Reclosure options for large Wind Turbines

This thesis studies the reclosure issues for large Wind Turbines (WT). Two major aspects were considered for the analysis and development of reclosure methods: (1) the possibility of exceeding stress limits in the WT's drive train and (2) the potential operational problems of the interconnected system. A CSMP computer program was developed to study the range of reclosure possibilities. These reclosure practices were classified into four categories according to the time at which reclosure is initiated and the type of control used prior to the reclosure operation. The categories are: Fast Reclosure (PR), Uncontrolled Reclosure (USR), Controlled Slow Reclosure (CSR), and No Reclosure (NR).

FR occurs in time to maintain classical first swing stability between the affected WTs and the power system, and no control other than breaker action is required. USR is initiated after the critical switching time without auxiliary control actions. CSR requires auxiliary WT controls and is initiated after the critical time for first swing stability. In the NR option, the affected WTS are shut down, restarted, and resynchronized in a normal startup mode.

Simulation results showed that due to the extremely short critical switching times, PR is not practical. USR may originate large electrical and mechanical transients representing a considerable risk of damage to the WT. If first swing stability is lost, reclosure should not be attempted during the unwinding of the low speed shaft.

CSR with a simple hub speed error controller is the most attractive solution for reclosure of large WTs, since it poses little risk of damage to the WT and only minor implications on power system operation. Since the NR option has the most potential to impose operating problems on the power system, it should not be used when temporary electrical disturbances occur near WTs.