Hierarchically Coordinated Protection: An Integrated Concept of Corrective, Predictive, and Inherently Adaptive Protection

1 INTRODUCTION This paper relates to a new protection paradigm where corrective, adaptive and predictive relaying features are introduced. The value of corrective relay operation can be assessed by looking at the situations when relay mis-operations occur. Analysis of recent historical blackouts has revealed that the power system catastrophic events happened following consecutive cascading events such as transmission line outages, overloads and malfunctions of protective relays [1]-[3]. In general, cascade events can be divided into two time stages. In the first stage, successive events are slow enough to be analyzed as steady-state. If no action occurs to restore the grid to the normal operation condition, and meanwhile several major disturbances occur causing fast transient stability violation, a system collapse will happen. This stage is named as second or irreversible stage. Early prediction and proper control actions during the first stage can prevent further unfolding of cascade events. When a transmission line is tripped due to the operation of protective relays, a relay mis-operation detection tool can confirm whether the relay operation was correct or the transmission line was healthy and incorrectly tripped [4]. The advantages of such tool could be itemized as higher reliability and redundancy, faster restoration and enhanced critical decision making during disturbances [5]. This tool can also support the reliable implementation of new applications such as transmission line switching (topology) control [6]. The value of adaptive relay operation [7]-[10] may be assessed by looking at the situations where adaptive features are desirable. So far, the protection challenges raised by DG integration in the system have been mostly looked at from the distribution side. However, with high penetration of DGs in the network, the protection concerns extend to transmission level also. According to the literature [11]-[12], one of the challenges that high levels of DG penetration create for the power transmission system protection is unintended bulk DG tipping following a disturbance in the transmission system. The interaction of system dynamics with sensitive control and protection measures which are necessary, according to IEEE standards, to prevent or minimize the existence of an inadvertent island, could lead to unintended tripping of DG. For example, if a short-circuit takes place in the transmission grid and its effects on voltage are propagated downstream to the distribution level, it may provoke the disconnection of a large amount of DG. Since these DG plants are tripped, a sudden increase in power flow coming from …