Distortion limits in international standards vs. reliability of power components: Always on the safe side as to low-order voltage harmonics?

Smart Grids with power converters for renewable energy sources require harmonic control. International Standards set limits to harmonic voltages and this paper investigates whether such limits are always “on the safe side” for power component reliability. By simulating the random variation of voltage harmonics according to the probabilistic limits given in EN 50160, reliability parameters are derived for typical LV and MV cables and capacitors via a probabilistic life model. The model caters not only for the temperature variation due to harmonic currents, but also for the effects of harmonic voltages on component insulation life through peak, shape and rms factors of the distorted voltage. The paper shows that even if harmonic distortion matches EN 50160 limits strictly, component life and reliability might be reduced with respect to rated sinusoidal operation significantly. Moreover, not only the peak, but also the shape factor of the distorted voltage plays a major role.