Design improvements in modern distribution transformers

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) is less by about 70% compared with traditional transformers (e.g. silicon steel-based transformer). However, amorphous transformers have disadvantages of high cost and high load loss parameter compared with traditional transformers. Furthermore, there are varieties of transformer capacities, and the customers who would buy new transformer have many choices.In this paper, the authors propose an algorithm for optimum transformer selection based on the load curve patterns of customers. It is possible to select the capacity that minimizes the total cost by measuring equivalent load Qe that is the root mean square of load. It becomes clear that amorphous transformer is effective in achieving substantial energy saving compared with traditional transformer.

Rising global electricity demand and the expansion of distribution networks require a critical assessment of component-level greenhouse gas contributions. Distribution transformers, although indispensable, have significant life-cycle carbon impacts due to the use of materials, manufacturing, and in-service losses. This study conducts a life-cycle assessment of a single-phase, 75 kVA oil-immersed distribution transformer manufactured in Newfoundland, one of the provinces with the cleanest, hydro-dominated grids in Canada, and evaluates it over a 40-year lifespan. Using a cradle-to-use boundary, the analysis quantifies embodied emissions from raw material extraction, manufacturing, and transportation, alongside operational emissions derived from empirically measured no-load and load losses. All the data are collected directly during the manufacturing process, ensuring high analytical fidelity. The energy efficiency of the transformer is analyzed in MATLAB version R2023b using measured no-load and load losses to generate efficiency, load characteristics under various operating conditions. Under varying load factor scenarios and based on Newfoundland’s 2025 grid intensity of 18 g CO2e/kWh, the lifetime operational emissions are estimated to range from 0.19 t CO2e under no-load operation to 4.4 t CO2e under full-load conditions. A linear regression-based decarbonization model using Microsoft Excel projects grid intensity to reach net-zero around 2037, two years beyond the provincial target, indicating that post-2037 transformer losses will remain energetically relevant but carbon-neutral. Sensitivity analysis reveals that temporary overloading can substantially elevate lifetime emissions, emphasizing the value of smart-grid-enabled load management and optimal transformer sizing. Comparative assessment with fossil fuel-intensive provinces across Canada demonstrates the dominant influence of grid generation mix on life-cycle emissions. Additionally, refurbishment scenarios indicate up to 50% reduction in cradle-to-gate emissions through material reuse and oil reclamation. The findings establish a scalable framework for integrating grid decarbonization trajectories, life-cycle carbon modelling, and circular-economy strategies into sustainable distribution network planning and transformer asset management.

This paper describes Amorphous Metal core Distribution Transformers (AMDT) and its potential to obtain economic and environmental benefits when pre-existing transformers are to be replaced. Vattenfall's ambition is to decrease losses within the Vattenfall Group's distribution network, thus contributing to the environment and economy, and hence confirm that this is an important issue for Vattenfall. Distribution transformers within the Vattenfall Group's distribution network in Sweden, Germany and Poland are investigated and presented in three different business cases that consider the current sizes, quantities, ages and load utilization. The inventory of the distribution transformers used at Vattenfall, indicates that conventional transformers of fairly high loss types have been selected over low loss types. Choosing low loss amorphous transformers when pre-existing transformers are to be replaced, means that the CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> emission will be significantly reduced. AMDT have the potential to reduce transformer no-load losses by up to 70% compared to conventional technology. This paper discusses the general aspects of AMDT transformer losses as well as the importance of using the Total Ownership Cost (TOC) method to determine the economic benefits whenever a unit is to be purchased.

Electric energy replacement is the umbrella term for the use of electric energy to replace oil (e.g., electric automobiles), coal (e.g., electric heating), and gas (e.g., electric cooking appliances), which increases the electrical load peak, causing greater valley/peak differences. On-load capacity regulating distribution transformers have been used to deal with loads with great valley/peak differences, so reasonably replacing conventional distribution transformers with on-load capacity regulating distribution transformers can effectively cope with load changes after electric energy replacement and reduce the no-load losses of distribution transformers. Before planning for on-load capacity regulating distribution transformers, the nodal effective load considering uncertainties within the life cycle after electric energy replacement was obtained by a Monte Carlo method. Then, according to the loss relation between on-load capacity regulating distribution transformers and conventional distribution transformers, three characteristic indexes of annual continuous apparent power curve and replacement criteria for on-load capacity regulating distribution transformers were put forward in this paper, and a set of distribution transformer replaceable points was obtained. Next, based on cost benefit analysis, a planning model of on-load capacity regulating distribution transformers which consists of investment profitability index within the life cycle, investment cost recouping index and capacity regulating cost index was put forward. The branch and bound method was used to solve the planning model within replaceable point set to obtain upgrading and reconstruction scheme of distribution transformers under a certain investment. Finally, planning analysis of on-load capacity regulating distribution transformers was carried out for electric energy replacement points in one urban distribution network under three scenes: certain load, uncertain load and nodal effective load considering uncertainties. Results showed that the planning method of on-load capacity regulating distribution transformers proposed in this paper was very feasible and is of great guiding significance to distribution transformer planning after electric energy replacement and the popularization of on-load capacity regulating distribution transformers.

High penetration level of rooftop small-scale renewable energy generation (REG) such as solar and wind power into the existing low voltage (LV) network would cause the flow of power in reverse direction. This would also vary the level of short-circuit current required for relays to operate. Relay settings would be required to properly detect the unpredictable fault current and isolate the faulty section. This paper investigates the impact of residential distributed generation (DG) penetration level on the typical UK low voltage network protection system. Studies were commenced to properly charge and discharge the home connected energy storage battery (ESB). ESB is used as a remedial measure to confine the flow of reverse power due to rooftop DGs. Penetration level DGs are modeled based on proper ESB charging and discharging states in daily load cycle. Short circuit analysis is simulated on Matlab/Simulink. The power flow from the transformer secondary is managed to avoid malfunctioning of relays according to daily load cycle. Short circuit analysis results are compared with the UK passive network to investigate the impact of the DG on the short circuit currents at distribution transformer.

A transformer based on only power electronics components is generally known as a Solid-State Transformer (SST). Presently, voltage control in the low voltage networks has become important because of the varying loads due to the growing penetration of distributed generations (such as photovoltaic systems and wind energy), and the integration of increasing amount of electric vehicles (EV) charging loads. A SST is designed to control the voltage of the network more efficiently in comparison to a conventional distribution transformer that is equipped with an on-load tap changer. It can also provide a DC voltage connection point which enables easy integration of a storage system or can provide fast charging points for the neighbourhood. Furthermore, SST can mitigate harmonic pollutions in the network and can improve the voltage quality of the network. In case of a conventional transformer, these extra functionalities can be obtained too, but this would require additional investments, like an inverter for storage/fast charging or a passive/active filter for harmonics mitigation. In this paper, the economic aspects of a SST is discussed and a cost-benefit analysis is presented in comparison to a conventional transformer, considering different future network scenarios.

To offer more personal safety and a better environmental behavior of electrical power supply, the usage of alternative insulation fluids is demanded in large power transformers. The minimizing of fire loads is another significant reason for these new liquids. A number of companies are offering such alternative insulation fluids which are already used in distribution transformers but there is still little experience with those liquids in large power transformers. One reason for this is missing maintenance information like limit values of the different DGA detectable gasses. For mineral oil there are many different interpretation methods for DGA (Dissolved Gas Analysis) results and also many known patterns for specific reasons of the increase of one or more gas values. This investigation shows which gas values change significantly caused by breakdown in an oil/cellulose insulation system resp. an ester/cellulose system. A test setup was created and experiments were done with mineral oil, a natural ester and a synthetic ester. A DGA analysis was carried out before and after several breakdowns in the liquids. With the results the gasses which indicate an oil/cellulose breakdown could be identified.

Insulation systems for electrical power and distribution transformers are being re-evaluated based on total owning cost from both economic and risk exposure perspectives. A developed high fire point dielectric fluid, based on natural esters, has superior safety, environmental, and health properties compared to current dielectric fluids. An insulation system developed for this fluid addresses the lower inherent resistance of esters to oxidation. Accelerated transformer life testing compares transformers using standard mineral oil to those with the natural esters dielectric system. Results of these accelerated life tests show the ester fluid to be suitable for transformer use and suggest the possibility of extended insulation life compared to mineral oil systems.

The future substation depends on finding a way to mitigate the effects of the drawbacks of the conventional legacy by employing the efficiency of the solid state switches [1]. This paper discusses the considerations of designing a distribution transformer that provides additional functions in regulating the voltage and controlling the reactive power that is injected in the distribution network, using a fractional rated converter attached partially with the windings of the transformer. This approach aims mainly to enhance the unit with more flexibility in controlling the voltage at the last mile of the network, in order to decrease the losses and meet the future expectations for low voltage networks modifications, and that by using a power electronic (PE) approach has less losses and more functionality (depending on the reliability of transformer and intelligence of PE). The design of a hybrid distribution transformer is detailed and its functionality in regulating the voltage is discussed as a combination between the features of one of the most reliable network devices, the transformer, and the effect of PE existence with less losses in both switching and conduction losses. Reduced ratings PE are used in this approach, whereby the solid state switches are controlled according to the immediate need for voltage control in low voltage (LV) networks.

Ester liquids show better flame resistance and higher biodegradation than mineral oil and are now being considered as liquid insulating material in 500 kV power transformers in the Southern Power Grid of China. Streaming electrification characteristics among different types of alternative liquids must be investigated to eliminate insulation failure of large power transformers. In this paper, a mini-static tester acknowledged by CIGRE WG A2 and D1 was established to investigate the streaming electrification of three different ester liquids that are widely used around the world: synthetic ester (MIDEL 7131), natural ester (FR3), and modified ester (Palm Fatty Acid Ester, PFAE). Mineral oil was also tested to compare the streaming electrification properties with ester liquids. Liquids were tested under different liquid temperatures from 20°C to 90°C and a liquid flow velocity range of 0.4-2.0 mL/s. Results showed that synthetic ester presented the highest streaming current, which is then followed by natural ester. The modified ester showed the lowest streaming current under every condition. However, the streaming current of all ester liquids was a thousand times higher than that of mineral oil. All liquids presented the same property in that the liquid flow velocity had a positive correlation with streaming current, but modified ester differed from other liquids in thermal properties. The streaming current of modified ester only decreased when the liquid temperature increased, but the streaming current of other liquids increased first and then decreased. The electrostatic charging tendency (ECT) measurement also presents the same order of magnitude difference as the streaming current.

Streaming electrification has been identified as one of the main failure reasons for large power transformers. Different measurement methods including pipe flow method, rotating disk method and mini-static tester have been proposed to investigate this phenomenon. In this paper, a small scale laboratory based pipe flow model is established. The streaming electrification characteristics of a conventional mineral oil and a synthetic ester liquid were compared. Parameters including flow velocity, pressboard condition and oil aging were studied. The results indicate that the ester liquid exhibits a much higher streaming current than the mineral oil at the investigated flow velocities. Aging of the oil facilitates the charging process in the mineral oil but decreases the streaming current in the ester liquid.

This paper addresses the impact of the increasing penetration of renewable solar photovoltaic (PV) in the power distribution grids. A collaborative project between the university and the local power distribution grid-s operator (PDO) led to this assessment, which addressed the operator-s specific concerns about how renewable energy-based generators might affect the power quality (PQ) in its grid system. There was evaluated the interaction between PV prosumers' installations and the hosting low voltage (LV) network, specifically the variations in voltage produced or amplified by prosumers, as well as the events experienced by these ones. For the purpose of the analysis, one-weekinterval PQ measurement have been processed at the outputs of real PV prosumers located in the LV network, as well as at the LV buses of the supplying substations. The behavior of different solar inverter technologies in the power grid is also examined. The bi-directional prosumer-grid influence is analyzed and the origin of PQ events are estimated. Measurements-based observations revealed a shared responsibility between PV generation conditions, solar inverter operation, and the hosting power grid. Lastly, general conclusions about measurement, analysis, and mitigation are provided.

This study aimed to compare the electrical characteristics of mineral oil-based nanoparticles to those of pure mineral oil. Mineral oil used in distribution transformers was mixed with aluminum oxide (Al2O3) nanoparticles, which serve as an insulator, with 0.01, 0.03, and 0.05 % mineral oil volume concentrations. The moisture content in mineral oil was measured beforehand, and the electrical tests were subsequently conducted in accordance with international standards. The moisture content test revealed that the combination of nanoparticles and mineral oil resulted in an increase in moisture content. As regards the test of AC withstanding voltage and negative polarity lightning impulse voltage, it was found that the mineral oil mixed with the nanoparticles had higher dielectric strength than the original mineral oil. In addition, the test results of positive polarity lightning impulse voltage demonstrated that with a mixture of mineral oil and the nanoparticles at a 0.01 % concentration, the positive polarity lightning impulse dielectric strength of the mineral oil increased. However, at concentrations of 0.03 and 0.05 %, it did not rise, regardless of the increasing volume of nanoparticles. The results, thus, showed promising directions for applications of nanoparticles in the development of electrical properties of mineral oil. HIGHLIGHTS The addition of Al2O3 nanoparticles to the mineral oil resulted in an increase in the oil moisture content. However, it was found that the moisture content in the mineral oil tended to decrease with the increase in the amount of nanoparticles The optimum nanofluid combination in terms of increased AC breakdown strength was created by adding Al2O3 nanoparticles to mineral oil at a rate of 0.05 vol% The Al2O3 nanoparticles being added to the mineral oil can give an increase in the impulse breakdown voltage with the negative polarity For the positive polarity of the impulse breakdown voltage, the best nanofluid mixture in terms of increased breakdown strength was produced by the addition of Al2O3 nanoparticles at a rate of 0.01 vol% to the mineral oil GRAPHICAL ABSTRACT

This article reports and discusses the results of impulse breakdown study of different insulating liquids under highly divergent electric field conditions. Samples of a natural ester (Envirotemp FR3), a synthetic ester (MIDEL 7131), and a naphthenic mineral oil (Shell Diala S4 ZX) at different levels of relative humidity were exposed to HV impulses with a nominal 7-μs rise time and 150-kV peak voltage of both positive and negative polarity. A strong dependence of the breakdown voltage and time to breakdown of the investigated dielectric liquids was observed with respect to the polarity of the applied HV impulses. It was shown that the FR3 natural ester liquid has a higher dielectric strength when exposed to positive impulse than when under negative impulse stress. The opposite breakdown behavior was observed for the synthetic ester MIDEL 7131 and the naphthenic oil Shell Diala S4 ZX which exhibited lower breakdown voltage under positive energization as compared with the negative energization. The breakdown voltage and prebreakdown time obtained in the present tests of the naphthenic oil, Shell Diala S4 ZX, lie between that of the ester liquids irrespective of impulse polarity. It has been established that no statistically significant variations exist in the breakdown parameters (breakdown voltage and time to breakdown) of the studied dielectric liquids as their relative humidity is increased under either impulse polarity. The obtained results will help in coordination of practical applications of low environmental impact dielectric fluids in power and pulsed power systems and components.

In the construction of Ultra High Voltage (UHV) AC project in china, the UHV AC transformer is very difficult to transport. Disintegrating transportation and on-Site assembly is an effective way to reduce transportation weight, solve transportation problems and reduce transportation costs. In China's Yuheng-Weifang UHV transmission project, the UHV auto-transformer with disintegrating transportation and on-site assembly is used in Jinzhong substation by Sate Grid Corp. of China for the first time. It is also the first engineering application of 1000kV class on-site assembly transformer at home and abroad. Compared with the conventional UHV Transformer, the design and manufacture of the On-site Assembly UHV Transformer is more difficult. The requirements of site assembly workshop and drying method and process were also studied emphatically. Through the research, it is concluded that the 1000MVA/1000kV main transformer has a better economic performance with the dual core limbs structure and the whole disassembly scheme, and the spare room as an assembling workshop is an economical design scheme. In engineering practice, the on-site assembled UHV Transformer adopts a movable gas phase drying device, which effectively improves the drying quality. In the acceptance test, no-load loss and no-load current measurement, load loss and short-circuit impedance measurement tests are added to test the influence of field assembly on the circuit and magnetic circuit. No-load loss measurement at 100% rated voltage and load loss at 50% rated current are achieved on site. At present, 4 on-Site assembly UHV transformers have been applied and work well in Jinzhong substation. The application of 1000kV on-site assembly transformers is helpful to enlarge the geographical range of UHV and EHV large transformer applications and reduce investment in equipment. The key technologies and successful application experience are introduced in this paper.