Pole Transformer Research Articles

Audible Noise From Amorphous Metal and Silicon Steel-Based Transformer Core

Model cores based on amorphous SA1 and HB1 alloys for pole transformers were prepared and their audible noise was measured in terms of A-weighted sound power level in a hemi-anechoic chamber in accordance with ISO 3744 standard. The two amorphous cores annealed under optimum conditions to minimize the audible noise showed the same sound power level of 56 dB as M3 core at their typical operating flux densities. It was found that A-weighted sound power levels increased above 1.4 T for SA1 core and above 1.5 T for HB1 core. This provides design limitations for transformer cores based on amorphous alloys.

An Evaluation of Amorphous Transformer using Load Curve Pattern Model for Pole Transformer

Energy loss in transformer is composed of no load loss and load loss. No load loss of amorphous transformer (i.e. amorphous metal-based transformer) could be reduced by about 70% compared with traditional transformers (e.g. silicon steel-based transformer). If amorphous transformers are adopted to pole transformers owned by electric companies, large amount of energy savings and reduction of CO2 could be realized. However, amorphous transformers have disadvantages of high initial cost and high load loss parameters compared with traditional transformers.Economies of pole transformers are evaluated in the paper by the sum of the initial cost and the power loss cost, that is calculated by the load curve pattern of pole transformers. Authors propose a load curve pattern model for pole transformers and analyze the effects in cases which amorphous transformers are adopted to pole transformers.Simulation results show that most of the losses in pole transformers are no load loss, and amorphous transformer is effective in achieving substantial energy savings as well as environmental benefits.

Zig-Zag 귄선에 의한 내철형 주상변압기 개발에 관한 연구

본 논문에서는 세계최초로 내철형 주상변압기 코일의 권선을 일반적인 권선방법에서 Zig-Zag(가칭) 권선방법으로 설계 제작하는 방법을 제안하였으며, 또한 바니시 함침공정을 생략하고 단락강도 및 절연내력을 향상시킬 수 있는 내철형 변압기용 권선의 신프레임 구조개발 내용을 제안하였다.<BR> 기존의 주상변압기 권선방법에 비하여 전기절연 측면에서 층간 절연지의 사용매수 및 두께를 획기적으로 절감할 수 있는 장점이 있다. 또한 원가절감과 손실저감 및 단락기계력 대처능력이 우수함을 검증하였으며 국내전력회사 배전계통 주상변압기에 유용하게 활용할 수 있다.

혼합절연을 이용한 초저손실급 주상변압기 개발에 관한 연구

주상변압기는 고객에게 직접 전력을 공급하는 설비로서 전력공급의 안정성확보를 위한 중요한 기자재 중 하나이다. 하지만 제조결함에 의한 3년 이내의 초기고장 또는 13년이 초과 사용한 후의 열화고장이 빈번히 발생하고 있어 변압기 품질분석을 통한 신뢰성이 개선된 주상변압기 개발이 필요하다. 본 논문에서는 열적, 기계적, 전기적으로 성능이 향상된 새로운 모델의 혼합절연 주상변압기를 개발하였다. 변압기의 기계적, 열적특성을 향상시키기 위한 혼합절연 방식에 대한 설계 및 제작방법을 제시하고 과부하시험을 시행하여 순간최대부하에 대응할 수 있도록 과부하내량 160[%] 까지 증가시킬 수 있음을 확인하였다. 또한 본 논문에서는 100[kVA] 1대를 시제품으로 제작하여 단락강도시험과 변압기 관련 절연시험을 시행하여 전자기계력의 분석과 단락강도설계 향상 방안에 대하여 설명하고 이와 관련하여 연구한 결과에 대해 논하였다.

Characteristic Impedances in Low-Voltage Distribution Systems for Power Line Communication

The input and output impedances in a low voltage distribution system is one of the most important matters for power line communication because from the viewpoint of communication, the attenuation characteristic of the high frequency signals is greatly caused by impedance mismatch during sending and receiving. The frequency range is from 1MHz to 30MHz. Therefore, this paper investigates the input and output impedances in order to understand the characteristic of high frequency signals in the low voltage distribution system between a pole transformer and an end user. For power line communication, the model of Korea's low voltage distribution system is proposed in a residential area and then the low voltage distribution system is set up in a laboratory. In the low voltage distribution system, S parameters are measured by using a network analyzer. Finally, input and output impedances are calculated using S parameters.

Lifetime Evaluation Method for Pole Transformer Based on Transient Temperature Analysis

From the viewpoint of reducing the cost of electric transport, a pole transformer has been operated, for a trial, under a short-time overloaded condition. It is not clear how long it takes a pole transformer to deteriorate under an overloaded condition, therefore, a pole transformer lifetime evaluation method is necessary. To realize this method, we developed a transient temperature calculation method from the load pattern and temperature of the outer section of the temperature, and evaluated its accuracy by comparing measurement results and calculations. We developed an estimation method of the degree of polymerization of insulating paper at varying temperature from the measurement result at various temperatures and times in the pole transformer atmosphere.

Development of Non-Destructive Optical Diagnostic Apparatus for Pole Transformers

In this study, we found that the reflective absorbance correlates with the average degree of polymerization of the insulating paper, the correlation coefficient being over 0.90. It was found out that the optical diagnostic method could be applied in the core degradation diagnosis of a pole transformer, and the indirect degradation diagnostic apparatus of the pole transformer using this technique was developed. Optical diagnostics is a method of analysis by presuming the degree of proceeding of the heat deterioration of the organic insulator from the difference in reflective absorbance of two wavelengths containing near-infrared light, and the life prediction is also possible by using chemical kinetics. In this diagnosis, the degree of deterioration of the insulating paper can be calculated quantitatively using the diagnostic master curve, which is obtained from accelerated heating experiments based on the chemical kinetics. The optical sensor consists of two kinds of optical fiber cables to attach and measure the reflective absorbance on the insulating papers in the oil, two kinds of near-IR (infrared) laser diodes (LD), 830nm and 1310nm, as light sources, and a photodiode as a detector, and so it is very compact and lightweight (less than 1.5kg).

Effect of Lightning Protective Devices Attached to Pole Transformers on Reduction of Overvoltage on Distribution Lines

Abstract: Class-10A solid-core insulators (BIL 90kV) have been used instead of class-6A pin insulators (BIL 60kV) in order to improve the insulation level of distribution lines. However, lightning protective devices attached to pole transformers may have the effect of reducing the overvoltages on phase conductors. We have investigated the lightning protection effect of devices attached to pole transformers by experiment and analysis using the EMTP (Electro-Magnetic Transients Program). The sparkover rate changes from 2.0˜3.3% to 5.5˜9.9% and increases 2.4˜2.8 times when the line insulator of the phase conductors is changed from class-10A to class-6A. It is thought that the insulation level of the line insulator can be reduced depending upon the local particularities, such as number of installed transformers, frequency of direct lightning stroke to the distribution line, and so on although the overall fault rate may increase to some extent.

A simplified cascade current-source inverter interconnected to a single-phase three-wire distribution system and its application to electric energy storage systems with batteries

A novel current source inverter system interconnected to the single-phase grid is proposed. It has the same construction as the conventional three-phase current source inverter that is interconnected to the single-phase three-wire distribution system. Though the proposed circuit has no output transformer, it can be equivalently performed as the single-phase double cascade inverter by diverting the pole transformer in the utility system. By controlling the appropriate scheme, the output currents can be obtained as the five-level waveforms and their distortions can be decreased sufficiently. It is applied to the interactive electric energy storage system with batteries and the basic discharging characteristics are discussed experimentally. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 150(2): 50–61, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.10380

Measured efficiency improvements of induction motors with thyristor/triac controllers

The deployment of inexpensive thyristor/triac controllers improve the efficiency and do not increase the power factor of induction motors (as measured at the input of pole transformer) operating under variable torque and constant speed constraints. Computer-aided testing yields detailed input/output powers for the drive. The improvement of the power factor does not increase the real-power capability (RPC) of a transformer supplying power to such drives due to current harmonics. Although the total harmonic current distortion (THDi) may exceed IEEE 519 and IEC 555 recommendations, recent publications show that the impact on the apparent power derating of a 25 kVA pole transformer is small if the THDi is less than 50%.

Measured Efficiency Improvements of Induction Motors with Thyristor/Triac Controllers

The deployment of inexpensive thyristor/triac controllers improve the efficiency and do not increase the power factor of induction motors (as measured at the input of pole transformer) operating under variable torque and constant speed constraints. Computer-aided testing yields detailed input/output powers for the drive. The improvement of the power factor does not increase the real-power capability (RPC) of a transformer supplying power to such drives due to current harmonics. Although the total harmonic current distortion (THDi) may exceed IEEE 519 and IEC 555 recommendations, recent publications show that the impact on the apparent power derating of a 25 kVA pole transformer is small if the THDi is less than 50%.

Nanostructure formation and soft magnetic properties evolution in Fe 91− xW xB 9 amorphous alloys

The crystallization behavior of the amorphous Fe 91− x W x B 9 (0< x<14), the microstructure and the soft magnetic properties of the nanocrystalline Fe–W–B alloys have been investigated. It was found that the primary crystallization precipitates consist of mixture of the bcc-Fe and bct-Fe 3B phases. The tungsten addition makes grain size decrease. The grain size of the primary Fe 91− x W x B 9 (6⩽ x⩽12) alloys was evaluated to be 18–9 nm. The small grain size seems to reflect the small growth rate of the primary precipitates resulting from re-distribution of the W element between the primary bcc-Fe, bct-Fe 3B and residual amorphous phases, which is due to their small solubility, large cohesive energy and small diffusivity to α-Fe. The best soft magnetic properties have been obtained for the Fe 91− x W x B 9 (6⩽ x⩽12) optimally annealed (900< T a<936 K) alloys. These nanostructured alloys show high magnetic flux density of 1.58–1.76 T, high permeability of 21.000–33.000 at 1 kHz and zero magnetostriction, simultaneously. This behavior is thought to result from the exchange magnetic coupling mechanism among the different ferromagnetic phases containing in these optimally annealed alloys. It is concluded that the nanocrystalline Fe–W–B optimally annealed alloys (6–12 at.% W) are suitable materials for core pole transformers.

Low core losses of nanocrystalline Fe–Zr–Nb–B soft magnetic alloys with high magnetic flux density

The soft magnetic properties of the nanocrystalline Fe–Zr–Nb–B alloys, which are mixed Fe–Zr–B alloy with negative magnetostriction and Fe–Nb–B alloy with positive one, have been investigated. The magnetostriction and the grain size of the Fe–Zr–Nb–B alloys show intermediate values between those of the Fe–Zr–B and Fe–Nb–B alloys. The soft magnetic properties are strongly affected by Zr+Nb amount and Zr/Nb ratio. The best soft magnetic properties have been obtained for the Fe 85.5Zr 2Nb 4B 8.5 alloy. The alloy shows a high permeability of 60 000 at 1 kHz, a high saturation magnetic flux density of 1.64 T and zero-magnetostriction, 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, and good thermal stability of the core loss. The nanocrystalline Fe–Zr–Nb–B alloy is therefore suitable for a core material for pole transformers.

Characteristics of elastic waves caused by corona discharges in an oil-immersed pole transformer

Measurements of elastic waves brought by a pulse of simulated corona discharge in an oil immersed pole transformer and a model tank filled with oil were performed in order to identify the location of insulation deterioration, using an acoustic emission (AE) technique. The detected AE signals were analyzed by means of a fast Fourier transform (FFT), and properties of elastic waves influenced by the existence of insulated windings and magnetic core for power transformation in the transformer were investigated. The result shows that almost all the initial AE signals detected on the-wall of the transformer tank were Lamb waves caused by the oscillation waves passing through the insulating paper and oil with repeating transmission, reflection and refraction. Also, it was possible to recognize whether the measured elastic wave was influenced by windings and their insulating papers or not, by FFT analysis. This suggests that the location accuracy of the corona discharge in the transformers would be improved.

Solvent cleaning of pole transformers containing PCB contaminated insulating oil

In 1989, it was discovered that the recycled insulation oil in pole transformers for electric power supply was contaminated with trace amounts of polychlorinated biphenyls (PCBs; maximum 50 mg-PCB/kg-insulation oil). In order to remove the PCBs from transformer components using n-hexane as a solvent, we investigated the relationship between progressive stages of dismantling and cleaning results. The results are summarized as follows: (1) Based on the cleaning test results, we made an estimate of the residual PCB amount on iron and copper components. By dismantling the test pole transformers into the “iron core and coil portion” and cleaning the components, we achieved a residual PCB amount that was below the limit of detection (0.05 mg-PCB/kg-material). To achieve a residual PCB amount below the limit of detection for the transformer paper component, it was necessary to cut the paper into pieces smaller than 5 mm. We were unable to achieve a residual PCB amount below the limit of detection for the wood component. (2) Compared to Japan's stipulated limited concentration standard values for PCBs, the results of the cleaning test show that cleaning iron or copper components with PCBs only on their surface with the solvent n-hexane will satisfy the limited concentration standard values when care is taken to ensure the component surfaces have adequate contact with the cleaning solvent.

Development of advanced built-in surge arresters for distribution system with new zinc-oxide elements

New zinc-oxide elements with a varistor voltage about twice that of conventional ones have been developed by reducing the ZnO grain size with a new additive, which enables halving of the series number of elements in a metal oxide surge arrester. Using these elements, we have developed advanced built-in surge arresters enclosed in 6.6 kV pole transformers and switchgear. The advanced arresters have been reduced in volume by 25% compared with conventional ones. This paper describes the specification and construction of the advanced arresters and the results of various evaluation tests.

Soft Magnetic Properties of Nanocrystalline Fe-Nb-B-P Alloys Produced in the Atmosphere by Melt-Spinning Method

The soft magnetic properties of nanocrystalline Fe-Nb-B and Fe-Nb-B-P alloys produced in the atmosphere by a melt-spinning method have been investigated. The nanocrystalline Fe 100-x-y Nb x B y ternary alloys show good soft magnetic properties, relative permeability (μ') above 35000 at a frequency of 1 kHz and coercive force (H c ) below 5.0 Am -1 , as well as high saturation magnetic induction (B s ) above 1.55 T T in the compositional range of x = 6.5-6.7 and y = 9.3-10.0 at%. The soft magnetic properties of the nanocrystalline Fe-Nb-B ternary alloys are improved by 0.5-1.5 at% substitution of P for B, without decreasing their B s . The magnetostriction (λ s ) value increases and the mean grain size of bcc-Fe phase (D) decreases slightly by substitution of P for B. The nanocrystalline Fe 84 Nb 6.5 B 9 P 0.5 and Fe 84 Nb 6.5 B 8.5 P 1 alloys show good soft magnetic properties, μ' of 46000-47000 at a frequency of 1 kHz, H c of 3.6-3.9 Am -1 and the core loss of the 0.09 Wkg -1 at maximum induction (B m ) of 1.33 T and a frequency of 50 Hz as well as high B s of 1.60 T, suggesting that these nanocrystalline Fe-Nb-B-P alloys are suitable for a core materials for pole transformers.

Development of Advanced Built-In Surge Arresters for Distribution Systems with New Zinc-Oxide Elements

New zinc-oxide elements with a varistor voltage about twice that of conventional ones have been developed by reducing the ZnO grain size with a new additive, which enables to halve the series number of elements in metal oxide surge arresters. Using these elements, we have developed advanced built-in surge arresters enclosed in 6.6 kV pole transformers and switchgear. The advanced arresters have been reduced in volume by 25% compared with conventional ones. This paper describes the specification and construction of the advanced arresters and the results of various evaluation tests.

Magnetic properties of zero-magnetostrictive nanocrystalline Fe–Zr–Nb–B soft magnetic alloys with high magnetic induction

The soft magnetic properties of the nanocrystalline Fe–Zr–Nb–B alloys have been investigated. The best soft magnetic properties have been obtained for the Fe 85.5Zr 2Nb 4B 8.5 alloy. The alloy shows a high permeability of 60,000 at 1 kHz, a high magnetic induction of 1.64 T and zero magnetostriction, 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. The nanocrystalline Fe–Zr–Nb–B alloy is therefore suitable for a core material for pole transformers.

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.