Traditional Distribution Transformer Research Articles

Modeling of direct AC/AC hybrid distribution transformer based on relaxed two port network theory

Traditional distribution transformers have shortcomings such as poor dynamic characteristics and unreasonable voltage compensation. It is difficult for them to meet the demand for power quality with the large-scale integration of new energy into the grid. Hybrid distribution transformers (HDTs) are an important means of addressing these issues. They have good flexibility in voltage regulation and huge development potential. To analyze the operating status and losses of an HDT, this study constructs a simplified equivalent impedance model for an HDT. First, the operating principle, characteristics, and voltage regulation range of a direct AC/AC HDT were analyzed. Second, based on the state–space averaging method, we obtain the HDT single-phase average circuit topology and construct an HDT relaxed two-port network model. Third, considering the operating losses of the transformer, Thevenin equivalent parameters of an HDT were derived. Then, a simplified equivalent impedance model for an HDT and the corresponding control strategies are presented. Finally, we verify the correctness and rationality of the proposed theory by constructing an HDT simulation model.

A data-driven multi-objective optimization framework for optimal integration planning of solid-state transformer fed energy hub in a distribution network

This study proposes an optimal planning technique for a solid-state transformer (SST) fed hybrid energy hub consisting of a wind turbine distributed generator (WTDG) and a battery energy storage system (BESS) in a distribution network (DN). The energy exchange within the energy hub and with the utility grid is regulated by an efficient energy management plan (EMP). The simultaneous planning of a WTDG-BESS energy hub in a DN fed through an SST is a challenging combinatorial optimization problem. It is not only about capacity allocation and placement, but also about charging and discharging dispatches of BESSs under dynamically altering system parameters with the intermittent nature of WTDG outputs and the operational limits of the system itself. As a result, simultaneous allocation becomes a mixed integer nonlinear programming (MINLP) problem, with the operational aspect acting as a limitation for the planning aspect and adding to the complexity of the problem. While the power flow takes into consideration the operational losses of the traditional distribution transformers (DT), the optimization problem reduces voltage deviations and energy losses of the DN. A 33-bus radial DN was used to test the proposed technique, and the outcomes of various case studies are included. The MINLP problem was addressed using the non-dominated sorted genetic algorithm (NSGA-II) in the MATLAB R2020a platform. The outcomes of the evaluation show an energy loss reduction (ELR) of 62%, while a voltage profile improvement (VPI) of 69% is obtained.

Detection Method of Distribution Transformer Based on Intelligent Switching Line Switch

Automatic and intelligent detection of distribution transformer is an important condition to ensure distribution network zero defect operation. The traditional distribution transformer quality detection system has low integration and automation, and a single function mode, which cannot meet the intelligent detection under different test scenarios. This paper introduces the basic principle of intelligent switching line, and develop a special automatic switching device according to the actual detection process. On this basis, an intelligent switching line switching device is designed according to the test requirements of distribution transformer. Finally, the actual test results show that the proposed distribution transformer detection method based on intelligent switching line switch can significantly reduce the detection time and improve the detection efficiency of distribution transformer.

Fuzzy logic-based management of hybrid distribution transformer using LoRa technology

Hybrid distribution transformers (HDT) has a better performance than traditional distribution transformers on improving power quality, such as reducing harmonics, unbalance, voltage fluctuations and low power factor in the future smart power distribution system. In order to increase the service life and reliability of hybrid distribution transformers, this paper proposed a remote management system using LoRa technology based on fuzzy logic. HDT based on fuzzy logic judgment system (FLJS) replaces the Boolean logic with fuzzy logic and several power quality problems including power factor, load-side current harmonics and voltage unbalance are considered, as well as grid-side voltage deviation and unbalance. The management system can dynamically adjust the working states of HDT according to the output results of the FLJS to reduce the use time of power electronic devices. Due to the application of LoRa, the management system can remotely adjust the parameters of the FLJS in real time for different distribution network nodes to avoid frequent switching of HDT working states. Meanwhile, it is able to remotely monitor the real-time working states and fault states of HDT to reduce recovery time and maintenance costs in case of HDT failure. Finally, simulation and experimental results are provided to verify the effectiveness of the proposed management system for HDT.

Virtual Submodule Predictive Control method for Power Electronic Transformer based on MMC Structure

In order to achieve flexible and efficient operation of intelligent power distribution, solving the problems of traditional distribution transformer such as large volume and weight, easy to generate harmonics when overload, and need supporting protection equipment to protect it when failure, etc. We propose a power electronic transformer structure based on modular multilevel converter (MMC). Firstly, we consider the multi-dimensional control target of MMC converter to establish a mathematical model. Then a virtual submodule predictive control method is proposed. The method introduces the concept of virtual submodule to realize the optimal switching state rapid mapping and reduce the switching loss of MMC. Finally, the experimental results show that the mmc-based power electronic transformer has excellent dynamic steady-state performance and can effectively overcome the high loss of traditional predictive control.

Research on power electronic transformer applied in AC/DC hybrid distribution networks

The AC/DC hybrid distribution network is one of the trends in distribution network development, which poses great challenges to the traditional distribution transformer. In this paper, a new topology suitable for AC/DC hybrid distribution network is put forward according to the demands of power grid, with advantages of accepting DG and DC loads, while clearing DC fault by blocking the clamping double sub-module (CDSM) of input stage. Then, this paper shows the typical structure of AC/DC distribution network that is hand in hand. Based on the new topology, this paper designs the control and modulation strategies of each stage, where the outer loop controller of input stage is emphasized for its two-control mode. At last, the rationality of new topology and the validity of control strategies are verified by the steady and dynamic state simulation. At the same time, the simulation results highlight the role of PET in energy regulation.

Comparison of core loss and magnetic flux distribution in amorphous and silicon steel core transformers

No-load losses are caused by the magnetizing current that needed to energize the transformers core. These losses are constant and occur 24 h a day, regardless of the load. So, the customers should pay the fixed monthly cost for these losses. In recent years, amorphous alloy has been used to improve distribution transformers performance with the decrease in No-load losses and the increase in the efficiency of transformers. This paper outlines the 2605SA1 amorphous core as a new development of the amorphous alloy with a higher saturation induction. This paper presents a comparison between traditional distribution transformers and amorphous distribution transformers. Distribution of flux density in two different transformers with amorphous core and M5-type silicon steel core has been simulated using 3-D finite element modelling. The simulation and modelling results have been compared with the tests results of 630 kVA, 34.5/0.4 kV prototypes manufactured in the TEK TRANSFORMER factory in Turkey. A good agreement has been obtained between the simulation and experimental results. The simulation and test results show that amorphous core considerably (about 63%) reduces the no-load power losses as well as efficiency of transformers.