Typical Distribution Transformer Research Articles

Lightning-induced voltages on low-voltage distribution lines

Special attention has been drawn to transients in low-voltage systems in recent years. As the surge withstand capabilities of low-voltage networks are much lower than those of medium-voltage lines, they are more susceptible to lightning-caused disturbances. One of the primary sources of overvoltages is related to indirect lightning strokes. Such overvoltages are highly dependent on the soil characteristics and generally tend to increase with the soil resistivity. Considering realistic conditions, this paper discusses the effects of different parameters on the phase-to-ground and phase-to-neutral lightning-induced voltages on the low-voltage side of a typical distribution transformer. In the case of high-resistivity soils or high ground resistance values, phase-to-ground voltages induced by indirect strokes can reach several tens of kilovolts. Phase-to-neutral voltages higher than 5 kV may be common if surge protective devices are not applied.

Creep failure analysis of crimp joints in aluminium and copper windings of distribution transformers

The present work investigates creep performance and contact resistance of Distribution Transformers (DTs) winding crimp joints under the influence of temperature and stress, aiming to reduce the failure rate of DTs. The integrity of crimp joints is crucial, as the field study revealed that a majority of crimp joints become unstable and show elevated contact resistance due to service exposure. These changes affect the steady-state creep rate of the crimp joint and the surrounding winding conductors, ultimately diminishing the operational lifespan of DTs. For experimentation, crimp joints with varying crimp points were fabricated for a 25 kVA DT using aluminium and copper conductors with diameters of 0.83 mm and 0.6 mm, respectively. For all types of joints i.e., Al-Al, Al-Cu and Cu-Cu, the 2-point crimp joint was identified as optimum in terms of tensile strength and contact resistance. The creep tests for the crimp joints were conducted under varying temperatures of 100 °C and 140 °C with stress levels of 40 MPa and 55 MPa as per ASTM E139-11. The steady-state creep rate and contact resistance of Al-Al crimp joints increased with an increase in temperature and stress. The creep life of DTs due to Al-Al and Al-Cu crimp joints is significantly less than the designed life of a typical DT. On the other hand, creep behaviour of copper winding crimp joints supports a significantly higher DT creep life even at a higher temperature of 140 °C and elevated stress of 55 MPa.

Reliability Evaluation of a Radial Feeder Configurations by Replacing the Distribution Transformer with the Solid-State Transformer

The radial feeder is the most typical power distribution system configuration for distributing power to the consumer through the distribution transformer. Distribution transformers are a key component of power distribution systems, they enable voltage transformation, improve safety, reduce energy losses, enhance network reliability, and facilitate the efficient distribution of electricity to consumers. Due to the lack of their role in balancing loads and integrating renewable energy sources, they must be replaced with an alternate solution for modernizing and optimizing distribution grids. A solid-state transformer (SST) is a power electronic device that, in many ways, may replace a typical distribution transformer (DTR). It also improves controllability and provides a direct current link, making it simple to integrate distributed energy sources on either sides of medium and low voltage. However, reliability is the most important parameter in restricting its applications. Modularity is one of the ways to improve reliability and availability by directly re-routing the power within the modular system. This work investigates the failure rate of a modular SST by determining the number of module units required in SST design based on the available IGBT ratings. Further, the reliability of a radial feeder is evaluated by considering the configuration of a) without AS and with DTRs, b) Without AS and replacement of DTRs with SST, c) With AS and DTRs, and d) With AS and replacement of DTRs with SST.

Study on the Sound Radiation Efficiency of a Typical Distribution Transformer

In the realm of power grids environmental protection, low-frequency harmonic noise radiated from transformers has always been the focus of attention for decades. The existing noise control technologies, such as traditional noise barriers, sound insulation enclosures, and damping panels, not only occupying a large space but also causing difficulties in heat dissipation and daily maintenance of transformers. Therefore, explorations on the theory and design of low-noise power transformers become particularly necessary. In this paper, we started from the concept of acoustic radiation efficiency and discussed the radiation efficiency of a typical distribution transformer with radiators. It is found that the overall radiation efficiency is reduced below 230 Hz (low-frequency band) due to radiator barriers compared with that of the flat transformer tank. Furthermore, the phase effect of vibration distribution was also studied with a validated BEM code, inspired by the “acoustic short circuit” phenomenon. It is verified that the acoustic short circuit phenomenon truly exists for a typical transformer enclosure and affects its sound radiation. These supporting results might lead to a promising noise reduction technology from the perspective of radiation control of transformer tanks, i.e., acoustic metamaterials for noise source phase control.

Cost-optimal as a tool for helping in designing distribution transformer using particle swarm optimization

PurposeThis paper aims to achieve an optimal design for distribution transformers considering cost and power losses. Particle swarm optimization (PSO) algorithm is used as an optimization tool for minimizing the objective functions of design procedure which are cost and electrical and iron losses.Design/methodology/approachIn this paper, distribution transformer losses are considered as operating costs. Also, transformer construction cost which depends on the amount of iron and copper in the structure is assumed as its initial cost. In addition, some other important constraints such as appropriate ranges of transformer efficiency, voltage regulation, temperature rise, no-load current, and winding fill factor are investigated in the design procedure. The PSO algorithm is applied to find optimum amount of needed copper and iron for a typical distribution transformer. Moreover, transformer impedance considered as a constraint to achieve an acceptable voltage regulation in the design process.FindingsIt is shown that the proposed design procedure provides a simple and effective approach to estimate the flux and current densities for minimizing the active part cost and active power losses which means reduction in amount of transformer total owning cost (TOC).Originality/valueThe methodology advances a proposal for reducing distribution transformers costs using PSO algorithm. The approach considers the aforementioned constraints and TOC to minimize the active part cost and maximize the efficiency. It is demonstrated that a designed transformer will not be optimum when the transformer losses over years are not considered in design procedure. Finally, the results prove the effectiveness of the proposed procedure in designing cost-effective distribution transformers from its initial cost until its whole life.

Distribution transformer lifetime analysis in the presence of demand response and rooftop PV integration

Many distribution transformers have already exceeded half of their expected service life of 35 years in the infrastructure of Western Power, the electric distribution company supplying southwest of Western Australia, Australia. Therefore, it is anticipated that a high investment on transformer replacement happens in the near future. However, high renewable integration and demand response (DR) are promising resources to defer the investment on infrastructure upgrade and extend the lifetime of transformers. This paper investigates the impact of rooftop photovoltaic (PV) integration and customer engagement through DR on the lifetime of transformers in electric distribution networks. To this aim, first, a time series modelling of load, DR and PV is utilised for each year over a planning period. This load model is applied to a typical distribution transformer for which the hot-spot temperature rise is modelled based on the relevant standard. Using this calculation platform, the loss of life and the actual age of distribution transformer are obtained. Then, various scenarios including different levels of PV penetration and DR contribution are examined, and their impacts on the age of transformer are reported. Finally, the equivalent loss of net present value of distribution transformer is formulated and discussed. This formulation gives major benefits to the distribution network planners for analysing the contribution of PV and DR on lifetime extension of the distribution transformer. In addition, the provided model can be utilised in optimal investment analysis to find the best time for the transformer replacement and the associated cost considering PV penetration and DR. The simulation results show that integration of PV and DR within a feeder can significantly extend the lifetime of transformers.

Comparison of conventional methodology and software CYMGRD when designing grounding systems of typical distribution transformer stations

Design of the grounding system of power system facilities largely depends on the soil composition and its electrical characteristics, voltage level, dimensions of the object and other factors. This paper presents two calculation procedures intended for the design of the grounding system of a typical distribution transformer station. The first one, frequently used by the designers in Serbia, is based on the application of simple empirical formulas and diagrams, relying on the regulations, national standards and technical recommendations. The second calculation approach is represented by the use of a specialized software, based on modern mathematical methods, the results of which are verified using valid international standards. A comparative analysis of the results obtained using both methodologies, as well as the opportunities they provide to the designer, are presented. Both methodologies can be used when designing new grounding systems, as well as when reconstructing or maintaining the existing ones.

Distribution System Recovery Voltage Characteristics: I - Transformer Secondary-Fault Recovery Voltage Investigation

Distribution transformer secondary faults are shown to be potentially difficult for a primary interrupting device to clear. Evaluation test programs, therefore, should include this type of fault-interrupting test. Secondary fault recovery voltage data presented is derived from synthetic techniques, field interrupting tests and laboratory interrupting tests. TRV frequency is confirmed to be inversely proportional to the transformer voltage rating, directly proportional to the one-half power of kVA rating, and dependent upon transformer and system grounding connections. The trend toward lower transformer impedances may create problems for interrupting devices since TRV frequencies and the resultant rates of rise of recovery voltage are higher. Laboratory circuits using typical distribution transformers can be set up to be equivalent to field conditions and are satisfactory for exploring the adequacy of interrupting devices for clearing transformer secondary faults.