Transformer Load Losses Research Articles

Assessment of Load Losses Caused by Harmonic Currents in Distribution Transformers Using the Transformer Loss Calculator Software

Transformer load losses cause various adverse effects, such as derating, a decreased lifetime, and greenhouse gas emissions. In this paper, the load losses caused by non-linear loads on distribution transformers are analyzed. For this study, the load loss expressions provided by the IEEE Standard C57.110 and ANSI/UL 1561-1562 were adapted to the usual case where the transformer currents differ in each phase. The novel load loss expressions adapted from the IEEE Standard C57.110 were applied using the software known as the “Transformer Loss Calculator” (TLC), implemented with LabVIEW. For the application of new load loss expressions, carbon dioxide (CO2) emissions were determined by multiplying the load losses by the emission factors of each country. The experimental results are based on the recordings made by a FLUKE 435 Series II analyzer on the second of two 1000 kVA transformers, feeding real residential distribution networks with very differently distorted loads. An analysis of these transformers shows that the annual energy losses and CO2 emissions obtained from the adapted load loss expressions could be more than 5% of those determined by the original IEEE and ANSI Standard expressions. Due to these percentage loss and emission differences, it is advisable to use the TLC software in transformer monitoring instruments.

Study on the Influence of Harmonics on Load Loss of Transformer

Under harmonic condition, transformer loss is significantly higher than that of traditional calculation method. It is necessary to re analyze the resistance model of transformer winding in harmonic environment. In this article, the harmonic loss model of transformer winding considering skin effect and proximity effect is established, and the characteristics of the conductor resistance of transformer winding are obtained by electromagnetic field principle analysis; the conductor resistance of typical harmonic current is measured by experiment, and the effectiveness of the model in reflecting the winding loss under harmonic condition is verified, which makes the load loss of transformer The calculation is more accurate.

Optimal distribution transformer sizing in a harmonic involved load environment via dynamic programming technique

Installation of a significant number of distributed generators (DGs), besides the application of non-sinusoidal loads such as; Plug-in Hybrid Electric Vehicles (PHEVs), in the emerging smart distribution networks and the industrial plants have posed a major challenge to the existing methods of optimal transformer sizing (OTS). The harmonic currents generated in these new environments not only substantially increase the transformer load losses, but also cause abnormal winding temperature rise and hence transformer excessive loss of life. Therefore, the harmonic contents of the loads currents should be accounted in choosing the appropriate size of distribution transformers. To address this concern of utilities, this paper introduces a new method to solve the OTS problem in such environments. It takes into account the effects of harmonics currents on excessive heat generation in a transformer and the transformer insulation loss of life due to these thermal stresses. This paper proposes a new dynamic programming (DP) framework to solve the OTS problem. Although the proposed DP method considers the transformer thermal equations, however, by introducing a novel variable named the depreciation cost, the consecutive stages of the proposed DP network are hold independent. Therefore, the proposed DP method does not require any supplementary heuristic algorithm to solve the OTS problem. In response, the proposed method is very fast and easy to implement. Comprehensive studies are carried out to validate the effectiveness of the proposed algorithm.

Comparing Transformer Derating Under Harmonic Load and Unbalanced Supply Voltage Based on IEEEC57.110 Standard and TESFEM By FHL And K_Factor

Transformers are generally designed in order to deliver the required power to the connected loads with minimum losses at nominal fequency. Nowadays , power quality affected by non-linear loads and unbalanced condition and causes deflection from a perfect sinusoidal waveform. This condition leads to additional losses, increase temperature and reduction of the useful life of the transformers. In order to avoid of these difficulties, the nominal capacity of transformer should be reduced. This paper studies the increase of losses and Derating of Distribution transformer, working under Different harmonic load and unbalanced supply voltage conditions. In this paper, the three dimensional finite element method (3-D) is utilized as a Instruments for viewing magnetic flux density on core and windings of distribution transformers. The computer simulation according to the use of the FEM has been improved in Ansoft - Maxwell. In section 2, a 3-D time stepping finite element method (TSFEM) is used in order to modeling the transformer under different harmonic load with (THD I =12% and 23%). The maximum flux density in the transformer windings under sinusoidal and different harmonic load condition has been investigated in this section. In section 3, the effect of harmonic load on transformer load losses Has been examined. The result shows that under harmonic load current , copper loss an eddy current losses significantly increases. In section 4, derating of transformer under harmonic load based on IEEE c57.110 standard and TSFEM by using k-factor and harmonic loss factor (H FL ) Has been done. The result shows that IEEE standard is a Conservative method for transformer derating under high harmonic current (THD I ) and TSFEM is a Convenient method for transformer derating in this condition. In section 5, The Performance of the transformer when the supply voltage are balanced compared to the case in which supply voltage is unbalance , the result shows that , the unbalanced voltage Causes increase in the both copper loss and core loss. Afterwards, Based on the data obtained from the TSFEM, a distribution transformer under different unbalanced condition has been derated

Operation Modes of HV/MV Substations

Operation Modes of HV/MV SubstationsA distribution network consists of high voltage grid, medium voltage grid, and low voltage grid. Medium voltage grid is connected to high voltage grid via substations with HV/MV transformers. The substation may contain one, mostly two but sometimes even more transformers. Out of reliability and expenditure considerations the two transformer option prevail over others mentioned. For two transformer substation, there may be made choice out of several operation modes: 1) two (small) transformers, with rated power each over 0.7 of maximum substation load, permanently in operation; 2) one (big) transformer, with rated power over maximum substation load, permanently in operation and small transformer in constant cold reserve; 3) big transformer in operation in cold season, small transformer-in warm one. Considering transformer load losses and no load losses and observing transformer loading factor β it can be said that the mode 1) is less advantageous. The least power losses has the mode 3). There may be singled out yet three extra modes of two transformer substations: 4) two big transformers in permanent operation; 5) one big transformer permanently in operation and one such transformer in cold reserve; 6) two small transformers in operation in cold season of the year, in warm season-one small transformer on duty. At present mostly two transformers of equal power each are installed on substations and in operation is one of them, hence extra mode 5). When one transformer becomes faulty, it can be changed for smaller one and the third operation mode can be practiced. Extra mode 4) is unpractical in all aspects. The mode 6) has greater losses than the mode 3) and is not considered in detail. To prove the advantage of the third mode in sense of power losses, the notion of effective utilization time of power losses was introduced and it was proven that relative value of this quantity diminishes with loading factor β. The use of advantageous substation option would make it possible to save notable amount of electrical energy but smaller transformer lifetime of this option must be taken into account as well.

Effects of harmonics on converter transformer load losses

Losses were measured during short-circuit tests on a 262.5 MVA, three-phase, five limb converter transformer at various frequencies from 50 Hz to 1 KHz. Using these and the calculated values of the harmonic currents produced by the AC/DC converter, load losses were determined. Variations of these losses with the converter firing angle, with the transformer reactance and with the load were studied. A simple method of loss calculation which has the potential for application at the design stage was developed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>