Research On Improving The Reliability Of The Excitation System’s Switch Of The300MW Coal-burning Generators

At present many300MW coal-burning generators in Guangdong province are equippedmain excitation system and auxiliary excitation system. Each excitation system can beswitched to the other automatically or manually when necessary to keep the generatoroperating reliably and steadily.When the generator is in normal operation or during its startup or outage processes themain excitation system is the first choice, but when the measuring system or the key switchesor the thyristor components etc fall in fault,the auxiliary excitation system have to be put intooperation. In return when the main excitation system is restored, it is should be back intooperation.The switch of the two excitation systems is in fact the transition during the twotypes of rectifying circuits. The process is: firstly put the standby excitation system intooperation, secondly reduce the running excitation system’s output and increase the newlyoperating system’s output. At last when the whole output is turned to the newly operatingsystem; take the once running system off operation. During the whole process there are threekey moments when the excitation parameters may fluctuate: the transient process during thestandby excitation system being switched on; the once operating system being switched off;during the process of excitation load being transferred. During these three processes thestructure of the circuit is changed so that the generator’s parameters including the reactivepower fluctuate and even some faults such as loss of excitation、under excitation、overexcitation occur. In this paper, taking the Pearl River power plant’s optimizations andmodifications to its four300MW generators as example, the author analysis the influences ofthe automatic switch of the excitation systems and use quick breakers instead of old DCbreakers、import quick-switch mode to guarantee transient and static stabilities.With regard to manual switch of the two excitation systems which is the key problem,author analysis the rectifier circuits’ changing and import preliminary compensation segmentto the AVR. The preliminary compensation segment can reduce the influence of the changingpreliminarily and largely, this make the process of the switch of the two excitation systemssmooth. This paper researched the theory and method on how to making the switch safe andreliable, it offered a new way to solve similar problems.