OVERVIEW

Extensive application of power electronics and other nonlinear components and loads creates single-time (e.g., spikes) and periodic (e.g., harmonics) events that could lead to serious problems within power system networks and its components (e.g., transformers). Some possible impacts of poor power quality on power transformers are

• saturating transformer core by changing its operating point on the nonlinear ? ? i curve,

• increasing core (hysteresis and eddy current) losses and possible transformer failure due to unexpected high losses associated with hot spots,

• increasing (fundamental and harmonic) copper losses,

• creating half-cycle saturation in the event of even harmonics and DC current,

• malfunctioning of transformer protective relays,

• aging and reduction of lifetime,

• reduction of efficiency,

• derating of transformers,

• decrease of the power factor,

• generation of parallel (harmonic) resonances and ferroresonance conditions, and

• deterioration of transformers insulation near the terminals due to high voltage stress caused by lightning and pulse-width-modulated (PWM) converters.

These detrimental effects call for the understanding of how harmonics affect transformers and how to protect them against poor power quality conditions. For a transformer, the design of a harmonic model is essential for loss calculations, derating, and harmonic power flow analysis.

This chapter investigates the behavior of transformers under harmonic voltage and current conditions, and introduces harmonic transformer models suitable for loss calculations, harmonic power flow analysis, and computation of derating functions. After a brief introduction of the conventional (sinusoidal) transformer model, transformer losses with emphasis on...