en dit was besluit om ’n HSGS waarde gelyk aan hierdie spannings waarde te gebruik. Die navorsings resultate wys dat insolators wat gemaak is met HTV silikon rubber presteer beter as insolators wat met EPDM silikon allooi rubber gemaak is onder al die verskillende toevoere. Dit wys ook dat RTV silikon rubber bedekte porselein presteer beter as Porselein en Glas insolators onder al die verskillende toevoere

An evaluation of different material line insulators under high voltage AC and bipolar DC excitation in a marine polluted environment

Thesis (MScEng)--Stellenbosch University, 2012.ENGLISH ABSTRACT: The worldwide increase in the popularity of high voltage direct current (HVDC) power transmission application has led to questions regarding the performance of high voltage alternating current (HVAC) insulators when energized under HVDC excitation. These questions have led researchers conduct numerous research projects worldwide. A particular question NamPower (the power utility in Namibia) has faced is: how do these insulators perform and age when energized under HVDC excitation in heavily polluted environments? This question was only partly answered by some insulator ageing tests conducted under laboratory conditions for HVDC excitation. However, the natural ageing tests on insulators, which are preferred, have to date been confined predominantly to HVAC excitation voltages. Thus, this research was initiated to investigate the natural ageing performance of insulators under both HVAC and HVDC excitations, when subjected to harsh marine pollution environments. This research project involved performance and ageing tests on three identical sets of line insulators made from different insulator materials, energised under HVAC and both polarities HVDC excitations respectively. The tests were conducted at Koeberg insulator pollution test station (KIPTS), which is a natural marine pollution insulator test station located near Cape Town, along the west coast of South Africa, approximately 50 m from the sea. The set of insulators consisted of EPDM silicone alloy rubber, HTV silicone rubber, RTV silicone rubber coated porcelain, Porcelain and Glass insulators. The HVAC excitation voltage was chosen as 12.7 kV r.m.s. phase-to-ground and it was decided to use a HVDC excitation voltage equal to this value. The research results showed that the insulators made from HTV silicone rubber performed better than the insulators made from EPDM silicone alloy rubber under all excitation voltages. It is also showed that RTV silicone rubber coated porcelain insulators performed better than Glass and Porcelain insulators under all excitation voltages.AFRIKAANSE OPSOMMING: Die wêreld wye toename in gewildheid van hoë spanning gelyk stroom (HSGS) krag transmisie aplikasie het gelei na vrae oor die effektieweteit van hoë spanning wissel stroom (HSWS) insolators in HSGS aplikasies. Hierdie vrae het gelei na baie navorsings projekte. Een vraag waarmee NamPower (die krag voorsienings maatskapy in Namibia) gekonfronteer was, was hoe gaan die insolators wat onderworpe is aan ’n HSGS toevoer reageer in ’n baie besoedelde omgewing. Hierdie vraag was slegs gedeeltelik beantwoord deur verouderings toetse op insolators wat gedoen is in ’n labaratorium met ’n HSGS toevoer. Inteendeel, die meeste natuurlike verouderings toetse op insolators, soos verkies, is meestal gedoen met ’n HSWS toevoer. Om hierdie rede was hierdie navorsing begin om natuurlike verouderings toetse te doen op insolators onderworpe beide aan HSWS en HSGS toevoere binne ’n marien besoedelde omgewing. Hierdie navorsings projek gaan oor prestering en verouderings toetse op drie, identiese, transmissie lyn insolator stelle, wat onderskeidelik onderworpe was aan HSWS en beide polariteite HSGS toevoere. Die toetse was gedoen by Koeberg insolator besoedeling toets stasie (KIBTS) wat naby Kaapstad geleë is langs die weskus van Suid Africa omtrent 50 m van die see. ’n Stel toets insolators bestaan uit EPDM silikon allooi rubber, HTV silikon rubber, RTV silikon rubber bedekte porselein, Porselein en Glas insolators. Die HSWS waarde waarmee die insolators getoets was, was 12.7 kV w.g.k., fase-na-grond, en dit was besluit om ’n HSGS waarde gelyk aan hierdie spannings waarde te gebruik. Die navorsings resultate wys dat insolators wat gemaak is met HTV silikon rubber presteer beter as insolators wat met EPDM silikon allooi rubber gemaak is onder al die verskillende toevoere. Dit wys ook dat RTV silikon rubber bedekte porselein presteer beter as Porselein en Glas insolators onder al die verskillende toevoere

Sub transmission insulator and conductor ageing in coastal environments.

Masters Degree. University of KwaZulu-Natal, Durban.Globally, power grids are gradually unbundling to encourage multiple sources of small to medium scale renewable generation, aiding in relieving demanding power constraints [1]. The additional generation product requires an effective and efficient power evacuation system; however, the constrained transmission and sub transmission systems are burdened with the higher power transfer limits coupled with aged infrastructure. Operations and maintenance strategies assist in alleviating the temporary system load increases; however, an asset management strategy is required to ensure that the power system operates at a peak without encouraging a redesign or replacement of the entire power system [2]. The guiding principles of an asset management strategy is understanding the effective utilization of sub systems and components. Effective utilization of components can only be achieved, once a useful lifespan is determined, replacing, refurbishing, or instituting life extension measures once the component end of life is neared. To avert underutilizing or overutilizing the asset, the asset age base needs to be determined incorporating in-situ conditions to provide a reliable and generic prediction model. In sub transmission and transmission systems, maintenance funding, is allocated to critical components such as insulators, ACSR phase conductor and galvanized steel shield wire. These high failure-impact components are susceptible to a higher rate of corrosion related failure, attributed to environmental conditions such as high humidity and high air contamination found in coastal environments. The corrosion models guided by ISO 9223 [3], makes use of empirical degeneration rates for Aluminium, Steel and Zinc. These models understate the initiation of the corrosion reaction for the first year only, requiring the derivation of an acceleration model to represent the degeneration of the composite conductor over its lifespan. The resulting model predicts the useful life of the conductor by measuring the loss in tensile strength attributed to corrosion. Age prediction modelling of the silicone composite insulator is achieved by predicting the loss of creepage or resistive layer on the insulator surface. The coastal environmental conditions, contribute significantly to degenerating the resistive layer leading to a flashover at line voltage. The validation of the insulator and conductor ageing models are achieved by comparing the calculated lifespans to measured field-samples tests. The results showed a standard deviation of 4 years between the measured and calculated values

Comparative laboratory performance characterisation of silicone rubber textured insulators

Silicone rubber (SiR) outdoor insulators are increasingly being deployed in new AC and DC high voltage transmission systems thanks to their superior performance in wet-polluted conditions compared to traditional porcelain and glass insulators. However, in severely polluted environments, sustained discharge activities and dry band arcing due to surface contamination cause tracking, erosion, and the loss of hydrophobicity on the SiR insulator surface. This degradation can accelerate damage to the insulator surfaces, increasing the probability of a flashover and enduring insulator failure. This thesis presents an experimental study on the electric performance of polluted and aged outdoor SiR polymeric insulators using AC and DC voltages. The research involved an extensive review of the published literature and an investigation of the performance of SiR insulators subjected to different ambient conditions and identifies the modes where most failure and degradation occurred on SiR surfaces. Experimental investigations were carried out to compare the aging performance of two 11kV SiR insulator designs using a rotating wheel dip test under AC and positive DC excitations. A standard polymeric insulator design was used and compared with insulators that had a textured surface. Both insulator designs were fabricated in-house using a vacuum casting machine. Several electrical parameters were measured during the test to characterise the performance of each insulator. Dry band arcing activities were mainly observed on the trunk surface of the conventional profile. A decrease in hydrophobicity was measured on the tested surfaces, and tracking and erosion defects were also observed on both insulator designs. Leakage current measurements showed that drying and discharge activity was greater for a conventional insulator compared with the textured insulator, and more severe degradation appeared under positive DC tests than under AC. These studies showed that insulators with a textured design can improve the performance of SiR insulators against tracking and erosion under AC and positive DC excitations. The electric field and potential distributions along the leakage surface of the 11 kV SiR insulators under dry clean and wet polluted conditions were studied using finite element method COMSOL Multiphysics. The critical of high field regions on SiR surfaces were identified and the power dissipated in the pollution layer along insulator surface was calculated. This study showed useful information about surface heating, which could be used to predict of the formation of dry bands. An investigation of the pollution layer characterisation on conventional and textured pattern designs is described. Several tests were conducted to evaluate the behaviour of the insulator surfaces under different conditions. ESDD and NSDD parameters were measured for different materials, and evaluations for each design were also performed. Leakage conductance measurements on surface designs were determined, and the distribution trends of surface conductance were also characterised. Different rectangular SiR samples were assessed, and an improvement for reducing the pollutant deposition on textured surfaces was observed. In 4-shed insulators, the textured design showed comparable ESDD value with conventional profile. Textured designs also showed slower growth of the leakage current than the conventional design. Clean fog tests (based on a high voltage ramp test) were carried out to investigate the flashover performance of conventional and textured insulator designs. For different ranges of wetting and pollution severity conditions, the textured design showed an improvement in the flashover performance that could reach 16 % compared to the conventional surface. This indicates that the textured surface seems to be more effective under severe ambient conditions. It was also observed that the textured insulator design can improve the electrical performance of SiR insulators under AC and DC voltages

Outdoor Insulation and Gas Insulated Switchgears

This book focuses on theoretical and practical developments in the performance of high-voltage transmission line against atmospheric pollution and icing. Modifications using suitable fillers are also pinpointed to improve silicone rubber insulation materials. Very fast transient overvoltage (VFTO) mitigation techniques, along with some suggestions for reliable partial discharge measurements under DC voltage stresses inside gas-insulated switchgears, are addressed. The application of an inductor-based filter for the protective performance of surge arresters against indirect lightning strikes is also discussed