Research On Optimal Coordination Of Inverse-Time Overcurrent Relay

Optimal coordination regards coordination relationship of protection as constraints and operation time of all relays as optimum target. This method shows the key point of coordination, based on which optimum settings of protection is completely collected, relay devices are well applied, and power system is able to work well. Attention has been drawn to optimal coordination method, being applied to offer the actual need of detailed model and accurate solution,which are called optimal model and optimal algorithm. This paper mainly discusses about the optimal model for the need of system according to the flaws found in optimal model.Modern power system is complex and changeful. It is not easy to build up a model of optimal coordination that meets the actual needs. From the point of the relation of relays and system, this paper focuses on the function of system under the application of relays and the influence from system to relays, both of which relate to the study of tuning model. Due to the excellent properties and wide applications of inverse-time overcurrent relays, based on which three respects are being discussed.First of all, the defect of existing model is analyzed, which considers all circuits as the same . The optimum object is modified from CCT weight, which is able to shorten operation time of the important circuit in order to improves the function of relays for the maintain system.Then, it is discussed that the uncertain factors in the system is caused to coordination. The objective function of optimization is inducted in the main uncertainty of factors. The constraints of relays are considered under different system states. Meanwhile, the uncertainty of inverse-time overcurrent relay is put forward. As a result, the ability of adjustment is able to be enhanced by the settings in different conditions.Finally, the selectivity of relays is discussed according to the any failure of inverse-time overcurrent relay. It is mentioned in the paper that the constraint of parameter in the same curves, and the criterion of parameter in the different characteristics curves. In terms of the constraint and criterion of parameter of optimal coordination method, the selectivity is able to work well under any fault without adding the preconceived faults and affecting the calculated amount.