Field breaker tripping options for generator static excitation systems with AC field circuit breakers - A case study
Short circuit contributions from synchronous generators can persist for several seconds even after the field circuit breaker is opened. Delayed tripping of an AC field circuit breaker can allow faster reduction of generator field current in some circumstances. Faster reduction of generator field current will reduce the energy in a short circuit and consequently reduce the damage caused by the short circuit. This paper describes a case study examining the issues associated with the decision to delay tripping of AC field circuit breakers.
Prevention of tank rupture of faulted power transformers by generator circuit breakers
Internal fault arcs in power step-up transformers occasionally occur at different locations inside the tank. In this study it has been investigated to what extent generator circuit breakers (GCB) between generator and transformer may prevent explosion or severe damage due to pressure rise caused by the fault arc. Using sources from literature, study of fault cases that occurred in the past, and research of arc-current and arc-voltage conditions, a procedure was established to check the probability to what extent a GCB may reduce severe transformer damage and increase safety by prevention of fire. Following this procedure some actual fault-case studies show that GCB are effective in saving the transformer tank with a probability up to more than 80 %. Comparison with failure data verify the calculations.
Solitary Orbital Paget Disease: A Case Report
Purpose: To describe the clinical findings in a patient who had developed painless supraorbital prominence. Methods: Clinical and histopathological findings of the case are reviewed and presented. Results: The patient had an isolated histologically confirmed Paget disease of the orbit. Local excision of the lesion was performed. Conclusion: Paget disease can present not only as a diffuse process but also as a painless, solitary lesion of the orbit.