K-Factor and transformer losses calculations under harmonics

Transformers are equipment designed to operate perfectly at linear loads. Nowadays with wide use of modern technology requirement and industry needs which utilize nonlinear loads, the transformers are subjected to more nonlinear loads. Many research studied the influence of harmonics upon transformers. This paper focuses on transformer losses calculations for the case study of Mubarak Pumping Station (MPS) with and without passive harmonic filters. Also harmonic indices including K-Factor transformer, Total Harmonic Distortion (THD), Harmonic Loss Factor (FHL) and de-rating of transformer are calculated. When distribution transformer is operating under harmonic load, the value of load losses is increased, while the no load losses increased with a little amount. No load losses of a distribution transformer under harmonic loads can increase its operating cost. K-Factor calculation depends upon the fundamental current and the harmonic current components, and it is an indicative value of the harmonic contents in the power system.

I. Introduction

Basic design of transformer is based on operation pure sinusoidal voltage and current at the desired rated values, but actually this cannot happen continuously. The reason is the industrial explosion in the technology of electronic products which cover most human life fields starting from domestic devices like microwave ovens, PC computers, fluorescent lamp, and gas discharge lighting up to huge industrial equipment like UPS (Uninterruptable Power Supply), motor speed drives (which depend upon variation of frequency), and arc furnaces. These are examples of non-linear loads which cause distortion of voltage and current waveforms. As a result, multiple integer components from the main frequency power supply voltage and current to be produced. These components are known as harmonics. The impact of harmonics on transformers is very important, where it increase losses and reduce the life time of transformer insulation.