Pole Transformer Research Articles

Compositional dependence of the soft magnetic properties of the nanocrystalline Fe–Zr–Nb–B alloys with high magnetic flux density

The compositional dependence of the soft magnetic properties of the nanocrystalline Fe–Zr–Nb–B alloys has been investigated. The magnetostriction (λs) and the grain size of the (Fe90Zr7B3)1−x(Fe84Nb7B9)x alloys, which are two typical ternary alloys mixed with the best soft magnetic properties, show intermediate values between those of the Fe90Zr7B3 with negative λs and the Fe84Nb7B9 with positive λs. However, the soft magnetic properties of the Fe–(Zr, Nb)7–B alloys are inferior to those of the Fe90Zr7B3 and the Fe84Nb7B9 alloys. The best soft magnetic properties have been obtained at Zr+Nb=6 at. %. The Fe85.5Zr2Nb4B8.5 alloy shows a high μe of 60 000 at 1 kHz, a high Bs of 1.64 T, and zero λs, simultaneously. The alloy also exhibits a very low core loss of 0.09 W/kg at 1.4 T and 50 Hz, which is extremely lower than that of Fe–Si–B amorphous alloys. The nanocrystalline Fe–Zr–Nb–B alloys with improved soft magnetic properties are therefore suitable for pole transformers.

ナノ結晶Ｆｅ‐Ｚｒ‐Ｎｂ‐Ｂ合金の軟磁気特性

The soft magnetic properties of nanocrystalline Fe-Zr-Nb-B alloys, which are mixtures of Fe-Zr-B alloy with negative magnetostriction and Fe-Nb-B alloy with positive magnetostriction, were investigated. The magnetostriction and grain size of the Fe-Zr-Nb-B alloys show values intermediate between those of Fe-Zr-B and Fe-Nb-B alloys. The soft magnetic properties are strongly affected by the Zr + Nb amount and Zr/Nb ratio. The best soft magnetic properties have been obtained for the Fe85.5Zr2Nb4B8.5 alloy. This alloy simultaneously exhibits a high permeability of 60,000 at 1 kHz, a high saturation magnetic flux density of 1.64 T, and zero-magnetostriction. The alloy also exhibits a very low core loss of 0.09 W/kg at 1.4 T and 50 Hz, which is far lower than that of Fe-Si-B amorphous, as well as good thermal stability of the core loss. Nanocrystalline Fe-Zr-Nb-B alloy is therefore suitable as a core material for pole transformers.

Sulfur evaporation and magnetic induction in thin-gauged 3%Si-Fe sheets

Singly oriented 3%Si-Fe is one of the most popular soft magnetic materials. Used as the core material of pole and power transformers, it is highly oriented to (110)[001] Goss texture and has one direction of easy magnetization in the rolling plane. The formation mechanism of Goss texture in thin-gauged 3%Si-Fe sheets can be explained by considering the influence of impurities (especially, sulfur) on the surface energy of (110) and other planes. It is the purpose of this study to investigate the effect of sulfur evaporation on the magnetic induction in thin-gauged 3%Si-Fe sheets by prolonged holding of silicon-iron melts or by annealing of hot-rolled plates.

Studies of elastic waves caused by corona discharges in oil

In order to diagnose the deterioration of insulation and evaluate its location in oil-filled pole transformers, measurements of elastic waves brought by corona discharges in oil were performed, based on an acoustic emission (AE) technique. The detected signals in these measurements were analyzed by means of a fast Fourier transform (FFT) and their properties were discussed theoretically. It was found that the AE signals due to the Lamb waves of symmetric mode caused in a thin steel tank could be recognized easily by the FFT analysis of initial stages of the detected AE signals. This suggests that the accuracy on location of the AE sources in the transformer would be improved. Also, it was shown that a low pass filter was effective in improving the location accuracy.

線路用避雷装置による柱上変圧器の雷害防止対策

線路用避雷装置による柱上変圧器の雷害防止対策

Local distribution on magnetic properties in grain-oriented silicon steel sheet

Grain-oriented silicon steel is the most important soft magnetic material used as core material of large transformers, large rotating machines, and pole transformers. Total loss of grain-oriented silicon steel tends to become lower with an increasing degree of texture. However, the material which has a higher degree of texture ordinarily contains larger grains, and the materials which have larger grains show higher total loss due to increased eddy current loss. As the gauge is reduced, the rate of decrease in total loss becomes lower for the thinner gauge due to increased hysteresis loss. However, the investigation of local magnetic properties due to grain situation in this sheet was not discussed from the viewpoint of the distribution of localized magnetic properties, for example, iron loss, hysteresis loop, behavior H vector (magnetic field strength) and B vector (Magnetic flux density). This paper describes the distribution of magnetic properties in high oriented silicon steel sheet, which are loss, hysteresis loop, and locus of field strength.

Relation of insulation resistance and deteriorated ratio of reference voltage of oil-immersed surge arrester elements enclosed in pole transformers

About ten years have passed since oil immersed surge arrester elements enclosed in 6.6 kV pole transformers were first used. At present, technical developments are being demanded to judge the soundness of these oil immersed surge arrester elements by a simple method, allowing one to judge easily whether these elements can be used or not onsite. The authors empirically investigated the correlation between the insulation resistance and the deteriorated ratio of the reference voltage of these oil-immersed surge arrester elements. It was found that the deterioration of the oil-immersed surge arrester elements can be detected by measuring the insulation resistance.

Effects of Rolling Conditions on Grain Orientation and Magnetic Properties of Thin-Gauged 3% Si-Fe Sheets

3% Si-Fe sheets are widely used as core material of large transformers, large rotating machines and pole transformers due to characteristic soft magnetic properties, where energy losses during magnetization are critically concerned. The magnetic characteristics in silicon iron arises from a preferred grain orientation, i.e. (110) [001] Goss texture which forms after cold rolling followed by secondary recrystallization. In this paper, effects of rolling direction on the grain orientation and magnetic properties of the thin-gauged 3% Si-Fe sheets are investigated.

溶剤洗浄方式による柱上変圧器構成材からのPCB除去に関する実証的研究

In 1989, trace of PCB (less than 50 mg PCB/kg insulation oil) was found in reclaimed oil used in some pole transformers. It was keenly required to remove the detrimental PCB in a reliable method. Elimination demonstration tests of PCB and the like were carried out by a solvent cleaning technique using some local transformers operating in site. They were broken down into classified metals by way of chilled crushing, and were subjected to preliminary cleaning for five minutes and then secondary cleaning for ten minutes, thus obtaining harmless iron, coppers and porcelains which could reduce their residual PCB lower than the lowest determination limit (0. 05 mg of PCB/kg of parts). Similarly, papers and woods were subjected to preliminary cleaning for sixty minutes and then secondary cleaning for six hundreds minutes, thus reducing their residual PCB at lower then the lowest determination limit, depending on the types of transformer. Further these tests demonstrated that the solvent cleaning system adapted for this test could be reliably operated, thus securing the ambient and work-environmental safety.

溶剤洗浄方式による柱上変圧器構成材からのPCB除去に関する実証的研究

In order to establish a method of disposing a trace of PCB contained in reclaimed insulating oil in pole transformers (50 mg PCB/kg or less) in a safe manner, a full-scale insulating oil removal test by means of solvent cleaning was conducted using a real transformer not containing PCB. Test conditions were determined to prepare for the decontamination test for transformers containing PCB, and safety of the facilities was confirmed. Major results obtained are shown as follows: (1) Satisfactory removal performance was obtained by breaking the transformer with the low-temperature crushing technique and sorting the members for cleaning. (2) It was estimated that residual PCB in ferrous materials, copper materials and ceramics could be redacted to the level below a preset limit after primary cleaning of five minutes and secondary cleaning of ten minutes, and that inpieces of paper and wooden chips could be reduced to the level of 0.1 mg PCB/kg members or below after primary cleaning of 60 minutes and secondary cleaning of 600 minutes or less. (3) It was confirmed that the facilities could be operated safely, and enviromental and working safety could be ensured.

Evaluation and application of oil-immersed zinc oxide elements enclosed in pole-mounted distribution transformers

Voltage due to lightning surge is now a major problem to be overcome to ensure full reliability of any power supply. Hence, gapless oil-immersed surge arresters using zinc oxide elements have been applied to pole transformers. These surge arresters are used as a means of insulation coordination for pole transformers. These arresters contribute to the reduction of the number of failure of pole transformers. This paper describes applications and effects of specially developed oil-immersed surge arresters in pole transformers on 6.6-kV distribution lines. © 1997 Scripta Technica, Inc. Electr Eng Jpn, 121(2): 37–46, 1997

Evaluation and application of oil‐immersed zinc oxide elements enclosed in pole‐mounted distribution transformers

Voltage due to lightning surge is now a major problem to be overcome to ensure full reliability of any power supply. Hence, gapless oil-immersed surge arresters using zinc oxide elements have been applied to pole transformers. These surge arresters are used as a means of insulation coordination for pole transformers. These arresters contribute to the reduction of the number of failure of pole transformers. This paper describes applications and effects of specially developed oil-immersed surge arresters in pole transformers on 6.6-kV distribution lines. © 1997 Scripta Technica, Inc. Electr Eng Jpn, 121(2): 37–46, 1997

Proving test on removal of PCB from pole transformer by vacuum heating separation method

In 1989, PCB was found in recycled insulation oils used in some pole transformers at a concentration of 50 mg per kg of insulation oil, prompting quick establishment of their safe separation method. One of the prospective methods for removing, for example, recycled insulation oils attached to and impregnated into the transformer coils, may be a vacuum heating separation method which heats and vaporizes PCB under vacuum conditions for separation. A proving test for the applicability of the specific vacuum heating separation method was carried out with actually used transformers, which confirmed that residual PCB on coils was minimized to less than the quantitative determination threshold of 0.05 mg per kg of insulation oil under the following standard applicable conditions: vacuum lower than 0.05 Torr; heating temperature 200 °C; and vacuum holding time 10 hours. Thus, the reduction of effects on the environment was verified. © 1997 Scripta Technica, Inc. Electr Eng Jpn 120(3): 17–28, 1997

Modeling of magnetizing and core-loss currents in single-phase transformers with voltage harmonics for use in power flow

This paper presents two approaches for calculating the iron-core and copper losses of a 25 kVA single-phase pole transformer subjected to low-frequency voltage harmonics: an approximate calculation and a finite-element computer model. These methods can be applied to any transformer of similar construction by simply changing the input data, and they can be used for most other single-phase transformers with small modifications. The approximate method is a technique for calculating the change in iron-core losses which can be done without a computer. The finite element computer model performs a quasi three-dimensional field analysis on the iron-core region and calculates the flux density (B) and iron-core losses in each finite element, as well as the magnetizing and core-loss currents. The results of either method can be used at pre-processing for a (harmonic) power flow program.

Proving test on removal of PCB from pole transformer by vacuum heating separation method

In 1989, PCB was found in recycled insulation oils used in some pole transformers at a concentration of 50 mg per kg of insulation oil, prompting quick establishment of their safe separation method. One of the prospective methods for removing, for example, recycled insulation oils attached to and impregnated into the transformer coils, may be a vacuum heating separation method which heats and vaporizes PCB under vacuum conditions for separation. A proving test for the applicability of the specific vacuum heating separation method was carried out with actually used transformers, which confirmed that residual PCB on coils was minimized to less than the quantitative determination threshold of 0.05 mg per kg of insulation oil under the following standard applicable conditions: vacuum lower than 0.05 Torr; heating temperature 200 °C; and vacuum holding time 10 hours. Thus, the reduction of effects on the environment was verified. © 1997 Scripta Technica, Inc. Electr Eng Jpn 120(3): 17–28, 1997

真空加熱分離方式による柱上変圧器構成材からのPCB除去に関する実証的研究

In 1989, PCB was found in recycled insulation oils used in some pole transformers at a concentration of 50 mg per kg of insulation oil, prompting quick establishment of their safe separation method. One of the prospective methods for removing, for example, recycled insulation oils attached to and impregnated into the transformer coils, may be a vacuum heating separation method which heats and vaporizes PCB under vacuum conditions for separation. A proving test for the applicability of the specific vacuum heating separation method was carried out with actually used transformers, which confirmed that residual PCB on coils was minimized to less than the quantitative determination threshold of 0.05 mg per kg of insulation oil under the following standard applicable conditions: vacuum lower than 0.05 Torr; heating temperature 200 °C; and vacuum holding time 10 hours. Thus, the reduction of effects on the environment was verified. © 1997 Scripta Technica, Inc. Electr Eng Jpn 120(3): 17–28, 1997

配電用柱上変圧器の直流偏磁現象

配電用柱上変圧器の直流偏磁現象

Nanocrystallization of Amorphous Fe–Zr–B–Cu Alloys and Low Frequency Soft Magnetic Properties

In nanocrystalline alloys reported to date, Fe-Zr-B(-Cu) alloys shows the highest saturation magnetization (higher than Fe-B-Si amorphous alloys), they are thus expected to be applied to power transformers used at B m =1.3 ∼ 1.4 T and f= 50 ∼ 60 Hz. Usually they are expected to be used in high frequencies because of their excellent permeabilities. The low frequency (50 Hz) magnetic properties of Fe 86 Zr x B 13-x Cu 1 nanocrystalline ribbons have been examined from the viewpoint of application to power transformers. Core loss W 13/50 (1.3 T, 50 Hz)=0.07 W/kg was observed in the annealed Fe 86 Zr 5 B 8 Cu 1 alloy. Magnetic induction B 1k (in a field of 1 kA/m) is 1.54T for the same sample. In annealing Fe 86 Zr x B 13-x Cu 1 (x= 5 ∼ 7) amorphous alloys, ultrafine bcc-Fe grains about 15 nm in size were obtained with remaining stable amorphous phases. The stable amorphous phase makes the grains very fine. The stability of the amorphous phase is related to the liquidus temperature T L that was measured during cooling and solidifying of the molten alloy of each composition in a furnace. When the grains grew during annealing, the amorphous phase changed its composition to exhibit lower T L and became more stable. The core loss W 13/50 shows the W∼D 6 dependence in the range of D=15 ∼ 25 nm. However, when the grain size was D=8 nm, the core loss does not show the D 6 dependence. The nanocrystalline Fe-Zr-B-Cu ribbons shows poor ductility, which should be improved if the materials are to be used in actual pole transformers.

A new medium/low-voltage transformer for use in rural public distribution networks

This article describes the development of a new pole transformer, designed to be unexplodable in the case of an internal fault, to be better adapted to withstand changing loads and to be compact. Laboratory bench tests led to the choice of the best suited liquid dielectric, silicone, combined with temperature-insensitive aramid fibre. An unusual constructive step was the designing of a tank made of injection-moulded aluminium with a built-in high-current fuse. A series of tests were undertaken by the Laboratoires des Renardieres on a number of transformers with simulated faults of different kinds. The results of these tests were used to check the validity of the original design options.

Experimental analysis of lightning overvoltages induced on low‐voltage distribution lines

AbstractProblems have often been caused in low‐voltage distribution lines such as single‐phase 100/200 V and three‐phase 200‐V systems. For instance, the burning of low‐voltage devices and the unnecessary operation of ground fault interrupters have occurred, which are caused possibly by lightning overvoltages.Experimental analysis was performed on the generation modes of lightning overvoltages on low‐voltage distribution lines.A scale model line, one‐fourth the size of an actual power distribution line of Tokyo Electric Power Company (TEPCO), was installed for experimental analysis on the lightning protection of an overhead ground wire, an overhead common grounding wire (system neutral conductor), surge arresters and pole transformers against the overvoltages induced on low‐voltage distribution lines due to a nearby lightning stroke.A balloon was flown at a location 30 km away from the scale model line in a normal direction to it. A 200‐m long wire is suspended from the balloon to simulate a lightning path. Pulse current is applied to the simulated path using a pulse generator and the voltages induced on the line conductors are measured.This paper analyzes those overvoltages by means of the experimental and the theoretical methods.