ISSN 2630-0583 (Print)
ISSN 2630-0656 (Online)
Journal of Current Science and Technology
Rangsit Journal of Arts and Sciences. Vol.3 No.1 , January - June 2013.
Performance analysis of zone 3 relay with state diagram under transient condition
Operation of a zone 3 distance relay can adversely affect the power system stability in certain severe conditions. An enhanced algorithm of a zone 3 distance relay employing the state diagram is a promising solution that could avoid false operation of such relay. Nonetheless, verification of its performance in transmission test systems under various disturbed conditions is necessary prior to actual implementation. In this study, critical functions of the enhanced zone 3 relay has been examined using the modified 9-bus WSCC test system, with the inclusion of the dynamics of the synchronous generators and the associated excitation and governor controls, which could have significant impacts on the measured voltages under transient periods. Simulated test results have confirmed the effectiveness of the enhanced zone 3 distance relay to differentiate the condition of the system overload from that of the short-circuit fault, and hence, the relay can determine trip signal correctly. However, when the system has encountered the overload condition, immediately followed by the short-circuit fault, it is found that the relay has possibility to miscalculate the situation, and hence, may not send out the trip signal in case the primary protection fails to operate. The role of remote back-up protection that is compromised in such case could still lead to the system blackout, eventually.