Specific Requirements for Distributed Generation Protection Considering the Power Quality

The present energy crisis drives to carry to an extreme the use of all the available energy sources, which need to be connected to the network in their closest point. Traditional electric systems are changing their characteristics, in what concerns to structure, operation, and especially on protection methodologies. The new protection problems of the different parts of the system are explained. The solution presents positive and negative aspects that impact the utility and the customer in different ways. The contributions of generators to short circuit currents is analyzed, especially the double fed generator. Philosophy changes are studied, such as: fault current bi-directionality, modification of the protection reach, failures of the overcurrent coordination due to current share, ferroresonance, etc. Solicitations to DG due to the normal unbalance of distribution systems are also studied. The protection of the generator is studied in function of the interconnection transformer, justifying and analyzing its connection type and grounding.  It is analyzed the discrepancy between the customers and utilities regarding the “islanding operation". The de-ionization without zero current is related with arc length and with “network power to DG power ratio”. It is concluded that DG application offers technical-economic advantages so much to the utility as to the user; and that the technology for these new protection approaches is already available, requiring of investments whose justification needs of a specific analysis for each particular case.