Grid Security Issues
- load generation balance planning in respect of active power for the further year, that is reviewed on a quarterly and then monthly basis, in sequence to ensure in which the frequency stays at the nominal level;
- Installation of capacitors or reactors to acquire a proper voltage profile in the grid;
- Line and transformer loading;
- Protection coordination;
- Monitoring of the grid; and
- Proper analysis of tripping of lines as well as of grid disturbance and taking corrective measures thereof.
Under-frequency and rate-of-change of frequency relays are installed as security measures to cut off load in case of gradual or sudden drop in generation, correspondingly, to ensure nominal frequency in the grid. Islanding schemes of important generators and loads are also planned as a last resort to isolate or island them in case of a blackout so in which the significant power stations and loads remain functional. Thus, these islands are made in such a way in which the generation and load in these islands approximately match.
Under operational planning, procedures are also created for restoration of grid in case of tripping of a few or more elements of the grid or for total blackout. This is done through the Regional Load Dispatch Centre responsible for real time operation of the regional grids, in consultation along with all the players included in grid operation. One of the points includes in grid restoration is the "black start", that means starting of a generating unit after a blackout. Because hydro generators need the least power for starting, they are normally started first or, instead, used for black start.
Commercial billing through the several generators is completed in accordance with the Availability Based Tariff approved through the Central Electricity Regulatory Commission. Under the Availability Based Tariff (ABT), the beneficiaries are needs to pay charges in three components, viz., annual fixed charges, energy charges and Unsheduled interchanges (UI) charges.
Annual fixed charges are needs to be paid through the beneficiaries irrespective of actual drawals or schedules. The implemented schedules, as described previously, are used for determination of the amounts payable as energy charges. Deviations from schedules are determined in 15-minute time blocks by special metering, and these deviations are priced depending on frequency. These deviations are known as unscheduled interchanges (UI).
The pricing for UI is connected to system frequency such in which the constituent causing the grid frequency to improve/worsen in worst conditions gets rewarded/penalised at higher price and vice versa. Additionally, the UI pool account is zero sum account that is the amounts received from constituents are distributed amongst the other constituents. As long as the actual generation/ drawal is equivalent to the given schedule, UI is zero and the payment on account of the third elements of Availability Tariff is zero. In case of under-drawal, a beneficiary is paid back to that extent according to the frequency dependent rate specified for deviations from schedule.