New Delhi: Solar and wind plants built after April 2027 may have to run a communication line alongside every power line leaving the plant, under a proposal going before the National Power Committee (NPC) this month. The requirement would apply to plants connected at 66 kV and above. At present, many renewable plants decide for themselves when to shut down, by watching the voltage and frequency at their own terminals for signs that they have been cut off from the wider grid. The proposal would replace that guesswork with a direct instruction sent down a wire from the substation.
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The proposal comes from a committee set up by the Central Electricity Authority (CEA), which has finished its work and submitted its report. It recommends that all transmission lines emanating from such plants "should be equipped with optical fibre/PLCC communication so that the DTT based AIP method can be implemented."
DTT stands for Direct Transfer Trip. It is a signal sent from the substation to the plant telling it to disconnect, and it needs a physical communication path to travel along, either optical fibre or a carrier signal riding on the power line itself. AIP is anti-islanding protection, the system that stops a plant from continuing to feed a stretch of network that has been separated from the rest of the grid.
Once that link is in place, the committee wants everything else switched off. In its words, "all other Islanding Detection Schemes for grid connected RE Plants shall be disabled."
Smaller plants face the same deadline with a different requirement. For those connected between 11 kV and 66 kV, the report says, "Plants to be commissioned after April 2027: Hybrid AIP must be used." A hybrid scheme combines the plant's own local detection with a signal from outside. The report goes before the 18th NPC meeting at Rajgir in Bihar on September 18, chaired by the Chairperson, CEA, Ghanshyam Prasad.
Plants that are already running are not given a date. Instead the committee sets an order of preference. Where a plant can support a hybrid scheme, it must use one. Where it cannot, it must use an active scheme, which probes the network and watches how it responds. Everything else is to be disabled.
Only where a plant can do neither does the oldest approach survive, and even then on a tight leash. These passive methods work by watching the electrical waveform at the plant's own terminals and inferring that something has gone wrong. They are cheap because they need no wires, and unreliable for the same reason, because a disturbance elsewhere on the grid can look much like a disconnection.
The committee names one such method and rules it out: "RoCoF method of Island detection is not recommended." RoCoF measures how fast the frequency is changing. Where a plant can manage only the other passive method, which tracks a sudden jump in the waveform's timing, the report allows it within limits: "If only Passive method is supported, then Vector shift > 10 degrees with a time delay of 1.8 sec be adopted so that the generation is tripped within 2 seconds of Island detection through this method."
The committee's brief explains the concern. It was asked to "review prevailing anti-islanding practices for RE Plants, examine reported mal operations, recommend a uniform national philosophy compatible with LVRT/HVRT and Grid Code requirements, assess the feasibility of including RE generation in islanding schemes, and examine protection issues arising from RE integration". A mal operation is a plant tripping off when it should have stayed on, taking its generation off the system for no reason.
The committee was chaired by SE (Protection), Western Regional Power Committee (WRPC), with members from NPC, the Southern Regional Power Committee, Grid Controller of India, POWER GRID, IIT Bombay, IISc Bangalore, equipment manufacturers and renewable developers. It met four times between December 2025 and April 2026.
One change it wants is not in its own hands. It proposes widening the frequency band at which inverter-based plants trip, to plus or minus 3 Hz either side of normal, with a delay of 1.8 seconds, so that ordinary grid wobbles stop knocking plants offline. For that, the report says, "a necessary amendment is required in clause B2(2) of the Central Electricity Authority (Technical Standards for Connectivity to the Grid) (Amendment) Regulations, 2019."
The second half of the report goes past islanding to a broader problem, and it is the part with the widest consequences. The equipment that detects faults on transmission lines was designed around conventional power stations. When a fault occurs, a spinning turbine dumps a large surge of current into it, and the protection relay recognises that surge and trips the line. Solar and wind plants connect through inverters, which cannot do this. They are electronic, and they hold their output close to their rated current whatever happens.
The report puts a number on the difference. "Converter-based resources generally contribute only about 1.1–1.4 p.u. fault current for a limited duration, and the magnitude, phase angle and sequence components are governed by inverter controls," it says. In plain terms, an inverter facing a short circuit produces barely more current than it does on a normal day.
The relay, waiting for a surge that never comes, may miss the fault or act late. The report lists what follows: "non-detection or delayed clearance of faults, distance-relay under-reach, unreliable directional earth-fault operation, incorrect phase selection, and delayed Zone-2 fault clearance at the grid end." Under-reach means the relay judges the fault to be farther down the line than it actually is, and so leaves it to somebody else to clear.
The committee's answer is to make inverters deliberately visible. When a fault is lopsided, affecting one or two phases rather than all three, it produces a distinctive electrical signature that relays can be tuned to spot. The report wants inverters to generate that signature on purpose. A full converter-based unit "shall be capable of injecting negative-sequence reactive current of 50 percent of its maximum current rating when the CBR unit terminal negative-sequence voltage is greater than or equal to 25 percent of nominal voltage", it says.
It also wants the two ends of a line talking to each other rather than each judging alone, recommending that operators "mandatorily implement permissive overreach schemes for distance protection on transmission lines connected to RE generation," along with duplicated line differential protection on lines running to renewable generators.
These too need a rule change. "The above provisions may be appropriately considered in the future amendments of the Central Electricity Authority (Technical Standards for Connectivity to the Grid) Regulations," the report says.
The third section deals with the opposite situation, where a section of the grid is cut off deliberately.
Under CEA's grid standards, quoted in the agenda, regional power committees must prepare islanding schemes "for separation of systems with a view to save healthy system from total collapse in case of grid disturbance." A city or an industrial belt is walled off with enough generation inside it to keep running while the rest of the system collapses around it.
Renewable plants have largely been kept out of these islands, because most of them cannot hold a frequency on their own. They follow the grid rather than setting it, and inside an island there is no grid to follow. The committee is willing to let them in, on conditions.
The main one is a floor on how much of the island's generation must come from machines or equipment that can set the frequency. "The ratio of conventional generation and/or grid-forming converter-based resources to GFL based RE generation should preferably be more than 70 percent," it says, referring to the grid-following plants that cannot.
Beyond that, the island must be able to rebalance itself second by second. An Automatic Load-Generation Balancing Scheme is called "a prerequisite for incorporating RE generation in an Islanding Scheme," load must be shed in blocks of 2 percent of the island's conventional capacity, and every participating renewable plant must carry the wire-based anti-islanding protection described earlier.
The trigger points are set higher than in a conventional island, which the committee attributes to the uncertainty of generation inside it and the shorter warning time available. Against a normal grid frequency of 50 Hz, preparatory load shedding would begin at 48.5 Hz and the island would break away at 48.1 Hz.
One exception is written in for battery storage. When a battery with grid-forming inverters is being used to restart a dead system, the report says the anti-islanding protection on those inverters "will have to be bypassed," because a system being restarted looks exactly like a system that has been cut off.
Fuel quality may stop excusing a shortfall. A generating station that cannot run at full output declares a lower capacity, and is then not held to the higher figure. A proposal before the meeting would stop stations from using poor coal quality as the reason. The agenda's logic is blunt: "If fuel quality variations are taken into account, the generating station may be relieved of its obligation to improve fuel quality." A new procedure would also require such shortfalls to be reported within 60 minutes and backed by second-by-second data covering the half hour either side. In the Western Region, fuel quality is currently accepted as a reason.
A rulebook for borrowing a spare transformer. Large transformers take months to procure, and a utility that loses one can be stuck. A national procedure up for approval would let state utilities borrow POWERGRID's spares, but "only in exceptional cases involving critical grid security, reliability, evacuation, transfer capability or continuity requirements." The loan would run up to 30 months, extendable by a year, against a bank guarantee equal to the cost of the equipment. "Ownership shall remain with POWERGRID, while the Borrower shall have only custodial responsibility," the draft says.
Meters at private transmission and renewable sites are going unsealed. Meters are physically sealed so that nobody can open them unnoticed. The agenda records that "presently no sealing is being carried out for meters installed at ISTS/TBCB licensee nodes and that there is lack of clarity regarding the sealing and opening of such meters, while the existing regulations primarily address ISTS interface points." Members have agreed that the metering rules need amending to put the Central Transmission Utility in charge of supervising this.
A meter that may not exist yet. In solar projects where the battery sits on the same side of the inverter as the panels, energy moving between the two never passes an ordinary meter, so it cannot be measured. A proposal seeks direct current meters at that point, recording every 15 minutes to a precision grade of 0.2S. Member (GO&D), CEA has asked manufacturers to examine the challenges in building one to that grade, and the Bureau of Indian Standards (BIS) has circulated a draft standard for comment.
Data centre loads under study with the IT industry. Grid-India has reported that CEA has set up a committee "to undertake a comprehensive study on various aspects of data centre loads, including performance characteristics, control strategies, reactive power requirements". Its members come from CEA, the transmission utility, the national and eastern load despatch centres, and NASSCOM.
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A question mark over Jaipur. At a review of all islanding schemes chaired by Power Secretary Pankaj Agarwal on July 9, Rajasthan's load despatch centre said long transmission corridors, dependence on generation far from the city, and the absence of enough generation close to the Jaipur load centre make a stable island difficult to establish there. The same meeting discussed using four-hour battery storage with grid-forming inverters inside islanding schemes, and decided a pilot study may be explored. The next NPC meeting will be hosted by the Southern Regional Power Committee.