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.
A New Methodology for Risk Analysis for Excitation System of Alternator in SHP using FIS
Preponderance of failures in a generator is due to excitation failure, thus it is pertinent to understand these failures, their reasons and ways to mitigate these failure modes. Failure mode and effect analysis is an ingrained tool that helps in increased availability and reliability of small hydropower plants. In this research, a FIS based methodology has been proposed to identify failure modes and prioritize maintenance action by calculating the Risk priority number. This calculation facilitates the utility to take preventive measures and ensure a safer and more reliable operation of the alternator in the powerhouse. This fuzzified approach to FMEA is a de viation from the traditional approach that gives a more tolerable range of RPN values by eliminating the role of human experts in maintenance prioritization. The model is implemented on a set of failure modes and an FMEA sheet is developed. The paper will be helpful for utilities and researchers involved with the operation and maintenance of small hydropower plants.
Prevention of high-fault rupture of pole-type distribution transformers
Violent rupture of distribution transformers has occurred with increasing frequency in recent years. The problem appears greatest with pole-type units at locations with high available short-circuit currents. This paper concerns the rupture of pole-type distribution transformers subjected to internal, submerged, arcing faults of high current magnitude. An analysis of a probable rupture process and tests of faulted transformers were used to obtain a simple semi-empirical equation for the internal transformer pressure rise. Limiting the I2t during the fault with current limiting fuses is shown to be a practical means of minimizing the probability of transformer rupture.