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The dc bias effects on the magnetizing and magnetic induction are analyzed through their harmonic characteristics. A model transformer in order to analyzed the harmonic characteristic of the single phase power transformer under dc bias condition. The effect of dc bias will seen by the dc current injected on the winding of experiment system. Effect of that the linear value is changed with the ac excitation...
An investigation of magnetizing current waveforms of single phase power transformer due to DC bias injection through simulation and experimental study is present in this paper. A method base on MATLAB simulation that is capable of predicting of magnetizing current without and with DC bias is used. The experimental study is done by the DC bias current injected simultaneously with AC source to primary...
The power quality (PQ) indicators, related to slow voltage variations, are expressed usually both absolute and relative values. Consequently, the paper presents the complete family of slow voltage variations indicators in expression of absolute, relative and percentage. The necessity of an expressive analysis of voltage variations led to idea of the voltage wave decomposition in actions and harmonics...
With regard to the first ± 660kV HVDC transmission line from Yinchuan to Qingdao, quantitative harmonic analysis of the main transformer in Yi Ming substation, about 65km away from the Qingdao converter station, is carried out based on an established nonlinear magnetic model by PSCAD/EMTDC. The results indicate that, both the odd and even harmonic components are getting much higher under DC bias than...
This paper presents a new multi-criteria stabilization algorithm of transformer differential protection. Proposed scheme bases on new criteria signals and appropriate operation thresholds. New algorithm employs fuzzy reasoning technique for better discrimination of inrush conditions. The developed stabilization algorithm has been tested with ATP-EMTP generated signals, proving to be reliable and much...
This paper presents an analysis of the main operating conditions that may lead to inappropriate differential protection operation. These conditions were simulated using the Alternative Transients Program (ATP) and the model of a real system. The saturable transformer was the main component of the ATP/EMTP simulations. The saturation and hysteresis effects are represented by a non-linear model of the...
This paper proposes a three-phase five legged wound transformer core constructed of two high permeability Si-Fe wound cores and two conventional Si-Fe wound cores. The two large internal wound cores are manufactured of high permeability, grain-oriented electrical steel. The two small outer wound cores are manufactured of conventional, grain-oriented electrical steel. The specific arrangement is based...
This paper aims to present the modeling and simulation of numerical differential protection of power transformers using the software ATP/ATPDraw and its MODELS environment. In order to validate the relay model, simulations were carried out using a simplified electrical power system whose parameters were obtained from a real system. The results reveal the advantages of using this type of modeling,...
To feed electric train, the structure of traction power supply system is very different from utility grid. The single-phase traction loads result in some problems, such as negative sequence, harmonics, reactive power and crossing neutral sections. Based on the existing traction power supply system, the active power filter is used to construct cophase traction power supply system. It not only eliminates...
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. The inventory of the distribution transformers indicates that conventional transformers of fairly high loss types have been selected over low loss types. Choosing low loss amorphous transformers when pre-existing...
This paper reviews the characteristics of inrush current and analyses its causes. The development of digital substation and the concept of integrated protection are also outlined. The paper studies different models to simulate several kinds of inrush and internal short-circuit fault. Through these models, the new composite algorithm is analysed in order to verify the reliability and sensitivity of...
Energization of unloaded transformer results mainly in magnetizing inrush currents having a high magnitude with harmonic-rich currents, when transformer cores are driven into saturation during energization. The currents cause many undesirable effects on transformer attribute; large dynamic forces inside it, life-span reduction, insulation deterioration and mechanical fatigue in windings support, as...
An optical fiber sensor based on harmonic detection for real time monitoring of dissolved gases in the insulating oil of high-voltage transformers has been developed for fault detection. The present work describes contributions to the optimization of the sensor system, using a DFB laser, which is modulated by the local oscillator of a lock-in amplifier, also used for harmonic detection of the spectral...
The paper describes in details construction and performance of a new measurement equipment - a resistive divider, designed for high voltage networks. The measurements at 400 kV require linear voltage reduction to the value acceptable by electronic equipment. The divider will be used for upmarket accurate measurements of higher harmonics and other voltage distortions. It can be also used for evaluation...
The optimization in the operation of distribution electric systems has become an acute problem. In order to evaluate some essential criteria (e.g., active power losses) the computation of power flow is absolutely necessary. Taking into account the real operating conditions (unbalance, harmonics) it is of great interest for accurate steady state estimation. The existent solutions proposed in literature...
Calculating additional losses of the transformer driven by load harmonics is very significant to economic, safe and efficient operation of transformer. Based on the transditional model of additional losses driven by load harmonics, the simplified model is put forward, as well as the calculation equation. According to the simplified model, a method to monitor the transformer harmonic losses online...
A novel scheme based on generalized leakage inductance (GLI) to distinguish the inrush current from the internal fault current in the power transformer is proposed. By eliminating the mutual flux linkage in the transformer loop equation and adopting the trapezoid principle, the GLI is calculated in the real time. According to the difference between the GLI and the leakage inductance obtained from...
This paper sets up a simulating model of single-phase transformer under DC bias in MATLAB. Using MATLAB software, the magnetization characteristic curves and exciting currents under no-load condition are simulated and analyzed. The result shows that the magnetization characteristic curves do not shift up, but they are no longer symmetrical under DC bias. They get saturate at one side of X axis. The...
The life of power distribution transformers has been greatly reduced by the significantly addition of electronic loads in the distribution system. The characteristics of loads now becoming more nonlinear which in turn produce more harmonics. Power transformers are constantly affected due to its location between the variety of loads at consumer's side and the power supply side. Additional loss at transformer...
This paper develops a technique to model the frequency response of a saturated transformer. This technique is used to determine the range of frequencies that will be generated when a transformer experiences saturation due to an injection of typically low frequency currents. This paper examines the case when a power transformer is saturated due to geomagnetically induced currents (GIC) caused by solar...
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