Abstract:
The main target of the large interconnected Power Systems (PS) present today is to
provide continuous and quality electricity supply to the consumers with highest
possible reliability. “Fast Valving” (FV) action of Steam Turbines is one of the most
effective elements for enhancing the transient stability of a power system in order to
maintain a healthy power supply under the large and sudden disturbances. FV plays a
significant role in mitigating the impact of sever disturbances by instantly decreasing
steam turbine power, thus ensuring the Power System Stability (PSS).
Sri Lankan power system currently comprises 4,043 MW generation capacity
consisting of 900 MW of coal power, 1,215 MW of oil burning thermal power, 1,720
MW of hydropower and 208 MW of non-conventional renewable energy sources
such as wind, mini hydro, biomass, and solar power plants. Lak Vijaya Power Plant
(LVPP) is the first and only coal power plant which is connected to Sri Lankan
Power System and it contributes almost 45% of total power requirement of the
nation. LVPP has three identical generating units driven by steam turbines each
having 300MW capacity.
Main objective of this research was to study the behaviour of “Over Speed Protection
Control” (OPC) unit of LVPP which has almost the same function of FV and to
establish the main objective of the OPC function. This study further investigates the
effects of FV scheme of LVPP on the transient stability of Sri Lankan Power System.
The study further explores the procedure to obtain the optimum valve actuation
timing of the Intercepting Valves (IVs) for the FV scheme while proving that FV has
much better control over transient stability than OPC. The results of the study further
unveil that proper selection of actuation timings of IVs for FV scheme of LVPP
steam turbines has a significant effect on enhancing the power system frequency
stability under transient conditions.
As the main objective of this study, the optimum ranges for actuation timings of IVs
for FV scheme of LVPP were found based on frequency stability of Sri Lankan
power system under the transient conditions and a set of timings for FV scheme were
recommended to set as actuation timings of IVs. The sensitivity of each time settings
were also examined and the relationships were clearly established.
