Protection and control of steam turbine generator using PLC

The protection and control system of boiler, turbine and generator which is a very sophisticated system involving modern technologies, is of utmost importance in any thermal power plants. In this paper the protection and control features of boiler, steam turbine and generator and discusses the main features of the system, structure and implementation for smooth automatic operation by using programmable logic controller (PLC) has been outlined. The demand of higher quality, greater efficiency and automated system has increased radically in the globalised world. To cope with this advancement this paper will be considered as an approach. In this study the protection and control features of a steam turbine is categorized in three phases: Boiler startup and fuel selection protection, Turbine self and mechanical protection and Generator protection. In the first phase, if all the protection features of boiler start up and fuel selection are silent condition and all the alarms are reset state only then the boiler will start up after completion of the furnace pre purging. Otherwise the master and other associated auxiliary fuel valves will be tripped. The second phase covers mainly all the mechanical protection of the steam turbine such as bearing failure, over speed, governor failure and also the generator circuit breaker open condition. If any protection feature initiates than turbine is tripped and close the trip and throttle (T&T) valve. In the third phase, the closing of the T&T valve or initiation of any generator protection features according to ANSI will disconnect the generator lockout relay to make the generator excitation off and disconnect the generator circuit breaker. Thus the entire cycle is carried out at various stages and each phase is detailed out in this study. This study proposes better flexibility in operation and control with low cost and less time for trouble shooting by PLC compared to the existing instrumentation system of 3MW STG unit of Ebara Power Engineering Company Ltd. in Eastern Refinery Ltd. It is anticipated that this paper will be very effective as the needs for automation is growing day by day. Keywords: PLC, Boiler and turbine protection and control, Sucosoft V5.02 Moeller PLC software