M. N. Moschakis and  V. V. Dafopoulos and  I. G. Andritsos and  E. S. Karapidakis and  J. M. Prousalidis,  The Effect of Transformer’s Vector Group on Retained Voltage Magnitude and Sag Frequency at Industrial Sites Due to Faults.   journal   = {International Journal of Electrical and Computer Engineering}, [online]. World Academy of Science, Engineering and Technology.
    July 2013, vol. 79(7). 835 - 841
    [viewed 16 September 2019]. Available from: https://publications.waset.org/pdf/16272.