Eruptions from the sun are correlated with sunspot cycles peaking every 11 years. They disrupt the earth’s dipole magnetic field and cause slowly varying currents in the ionosphere and magnetosphere. These currents induce quasi-dc currents called Geomagnetically Induced Currents (GICs) which flow through, disrupt and damage man-made systems

Aims: We study both the short term and long term effects of solar activity on the large transformers (150 kV and 400 kV) of the Greek national electric grid.Methods:We use data analysis and various statistical methods and models. Results: Contrary to com-mon belief in PPC Greece, we see that there are considerable both short term (immediate) and long term effects of solar activity onto large transformers in a mid-latitude country like Greece. Our results can be summarised as follows: 1. For the short term effects: During 1989–2010 there were 43 ‘‘stormy days’ ’ (namely days with for example Ap 100) and we had 19 failures occurring during a stormy day plus or minus 3 days and 51 failures occurring during a stormy day plus or minus 7 days. All these failures can be directly related to Geomagnetically Induced Currents (GICs). Explicit cases are briefly pre-sented. 2. For the long term effects, again for the same period 1989–2010, we have two main results: (i) The annual number of transformer failures seems to follow the solar activity pattern. Yet the maximum number of transformer failures occurs about half a solar cycle after the maximum of solar activity. (ii) There is statistical correlation between solar activity expressed using various newly defined long term solar activity indices and the annual number of transformer failures. These new long term solar activity indices were defined using both local (from the geomagnetic station in Greece) and global (planetary averages) geomagnetic data. Applying both linear and non-linear statis-

The copyright of this thesis vests in the author. No quotation from it or information derived from it is to be published without full acknowledgement of the source. The thesis is to be used for private study or non-commercial research purposes only. Published by the University of Cape Town (UCT) in terms of the non-exclusive license granted to UCT by the author. Un ive rsi ty f C ap e T ow n

The copyright of this thesis vests in the author. No quotation from it or information derived from it is to be published without full acknowledgement of the source. The thesis is to be used for private study or non-commercial research purposes only. Published by the University of Cape Town (UCT) in terms of the non-exclusive license granted to UCT by the author. DECLARATION I, Lameka Amuanyena, hereby declare that unless properly referenced and acknowledged, the work contained in this thesis is my own work.