Figure 3 shows the all the year-wise adjustments in the allowable frequency range. It is clearly evident how wisely the commission has continued to adjust the operating range, which has achieved significant milestones in achieving better grid discipline that is discussed in the latter section.
Now, considering the shift in the way of trading power from bilateral trading to the power exchanges like Indian Energy Exchange & Power Exchange of India Limited, Table 8 shows the volume of electricity trading by various methods like UI transaction, power exchange transaction, and total bilateral transactions. Also, Figure 4 shows the UI’ s contribution in total short term transaction since after the power exchanges came into the picture.
Following section illustrates some of the benefits through ABT implementation:
- Remarkable Improvement in the grid frequency The frequency profile of all regions has been greatly improved after ABT has been implemented and Figure 5 shows the frequency comparison of all regions within one year of pre-ABT and post-ABT.
- Improved frequency profile on Northern region Figure 6 shows the remarkable change in the frequency profile after ABT has been introduced, and it can be seen how the average grid frequency is approaching the nominal value of grid frequency.
- Before ABT was introduced in the Southern zone, the grid frequency normally waved around 48Hz, but since after its implementation, the southern grid frequency ranged from 49Hz to 50.5Hz for 99% of the time compared to around 80% in November 2002 and 31% in August 2002. This also addressed many stakeholder’s concern, as it balanced the varying frequency spectrum of the Southern region, which was low to 47.8 Hz and was high up to 52 Hz in the Eastern region.
- Lesser mismatch in scheduled and actual drawl Figure 7 illustrates how the gap in scheduled and actual drawl has been reduced, which is good for maintaining discipline in grid.
- Better under-drawl/over-drawl strategy & utilization of other resources The ABT mechanism allows strategic over-drawing / under-drawing with the deviations priced at frequency-related levels within the permissible frequency band. Tata Power Company (TPC) had unused capacity of 100-300 MW during off-peak hours, which was utilized by MSEB that otherwise before ABT was may not be exploited by MSEB.
Stability in power system : Example of 31 GW load fall at 21:00 on 5th April, 2020
According to , the all India energy consumption on 18.03.2020 (regular day) was 3586 GWh while the all Indian energy consumption on 25.03.2020 (a day in a lockdown) was 2777 GWh so, approximate percentage drop in energy consumption can be calculated as:
Percentage drop=(Erd–Ejcd)/Erd (5)
= (3586 – 2777)/3586 = 22.55 %
Therefore, it is calculated that the energy consumption fell by 22.55 percent in a lockdown day compared to a regular day and this fall is projected to increase day by day till the lockdown removes and everything revives back to normal. Also, in the midst of the darkness spread by the corona pandemic, PM Narendra Modi requested Indians to turn off their lights on April 5, 2020 at 9 p.m. and light a candle or lamp to dispel the darkness spread by coronavirus and exemplify a collective determination to defeat the disease. Unlike normal operation, maintaining a stable grid was not an easy task for grid operators when the load would suddenly fall at 21:00 and eventually rise at 21:09. The expected all India demand fall during this period of 9 minutes was around 12000 – 14000 MW considering that only lights would be switched off but the total reduction in all India demand recorded during the event was 31089 MW. The power demand also dropped from 117 GW to 85.3 GW within a period of 4-5 minutes and engineers at all levels managed this very well. Figure 8 shows how beautifully operators managed to stabilized grid frequency back to 50 Hz at 22:03 pm even after uneven sudden load fall and rise (the data shown is as per the live frequency shown on the SRLDC’s website).
By 1st November, 2003 ABT was implemented in all the five respective regions and its adoption has proved to be very effective in maintaining a stable grid frequency to its 50 Hz nominal value. The commission kept on amending IEGC & ABT, bringing new tariff regulations like additional UI charges in the view of improving the grid discipline. After the implementation of ABT, the commission has continuously revised UI price vector, ceiling rates etc. in its annual reports. The article showed the trend of changes in ceiling rate from initial 570 paise per kWh in 2002-03 to 745 paise per kWh in 2006-07 followed by 735 paise per kWh in 2008-09. The permissible frequency range is attenuated from the initial range of 49 – 50.5 Hz in 2002-03 to 49.9 – 50.05 Hz in 2014. All major changes in ABT are addressed and plotted, even a suspected step to weaken the ABT tariff policy was also identified in 2014-15 which fully prohibited the under-drawl / over-drawl of power. This article demonstrated how the northern region has continued to improve the annual average grid frequency from 49.37 Hz in 2005-06 to 50.07 in 2013-14 and 49.97 in 2018-19 since after the successful incorporation of ABT regime. An event was also elaborated in order to exhibit the achieved efficiency regarding stability in operation of the Indian power system. It was also calculated that all India’s energy intake fell by 22.55 percent on a lockdown day compared to a normal day and it is comfortably presumed that this significant reduction will increase till the lockdown continues.
B-Tech third-year student
Madan Mohan Malaviya University of Technology,
Gorakhpur (U.P.) in Electrical Engineering
Dr. Prabhakar Tiwari
Department of Electrical Engineering,
Madan Mohan Malaviya University of Technology
Prof SN Singh
Professor, Department of Electrical Engineering
Indian Institute of Technology Kanpur -208016