Power Transformer Applications Research Articles

Performance of a prototype power transformer constructed by nanocrystalline Fe-Co-Si-B-P-Cu soft magnetic alloys

To clarify the feasibility and performance of Fe81.2Co4Si0.5B9.5P4Cu0.8 alloy (with trade name NANOMET®) for electrical power applications, a prototype transformer was constructed. After surface treatment, as-quenched ribbons with a constant width of 50 mm and a thickness of ∼30 μm were wound into a toroidal shape. Nanocrystallization of toroidal core was performed by immersing it in a salt at 673 K for 180 s. The transformer constructed in the present work exhibit low core loss similar to the transformer constructed by a commercial Fe-based amorphous alloy. In spite of issues related to the annealing/nano-crystallization of the core, the feasibility for commercialization of NANOMET in power transformer applications can be confirmed. We believe the potential of NANOMET as core material for next generation of power transformer seems to be huge.

Cation distribution controlled dielectric, electrical and magnetic behavior of In3+ substituted cobalt ferrites synthesized via solid-state reaction technique

We report the structural, cation distribution, dielectric, electrical and magnetic properties of CoFe2−xInxO4 (0.0 ≤ x ≤ 0.6) ferrites. Rietveld fitted X-ray diffraction (XRD) patterns confirm the formation of single phase cubic spinel structure with Fd3m space group for all the samples. The comprehensive analysis of XRD based cation distribution has been performed to see the effect of In3+ ions substitution on various structural parameters such as site ionic radii, edge and bond lengths, interionic distances etc. The dielectric constant and tangent loss have been studied as a function of temperature and frequency. The dielectric data presented in electric modulus form reveals the presence of non-Debye relaxation behavior in considered ferrites. Both the AC and DC conductivities as a function of temperature are found to decrease with increasing In3+ content. The power law behavior of AC-conductivity indicates a strong correlation among electrons in these systems. The isothermal magnetization versus applied field curves with high field slope and significant coercivity suggest that studied materials are highly anisotropic with canted spin structures and exhibit ferrimagnetic behavior at 300 K. Magnetization gets enhanced up to 40% of In3+ substitution. The observed low dielectric losses and high resistivity can find their application in power transformers at high frequencies.

Investigations on PD Characteristics of Thermal aged Palm and Corn Oil for Power Transformer Insulation Applications

Partial discharge (PD) detection plays a major role in the life time assessment of liquid insulation in power transformers. Many research works are being carried out to replace conventional mineral oil insulation in transformers by vegetable oils. It is necessary to understand the PD characteristics of vegetable oils before recommending them as an alternate for mineral oil. In this paper, the breakdown strength and PD characteristics of palm and corn oil were investigated in both unaged and thermally aged conditions. Laboratory experiments were performed as per IEC test procedures. PD signals were measured using wide band detection system. Phase resolved PD pattern of vegetable oils and mineral oil were compared. Effect of increase in voltage stress on the PD pattern of palm and corn oil were studied. Time and frequency domain analysis of PD pulses at needle-plane electrode configuration was carried out. Statistical analysis of PD pattern i.e. skewness and shape parameter variations with respect to applied thermal stress were also carried out. From the results, it is observed that palm and corn oils have better breakdown strength and PD characteristics even under long-term thermal stress and hence they can be used for power transformer applications.

Analysis of partial discharge characteristics of natural esters as dielectric fluid for electric power apparatus applications

Petroleum based mineral oils are generally used for electric power apparatus insulation and cooling applications. Since the conventionally used mineral oils are not biodegradable and difficult to decompose, there is a need for the development of alternate vegetable based insulation oils for such applications. Formation of partial discharges plays a major role in determining the life time of liquid insulation. Reports on partial discharge characteristics of thermal aged natural ester fluids for high voltage applications are scanty. The major aim of this research work is to understand the partial discharge characteristics of natural esters as a dielectric fluid for power transformer and other electric power apparatus insulation applications. Laboratory experiments are performed as per IEC (International Electro technical Commission) test procedures in order to understand the breakdown voltage and partial discharge characteristics of vegetable oils such as corn oil and palm oil under both virgin and thermal aged conditions. This paper presents a comparative assessment of the PD characteristics of thermal aged natural ester fluids with respect to mineral oil. Time and frequency domain analysis of PD pulse at both needle-plane and rod-plane electrode configurations are studied. Statistical analysis of PD pattern is also carried out. This analysis collects the typical PD patterns from natural ester fluids in order to find its suitability for power transformer and electric power apparatus applications.

High Density Ferrite Materials for Power Transformer Applications

High Density Ferrite Materials for Power Transformer Applications

Practical recommendations for population PK studies with sampling time errors

Population pharmacokinetic (PK) data collected from routine clinical practice offers a rich source of valuable information. However, in observational population PK data, accurate time information for blood samples is often missing, resulting in measurement errors (ME) in the sampling time variable. The goal of this study was to investigate the effects on model parameters when a scheduled time is used instead of the actual blood sampling time, and to propose ME correction methods. Simulation studies were conducted based on two major factors: the curvature in PK profiles and the size of ME. As ME correction methods, transform both sides (TBS) models were developed with application of Box-Cox power transformation and Taylor expansion. The TBS models were compared to a conventional population PK model using simulations. The most important determinant of bias due to time ME was the degree of curvature (nonlinearity) in PK profiles; the smaller the curvature around sampling times, the smaller the associated bias. The second important determinant was the magnitude of ME; the larger the ME, the larger the bias. The proposed TBS models performed better than a conventional population PK modeling when curvature and ME were substantial. Time ME in sampling time can lead to bias on the parameter estimators. The following practical recommendations are provided: 1) when the curvature of PK profiles is small, conventional population PK modeling is robust to even large ME; and 2) when the curvature is moderate or large, the proposed methodology reduces bias in parameter estimates.

Enhancing the critical characteristics of natural esters with antioxidants for power transformer applications

The energy demand of the whole world is dominated by petroleum products for centuries in the field of critical application like electricity. The application of mineral oil in power system equipment like transformer is potentially hazardous to environment. The exploitation of petroleum oil is running out of demand and in the near future, oil scarcity exists. This work focuses in identifying alternate dielectric for replacing traditional mineral oil. India is a tropical country, which produces vegetable oils like sunflower oil, palm oil, coconut oil, mustard oil, corn oil, soybean oil and rice bran oil profusely and it can be used as dielectric fluids in transformer. To be more proficient in the operation of transformer, these vegetable oils should be converted in to superior dielectric fluids. This work also embraces the individual and combinatorial effect of selected natural and synthetic antioxidants in natural ester. For investigation sunflower oil, rice bran oil, soybean oil and corn oil are chosen. The critical parameters like breakdown voltage, viscosity, flash point and fire point are calculated according to IEC and ASTM standards before and after addition of antioxidants with vegetable oils. Astoundingly it is found that the use of natural and synthetic antioxidants can enhance the critical parameters of natural ester for transformer application and the antioxidant activity in the natural ester is discussed. The interpolation functions are calculated based on the results obtained in minimum and maximum concentration of antioxidant added. These functions are used to predict the intermediate output variations caused for each antioxidant concentrations (in gram).

Prediction and evaluation of the cooling performance of radiators used in oil-filled power transformer applications with non-direct and direct-oil-forced flow

Lifetime and reliability of a power transformer are highly dependent on cooling modes as excessive heat generation is the major cause of deteriorating insulation performance. For these reasons, optimal cooling design is necessary to avoid operating faults and materials degradation due to thermal damage. This paper presents prediction and experimental study on the cooling performance of radiators used in oil-filled power transformer applications with non-direct flow (ONAN) and direct-oil-forced flow (ODAN). Radiator temperature distribution and cooling performance was predicted using theoretical calculations, then validated using CFD simulation results. In the experiment, cooling capacity was evaluated with the ONAN and the ODAN flow. For ODAN flow, the maximum cooling capacity was enhanced 20.1% more than ONAN flow. These results confirm that the prediction and the evaluation of radiator cooling performance can be applied to design optimization of cooling mode for oil-filled power transformer applications.

Improving the Dynamic Performance of Distribution Electronic Power Transformers Using Sliding Mode Control

These days, the application of electronic power transformers (EPTs) is expanding in place of ordinary power transformers. These transformers can transmit power via three or four wire converters. Their dynamic performance is extremely important, due to their complex structure. In this paper, a new method is proposed for improving the dynamic performance of distribution electronic power transformers (DEPT) by using sliding mode control (SMC). Hence, to express the dynamic characteristics of a system, different factors such as the voltage unbalance, voltage sag, voltage harmonics and voltage flicker in the system primary side are considered. The four controlling aims of the improvement in dynamic performance include: 1) maintaining the input currents so that they are in sinusoidal form and in phase with the input voltages so they have a unity power factor, 2) keeping the dc-link voltage within the reference amount, 3) keeping the output voltages at a fixed amount and 4) keeping the output voltages in sinusoidal and symmetrical forms. Simulation results indicate the potential and capability of the proposed method in improving DEPT behavior.

Underlying Assumptions of the Power-Normal Distribution

In the power transformation (Box & Cox, 1964), parameters are usually estimated under the assumption that the transformed distribution is a normal distribution even though the transformed distribution is a truncated normal distribution. In the present paper, we evaluate the asymptotic influence of the truncation on estimation of the parameters of the power-normal distribution (Goto, Uesaka, & Inoue, 1979), which specifies original observations before the application of power transformation. Then we demonstrate that when the degree of the truncation of the transformed distribution is large, the parameter estimates based on the ordinary estimation method which ignore the truncation might have large bias through the simulation study and the case study.

Magnetoelectric coupling, efficiency, and voltage gain effect in piezoelectric-piezomagnetic laminate composites

The magnetoelectric (ME) effect of piezoelectric-magnetostrictive laminate composites, which is a product tensor, has been studied. Based on piezoelectric and piezomagnetic constituent equations, the longitudinal-mode vibration and equivalent circuits have been derived. The effective magnetoelectric coupling coefficient, voltage-gain, and output efficiency have been determined. Our results show: (i) that there is an extreme high voltage gain effect of >260 under resonance drive: the induced ME voltage is much higher than the input voltage to the coils for magnetic excitation; (ii) that there is an optimum ratio of the piezoelectric to piezomagnetic layer thicknesses, which results in maximum effective magnetoelectric coupling; and (iii) that the maximum output efficiency of magnetoelectric laminate at resonance drive is ∼98%, if eddy currents are neglected. This high ME voltage gain effect offers potential for power transformer applications.

Development of the industrial scale Ag/Bi-2223 tape

Tape shaped silver-sheathed Bi-2223 superconducting wire (Bi-2223 tape) technologies are reported. The operations of superconducting apparatus at liquid nitrogen temperature or at 20–30 K are expectable by using Bi-2223-tapes. The reduction of AC loss at 77 K is critical for power cable application, such as electric transmission cable and transformer prototypes. Thinning of the tape thickness and twisting of the tapes are the main techniques for the reduction of AC loss. For the power transformer application, coating technology is investigated to have good electrical insulation. The refrigerator-cooled magnet for industrial use is another example of the superconducting apparatus operating at 20–30 K. It is important to know the critical current density dependence on the applied magnetic field ( J c– B dependence) for the magnet design. It was confirmed that J c of the Bi-2223 tape, which shows J c=30 kA/cm 2 at 77 K in self-magnetic field, exceeds 100 kA/cm 2 at 20 K, and 1 T.

Improved high-temperature cobalt-iron alloy for square-loop and power transformer applications

Improved high-temperature cobalt-iron alloy for square-loop and power transformer applications

Transport Influence on the Design and Application of Power Transformers

Transport Influence on the Design and Application of Power Transformers

Technical assessment of 6[fraction one-half]% (wt.) silicon iron for possible application in power transformers

A comparison of the properties of 6½%(wt.) and 3%(wt.) silicon iron has been made, based on measurements of the magnetostriction constants, the anisotropy constants, the static hysteresis loss and the power loss at 50c/s, of single-crystal specimens. The loss measurements were made on small stacks consisting of six 0.013 in-thick picture frames cut with their limbs along [100] directions.The results show that:(a) the power loss of single-crystal 3% silicon iron is about 0.3W/kg lower than that of commercial material at 15kGs(b) the power loss of single-crystal 6½% silicon iron is 0.2W/kg lower than that of single-crystal 3% silicon iron at 15kGs(c) the magnetostriction constant is reduced to about one-tenth of the value of 3% silicon iron (with obvious advantages from the point of view of noise reduction)(d) the first anisotropy constant is about two-thirds of that of 3% silicon iron, so it will still be necessary to produce the silicon iron in oriented form.Although it is expected that a reduction in power loss of about 20% can be achieved by increasing the silicon content from 3% to 6½%, this is accompanied by a reduction in the magnetic saturation induction. After taking all factors into account it is unlikely that an extra cost of more than £30 per ton can be paid for commercial grain-oriented 6½% silicon iron.

Magnet wire for 600 C temperature transformers

As a part of work performed on a government contract, magnet-wire materials were investigated for application in electronic power transformers and inductors. One of the most critical environments specified for the application was 1,000-hour life in the ambient temperature range - 65 C (degrees centigrade) to 500 C. This paper summarizes the planning and results of an ultrahigh-temperature heat-aging program designed to screen selectively the most promising magnet wires to meet this requirement.

A study of the economics of power transformer application

In order to pick the proper power transformer for a certain application many factors must be taken into account. Each transformer location on each system must be considered separately in the light of these factors.

Selection and application of power transformers

THE CHOICE of a power transformer is governed largely by the characteristics of the system, the precedents set by previous purchases, and the established standards of the industry. Any discussion of the selection of transformers must deal to a considerable extent with standards. Several important features of power transformers, with particular attention paid to the relation between the needs of the operating system and the standardization activities now in progress, will be discussed here.

Economic aspects of large power transformers

FIXED RATES and rising costs of construction and operation have posed a financial problem for many electrical utilities. Because transformers represent 25 to 40 per cent of a utility's expenditure for electric equipment and nearly one-half of this capacity is in large units used for transmission of bulk power, proper selection and application of large power transformers offers one avenue for a substantial reduction in the total system investment.

Selection and Application of Power Transformers

THE CHOICE of a power transformer is governed largely by the characteristics of the system, the precedents set by previous purchases, and the established standards of the industry. Any discussion of the selection of transformers must deal to a considerable extent with standards. Several important features of power transformers, with particular attention paid to the relation between the needs of the operating system and the standardization activities now in progress, will be discussed here.