Abstract
Controlled islanding has been proposed as a last resort action to stop blackouts from happening when all standard methods have failed. Successful controlled islanding has to deal with three important issues: when, and where to island, and the evaluation of the dynamic stability in each island after islanding. This paper provides a framework for preventing wide-area blackouts using wide area measurement systems (WAMS), which consists of three stages to execute a successful islanding strategy. Normally, power system collapses and blackouts occur shortly after a cascading outage stage. Using such circumstances, an adapted single machine equivalent (SIME) method was used online to determine transient stability before blackout was imminent, and was then employed to determine when to island based on transient instability. In addition, SIME was adopted to assess the dynamic stability in each island after islanding, and to confirm that the chosen candidate island cutsets were stable before controlled islanding was undertaken. To decide where to island, all possible islanding cutsets were provided using the power flow (PF) tracing method. SIME helped to find the best candidate islanding cutset with the minimal PF imbalance, which is also a transiently stable islanding strategy. In case no possible island cutset existed, corresponding corrective actions such as load shedding and critical generator tripping, were performed in each formed island. Finally, an IEEE 39-bus power system with 10 units was employed to test this framework for a three-stage controlled islanding strategy to prevent imminent blackouts.
Highlights
Power blackouts are still a recurring problem around the world and the search continues to develop ever-better methods for their prediction and prevention
In this paper we only investigate transient stability in the hypothesis of this research, which leads to blackouts during cascading outages
In terms of “when to island” in this controlled islanding scheme, single machine equivalent (SIME) was applied to assess the transient stability before imminent blackout to determine the appropriate time to split the network
Summary
Power blackouts are still a recurring problem around the world and the search continues to develop ever-better methods for their prediction and prevention. This paper concentrates on controlled islanding, which has been proposed as the last-line of defense when all the usual protection measures have failed and a blackout is imminent [1,2]. As is the case in the US/Canada [3], the dynamic process accompanying a blackout consists of four stages [4]: slow cascading trips, fast cascading, oscillation and collapse. In the slow cascading stage, transmission lines are tripped by protection due to overloads. Once a line is tripped, the power flow (PF) on the tripped line has to be shared by neighboring lines, which may cause violation of the thermal rating on adjacent lines and lead to further cascading trips. As more and more lines are tripped, power cannot be delivered to some loads.
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