Are the Limits to Harmonic Voltages given by International Standards on the Safe Side from the Viewpoint of Power Component Reliability?

Power quality disturbances in “Smart Grids” encompass harmonic distortion. International standards such as IEC 61000 or EN 50160 set limits to harmonic voltages in public networks. This paper investigates whether such limits are always “on the safe side” from the viewpoint of the reliability of power components, by employing a probabilistic life model for estimating some reliability parameters of power devices operating in distorted regime. The model accounts not only for a possible temperature rise due to distorted current, but also for the effects of harmonic voltages on component insulation life via peak, shape and rms factors of the distorted voltage. Reliability parameters are derived for typical LV and MV cables and capacitors by simulating the random variation of voltage harmonics according to the probabilistic limits given in EN 50160. The application – that considers the role played by the phase-shift between voltage harmonics and the fundamental - shows that even if harmonic distortion matches EN 50160 limits, component life and reliability may be reduced significantly with respect to rated sinusoidal operation. Furthermore, not only the peak, but also the shape factor of the distorted voltage plays a nonnegligible role.