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

Abstract

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 bynon-linearloads 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 maximumflux 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 significantlyincreases. 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
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