Three-phase Distribution Transformer Research Articles

Structure optimization design and magneto-mechanical characteristics analysis of amorphous alloy with oriented silicon steel composite wound core

Three-dimensional wound cores are widely used in three-phase distribution transformer due to the symmetrical magnetic circuit structure. Amorphous alloy and oriented silicon steel are two kinds of ferromagnetic materials commonly used to make distribution transformer cores, each has own advantages and disadvantages in magnetic and mechanical characteristics. The amorphous alloy and oriented silicon steel composite core can synthesize the advantages of both. In this paper, a double-layer composite wound core (DCWC) structure is proposed and the corresponding dual nonlinear electric circuit and magnetic circuit coupling model is established. A structure optimization design method for the DCWC based on the free parameter scanning method is proposed by taking the percentage of oriented silicon steel in the composite core and the structure parameters as free variables. Based on the proposed optimization design method, a DCWC is designed and the experimental prototypes are manufactured. Further, the flux density distribution, core loss and mechanical vibration displacement of the DCWC are analyzed, and the effectiveness of the proposed method is verified by comparing with the measured results.

Design of a Three-Phase Shell-Type Distribution Transformer Using Evolutionary Algorithms

In this paper, three metaheuristic optimization algorithms: genetic algorithm (GA), particle swarm optimization (PSO), and differential evolution (DE) are compared in terms of minimizing the total owning cost (TOC) of the active part of a three-phase shell-type distribution transformer. The three methods use six inputs: power rating, primary voltage, secondary voltage, primary and secondary winding connections, and frequency. The TOC of the transformer, which includes the cost of the basic materials of the transformer plus the cost of losses, is minimized under the imposed constraints (excitation current, impedance, no-load losses, load losses, and efficiency) usually specified in the standards. As a case study, the three algorithms are applied to optimize the design of a three-phase shell-type distribution transformer of 750 kVA. All applied metaheuristic algorithms provide good results, while DE avoids local optima leading to better TOC reduction. The results of the optimization algorithms used are superior to those of the manufacturer, showing a 6% TOC reduction. Optimization of the design of a power transformer may have important implications for reducing greenhouse gas emissions and extending the lifetime of the equipment.

Study of Transformer Harmonic Loss Characteristic in Distribution Network Based on Field-Circuit Coupling Method

One of the primary causes of additional losses in dry-type distribution transformers is harmonic disturbances in the distribution network. It is critical to investigate the change law of trans-former losses under harmonic conditions. The effect of harmonics on transformer core losses and winding losses is first investigated in this paper. The field-circuit coupling method is then used to create a finite element model of a three-phase phase dry type distribution transformer. Finally, the relationship between core loss and harmonic voltage, winding loss and harmonic current is calculated and analyzed for each harmonic frequency. The AC resistance factor model is found to be more accurate than the conventional model in calculating transformer harmonic winding losses. This paper’s findings have significant theoretical implications for the analysis of harmonic losses and loss reduction in distribution networks.

Frequency Response Analysis: An Enabling Technology to Detect Internal Faults within Critical Electric Assets

Frequency Response Analysis (FRA) technique has been recognized by worldwide utilities as a matured technology to assess the mechanical integrity of power transformers. While some industrial critical assets such as induction motors have the same construction principle as power transformers, the application of FRA technique to induction motors has not yet been fully explored. This paper presents analogical experimental studies for the application of FRA on power transformers and induction motors. For a consistent analogy, the FRA technique has been employed to detect short and open circuit turns in both appliances, which helps explore a wider scope of the FRA applications on rotating machines. In this regard, experimental FRA measurements are performed on an 11/0.415 kV, 500 kVA, three-phase distribution transformer and a 5.5 HP three-phase induction motor. Several short and open circuit faults are staged on the windings of both tested equipment and the FRA signature is recorded and compared with the reference signature at no fault. To quantify the impact of faults on the FRA signature, several statistical indicators are used and threshold limits for these indicators are proposed to automate the interpretation process. Results reveal a good correlation between the FRA signatures of induction motors and power transformers that attests to the feasibility of using FRA technique to detect various faults within large rotating machines.

Impact of Solar Intensity on Photovoltaic-Generated Current Harmonics and Transformer Life: A Mathematical Model With Experimental Validation

Abstract With the rising penetration of photovoltaic (PV) plants on low voltage distribution systems, the generation of current harmonics as well as its impact on transformer operation is a current concern. The present research work develops a mathematical relationship of solar intensity (I(t)) with PV-inverter-generated total harmonic distortion of current (THDi,inv.), and then uses IEEE recommendations to present the impact of THDi,inv. on the life of a three-phase distribution transformer (TPDT). The validation of the presented model is done by real-time data monitoring from a 100-kWp solar roof-top photovoltaic (SRTPV) system, integrated with an 11-kV grid supply through a 63-kVA TPDT in the composite environment of north India. According to the results, decreasing I(t) values from 857 W/m2 to 35 W/m2 raise THDi,inv. from 3.57% to 63.43%. It is also observed that the production of poor THDi,inv. is high in the winter season (daily average = 27.44%) in comparison to their values in the summer season (daily average = 15.21%). For I(t) values less than 315 W/m2, the generation of large THDi,inv. (above 15%) takes place and it increases the loss of life of TPDT by a factor of 6.0.

Optimal Design and Performance Analysis of Three-phase Distribution Transformer with Variable Loading

Electrical power passes through several transformers after generation through consumption. The final stage of any power system consists of many small-rating distribution transformers. Since the loads connected to these transformers vary with time, their effective design and operation with variable loading conditions are crucial for the system to operate efficiently and reliably. In most previous works, loads connected to these transformers are treated as constant power and stray losses of the transformers are neglected in the calculations. Neglecting the load variation and stray losses reduces the transformer life span noticeably and impairs grid quality and reliability. In this work, a small-rating distribution transformer is designed and analyzed analytically and numerically. Detailed procedures on the conventional design are presented with the general design issues. The effect of variable loading on the transformer’s power losses, efficiency, temperature rise, voltage regulation, and output voltage variation is analytically and numerically investigated. Results show that the rating and power factor of the load significantly influence the performance characteristics of the transformer.

FINITE-ELEMENT CALCULATION OF ELECTROMAGNETIC FORCES IN THE DEFERENT SHAPES OF DISTRIBUTION TRANSFORMERS WINDING UNDER SHORT CIRCUIT CONDITION

This paper is concerned with calculating the electromagnetic forces in the windings of distribution transformers with different shapes of coils. The electromagnetic forces as well as the magnetic flux density and their distribution were analyzed and calculated using Finite Element Method (FEM). The Finite Element models of the distribution transformers with non-linear magnetic characteristics for the iron core are built using FEM software "ANSYS". In this paper, the static analysis method is based on two-dimensional models, and these models have been solved by using the formula for the magnetic vector voltage (A). Three types of three-phase distribution transformers were adopted, each with a capacity of 250 kVA and a voltage ratio is 11/0.416 kV. These types of transformers with different shapes of coils are stack core transformer with oval coil, wound core transformer with rectangular coil, and stack core transformer with cylindrical coil. The results obtained from the FEM analysis agreed with the design calculations which depend on the conventional design formulas. The most important contributions of this study are to building two-dimensional models for different types of distribution transformers. Calculating electromagnetic forces in transformers winding during short circuit conditions in different coil shapes. Studding the effect of the shape of the coils on the calculation of the electromagnetic forces in them. This work can save time, effort, and cost for transformer manufacturers in calculating the electromagnetic forces, also using this model for the virtual test leads to avoid the risk, and efforts spent to do the real short-circuit test.

Detection and Analysis of Partial Discharges in Oil-Immersed Power Transformers Using Low-Cost Acoustic Sensors

Partial Discharge (PD) is one of the symptoms of an electrical insulation problem, and its permanence can lead to the complete deterioration of the electrical insulation in high-voltage equipment such as power transformers. The acoustic emission (AE) method is a well-known technique used to detect and localize PD activity inside oil-filled transformers. However, the commercially available monitoring systems based on acoustic sensors still have a high cost. This paper analyses the ability of low-cost piezoelectric sensors to identify PDs within oil-filled power transformers. To this end, two types of low-cost piezoelectric sensors were fully investigated using time-domain, frequency-domain, and time-frequency analysis, separately. Thereafter, the effectiveness of these sensors for PD detection and monitoring was studied. A three-phase distribution transformer filled with oil was examined. PDs were produced inside an oil-immersed transformer by applying a high voltage over two copper electrodes, and the AE sensors were coupled to the housing of the transformer. By extracting typical features from the AE signals, the PD signals were differentiated from on-site noise and interference. The AE signals were analyzed using acoustic signal metrics such as peak value, energy criterion, and other statistical parameters. The obtained results indicated that the used low-cost piezoelectric sensors have the capability of PD monitoring within power transformers.

Voltage Profile Enhancement and Power Loss Reduction with Economic Feasibility Using Small Capacity Distribution Transformers

Usually, rural areas can be electrified via three-phase distribution transformers with relatively large capacities. In such areas, low voltage lines are used for long distances, which cause power losses and voltage drop for different types of consumers. Reducing losses and improving voltage profiles in rural distribution networks are significant challenges for electricity distribution companies. However different solutions were proposed in the literature to overcome these challenges, most of them face difficulties when applied in the conventional distribution network. To address the above issues, an applicable solution is proposed in this paper by installing a number of small-capacity distribution transformers instead of every single large-capacity transformer in rural areas. The proposed approach is implemented in the branch network of Al-Hoqool village, which belongs to the Nineveh distribution network. The network has been inspected on-site, drawn, and analyzed using the electrical systems analysis program (ETAP). The analysis showed that using the single-phase pole-mounted transformers can improve the voltage in the network’s end by 29% and enhance the voltage profile for all consumers. The analysis has also demonstrated that the modification can reduce the total power losses by 78% compared to the existing network. Concerning the economic aspect, the payback period for the proposed network is assigned to be 20 months.

Mathematical modelling and experimental validation for impact of high solar cell temperature on transformer loading and life

The penetration of grid connected solar rooftop PV (SRTPV) system in the low voltage distribution network is continuously increasing. The need to model the effect of these systems especially solar cell temperature (SCT) effect on the distribution transformer is an issue in the current scenario. In this research work, a mathematical model has been developed for SCT dependent transformer loading and the impact of these parameters on the life of distribution transformer is presented by using the IEEE guidelines. The presented model has been experimentally validated by real-time measurement of parameters of a 100kWp grid connected SRTPV system integrated to 63kVA three phase distribution transformer (TPDT) for the composite climate condition of Ghaziabad, India. The result shows that with every 5°C increase in SCT above the reference temperature, the transformer loading is increased by 2.5%. From past one year collected data, it is observed that the loss factor of TPDT life has reached the value of 0.21 at STC and hot spot temperature (HST) values of 68.20 and 158°C respectively.

The influence of harmonic distortion on losses and efficiency of three-phase distribution transformer

The operation of non-linear load leads to distortion on system and equipment. The nonlinear relation between voltage and current implies higher frequency components of current and voltage called harmonic. This may constitute distortion on the fundamental waveform. If this distorted waveform applies to a transformer, it may lead to additional losses and therefore reduces transformer efficiency. The losses occur due to the degree of harmonic distortion, commonly called total harmonic distortion (THD). This paper discusses the operating condition of three-phase transformer serving nonlinear load in the form of power converter. The related impacts of THD on voltage and current, additional power losses and its efficiency are analysed. The calculation is implemented on a 200 kVA three-phase transformer serving a rectifier supplying a balanced inductive load. For analysis purpose the system is simulated using Simulink in MATLAB environment. From the generated results it is identified the THD of voltage and current distortions of 19% and 18%, respectively. These distortion is analysed to confirm the standard of IEEE 519-2014 verifying the distortions exceeding the maximum limit for both voltage and current. The effect of harmonic on transformer loss is also observed. The loss is calculated taking into account all parameters ensuring the calculation is valid. The result indicates the increase of loss due to considering harmonic distortion from 0.62 kW to 1.854 kW causing reduction of efficiency from 99.65% to 98.97%. This loss addition implies a derating of the transformer to avoid transformer overload that may shorten the device’s lifetime.

Three-phase distribution transformer connections modeling based on matrix operation method by phase-coordinates

This paper proposes a matrix operation method for modeling the three-phase transformer by phase-coordinates. Based on decoupling theory, the 12 × 12 dimension primitive admittance matrix is obtained at first employing the coupling configuration of the windings. Under the condition of asymmetric magnetic circuits, according to the boundary conditions for transformer connections, the transformers in different connections enable to be modeling by the matrix operation method from the primitive admittance matrix. Another purpose of this paper is to explain the differences of the phase-coordinates and the positive sequence parameters in the impedances of the transformers. The numerical testing results in IEEE-4 system show that the proposed method is valid and efficient.

Influence of Load Factors on Distribution Transformer Noise

Theoretical relations between load factors and distribution transformer noise are analysed. A 10kV/400kVA three-phase oil-immersed distribution transformer is used for sound pressure level test in various load conditions including various load ratios, unbalanced loads and power factors. The sound pressure levels of distribution transformer in different load conditions are compared and analysed. The results can be referenced for the field noise and vibration control of distribution power transformers.

The Influence of Load on the Vibration and Noise Characteristics of Transformer

In order to further understand and grasp the impact of load on the vibration and noise characteristics of the transformer, this article analyzes the impact of load factors, power factor, harmonic current, three-phase unbalance and other load factors on transformer vibration and noise from the perspective of transformer vibration mechanism. A 10kV/200kVA three-phase oil-immersed distribution transformer was used as the object. Experiments were conducted to study the changes in the spectrum distribution, noise intensity and A-weighted sound pressure level of the transformer vibration and noise under the influence of different load factors. The results show that: when the frequency increases, the amplitude of the 100Hz fundamental frequency in the vibration noise signal increases, and the noise level increases accordingly; when the power factor increases, the amplitude of the odd frequency components in the vibration noise signal gradually decreases with the increase of the power factor. There is no obvious fluctuation in amplitude except 100Hz. When the harmonic current and the three-phase are unbalanced, the spectral components become complicated and accompanied by a large number of odd-order frequency multiplication components. With the increase of harmonic content, the amplitude of vibration noise signal and A-weighted sound pressure level increase significantly; the degree of unbalance and the occurrence of unbalance have a greater impact on the amplitude of vibration noise signal and A-weighted sound pressure level. The research in this paper provides a reference for the noise suppression of power equipment and the fault diagnosis technology based on vibration and noise signals.

Application of Infrared Thermography in Fault Detection and Preventive Maintenance in Three-Phase Distribution Transformers

Application of Infrared Thermography in Fault Detection and Preventive Maintenance in Three-Phase Distribution Transformers

Power Losses Analysis in a Three-Phase Distribution Transformer Using Artificial Neural Networks

This research article presents the analysis of power losses in a three - phase distribution transformer, 100 kVA 22 kV-400/230V by using artificial neutral networks that can analyze the power losses in distribution transformer faster and use less variables than the original method. The measurement data were collected 100,000 sets at the transformer manufacturer factory by setting the current flow from 1% to 100% at temperature 30 °C, 35 °C, 40 °C, 45 °C, 50 °C, 55°C, 60 °C, 65 °C, 70 °C, and 75 °C to calculate the power losses in a distribution transformer. The collected data were divided 80,000 sets to use for training in order to find parameters of artificial neutral networks and 20,000 sets were used for the artificial neutral networks input in order to calculate power losses in a distribution transformer. From the power losses in the distribution transformer of artificial neutral networks testing compared with the calculated valued from the measurement. The percentage error was at the satisfactory level and can be applied to design the testing of power losses in the distribution transformer in the future.

Enhancement of the Thermal Performance Characteristics of an Electrical Power Transformer

A 3D numerical simulation was conducted to test the effects of the geometrical and operational parameters on the cooling performance of a three-phase electrical distribution transformer (250 kVA oil natural air natural (ONAN)). The geometric parameters include the shape of the transformer (rectangular, circular, and hexagonal), fins shape (rectangular, semicircular, and trapezoidal) as well it arrangement (asymmetric fin heights and perforated fins). Both of oil temperature and thermal load have been used as boundary conditions. In order to verify the reliability of the numerical model, comparison between numerical results and experimental finding has been done. The results have indicated that the circular and hexagonal shapes reduced the average oil temperature by 3.4% and 4.7%, respectively, compared to the traditional transformer shape (rectangular). Furthermore, the lowest average oil temperature was observed for the trapezoidal fin, followed by the rectangular and semicircular fins. Additionally, it has been noticed that the asymmetric fin heights of the trapezoidal and perforated trapezoidal fins been contributed to the improvement of the cooling performance of the transformer. Furthermore, the best thermal performance was obtained with the trapezoidal perforated fin to compared other arrangement of fins. Finally, the highest reduction in oil has been obtained by the use of hexagonal transformer with a perforated trapezoidal fin approximately by 12% compared to traditional rectangular transformer. Hence, it can be concluded that the shape of the transformer and fins play an important role in thermal performance of such systems.

Enhancement of the Thermal Performance Characteristics of an Electrical Power Transformer

A 3D numerical simulation was conducted to test the effects of the geometrical and operational parameters on the cooling performance of a three-phase electrical distribution transformer (250 kVA oil natural air natural (ONAN)). The geometric parameters include the shape of the transformer (rectangular, circular, and hexagonal), fins shape (rectangular, semicircular, and trapezoidal) as well it arrangement (asymmetric fin heights and perforated fins). Both of oil temperature and thermal load have been used as boundary conditions. In order to verify the reliability of the numerical model, comparison between numerical results and experimental finding has been done. The results have indicated that the circular and hexagonal shapes reduced the average oil temperature by 3.4% and 4.7%, respectively, compared to the traditional transformer shape (rectangular). Furthermore, the lowest average oil temperature was observed for the trapezoidal fin, followed by the rectangular and semicircular fins. Additionally, it has been noticed that the asymmetric fin heights of the trapezoidal and perforated trapezoidal fins been contributed to the improvement of the cooling performance of the transformer. Furthermore, the best thermal performance was obtained with the trapezoidal perforated fin to compared other arrangement of fins. Finally, the highest reduction in oil has been obtained by the use of hexagonal transformer with a perforated trapezoidal fin approximately by 12% compared to traditional rectangular transformer. Hence, it can be concluded that the shape of the transformer and fins play an important role in thermal performance of such systems.

Study of winding vibration and transmission characteristics of three-phase oil-immersed distribution transformer based on FEA

In this paper, the magnetic-structure-acoustic multi-physical field model of S13-M400/10 distribution transformer is established through the FEA software. The harmonic response analysis method is used to study the winding vibration and transmission characteristics of the transformer. The simulation results show that the flux leakage distribution of windings on each core column is mainly determined by the current flowing through these windings. The radial and axial acceleration distributions of the windings are U shape and M shape respectively along the winding height. The acceleration of B phase windings is smaller than that of A and C phase windings. The vibration of the oil tank surface is concentrated in its middle and lower part. The tank side vibration is mainly affected by the vibration of the nearest phase windings, while the tank front vibration is affected by the vibration of the three-phase windings together. This study is of great significance for further studies of the vibration characteristics of the transformer under unbalanced load and proposing the vibration reduction and noise reduction measures for the distribution transformer.

Heat Generation and Failure in Padmount Transformers Due to Zero Sequence Saturation

After a transformer failed following a double-phase fault, there was an interest in understanding how the fault mechanism led to the failure. This paper investigates this fault condition in detail and demonstrates the underlying challenges in correcting the failure. The electrical and thermal system models were developed and simulated to analyze the transformer response under double-phase fault conditions. Experimental measurements validated the simulation results on a real three-phase distribution transformer. This paper presents the results from simulated and experimental analysis from double-phase fault on a Yg–Yg distribution transformer.