Comparative Efficiency Study of Protective Relays Schemes in Wind Energy Conversion Systems

Since the performance of wind energy conversion systems is unsatisfactory, one of the main concerns about systems planning and operation should be better reliability of the components and their operation. Among others, the attention should affect protection systems, and relays incorporated to. Relays have two alternative ways in which they can be unreliable, i.e., may fail to operate when they are expected to, or may operate when it is undesired. This leads to a two-pronged definition of protective relay, i.e., it must be dependable and secure. One of a few options of relays reliability enhancement can be use of logical redundancy, i.e. series, parallel, 2-out-of-3. The advisability of using a given type of redundancy (instead of single relay), can be evaluated relying on efficiency of relays operation. Both the structural reliability and the operation reliability must be taken into consideration. The efficiency of different types of redundancy can be measured based on economical criterion and incorporate the costs of incorrect operation, i.e., failure to trip caused by undetected fault, undesired trip, and repair of faulted relay(s). The efficiency of different protective relays scheme can be investigated relying on semi-Markov models. In the paper, four models are investigated in detail. As an example, the comparative efficiency study of these schemes are presented.