Lessons learned from the generator loss of field at a cogeneration thermal power plant in Taiwan

The contribution of this paper is that we present experiences from dealing with practical issues related to synchronous machine stability events. We describe and analyze the scenarios of generator loss-of-field occurring two times at a cogeneration thermal power plant in Taiwan in the years 2003 and 2005. Since the total production loss from both events was quite large, some improvements have been implemented to prevent the recurrence of similar events in the future. They consist of installing the sequence of events recorder at the generator output terminal, regulating the generator lagging power factor operation from 0.95-0.99 to 0.91, adjusting the tap position to decrease the secondary voltage of the 161 kV/161 kV interconnecting transformer, operating the phase-leading capacitors attached with a multi-stage chain cut-off control unit, and running two or three generators in automatic voltage regulation mode instead of automatic power factor regulation mode. Although similar events occurred twice at the same power plant in 2006, the generating units were capable of continuous stable operation which had effectively verified the improvements of operational changes. In conclusion, we suggest that the operating modes of generators in a cogeneration plant should reexamine constantly as well as monitor power quality of different end-user sectors continuously in order to ensure the security of power-system operation.