A Plan of Islanding Scheme for Pune City

The availability of electrical energy ensures development and progress while its non-availability means stagnation or ‘back tracking’. The condition of ‘No Power’ [1] is the costliest state and leads to social, economical and production loss. Power system blackout means inconvenience and hardship to society. Uninterrupted power supply is essential for the national productivity and social structure and hence system must be made flawless at any cost. Reliable and disturbance free electric power supply is recognized as a key to ‘Societal progress throughout the world’. Grid failure occurs due to continued overstressing, low frequency operation, increased load demand, peaking characteristics of the demand, ineffective load control, reduced level of security due to opening of interstate lines and violation of grid discipline. After occurrence of severe system disturbances, the system may split into parts, which may or may not survive depending on the load generation balance. The part system containing the generation sources and certain loads, which are planned to be separated from the main grid during system disturbance at, preconceived points either through under frequency and / or directional power relays are called ‘Islands’[2]. During restoration due to wide fluctuations in the frequency it becomes very difficult to maintain the load-generation balance. Inability to control the frequency may lead to unsuccessful restoration. Repeated collapse of the system island due to tripping of generators either due to over frequency or under frequency causes delay in getting normalcy. In this situation the computer-computer links between the State Load Despatch Centre (SLDC) and Area Load Despatch Centre (ALDC) play a key role [3]. The priority during the restoration period such as railway traction, essential consumers such as water supply scheme, hospitals etc and lastly to the civil societies should be given. It is also necessary to have provision of disturbance recorder and event logger at power generation stations and various interconnected substations. These and other major aspects are considered in proposing the islanding scheme of the Pune city.