Electric vehicles (EVs) have remarkably emerged as an alternative for internal combustion engines. With high penetration levels of the EVs, its addition to the existing distribution line infrastructure affects the power quality and grid stability. Additionally, EV charging loads are characteristically different as they are mobile compared to other fixed node-connected loads. Proposing solutions without considering these factors may result in grid congestion and subsequent over/under compensations. Another emerging dynamics co-occurring in the distribution system is high penetration levels of renewable energy in the utility grid. Although these dynamics pose challenges in stable grid operation, it also gives opportunities for solving some of the grid integration issues of EV loads. Thus, the effect of adding EV charging load to the existing low voltage distribution system must be analyzed by considering different criteria such as grid impact with different EV chargers, mobile nature of EV load, power quality, voltage profile, and spread/peak demand of load curve. This paper presents a detailed report on the impact analysis of EV integration on the component and system levels. For analyzing the effect on power quality (component level), grid pollution contributed by EV chargers along with possible solutions is elucidated. Detailed discussion on the significance of EV load location, existing load distribution, and nature of EV charging load distribution is presented by considering different feeders and different load curves. These discussions are supported with simulated case studies followed by a review of existing literature for enhanced understanding. Finally, techniques employed to effectively model the mobile nature of EV load and distributed EVs potential to provide ancillary solutions are also explained.

Comprehensive review & impact analysis of integrating projected electric vehicle charging load to the existing low voltage distribution system

Modeling and simulation of transformer loading capability and hot spot temperature under harmonic conditions

The significance of harmonics in power systems has increased substantially due to the use of solid state controlled loads and other high frequency producing devices. An important consideration when evaluating the impact of harmonics is their effect on power system components and loads. Transformers are major components in power systems. Supplying non-linear loads by transformer leads to higher losses, early fatigue of insulation, and reduction of the useful life of transformer. To prevent these problems rated capacity of transformer supplying non-linear loads must be reduced. This paper reviews the non linear loads effects on the transformers and the standard IEEE procedures for derating of the transformers which are under distorted currents. The equivalent losses and capacity of a typical 25 KVA single phase transformer is then evaluated using analysis and simulations in MATLAB/Simulink-based on useful model of transformer under harmonic condition- and results are compared.

Comparison of distribution transformer losses and capacity under linear and harmonic loads

Transformers are one of the main equipments of distribution systems. Increase in transformer loss is mostly the source of the damages, and caused by increased harmonic contents, especially current harmonic. These losses will result in an increase in temperature of various parts of transformer, especially its hot-spot temperature, and this temperature increase leads to insulation life reduction. Therefore, it seems necessary to know the harmonic orders and estimate hot-spot temperature of the transformer, which can help predicting the remaining life of the transformer. In this paper, relations associated with transformer life and losses are reviewed. The equivalent losses and capacity of a typical distribution transformer have been evaluated using simulation in MATLAB/SIMULINK based on its model under harmonic condition. Then, hot-spot temperature and remaining life of the transformer are estimated. In addition, the transformer has been simulated using Finite Element Method in MAXWELL software. Finally, results are discussed and compared.

Investigation on impact of current harmonic contents on the distribution transformer losses and remaining life

The currently high energy efficiency demands and control requirements impose an extensive usage of power electronic devices and circuits in both domestic and industrial applications. These intrinsic nonlinear loads generate prominent level distortion of the electric current waveforms, which lead to additional losses and thermal stress within the power supply distribution system. Thus, due to the supplementary harmonic losses, the power transformer, experience an increase of its hot-spot temperature that may cause the machine insulation failure and ultimately the transformer lifetime expectancy reduction. In order to overcome these undesirable consequences, the reduction of the apparent power rating of the transformer (derating) is commonly adopted. This paper quantitatively investigates the nonsinusoidal steady state of the transformer by evaluating the losses distribution within the machine, its hot-spot temperature rise and the corresponding transformer loss of life. The computation procedure is exemplified on a 250 kVA liquid filled three-phase power distribution transformer that supplies both linear and nonlinear industrial loads.

Losses and temperature rise within power transformers subjected to distorted currents

Transformers are normally designed and built for utilizing at rated frequency and prefect sinusoidal loads. Supplying non-linear loads by transformer leads to higher losses, early fatigue of insulation, and reduction of the useful life of transformer. To prevent these problems rated capacity of transformer supplying non-linear loads must be reduced. In this paper, at first, a useful model of transformer under harmonic condition is presented. The model in addition to ordinary parameters includes a potential difference defined as the second derivative of the load current that represents eddy current losses in windings and the other stray losses represented as a resistor in series with the leakage inductance and dc resistance. Finally, losses and capacity of 50 KVA transformer under harmonic load current is calculated. This model simulated in MATLAB/Simulink and then its results are compared with losses and capacity calculated by standard.

S.B. Sadati

Papers

Comparison of distribution transformer losses and capacity under linear and harmonic loads

Derating of transformers under non-sinusoidal loads