Towards Higher Voltages: Enabling bulk power transfer and better grid reliability

Enabling bulk power transfer and better grid reliability

In a power-hungry country like India, the generation segment has garnered much more attention compared to the transmission segment. It is only during events such as the 2012 blackout that attention shifts towards the country’s transmission network. In order to meet the government’s ambitious generation targets, it is crucial that proper power evacuation infrastructure is in place to ensure reliable power supply with minimum technical losses.

High voltage transformers form a crucial link in the transmission network as they help supply bulk power from the generation source to load centres. In India, the extra high voltage (EHV) transformer capacity is at the 110 kV, 220/230 kV, 400 kV and 765 kV alternating current (AC) levels. The high voltage direct current (HVDC) capacity is at the ±500 kV and ±800 kV levels, which fall under the category of ultra high voltage (UHV) transformers. At present, domestic manufacturers have the capability to produce transformers of up to 1,200 kV rating.

Growth of EHV and UHV transformers in India

A number of factors have led to the increased demand for high-voltage transformers. This demand is essentially driven by the creation of high capacity, long distance corridors to deliver electricity to high demand regions and the development of green energy corridors for integrating the increasing influx of renewable energy into the grid. In order to cater to future load demand and ease transmission congestion, it is imperative that the transformer capacity is enhanced so that more power can be evacuated from one region to the other. In India, 6,000 MW of capacity was added at the ±800 kV HVDC level during the Twelfth Plan period. Between 2012 and 2017, the share of 765 kV transformer capacity increased by 16.5 per cent while the share of 220 kV transformer capacity declined from 56.64 per cent to 42.25 per cent. These statistics highlight the sector’s shift to higher voltage transformers to enable the transfer of bulk power over longer distances, as well as help optimise right of way, minimise losses and improve grid reliability.

While the EHV transformer network is growing at a fast pace, there has also been an increase in demand for UHV transformers in the country owing to DC technology’s efficiency in transmitting a large quantum of power over long distances with minimum losses. Another reason for the increase in demand is India’s plan to import power from neighbouring hydropower-rich countries like Bhutan and Nepal. India is looking to deploy 1,200 kV UHV AC technology, following the successful commissioning of the 1,200 kV Bina National Test Station in 2016. Under this, the existing 350 km 400 kV Wardha–Aurangabad line will be upgraded to 1,200 kV, marking it as the highest voltage capacity globally.

Future demand and transformer requirement

As per the draft National Electricity Plan (Volume-II) Transmission prepared by the Central Electricity Authority (CEA), the total transformer capacity (at 220 kV and above) is estimated to reach 979,637 MVA by March 2022. In order to achieve the target, HVDC and AC substation capacities of 14,000 MW and 282,260 MVA respectively have to be added during the period 2017-22. Based on the average MVA rating for each transformer type, India Infrastructure Research has projected that the capacity addition for 765 kV transformers will be 98,500 MVA and 92,935 MVA at the 230/220 kV level. In sum, 765 kV and 400 kV transformers will drive demand for the EHV transformer market.

Going forward, parameters such as total load to be catered to by the substation of a specific voltage, MVA capacity and the number of feeders permissible need to be considered with regard to an EHV substations in a system. To this end, the CEA’s draft NEP-Transmission states that the maximum short-circuit level on any new substation bus should not exceed 80 per cent of the rated short-circuit capacity of the substation.

The way forward

Transformer capacity has undergone an evolution in India. For strengthening the transmission network, additional substations will be needed to avoid overloading of the existing system, including adoption of next higher voltages. Further, system studies need to be undertaken for different peak load scenarios for better planning. With the upgradation of technologies such as HVDC, phase shifting transformers and controlled switching devices, coupled with the huge investments proposed across the power sector, the transformer industry in India is slated for growth.