Power sector on high alert
THE nine-minute 'lights-off' exercise scheduled for Sunday evening, as per Prime Minister Narendra Modi's appeal to people across the country, has forced the grid operator to initiate an elaborate set of contingency measures to avert any crisis caused by the sudden massive load reduction quickly followed by a sharp increase.
These measures include tapering thermal output and increasing generation from hydro and gas stations to enable ramping up and down of power during the episode, calling for all personnel to be present on duty across the country and even requisitioning for "black start facilities" to be kept active as a contingency measure. This refers to the set of restoration procedures at regional load despatch centres alluding to the possibility of potential grid failure and having to restart the grid from scratch.
After many states, through their respective state load despatch centres, flagged risks to the grid from the proposed move, the national grid operator, Power System Operation Corporation Ltd (POSOCO), issued a detailed a 30-point guideline Saturday to load despatch centres at the state, regional and national level. The objective is to counterbalance the expected sharp reduction in load and the subsequent recovery, which it has termed as "unprecedented".
"These apprehensions are misplaced," said the Ministry of Power in a statement Saturday. "The Indian electricity grid is robust and stable and adequate arrangements and protocols are in place to handle the variation in demand."
The ministry also clarified that the PM's appeal is to only switch off lights and not other appliances. The statement said, "The appeal of the Hon Prime Minister is to simply switch off the lights in their homes from 9 pm to 9.09 pm on April 5. There is no call to switch off either street lights or appliances like Computers, TVs, Fans, Refrigerators and ACs in the homes. "The lights in Hospitals and all other essential services like Public Utilities, Municipal Services, Offices, Police Stations, Manufacturing Facilities, etc will remain on…All local bodies have been advised to keep the street lights on for public safety."
PIB Principal Director General KS Dhatwalia also appealed to people to not use alcohol-based hand sanitizers before lighting candles on Sunday.
From the grid managers' perspective, the primary concern is that just before 9 pm, there may be unprecedented load reduction, followed by sudden increase in load post 9.09 pm. During this lights-out exercise, about 11,344-12,879 MW of load nationwide is expected to drop suddenly and then come on stream a few minutes later — the equivalent of five large thermal generating stations going off together.
POCOSO's 30-point detailed guidelines, issued under three broad heads — generation scheduling and frequency control; voltage control measures: and general guidelines — include basic checklists such as all clocks at generating stations being synchronized to Indian standard time, strengthening of the control room staff across the NLDC and all load despatch centres staying "in alert mode and monitor the grid closely in order to take care of any contingency".
Distribution companies are being warned to ensure that distribution substations, housing society and residential apartments main supply shall not be switched off at either the feeder or mains level.
On the generation side, too, there are a series of detailed contingency planning measures.
During evening peak hours — from 6.10 pm to 8 pm — hydro generation is to be reduced "and conserved" for providing flexibility for the 9 pm event. During this time, thermal and gas generation are to be scheduled to manage the peak demand. After peak hours, major thermal Inter-State Generating Stations generation are to be "gradually reduced to near technical minimum level of 60 per cent by 8.55 pm and simultaneously hydro generation is to be increased to maintain the load generation balance".
Hydro generation and gas generation — both of which offer more flexibility as compared to coal-fired units in ramping up and down in line with the requirements of the grid — are to be specifically ramped down starting from 8.57 pm, depending on the system frequency. Gas-based units have been specifically instructed to ramp down to the "minimum level".
Subsequent to this, ramping up of thermal units are to be carried out from 9.05 pm on. And from 9.09 pm on, hydro generation is then to be ramped up to meet the increase in load. Following this, "after the stabilization of system parameters", hydro units are to be withdrawn in consultation with the regional and state load despatch centres.
At the state, regional and national load despatch centres, some of which have been functioning on a rotational staffing basis on account of the lockdown, there are specific instructions of all hands needing to be on deck. "All RLDCs/ SLDCs & NLDC (regional, state and national load despatch centres) are advised to extend the evening shift timings till 10 pm preferably and allow overlap with the incoming night shift."
All senior personnel have been asked to be available at the generating stations, substations, Load Despatch Centers (LDCs) between 6 pm to 10 pm on Sunday as a matter of abundant caution.
India is one of the largest synchronous interconnected grids in the world, with an installed capacity of about 370 gigawatts (3,70,000 mega watts) and a normal baseload power demand of roughly 150 gigawatts.
When an exigency occurs, like an outage at a power plant or the tripping of a transmission line or sudden change in electrical demand, the operator needs to ensure that there is an automatic corrective response, failing which the operator then needs to manually intervene to avert a crisis.
While domestic load is about 30-32 per cent of total load during the normal times, the grid load currently, because of the lockdown, is largely accounted for by domestic load.
The normal baseload power demand of roughly 150 gigawatts has already dropped by 20 per cent since most of industry and commercial establishments are not operational. So the lighting load, as a percentage of total load, is much higher now and the impact of a sudden drop in lighting load could be more accentuated than in regular times.
There is, however, hope that the airconditioning load in the country's western and southern regions would act as a counterbalance. In the west and south, the airconditioning load is already high, which could ensure that the switching off of the light could place a lesser stress on the grid.
(Inputs and image from theindianexpress.com)
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